First commit

58 files changed, 4818 insertions, 0 deletions

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
new file mode 100644
index 0000000..77be1e5
--- /dev/null
+++ b/src/CMakeLists.txt
@@ -0,0 +1,20 @@
+# nanowasm, a tiny WebAssembly/Wasm interpreter
+# Copyright (C) 2023-2024  Xavier Del Campo Romero
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+target_sources(${PROJECT_NAME} PRIVATE
+    fstrcmp.c
+    interp.c
+    leb128.c
+    load.c
+    run.c
+    search.c
+    start.c
+    stop.c
+    types.c
+)
+add_subdirectory(op)
+add_subdirectory(section)
diff --git a/src/fstrcmp.c b/src/fstrcmp.c
new file mode 100644
index 0000000..b26baa8
--- /dev/null
+++ b/src/fstrcmp.c
@@ -0,0 +1,41 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/fstring.h>
+#include <nw/log.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+int fstrcmp(const char *str, FILE *const f, const bool abort)
+{
+    int ret = 0;
+
+    for (size_t i = 0; i < strlen(str); i++)
+    {
+        uint8_t byte;
+
+        if (!fread(&byte, sizeof byte, 1, f))
+        {
+            LOG("%s: fread(3) failed, feof=%d, ferror=%d\n",
+                __func__, feof(f), ferror(f));
+            return -1;
+        }
+        else if (byte != str[i])
+        {
+            if (abort)
+                return -1;
+            else
+                ret = -1;
+        }
+    }
+
+    return ret;
+}
diff --git a/src/interp.c b/src/interp.c
new file mode 100644
index 0000000..3a32df0
--- /dev/null
+++ b/src/interp.c
@@ -0,0 +1,516 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nanowasm/nw.h>
+#include <nw/log.h>
+#include <nw/interp.h>
+#include <nw/opcodes.h>
+#include <nw/ops.h>
+#include <nw/sections.h>
+#include <nw/types.h>
+#include <errno.h>
+#include <limits.h>
+#include <inttypes.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static const enum opcode initexpr_opcodes[] =
+{
+    OP_NOP,
+    OP_END,
+    OP_I32_CONST,
+    OP_I64_CONST,
+    OP_F32_CONST,
+    OP_F64_CONST
+};
+
+const struct interp_set interp_initexpr_set =
+{
+    .opcodes = initexpr_opcodes,
+    .n = sizeof initexpr_opcodes / sizeof *initexpr_opcodes
+};
+
+static int (*const ops[])(struct nw_interp *) =
+{
+    [OP_UNREACHABLE] = op_unreachable,
+    [OP_NOP] = op_nop,
+    [OP_BLOCK] = op_block,
+    [OP_LOOP] = op_loop,
+    [OP_IF] = op_if,
+    [OP_ELSE] = op_else,
+    [OP_END] = op_end,
+    [OP_BR] = op_br,
+    [OP_BR_IF] = op_br_if,
+    [OP_BR_TABLE] = op_br_table,
+    [OP_RETURN] = op_return,
+    [OP_CALL] = op_call,
+    [OP_CALL_INDIRECT] = op_call_indirect,
+    [OP_GET_LOCAL] = op_get_local,
+    [OP_SET_LOCAL] = op_set_local,
+    [OP_TEE_LOCAL] = op_tee_local,
+    [OP_GET_GLOBAL] = op_get_global,
+    [OP_SET_GLOBAL] = op_set_global,
+    [OP_I32_LOAD] = op_i32_load,
+    [OP_I32_STORE] = op_i32_store,
+    [OP_I32_CONST] = op_i32_const,
+    [OP_I64_CONST] = op_i64_const,
+    [OP_F32_CONST] = op_f32_const,
+    [OP_F64_CONST] = op_f64_const,
+    [OP_I32_SUB] = op_i32_sub
+};
+
+int interp_run(struct nw_interp *const i)
+{
+    uint8_t op;
+
+    if (!fread(&op, sizeof op, 1, i->f))
+    {
+        LOG("%s: fread(3) failed, feof=%d, ferror=%d\n", __func__, feof(i->f),
+            ferror(i->f));
+        i->exception = "I/O error";
+        return -1;
+    }
+    else if (op >= sizeof ops / sizeof *ops)
+    {
+        LOG("%s: invalid opcode %#" PRIx8 "\n", __func__, op);
+        i->exception = "invalid opcode";
+        return -1;
+    }
+    else if (!ops[op])
+    {
+        LOG("%s: unsupported opcode %#" PRIx8 "\n", __func__, op);
+        i->exception = "invalid opcode";
+        return -1;
+    }
+
+    return ops[op](i);
+}
+
+static int run_opcode_limited(struct nw_interp *const in,
+    const struct interp_set *const set)
+{
+    uint8_t op;
+
+    if (!fread(&op, sizeof op, 1, in->f))
+    {
+        LOG("%s: fread(3) failed, feof=%d, ferror=%d\n",
+            __func__, feof(in->f), ferror(in->f));
+        in->exception = "I/O error";
+        return -1;
+    }
+
+    for (size_t i = 0; i < set->n; i++)
+        if (op == set->opcodes[i])
+            return ops[op](in);
+
+    LOG("%s: unexpected opcode %#" PRIx8 "\n", __func__, op);
+    in->exception = "invalid opcode";
+    return -1;
+}
+
+int interp_run_limited(struct nw_interp *const i,
+    const struct interp_set *const set)
+{
+    while (!i->exit)
+        if (run_opcode_limited(i, set))
+        {
+            LOG("%s: run_opcode_limited failed\n", __func__);
+            return -1;
+        }
+
+    return 0;
+}
+
+int interp_check_opcode(const uint8_t op, FILE *const f)
+{
+    static int (*const checks[])(FILE *) =
+    {
+        [OP_UNREACHABLE] = check_unreachable,
+        [OP_NOP] = check_nop,
+        [OP_BLOCK] = check_block,
+        [OP_LOOP] = check_loop,
+        [OP_IF] = check_if,
+        [OP_ELSE] = check_else,
+        [OP_END] = check_end,
+        [OP_BR] = check_br,
+        [OP_BR_IF] = check_br_if,
+        [OP_BR_TABLE] = check_br_table,
+        [OP_RETURN] = check_return,
+        [OP_CALL] = check_call,
+        [OP_CALL_INDIRECT] = check_call_indirect,
+        [OP_GET_LOCAL] = check_get_local,
+        [OP_SET_LOCAL] = check_set_local,
+        [OP_TEE_LOCAL] = check_tee_local,
+        [OP_GET_GLOBAL] = check_get_global,
+        [OP_SET_GLOBAL] = check_set_global,
+        [OP_I32_LOAD] = check_i32_load,
+        [OP_I32_STORE] = check_i32_store,
+        [OP_I32_CONST] = check_i32_const,
+        [OP_I64_CONST] = check_i64_const,
+        [OP_F32_CONST] = check_f32_const,
+        [OP_F64_CONST] = check_f64_const,
+        [OP_I32_SUB] = check_i32_sub
+    };
+
+    if (op >= sizeof checks / sizeof *checks)
+    {
+        LOG("%s: invalid opcode %#" PRIx8 "\n", __func__, op);
+        return 1;
+    }
+    else if (!checks[op])
+    {
+        LOG("%s: unsupported opcode %#" PRIx8 "\n", __func__, op);
+        return 1;
+    }
+
+    return checks[op](f);
+}
+
+int interp_start(const struct nw_interp_cfg *const cfg, FILE *const f,
+    struct nw_interp *const i)
+{
+    *i = (const struct nw_interp)
+    {
+        .f = f,
+        .cfg = *cfg
+    };
+
+    return 0;
+}
+
+void *interp_stackptr(const struct nw_interp *const i)
+{
+    return (char *)i->cfg.stack.buf + i->stack_i;
+}
+
+static int push_frame(struct nw_interp *const i,
+    const struct nw_frame *const src)
+{
+    struct nw_frame *const dst = interp_stackptr(i);
+
+    if (interp_stack_push(i, src, sizeof (*src)))
+    {
+        LOG("%s: interp_stack_push failed\n", __func__);
+        return -1;
+    }
+    else if (i->fp)
+        i->fp->next = dst;
+
+    i->fp = dst;
+    return 0;
+}
+
+static bool mul_overflow(const size_t a, const size_t b)
+{
+    return a && (a * b) / a != b;
+}
+
+static void init_i32(const varuint32 count, void *const p)
+{
+    for (int32_t *i = p; i - (const int32_t *)p < count; i++)
+        *i = 0;
+}
+
+static void init_i64(const varuint32 count, void *const p)
+{
+    for (int64_t *i = p; i - (const int64_t *)p < count; i++)
+        *i = 0;
+}
+
+static void init_f32(const varuint32 count, void *const p)
+{
+    for (float *i = p; i - (const float *)p < count; i++)
+        *i = 0;
+}
+
+static void init_f64(const varuint32 count, void *const p)
+{
+    for (double *i = p; i - (const double *)p < count; i++)
+        *i = 0;
+}
+
+static void init_locals(const enum value_type type, const varuint32 count,
+    void *const p)
+{
+    static void (*const init[])(varuint32, void *) =
+    {
+        [VALUE_TYPE_I32] = init_i32,
+        [VALUE_TYPE_I64] = init_i64,
+        [VALUE_TYPE_F32] = init_f32,
+        [VALUE_TYPE_F64] = init_f64
+    };
+
+    init[type](count, p);
+}
+
+static int push_locals(struct nw_interp *const i,
+    const struct nw_frame *const f)
+{
+    const enum value_type t = f->local_type;
+    const size_t typesz = get_type_size(t);
+    const unsigned long n = f->n_locals;
+
+    if (mul_overflow(typesz, f->n_locals))
+    {
+        LOG("%s: local variables size mul overflow", __func__);
+        i->exception = "mul overfllow";
+        return -1;
+    }
+
+    const size_t totalsz = typesz * n, max = i->cfg.stack.n;
+
+    if (totalsz > max || i->stack_i > max - totalsz)
+    {
+        LOG("%s: cannot allocate locals\n", __func__);
+        i->exception = "stack overflow";
+        return 1;
+    }
+
+    init_locals(t, n, interp_stackptr(i));
+    i->stack_i += totalsz;
+    return 0;
+}
+
+static int do_push_labels(struct nw_interp *const i,
+    const struct nw_frame *const fr)
+{
+    size_t n = 0;
+
+    for (;;)
+    {
+
+        interp_check_opcode();
+    }
+}
+
+static int push_labels(struct nw_interp *const i,
+    const struct nw_frame *const fr)
+{
+    FILE *const f = i->f;
+    const long orig = ftell(f);
+
+    if (orig < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+    else if (do_push_labels(i, fr))
+    {
+        LOG("%s: do_push_labels failed\n", __func__);
+        return -1;
+    }
+    else if (fseek(f, orig, SEEK_SET))
+    {
+        LOG("%s: fseek(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    return -1;
+}
+
+int interp_push(struct nw_interp *const i, const struct nw_frame *const f)
+{
+    if (push_frame(i, f))
+    {
+        LOG("%s: push_frame failed\n", __func__);
+        return -1;
+    }
+    else if (push_locals(i, f))
+    {
+        LOG("%s: push_locals failed\n", __func__);
+        return -1;
+    }
+    else if (push_labels(i, f))
+    {
+        LOG("%s: push_labels failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+struct retval_priv
+{
+    enum value_type type;
+
+    union
+    {
+        int32_t i32;
+        int64_t i64;
+        float f32;
+        double f64;
+    } u;
+};
+
+static void get_i32(const void *const buf, struct retval_priv *const rp)
+{
+    rp->u.i32 = *(((const int32_t *)buf) - 1);
+}
+
+static void get_i64(const void *const buf, struct retval_priv *const rp)
+{
+    rp->u.i64 = *(((const int64_t *)buf) - 1);
+}
+
+static void get_f32(const void *const buf, struct retval_priv *const rp)
+{
+    rp->u.f32 = *(((const float *)buf) - 1);
+}
+
+static void get_f64(const void *const buf, struct retval_priv *const rp)
+{
+    rp->u.f64 = *(((const double *)buf) - 1);
+}
+
+static int get_retval(struct nw_interp *const i,
+    struct retval_priv *const rp)
+{
+    const struct retval *const r = &i->fp->retval;
+    const size_t sz = get_type_size(r->type), max = i->cfg.stack.n;
+
+    if (max < sz || i->stack_i >= max - sz)
+    {
+        static const char exc[] = "stack underflow";
+
+        LOG("%s: %s\n", __func__, exc);
+        i->exception = exc;
+        return -1;
+    }
+
+    const void *const buf = (const char *)interp_stackptr(i) - sz;
+    static void (*const get[])(const void *, struct retval_priv *) =
+    {
+        [VALUE_TYPE_I32] = get_i32,
+        [VALUE_TYPE_I64] = get_i64,
+        [VALUE_TYPE_F32] = get_f32,
+        [VALUE_TYPE_F64] = get_f64
+    };
+
+    get[r->type](buf, rp);
+    rp->type = r->type;
+    i->stack_i -= sz;
+    return 0;
+}
+
+int interp_pop(struct nw_interp *const i)
+{
+    if (!i->fp)
+    {
+        static const char exc[] = "no frame pointer";
+
+        LOG("%s: %s\n", __func__, exc);
+        i->exception = exc;
+        return -1;
+    }
+
+    const struct retval *const r = &i->fp->retval;
+    struct retval_priv rp;
+
+    if (r->returns && get_retval(i, &rp))
+    {
+        LOG("%s: get_retval failed\n", __func__);
+        return -1;
+    }
+
+    const char *const stackptr = interp_stackptr(i);
+    const ptrdiff_t diff = stackptr - (const char *)i->fp;
+
+    i->stack_i -= diff;
+
+    if (!(i->fp = i->fp->prev))
+    {
+        /* Entry point is always assumed to return int, which is
+         * defined as an i32 variable according to Wasm. */
+        if (rp.type != VALUE_TYPE_I32)
+        {
+            LOG("%s: expected i32 return type, got %s\n", __func__,
+                value_type_tostr(rp.type));
+            i->exception = "unexpected return type";
+            return -1;
+        }
+
+        i->retval = rp.u.i32;
+        i->exit = true;
+    }
+
+    return 0;
+}
+
+int interp_stack_push(struct nw_interp *const i, const void *const src,
+    const size_t n)
+{
+    void *const dst = interp_stackptr(i);
+
+    if (i->cfg.stack.n < n || i->stack_i > i->cfg.stack.n - n)
+    {
+        LOG("%s: stack overflow\n", __func__);
+        i->exception = "stack overflow";
+        return -1;
+    }
+
+    memcpy(dst, src, n);
+    i->stack_i += n;
+    return 0;
+}
+
+int interp_stack_pop(struct nw_interp *const i, void *const dst,
+    const size_t n)
+{
+    if (i->stack_i < n)
+    {
+        LOG("%s: stack underflow\n", __func__);
+        i->exception = "stack underflow";
+        return -1;
+    }
+
+    i->stack_i -= n;
+    memcpy(dst, interp_stackptr(i), n);
+    return 0;
+}
+
+int interp_heap_store(struct nw_interp *const i, const size_t addr,
+    const void *const src, const size_t n)
+{
+    if (i->cfg.heap.n < n || addr > i->cfg.heap.n - n)
+    {
+        static const char exc[] = "heap overflow";
+
+        LOG("%s: %s\n", __func__, exc);
+        i->exception = exc;
+        return -1;
+    }
+
+    void *const dst = (char *)i->cfg.heap.buf + addr;
+
+    memcpy(dst, src, n);
+    return 0;
+}
+
+int interp_heap_load(struct nw_interp *const i, const size_t addr,
+    void *const dst, const size_t n)
+{
+    const size_t max = i->cfg.heap.n;
+
+    if (max < n || addr > max - n)
+    {
+        static const char exc[] = "heap out-of-bounds access";
+
+        LOG("%s: %s (%lu, max %zu)\n", __func__, exc, (unsigned long)addr, max);
+        i->exception = exc;
+        return -1;
+    }
+
+    const void *const src = (const char *)i->cfg.heap.buf + addr;
+
+    memcpy(dst, src, n);
+    return 0;
+}
diff --git a/src/leb128.c b/src/leb128.c
new file mode 100644
index 0000000..3c3c8a5
--- /dev/null
+++ b/src/leb128.c
@@ -0,0 +1,71 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/leb128.h>
+#include <nw/log.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+
+/* The functions below are (somewhat heavily) modified versions of those
+ * provided by the wac project: https://github.com/kanaka/wac */
+
+/*
+ * Copyright (C) Joel Martin <github@martintribe.org>
+ * The wac project is licensed under the MPL 2.0 (Mozilla Public License
+ * 2.0). The text of the MPL 2.0 license is included below and can be
+ * found at https://www.mozilla.org/MPL/2.0/
+ */
+
+static int read_LEB(FILE *const f, const unsigned maxbits,
+    const bool sign, unsigned long long *const out)
+{
+    unsigned long long result = 0;
+    unsigned shift = 0, bcnt = 0;
+    uint8_t byte;
+
+    for (;;)
+    {
+        if (!fread(&byte, sizeof byte, 1, f))
+            return -1;
+
+        result |= (unsigned long long)(byte & 0x7f) << shift;
+        shift += 7;
+
+        if (!(byte & 0x80))
+            break;
+        else if (++bcnt > (maxbits + 7 - 1) / 7)
+        {
+            LOG("%s: overflow\n", __func__);
+            return -1;
+        }
+    }
+
+    if (sign && (shift < maxbits) && (byte & 0x40))
+        result |= -1ll << shift;
+
+    *out = result;
+    return 0;
+}
+
+int leb128_read_unsigned(FILE *const f, const unsigned maxbits,
+    unsigned long long *const out)
+{
+    return read_LEB(f, maxbits, false, out);
+}
+
+int leb128_read_signed(FILE *const f, const unsigned maxbits,
+    long long *const out)
+{
+    unsigned long long value;
+    const int ret = read_LEB(f, maxbits, true, &value);
+
+    *out = value;
+    return ret;
+}
diff --git a/src/load.c b/src/load.c
new file mode 100644
index 0000000..2ba0fcc
--- /dev/null
+++ b/src/load.c
@@ -0,0 +1,178 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nanowasm/nw.h>
+#include <nw/sections.h>
+#include <nw/types.h>
+#include <errno.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static int check_magic(FILE *const f)
+{
+    static const uint8_t m[] = {'\0', 'a', 's', 'm'};
+    uint8_t magic[sizeof m];
+
+    if (!fread(magic, sizeof magic, 1, f))
+    {
+        LOG("%s: fread(3) failed, feof=%d, ferror=%d\n",
+            __func__, feof(f), ferror(f));
+        return -1;
+    }
+    else if (memcmp(magic, m, sizeof magic))
+    {
+        LOG("%s: wrong magic bytes\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+static int check_version(FILE *const f)
+{
+    static const uint8_t v[] = {1, 0, 0, 0};
+    uint8_t version[sizeof v];
+
+    if (!fread(version, sizeof version, 1, f))
+    {
+        LOG("%s: fread(3) failed, feof=%d, ferror=%d\n", __func__, feof(f),
+            ferror(f));
+        return -1;
+    }
+    else if (memcmp(version, v, sizeof version))
+    {
+        LOG("%s: wrong version\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+static int load_section(const struct nw_mod_cfg *const cfg,
+    struct nw_mod *const m, FILE *const f)
+{
+    static int (*const fn[])(const struct section *, struct nw_mod *,
+        unsigned long) =
+    {
+        section_custom_check,
+        section_type_check,
+        section_import_check,
+        section_function_check,
+        section_table_check,
+        section_memory_check,
+        section_global_check,
+        section_export_check,
+        section_start_check,
+        section_element_check,
+        section_code_check,
+        section_data_check
+    };
+
+    const struct section s =
+    {
+        .cfg = cfg,
+        .f = f
+    };
+
+    varuint7 section;
+    varuint32 len;
+    int ret;
+
+    if (varuint7_read(f, &section))
+    {
+        if (feof(f))
+            return 0;
+
+        LOG("%s: varuint7_read failed\n", __func__);
+        return 1;
+    }
+    else if (section >= sizeof fn / sizeof *fn)
+    {
+        LOG("%s: invalid section %u\n", __func__, (unsigned)section);
+        return 1;
+    }
+    else if (varuint32_read(f, &len))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return 1;
+    }
+    else if ((ret = fn[section](&s, m, len)))
+        LOG("%s: failed to load section %u\n", __func__, (unsigned)section);
+
+    return ret;
+}
+
+static int load_sections(const struct nw_mod_cfg *const cfg,
+    struct nw_mod *const m, FILE *const f)
+{
+    while (!feof(f))
+        if (load_section(cfg, m, f))
+        {
+            LOG("%s: load_section failed\n", __func__);
+            return -1;
+        }
+
+    return 0;
+}
+
+static int load(const struct nw_mod_cfg *const cfg, struct nw_mod *const m,
+    FILE *const f)
+{
+    if (check_magic(f))
+    {
+        LOG("%s: load_magic failed\n", __func__);
+        return -1;
+    }
+    else if (check_version(f))
+    {
+        LOG("%s: check_version failed\n", __func__);
+        return -1;
+    }
+    else if (load_sections(cfg, m, f))
+    {
+        LOG("%s: load_sections failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+int nw_load(const struct nw_mod_cfg *const cfg, struct nw_mod *const m)
+{
+    int ret = -1;
+    FILE *const f = fopen(cfg->path, "rb");
+
+    *m = (const struct nw_mod){.cfg = *cfg};
+
+    if (!f)
+    {
+        LOG("%s: fopen(3) %s: %s\n", __func__, cfg->path, strerror(errno));
+        goto end;
+    }
+    else if (load(cfg, m, f))
+    {
+        LOG("%s: load failed\n", __func__);
+        goto end;
+    }
+
+    ret = 0;
+
+end:
+    if (f && fclose(f))
+    {
+        LOG("%s: fclose(3) %s: %s\n", __func__, cfg->path, strerror(errno));
+        ret = -1;
+    }
+
+    return ret;
+}
diff --git a/src/op/CMakeLists.txt b/src/op/CMakeLists.txt
new file mode 100644
index 0000000..7bf27de
--- /dev/null
+++ b/src/op/CMakeLists.txt
@@ -0,0 +1,13 @@
+# nanowasm, a tiny WebAssembly/Wasm interpreter
+# Copyright (C) 2023-2024  Xavier Del Campo Romero
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+add_subdirectory(call)
+add_subdirectory(constants)
+add_subdirectory(control_flow)
+add_subdirectory(memory)
+add_subdirectory(numeric)
+add_subdirectory(variable_access)
diff --git a/src/op/call/CMakeLists.txt b/src/op/call/CMakeLists.txt
new file mode 100644
index 0000000..527f35d
--- /dev/null
+++ b/src/op/call/CMakeLists.txt
@@ -0,0 +1,11 @@
+# nanowasm, a tiny WebAssembly/Wasm interpreter
+# Copyright (C) 2023-2024  Xavier Del Campo Romero
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+target_sources(${PROJECT_NAME} PRIVATE
+    call.c
+    call_indirect.c
+)
diff --git a/src/op/call/call.c b/src/op/call/call.c
new file mode 100644
index 0000000..19355ca
--- /dev/null
+++ b/src/op/call/call.c
@@ -0,0 +1,79 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/interp.h>
+#include <nw/search.h>
+#include <nw/sections.h>
+#include <nw/types.h>
+#include <errno.h>
+#include <stdio.h>
+#include <string.h>
+
+static int call(struct nw_interp *const i, const varuint32 function_index)
+{
+    FILE *const f = i->f;
+    const struct nw_mod *const m = i->cfg.m;
+    struct nw_frame fr = {0};
+    struct search_fn fn;
+
+    /* TODO: treat import functions. */
+    if (search_fn(function_index, m, f, &fn))
+    {
+        LOG("%s: search_fn failed\n", __func__);
+        return -1;
+    }
+    else if (section_type_push(f, m, fn.index, &fr))
+    {
+        LOG("%s: section_type_push failed\n", __func__);
+        return -1;
+    }
+    else if (section_code_push(f, fn.start, &fr))
+    {
+        LOG("%s: section_code_push failed\n", __func__);
+        return -1;
+    }
+    else if (interp_push(i, &fr))
+    {
+        LOG("%s: interp_push failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+static int op(struct nw_interp *const i, FILE *const f)
+{
+    varuint32 function_index;
+
+    if (varuint32_read(f, &function_index))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return -1;
+    }
+    else if (i && call(i, function_index))
+    {
+        LOG("%s: call failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+int op_call(struct nw_interp *const i)
+{
+    return op(i, i->f);
+}
+
+int check_call(FILE *const f)
+{
+    return op(NULL, f);
+}
diff --git a/src/op/call/call_indirect.c b/src/op/call/call_indirect.c
new file mode 100644
index 0000000..bae8a57
--- /dev/null
+++ b/src/op/call/call_indirect.c
@@ -0,0 +1,49 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <stdio.h>
+
+static int op(struct nw_interp *const i, FILE *const f)
+{
+    varuint32 type_index;
+    varuint1 reserved;
+
+    if (varuint32_read(f, &type_index))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return 1;
+    }
+    else if (varuint1_read(f, &reserved))
+    {
+        LOG("%s: varuint1_read failed\n", __func__);
+        return 1;
+    }
+    else if (reserved)
+    {
+        LOG("%s: unexpected non-zero reserved value %u\n",
+            __func__, (unsigned)reserved);
+        return 1;
+    }
+
+    return 0;
+}
+
+int op_call_indirect(struct nw_interp *const i)
+{
+    return op(i, i->f);
+}
+
+int check_call_indirect(FILE *const f)
+{
+    return op(NULL, f);
+}
diff --git a/src/op/constants/CMakeLists.txt b/src/op/constants/CMakeLists.txt
new file mode 100644
index 0000000..e5cc8c5
--- /dev/null
+++ b/src/op/constants/CMakeLists.txt
@@ -0,0 +1,13 @@
+# nanowasm, a tiny WebAssembly/Wasm interpreter
+# Copyright (C) 2023-2024  Xavier Del Campo Romero
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+target_sources(${PROJECT_NAME} PRIVATE
+    f32_const.c
+    f64_const.c
+    i32_const.c
+    i64_const.c
+)
diff --git a/src/op/constants/f32_const.c b/src/op/constants/f32_const.c
new file mode 100644
index 0000000..c0c51b9
--- /dev/null
+++ b/src/op/constants/f32_const.c
@@ -0,0 +1,38 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <stddef.h>
+#include <stdio.h>
+
+static int op(struct nw_interp *const i, FILE *const f)
+{
+    varuint32 value;
+
+    if (varuint32_read(f, &value))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+int op_f32_const(struct nw_interp *const i)
+{
+    return op(i, i->f);
+}
+
+int check_f32_const(FILE *const f)
+{
+    return op(NULL, f);
+}
diff --git a/src/op/constants/f64_const.c b/src/op/constants/f64_const.c
new file mode 100644
index 0000000..d88398c
--- /dev/null
+++ b/src/op/constants/f64_const.c
@@ -0,0 +1,38 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <stddef.h>
+#include <stdio.h>
+
+static int op(struct nw_interp *const i, FILE *const f)
+{
+    varuint64 value;
+
+    if (varuint64_read(f, &value))
+    {
+        LOG("%s: varuint64_read failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+int op_f64_const(struct nw_interp *const i)
+{
+    return op(i, i->f);
+}
+
+int check_f64_const(FILE *const f)
+{
+    return op(NULL, f);
+}
diff --git a/src/op/constants/i32_const.c b/src/op/constants/i32_const.c
new file mode 100644
index 0000000..19161d3
--- /dev/null
+++ b/src/op/constants/i32_const.c
@@ -0,0 +1,51 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <nw/interp.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+static int set_value(struct nw_interp *const i, const int32_t src)
+{
+    return interp_stack_push(i, &src, sizeof src);
+}
+
+static int op(struct nw_interp *const i, FILE *const f)
+{
+    varint32 value;
+
+    if (varint32_read(f, &value))
+    {
+        LOG("%s: varint32_read failed\n", __func__);
+        return -1;
+    }
+    else if (i && set_value(i, value))
+    {
+        LOG("%s: set_value failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+int op_i32_const(struct nw_interp *const i)
+{
+    return op(i, i->f);
+}
+
+int check_i32_const(FILE *const f)
+{
+    return op(NULL, f);
+}
diff --git a/src/op/constants/i64_const.c b/src/op/constants/i64_const.c
new file mode 100644
index 0000000..53f4237
--- /dev/null
+++ b/src/op/constants/i64_const.c
@@ -0,0 +1,38 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <stddef.h>
+#include <stdio.h>
+
+static int op(struct nw_interp *const i, FILE *const f)
+{
+    varint64 value;
+
+    if (varint64_read(f, &value))
+    {
+        LOG("%s: varint32_read failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+int op_i64_const(struct nw_interp *const i)
+{
+    return op(i, i->f);
+}
+
+int check_i64_const(FILE *const f)
+{
+    return op(NULL, f);
+}
diff --git a/src/op/control_flow/CMakeLists.txt b/src/op/control_flow/CMakeLists.txt
new file mode 100644
index 0000000..832f09e
--- /dev/null
+++ b/src/op/control_flow/CMakeLists.txt
@@ -0,0 +1,20 @@
+# nanowasm, a tiny WebAssembly/Wasm interpreter
+# Copyright (C) 2023-2024  Xavier Del Campo Romero
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+target_sources(${PROJECT_NAME} PRIVATE
+    block.c
+    br.c
+    br_if.c
+    br_table.c
+    else.c
+    end.c
+    if.c
+    loop.c
+    nop.c
+    return.c
+    unreachable.c
+)
diff --git a/src/op/control_flow/block.c b/src/op/control_flow/block.c
new file mode 100644
index 0000000..56f72f1
--- /dev/null
+++ b/src/op/control_flow/block.c
@@ -0,0 +1,75 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/interp.h>
+#include <nw/types.h>
+#include <errno.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <string.h>
+
+static int push(struct nw_interp *const i, FILE *const f)
+{
+    const long pc = ftell(f);
+
+    if (pc < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        i->exception = "I/O error";
+        return -1;
+    }
+
+    struct nw_frame *const fp = i->fp;
+    struct nw_block *const p = interp_stackptr(i);
+    const struct nw_block b =
+    {
+        .pc = pc,
+        .prev = fp->last_block
+    };
+
+    if (interp_stack_push(i, &b, sizeof b))
+    {
+        LOG("%s: interp_stack_push failed\n", __func__);
+        return -1;
+    }
+
+    fp->last_block = p;
+    return 0;
+}
+
+static int op(struct nw_interp *const i, FILE *const f)
+{
+    varint7 sig;
+
+    if (varint7_read(f, &sig))
+    {
+        LOG("%s: varint7_read failed\n", __func__);
+        return -1;
+    }
+    else if (i && push(i, f))
+    {
+        LOG("%s: push failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+int op_block(struct nw_interp *const i)
+{
+    return op(i, i->f);
+}
+
+int check_block(FILE *const f)
+{
+    return op(NULL, f);
+}
diff --git a/src/op/control_flow/br.c b/src/op/control_flow/br.c
new file mode 100644
index 0000000..df3aacb
--- /dev/null
+++ b/src/op/control_flow/br.c
@@ -0,0 +1,38 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <stddef.h>
+#include <stdio.h>
+
+static int op(struct nw_interp *const i, FILE *const f)
+{
+    varuint32 relative_depth;
+
+    if (varuint32_read(f, &relative_depth))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+int op_br(struct nw_interp *const i)
+{
+    return op(i, i->f);
+}
+
+int check_br(FILE *const f)
+{
+    return op(NULL, f);
+}
diff --git a/src/op/control_flow/br_if.c b/src/op/control_flow/br_if.c
new file mode 100644
index 0000000..25bfdee
--- /dev/null
+++ b/src/op/control_flow/br_if.c
@@ -0,0 +1,95 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/interp.h>
+#include <nw/types.h>
+#include <errno.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <string.h>
+
+static int branch(struct nw_interp *const i, const varuint32 relative_depth)
+{
+    const struct nw_block *b = i->fp->last_block;
+    static const char exc[] = "relative depth and block count mismatch";
+
+    for (varuint32 d = 0; b && d < relative_depth; d++)
+        b = b->prev;
+
+    if (!b)
+    {
+        LOG("%s: %s\n", __func__, exc);
+        i->exception = exc;
+        return -1;
+    }
+
+    if (fseek(i->f, b->pc, SEEK_SET))
+    {
+        LOG("%s: fseek(3): %s\n", __func__, strerror(errno));
+        i->exception = "I/O error";
+        return -1;
+    }
+
+    return 0;
+}
+
+static bool cond(struct nw_interp *const i)
+{
+    int32_t value;
+
+    if (interp_stack_pop(i, &value, sizeof value))
+    {
+        LOG("%s: interp_stack_pop failed\n", __func__);
+        return -1;
+    }
+
+    return value;
+}
+
+static int br_if(struct nw_interp *const i, const varuint32 relative_depth)
+{
+    if (cond(i) && branch(i, relative_depth))
+    {
+        LOG("%s: branch failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+static int op(struct nw_interp *const i, FILE *const f)
+{
+    varuint32 relative_depth;
+
+    if (varuint32_read(f, &relative_depth))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return 1;
+    }
+    else if (i && br_if(i, relative_depth))
+    {
+        LOG("%s: br_if failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+int op_br_if(struct nw_interp *const i)
+{
+    return op(i, i->f);
+}
+
+int check_br_if(FILE *const f)
+{
+    return op(NULL, f);
+}
diff --git a/src/op/control_flow/br_table.c b/src/op/control_flow/br_table.c
new file mode 100644
index 0000000..837cdcd
--- /dev/null
+++ b/src/op/control_flow/br_table.c
@@ -0,0 +1,56 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <stddef.h>
+#include <stdio.h>
+
+static int op(struct nw_interp *const i, FILE *const f)
+{
+    varuint32 target_count, default_target;
+
+    if (varuint32_read(f, &target_count))
+    {
+        LOG("%s: varuint32_read target_count failed\n", __func__);
+        return -1;
+    }
+
+    for (varuint32 i = 0; i < target_count; i++)
+    {
+        varuint32 target_table;
+
+        if (varuint32_read(f, &target_table))
+        {
+            LOG("%s: varuint32_read target_table failed\n",
+                __func__);
+            return -1;
+        }
+    }
+
+    if (varuint32_read(f, &default_target))
+    {
+        LOG("%s: varuint32_read default_target failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+int op_br_table(struct nw_interp *const i)
+{
+    return op(i, i->f);
+}
+
+int check_br_table(FILE *const f)
+{
+    return op(NULL, f);
+}
diff --git a/src/op/control_flow/else.c b/src/op/control_flow/else.c
new file mode 100644
index 0000000..fb839f0
--- /dev/null
+++ b/src/op/control_flow/else.c
@@ -0,0 +1,21 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+
+int op_else(struct nw_interp *const i)
+{
+    return -1;
+}
+
+int check_else(FILE *const f)
+{
+    return 0;
+}
diff --git a/src/op/control_flow/end.c b/src/op/control_flow/end.c
new file mode 100644
index 0000000..5f193d9
--- /dev/null
+++ b/src/op/control_flow/end.c
@@ -0,0 +1,24 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <stdbool.h>
+
+int op_end(struct nw_interp *const i)
+{
+    /* TODO: this is not correct. end can appear anywhere in a function. */
+    i->exit = true;
+    return 0;
+}
+
+int check_end(FILE *const f)
+{
+    return 0;
+}
diff --git a/src/op/control_flow/if.c b/src/op/control_flow/if.c
new file mode 100644
index 0000000..1d5e838
--- /dev/null
+++ b/src/op/control_flow/if.c
@@ -0,0 +1,36 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+
+static int op(struct nw_interp *const i, FILE *const f)
+{
+    varint7 sig;
+
+    if (varint7_read(f, &sig))
+    {
+        LOG("%s: varint7_read failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+int op_if(struct nw_interp *const i)
+{
+    return op(i, i->f);
+}
+
+int check_if(FILE *const f)
+{
+    return op(NULL, f);
+}
diff --git a/src/op/control_flow/loop.c b/src/op/control_flow/loop.c
new file mode 100644
index 0000000..5020f23
--- /dev/null
+++ b/src/op/control_flow/loop.c
@@ -0,0 +1,36 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+
+static int op(struct nw_interp *const i, FILE *const f)
+{
+    varint7 sig;
+
+    if (varint7_read(f, &sig))
+    {
+        LOG("%s: varint7_read failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+int op_loop(struct nw_interp *const i)
+{
+    return op(i, i->f);
+}
+
+int check_loop(FILE *const f)
+{
+    return op(NULL, f);
+}
diff --git a/src/op/control_flow/nop.c b/src/op/control_flow/nop.c
new file mode 100644
index 0000000..356b7b0
--- /dev/null
+++ b/src/op/control_flow/nop.c
@@ -0,0 +1,22 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/interp.h>
+
+int op_nop(struct nw_interp *const i)
+{
+    return 0;
+}
+
+int check_nop(FILE *const f)
+{
+    return 0;
+}
diff --git a/src/op/control_flow/return.c b/src/op/control_flow/return.c
new file mode 100644
index 0000000..abddea7
--- /dev/null
+++ b/src/op/control_flow/return.c
@@ -0,0 +1,30 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/interp.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <stdio.h>
+
+int op_return(struct nw_interp *const i)
+{
+    if (interp_pop(i))
+    {
+        LOG("%s: interp_pop failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+int check_return(FILE *const f)
+{
+    return 0;
+}
diff --git a/src/op/control_flow/unreachable.c b/src/op/control_flow/unreachable.c
new file mode 100644
index 0000000..8f1982c
--- /dev/null
+++ b/src/op/control_flow/unreachable.c
@@ -0,0 +1,25 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <stdbool.h>
+#include <stdio.h>
+
+int op_unreachable(struct nw_interp *const i)
+{
+    i->exception = "Unreachable instruction";
+    i->exit = true;
+    return 1;
+}
+
+int check_unreachable(FILE *const f)
+{
+    return 0;
+}
diff --git a/src/op/memory/CMakeLists.txt b/src/op/memory/CMakeLists.txt
new file mode 100644
index 0000000..ca4ba5a
--- /dev/null
+++ b/src/op/memory/CMakeLists.txt
@@ -0,0 +1,12 @@
+# nanowasm, a tiny WebAssembly/Wasm interpreter
+# Copyright (C) 2023-2024  Xavier Del Campo Romero
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+target_sources(${PROJECT_NAME} PRIVATE
+    current_memory.c
+    i32_load.c
+    i32_store.c
+)
diff --git a/src/op/memory/current_memory.c b/src/op/memory/current_memory.c
new file mode 100644
index 0000000..c67d425
--- /dev/null
+++ b/src/op/memory/current_memory.c
@@ -0,0 +1,44 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <stddef.h>
+#include <stdio.h>
+
+static int op(struct nw_interp *const i, FILE *const f)
+{
+    varuint1 reserved;
+
+    if (varuint1_read(f, &reserved))
+    {
+        LOG("%s: varuint1_read failed\n", __func__);
+        return 1;
+    }
+    else if (reserved)
+    {
+        LOG("%s: unexpected non-zero reserved value %u\n",
+            __func__, (unsigned)reserved);
+        return 1;
+    }
+
+    return 0;
+}
+
+int op_current_memory(struct nw_interp *const i)
+{
+    return op(i, i->f);
+}
+
+int check_current_memory(FILE *const f)
+{
+    return op(NULL, f);
+}
diff --git a/src/op/memory/i32_load.c b/src/op/memory/i32_load.c
new file mode 100644
index 0000000..04dbec7
--- /dev/null
+++ b/src/op/memory/i32_load.c
@@ -0,0 +1,76 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/interp.h>
+#include <nw/types.h>
+#include <stddef.h>
+#include <stdio.h>
+
+static int load(struct nw_interp *const i, const varuint32 flags,
+    const varuint32 offset)
+{
+    enum {ALIGN = 2};
+    int32_t value;
+
+    if (flags != ALIGN)
+    {
+        LOG("%s: expected 32-bit alignment (%d), got %lu\n",
+            __func__, ALIGN, (unsigned long)flags);
+        i->exception = "unaligned access";
+        return -1;
+    }
+    else if (interp_heap_load(i, offset, &value, sizeof value))
+    {
+        LOG("%s: interp_heap_load failed\n", __func__);
+        return -1;
+    }
+    else if (interp_stack_push(i, &value, sizeof value))
+    {
+        LOG("%s: interp_stack_push failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+static int op(struct nw_interp *const i, FILE *const f)
+{
+    varint32 flags, offset;
+
+    if (varint32_read(f, &flags))
+    {
+        LOG("%s: varint32_read flags failed\n", __func__);
+        return 1;
+    }
+    else if (varint32_read(f, &offset))
+    {
+        LOG("%s: varint32_read offset failed\n", __func__);
+        return 1;
+    }
+    else if (i && load(i, flags, offset))
+    {
+        LOG("%s: load failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+int op_i32_load(struct nw_interp *const i)
+{
+    return op(i, i->f);
+}
+
+int check_i32_load(FILE *const f)
+{
+    return op(NULL, f);
+}
diff --git a/src/op/memory/i32_store.c b/src/op/memory/i32_store.c
new file mode 100644
index 0000000..212cd86
--- /dev/null
+++ b/src/op/memory/i32_store.c
@@ -0,0 +1,125 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <nw/interp.h>
+#include <stdint.h>
+#include <stddef.h>
+#include <stdio.h>
+
+static int store(struct nw_interp *const i, const varuint32 flags,
+    const varuint32 offset)
+{
+    enum {ALIGN = 2};
+
+    if (flags != ALIGN)
+    {
+        LOG("%s: expected 32-bit alignment (%d), got %lu\n",
+            __func__, ALIGN, (unsigned long)flags);
+        i->exception = "unaligned access";
+        return -1;
+    }
+
+    int32_t value, addr;
+
+    if (interp_stack_pop(i, &value, sizeof value))
+    {
+        LOG("%s: inter_stack_pop value failed\n", __func__);
+        return -1;
+    }
+    else if (interp_stack_pop(i, &addr, sizeof addr))
+    {
+        LOG("%s: inter_stack_pop addr failed\n", __func__);
+        return -1;
+    }
+    else if (offset > SIZE_MAX - addr)
+    {
+        static const char exc[] = "offset address overflow";
+
+        LOG("%s: %s\n", __func__, exc);
+        i->exception = exc;
+        return -1;
+    }
+    else if (interp_heap_store(i, offset + addr, &value, sizeof value))
+    {
+        LOG("%s: interp_heap_store failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+#if 0
+    stack_i -= sizeof addr;
+
+    if (max < addr || offset >= max - addr)
+    {
+        LOG("%s: heap overflow\n", __func__);
+        i->exception = "heap overflow";
+        return -1;
+    }
+
+    const size_t raddr = offset + addr;
+
+    if (raddr % sizeof addr)
+    {
+        LOG("%s: unaligned memory address\n", __func__);
+        i->exception = "unaligned access";
+        return -1;
+    }
+    else if (stack_i < sizeof (uint32_t))
+    {
+        LOG("%s: stack underflow (value)\n", __func__);
+        i->exception = "stack underflow";
+        return -1;
+    }
+
+    const int32_t value = htoni32(*stackptr);
+    void *dst = &((char *)i->cfg.heap.buf)[raddr];
+
+    *(int32_t *)dst = value;
+    stack_i -= sizeof addr;
+    i->stack_i = stack_i;
+    return 0;
+#endif
+}
+
+static int op(struct nw_interp *const i, FILE *const f)
+{
+    varuint32 flags, offset;
+
+    if (varuint32_read(f, &flags))
+    {
+        LOG("%s: varint32_read flags failed\n", __func__);
+        return -1;
+    }
+    else if (varuint32_read(f, &offset))
+    {
+        LOG("%s: varint32_read offset failed\n", __func__);
+        return -1;
+    }
+    else if (i && store(i, flags, offset))
+    {
+        LOG("%s: store failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+int op_i32_store(struct nw_interp *const i)
+{
+    return op(i, i->f);
+}
+
+int check_i32_store(FILE *const f)
+{
+    return op(NULL, f);
+}
diff --git a/src/op/numeric/CMakeLists.txt b/src/op/numeric/CMakeLists.txt
new file mode 100644
index 0000000..a259506
--- /dev/null
+++ b/src/op/numeric/CMakeLists.txt
@@ -0,0 +1,10 @@
+# nanowasm, a tiny WebAssembly/Wasm interpreter
+# Copyright (C) 2023-2024  Xavier Del Campo Romero
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+target_sources(${PROJECT_NAME} PRIVATE
+    i32_sub.c
+)
diff --git a/src/op/numeric/i32_sub.c b/src/op/numeric/i32_sub.c
new file mode 100644
index 0000000..c3d1352
--- /dev/null
+++ b/src/op/numeric/i32_sub.c
@@ -0,0 +1,66 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/interp.h>
+#include <nw/types.h>
+#include <inttypes.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+/* Inspired by "INT32-C. Ensure that operations on signed integers do
+ * not result in overflow". */
+static bool signed_overflow(const int32_t a, const int32_t b)
+{
+    return (b > 0 && a < INT32_MIN + b)
+        || (b < 0 && a > INT32_MAX + b);
+}
+
+int op_i32_sub(struct nw_interp *const i)
+{
+    int32_t op1, op2;
+
+    if (interp_stack_pop(i, &op2, sizeof op2))
+    {
+        LOG("%s: interp_stack_pop %s failed\n", __func__, "op2");
+        return -1;
+    }
+    else if (interp_stack_pop(i, &op1, sizeof op1))
+    {
+        LOG("%s: interp_stack_pop %s failed\n", __func__, "op1");
+        return -1;
+    }
+    else if (signed_overflow(op2, op1))
+    {
+        LOG("%s: signed integer overflow (op1=%" PRIi32 ", op2=%" PRIi32 ")\n",
+            __func__, op1, op2);
+        i->exception = "signed integer overflow";
+        return 1;
+    }
+
+    const int32_t result = op2 - op1;
+
+    if (interp_stack_push(i, &result, sizeof result))
+    {
+        LOG("%s: interp_stack_push failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+int check_i32_sub(FILE *const f)
+{
+    return 0;
+}
diff --git a/src/op/variable_access/CMakeLists.txt b/src/op/variable_access/CMakeLists.txt
new file mode 100644
index 0000000..314b5bf
--- /dev/null
+++ b/src/op/variable_access/CMakeLists.txt
@@ -0,0 +1,14 @@
+# nanowasm, a tiny WebAssembly/Wasm interpreter
+# Copyright (C) 2023-2024  Xavier Del Campo Romero
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+target_sources(${PROJECT_NAME} PRIVATE
+    get_global.c
+    get_local.c
+    set_global.c
+    set_local.c
+    tee_local.c
+)
diff --git a/src/op/variable_access/get_global.c b/src/op/variable_access/get_global.c
new file mode 100644
index 0000000..d38f2d0
--- /dev/null
+++ b/src/op/variable_access/get_global.c
@@ -0,0 +1,100 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/interp.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+static int get_i32(struct nw_interp *const i, const void *const src)
+{
+    return interp_stack_push(i, src, sizeof (int32_t));
+}
+
+static int get_i64(struct nw_interp *const i, const void *const src)
+{
+    return interp_stack_push(i, src, sizeof (int64_t));
+}
+
+static int get_f32(struct nw_interp *const i, const void *const src)
+{
+    return interp_stack_push(i, src, sizeof (float));
+}
+
+static int get_f64(struct nw_interp *const i, const void *const src)
+{
+    return interp_stack_push(i, src, sizeof (double));
+}
+
+static int get_global(struct nw_interp *const i, const varuint32 global_index)
+{
+    struct nw_gframe *gfr;
+    varuint32 idx;
+
+    for (idx = global_index, gfr = i->gfp; gfr; gfr = gfr->next)
+        if (idx == global_index)
+            break;
+
+    if (!gfr)
+    {
+        LOG("%s: cannot access global variable %lu\n", __func__,
+            (unsigned long)global_index);
+        i->exception = "global variable index out of bounds";
+        return -1;
+    }
+
+    static int (*const get[])(struct nw_interp *, const void *) =
+    {
+        [VALUE_TYPE_I32] = get_i32,
+        [VALUE_TYPE_I64] = get_i64,
+        [VALUE_TYPE_F32] = get_f32,
+        [VALUE_TYPE_F64] = get_f64,
+    };
+
+    if (get[gfr->type](i, gfr + 1))
+    {
+        LOG("%s: get type %s failed\n", __func__, value_type_tostr(gfr->type));
+        return -1;
+    }
+
+    return 0;
+}
+
+static int op(struct nw_interp *const i, FILE *const f)
+{
+    varuint32 global_index;
+
+    if (varuint32_read(f, &global_index))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return 1;
+    }
+    else if (i && get_global(i, global_index))
+    {
+        LOG("%s: get_global failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+int op_get_global(struct nw_interp *const i)
+{
+    return op(i, i->f);
+}
+
+int check_get_global(FILE *const f)
+{
+    return op(NULL, f);
+}
diff --git a/src/op/variable_access/get_local.c b/src/op/variable_access/get_local.c
new file mode 100644
index 0000000..745a2e7
--- /dev/null
+++ b/src/op/variable_access/get_local.c
@@ -0,0 +1,112 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <nw/interp.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+static int get_i32(struct nw_interp *const i, const void *const data,
+    const varuint32 idx)
+{
+    const int32_t *const src = (const int32_t *)data + idx;
+
+    return interp_stack_push(i, src, sizeof (*src));
+}
+
+static int get_i64(struct nw_interp *const i, const void *const data,
+    const varuint32 idx)
+{
+    const int64_t *const src = (const int64_t *)data + idx;
+
+    return interp_stack_push(i, src, sizeof (*src));
+}
+
+static int get_f32(struct nw_interp *const i, const void *const data,
+    const varuint32 idx)
+{
+    const float *const src = (const float *)data + idx;
+
+    return interp_stack_push(i, src, sizeof (*src));
+}
+
+static int get_f64(struct nw_interp *const i, const void *const data,
+    const varuint32 idx)
+{
+    const double *const src = (const double *)data + idx;
+
+    return interp_stack_push(i, src, sizeof (*src));
+}
+
+static int get_local(const varuint32 local_index, struct nw_interp *const i)
+{
+    struct nw_frame *fr;
+    varuint32 idx;
+
+    for (idx = local_index, fr = i->fp; fr; fr = fr->next)
+        if (idx < fr->n_locals)
+            break;
+
+    if (!fr)
+    {
+        LOG("%s: cannot access local variable %lu\n", __func__,
+            (unsigned long)local_index);
+        i->exception = "local variable index out of bounds";
+        return -1;
+    }
+
+    static int (*const get[])(struct nw_interp *, const void *, varuint32) =
+    {
+        [VALUE_TYPE_I32] = get_i32,
+        [VALUE_TYPE_I64] = get_i64,
+        [VALUE_TYPE_F32] = get_f32,
+        [VALUE_TYPE_F64] = get_f64,
+    };
+
+    if (get[fr->local_type](i, fr + 1, idx))
+    {
+        LOG("%s: get type %d failed\n", __func__, fr->local_type);
+        return -1;
+    }
+
+    return 0;
+}
+
+static int op(struct nw_interp *const i, FILE *const f)
+{
+    varuint32 local_index;
+
+    if (varuint32_read(f, &local_index))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return 1;
+    }
+    else if (i && get_local(local_index, i))
+    {
+        LOG("%s: get_local failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+int op_get_local(struct nw_interp *const i)
+{
+    return op(i, i->f);
+}
+
+int check_get_local(FILE *const f)
+{
+    return op(NULL, f);
+}
diff --git a/src/op/variable_access/set_global.c b/src/op/variable_access/set_global.c
new file mode 100644
index 0000000..d1229c5
--- /dev/null
+++ b/src/op/variable_access/set_global.c
@@ -0,0 +1,38 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <stddef.h>
+#include <stdio.h>
+
+static int op(struct nw_interp *const i, FILE *const f)
+{
+    varuint32 global_index;
+
+    if (varuint32_read(f, &global_index))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return 1;
+    }
+
+    return 0;
+}
+
+int op_set_global(struct nw_interp *const i)
+{
+    return op(i, i->f);
+}
+
+int check_set_global(FILE *const f)
+{
+    return op(NULL, f);
+}
diff --git a/src/op/variable_access/set_local.c b/src/op/variable_access/set_local.c
new file mode 100644
index 0000000..8cf6440
--- /dev/null
+++ b/src/op/variable_access/set_local.c
@@ -0,0 +1,124 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+
+static int set_i32(struct nw_interp *const i, void *const data,
+    const varuint32 idx)
+{
+    const void *const stackptr = (const char *)i->cfg.stack.buf + i->stack_i;
+    const int32_t *const src = (const int32_t *)stackptr - 1;
+    int32_t *const dst = (int32_t *)data + idx;
+
+    *dst = *src;
+    return 0;
+}
+
+static int set_i64(struct nw_interp *const i, void *const data,
+    const varuint32 idx)
+{
+    const void *const stackptr = (const char *)i->cfg.stack.buf + i->stack_i;
+    const int64_t *const src = (const int64_t *)stackptr - 1;
+    int64_t *const dst = (int64_t *)data + idx;
+
+    *dst = *src;
+    return 0;
+}
+
+static int set_f32(struct nw_interp *const i, void *const data,
+    const varuint32 idx)
+{
+    const void *const stackptr = (const char *)i->cfg.stack.buf + i->stack_i;
+    const float *const src = (const float *)stackptr - 1;
+    float *const dst = (float *)data + idx;
+
+    *dst = *src;
+    return 0;
+}
+
+static int set_f64(struct nw_interp *const i, void *const data,
+    const varuint32 idx)
+{
+    const void *const stackptr = (const char *)i->cfg.stack.buf + i->stack_i;
+    const double *const src = (const double *)stackptr - 1;
+    double *const dst = (double *)data + idx;
+
+    *dst = *src;
+    return 0;
+}
+
+static int set_local(const varuint32 local_index, struct nw_interp *const i)
+{
+    struct nw_frame *fr;
+    varuint32 idx;
+
+    for (idx = local_index, fr = i->fp; fr; fr = fr->next)
+        if (idx < fr->n_locals)
+            break;
+
+    if (!fr)
+    {
+        LOG("%s: cannot access local variable %lu\n", __func__,
+            (unsigned long)local_index);
+        i->exception = "local variable index out of bounds";
+        return -1;
+    }
+
+    static int (*const set[])(struct nw_interp *, void *, varuint32) =
+    {
+        [VALUE_TYPE_I32] = set_i32,
+        [VALUE_TYPE_I64] = set_i64,
+        [VALUE_TYPE_F32] = set_f32,
+        [VALUE_TYPE_F64] = set_f64,
+    };
+
+    if (set[fr->local_type](i, fr + 1, idx))
+    {
+        LOG("%s: set type %d failed\n", __func__, fr->local_type);
+        return -1;
+    }
+
+    return 0;
+}
+
+static int op(struct nw_interp *const i, FILE *const f)
+{
+    varuint32 local_index;
+
+    if (varuint32_read(f, &local_index))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return 1;
+    }
+    else if (i && set_local(local_index, i))
+    {
+        LOG("%s: set_local failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+int op_set_local(struct nw_interp *const i)
+{
+    return op(i, i->f);
+}
+
+int check_set_local(FILE *const f)
+{
+    return op(NULL, f);
+}
diff --git a/src/op/variable_access/tee_local.c b/src/op/variable_access/tee_local.c
new file mode 100644
index 0000000..00d7832
--- /dev/null
+++ b/src/op/variable_access/tee_local.c
@@ -0,0 +1,38 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/ops.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <stddef.h>
+#include <stdio.h>
+
+static int op(struct nw_interp *const i, FILE *const f)
+{
+    varuint32 local_index;
+
+    if (varuint32_read(f, &local_index))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return 1;
+    }
+
+    return 0;
+}
+
+int op_tee_local(struct nw_interp *const i)
+{
+    return op(i, i->f);
+}
+
+int check_tee_local(FILE *const f)
+{
+    return op(NULL, f);
+}
diff --git a/src/run.c b/src/run.c
new file mode 100644
index 0000000..e1cca7d
--- /dev/null
+++ b/src/run.c
@@ -0,0 +1,42 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nanowasm/nw.h>
+#include <nw/interp.h>
+#include <nw/log.h>
+#include <nw/search.h>
+#include <errno.h>
+#include <stdio.h>
+#include <string.h>
+
+enum nw_state nw_run(struct nw_inst *const i)
+{
+    struct nw_interp *const in = &i->interp;
+    union nw_inst_state *const s = &i->state;
+
+    if (interp_run(in))
+    {
+        LOG("%s: interp_run failed\n", __func__);
+
+        if (in->exception)
+        {
+            s->exception = in->exception;
+            return NW_STATE_EXCEPTION;
+        }
+
+        return NW_STATE_FATAL;
+    }
+    else if (in->exit)
+    {
+        s->retval = in->retval;
+        return NW_STATE_RETURNED;
+    }
+
+    return NW_STATE_AGAIN;
+}
diff --git a/src/search.c b/src/search.c
new file mode 100644
index 0000000..622b74c
--- /dev/null
+++ b/src/search.c
@@ -0,0 +1,181 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/search.h>
+#include <nw/log.h>
+#include <nw/fstring.h>
+#include <nw/sections.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <errno.h>
+#include <stdint.h>
+#include <string.h>
+
+static int ensure_export(const char *const fn,
+    const struct nw_mod *const m, FILE *const f, varuint32 *const out)
+{
+    if (!m->sections.export)
+    {
+        LOG("%s: export section not found", __func__);
+        return -1;
+    }
+    else if (fseek(f, m->sections.export, SEEK_SET))
+    {
+        LOG("%s: fseek(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    varuint32 count;
+
+    if (varuint32_read(f, &count))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return -1;
+    }
+
+    for (varuint32 i = 0; i < count; i++)
+    {
+        varuint32 len;
+        bool found = false;
+
+        if (varuint32_read(f, &len))
+        {
+            LOG("%s: varuint32_read failed\n", __func__);
+            return -1;
+        }
+        else if (len != strlen(fn))
+        {
+            if (fseek(f, len, SEEK_CUR))
+            {
+                LOG("%s: fseek(3): %s\n", __func__, strerror(errno));
+                return -1;
+            }
+        }
+        else if (!fstrcmp(fn, f, false))
+            found = true;
+
+        uint8_t kind;
+
+        if (!fread(&kind, sizeof kind, 1, f))
+        {
+            LOG("%s: fread(3) failed: feof=%d, ferror=%d\n", __func__,
+                feof(f), ferror(f));
+            return -1;
+        }
+
+        varuint32 index;
+
+        if (varuint32_read(f, &index))
+        {
+            LOG("%s: varuint32_read failed\n", __func__);
+            return -1;
+        }
+        else if (found)
+        {
+            if (kind != NW_KIND_FUNCTION)
+            {
+                LOG("%s: expected kind %d, got %d\n", __func__,
+                    NW_KIND_FUNCTION, kind);
+                return -1;
+            }
+
+            *out = index;
+            return 0;
+        }
+    }
+
+    return -1;
+}
+
+static int get_function_index(const struct nw_mod *const m,
+    const varuint32 index, varuint32 *const findex)
+{
+    const size_t n = m->cfg.n_imports;
+
+    if (index < n)
+    {
+        LOG("%s: index (%lu) must be greater than number of imports (%zu)\n",
+            __func__, (unsigned long)index, n);
+        return -1;
+    }
+
+    *findex = index - n;
+    return 0;
+}
+
+static int get_fn_start(const struct nw_mod *const m, FILE *const f,
+    const varuint32 index, struct search_fn *const out)
+{
+    const struct section s =
+    {
+        .cfg = &m->cfg,
+        .f = f
+    };
+
+    struct section_function sf;
+    struct section_code c;
+
+    if (section_function(&s, m, index, &sf))
+    {
+        LOG("%s: section_function failed\n", __func__);
+        return -1;
+    }
+    else if (section_code(&s, m, index, &c))
+    {
+        LOG("%s: section_code failed\n", __func__);
+        return -1;
+    }
+
+    out->start = c.start;
+    out->index = index;
+    return 0;
+}
+
+int search_exported_fn(const char *const fn, const struct nw_mod *const m,
+    FILE *const f, struct search_fn *const out)
+{
+    varuint32 index, findex;
+
+    if (ensure_export(fn, m, f, &index))
+    {
+        LOG("%s: %s not an exported function\n", __func__, fn);
+        return -1;
+    }
+    else if (get_function_index(m, index, &findex))
+    {
+        LOG("%s: get_function_index failed\n", __func__);
+        return -1;
+    }
+    else if (get_fn_start(m, f, findex, out))
+    {
+        LOG("%s: get_fn_start %s failed\n", __func__, fn);
+        return -1;
+    }
+
+    return 0;
+}
+
+int search_fn(const varuint32 index, const struct nw_mod *const m,
+    FILE *const f, struct search_fn *const out)
+{
+    varuint32 findex;
+
+    if (get_function_index(m, index, &findex))
+    {
+        LOG("%s: get_function_index failed\n", __func__);
+        return -1;
+    }
+    else if (get_fn_start(m, f, findex, out))
+    {
+        LOG("%s: get_fn_start failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
diff --git a/src/section/CMakeLists.txt b/src/section/CMakeLists.txt
new file mode 100644
index 0000000..772dd3f
--- /dev/null
+++ b/src/section/CMakeLists.txt
@@ -0,0 +1,22 @@
+# nanowasm, a tiny WebAssembly/Wasm interpreter
+# Copyright (C) 2023-2024  Xavier Del Campo Romero
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+target_sources(${PROJECT_NAME} PRIVATE
+    code.c
+    common.c
+    custom.c
+    data.c
+    element.c
+    export.c
+    function.c
+    global.c
+    import.c
+    memory.c
+    start.c
+    table.c
+    type.c
+)
diff --git a/src/section/code.c b/src/section/code.c
new file mode 100644
index 0000000..da45047
--- /dev/null
+++ b/src/section/code.c
@@ -0,0 +1,429 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nanowasm/nw.h>
+#include <nw/opcodes.h>
+#include <nw/interp.h>
+#include <nw/sections.h>
+#include <nw/types.h>
+#include <errno.h>
+#include <inttypes.h>
+#include <limits.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+
+static int check_body(FILE *const f, const unsigned long n)
+{
+    unsigned long rem = n;
+
+    while (rem)
+    {
+        const long before = ftell(f);
+        uint8_t byte;
+
+        if (before < 0)
+        {
+            LOG("%s: ftell(3) before: %s\n", __func__, strerror(errno));
+            return -1;
+        }
+        else if (!fread(&byte, sizeof byte, 1, f))
+        {
+            LOG("%s: fread(3) failed, feof=%d, ferror=%d\n",
+                __func__, feof(f), ferror(f));
+            return -1;
+        }
+        else if (rem == 1 && byte != OP_END)
+        {
+            LOG("%s: unexpected opcode %#" PRIx8 " at body end\n",
+                __func__, byte);
+            return -1;
+        }
+        else if (interp_check_opcode(byte, f))
+        {
+            LOG("%s: interp_check_opcode failed\n", __func__);
+            return -1;
+        }
+
+        const long after = ftell(f);
+
+        if (after < 0)
+        {
+            LOG("%s: ftell(3) after: %s\n", __func__, strerror(errno));
+            return -1;
+        }
+
+        rem -= after - before;
+    }
+
+    return 0;
+}
+
+#if 0
+
+static int push_locals(struct nw_interp *const i,
+    const struct nw_frame *const f)
+{
+    const enum value_type t = f->local_type;
+    const size_t typesz = get_type_size(t);
+    const unsigned long n = f->n_locals;
+
+    if (mul_overflow(typesz, f->n_locals))
+    {
+        LOG("%s: local variables size mul overflow", __func__);
+        i->exception = "mul overfllow";
+        return -1;
+    }
+
+    const size_t totalsz = typesz * n, max = i->cfg.stack.n;
+
+    if (totalsz > max || i->stack_i > max - totalsz)
+    {
+        LOG("%s: cannot allocate locals\n", __func__);
+        i->exception = "stack overflow";
+        return 1;
+    }
+
+    init_locals(t, n, interp_stackptr(i));
+    i->stack_i += totalsz;
+    return 0;
+}
+
+static int push_block(struct nw_interp *const i)
+{
+    const long pc = ftell(i->f);
+
+    if (pc < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    const struct nw_block b =
+    {
+        .pc = pc
+    };
+
+    if (interp_stack_push(i, &b, sizeof b))
+    {
+        LOG("%s: interp_stack_push failed\n", __func__);
+        return -1;
+    }
+
+    struct nw_block *const p = (struct nw_block *)interp_stackptr(i) - 1;
+
+    if (i->fp->block)
+    {
+        for (struct nw_block *b = i->fp->block; b; b = b->next)
+            if (!b->next)
+            {
+                b->next = p;
+                break;
+            }
+    }
+    else
+        i->fp->block = p;
+
+    return 0;
+}
+
+static int loop_push_blocks(struct nw_interp *const i)
+{
+    for (;;)
+    {
+        uint8_t op;
+
+        if (!fread(&op, sizeof op, 1, i->f))
+        {
+            LOG("%s: fread(3) failed, feof=%d, ferror=%d\n", __func__,
+                feof(i->f), ferror(i->f));
+            i->exception = "I/O error";
+            return -1;
+        }
+        else if (op >= sizeof ops / sizeof *ops)
+        {
+            LOG("%s: invalid opcode %#" PRIx8 "\n", __func__, op);
+            i->exception = "invalid opcode";
+            return -1;
+        }
+        else if (interp_check_opcode(op, i->f))
+        {
+            LOG("%s: interp_check_opcode failed\n", __func__);
+            return -1;
+        }
+
+        switch (op)
+        {
+            case OP_END:
+                return 0;
+
+            case OP_BLOCK:
+                if (push_block(i))
+                {
+                    LOG("%s: push_block failed\n", __func__);
+                    return -1;
+                }
+
+                break;
+
+            default:
+                break;
+        }
+    }
+}
+
+static int push_blocks(struct nw_interp *const i,
+    const struct nw_frame *const fr)
+{
+    FILE *const f = i->f;
+    const long orig = ftell(f);
+
+    if (orig < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+    else if (loop_push_blocks(i))
+    {
+        LOG("%s: loop_push_blocks failed\n", __func__);
+        return -1;
+    }
+    else if (fseek(f, orig, SEEK_SET))
+    {
+        LOG("%s: fseek(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    return 0;
+}
+#endif
+
+static int push_local_count(struct nw_frame *const f, const varuint32 count,
+    const varint7 type)
+{
+    enum value_type vtype;
+
+    if (get_value_type(type, &vtype))
+    {
+        LOG("%s: get_value_type failed\n", __func__);
+        return -1;
+    }
+
+    f->n_locals = count;
+    f->local_type = vtype;
+    return 0;
+}
+
+static int check_local(FILE *const f, struct nw_frame *const fr)
+{
+    varuint32 count;
+    varint7 type;
+
+    if (varuint32_read(f, &count))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return -1;
+    }
+    else if (varint7_read(f, &type))
+    {
+        LOG("%s: varint7_read failed\n", __func__);
+        return -1;
+    }
+    else if (fr && push_local_count(fr, count, type))
+    {
+        LOG("%s: push_local_count failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+static int check_locals(FILE *const f, struct nw_frame *const fr)
+{
+    varuint32 local_count;
+
+    if (varuint32_read(f, &local_count))
+    {
+        LOG("%s: varuint32_read local_count failed\n", __func__);
+        return -1;
+    }
+
+    for (varuint32 i = 0; i < local_count; i++)
+        if (check_local(f, fr))
+        {
+            LOG("%s: check_local failed\n", __func__);
+            return -1;
+        }
+
+    return 0;
+}
+
+static int check_function_body(FILE *const f, long *const out)
+{
+    varuint32 body_size;
+
+    if (varuint32_read(f, &body_size))
+    {
+        LOG("%s: varuint32_read body_size failed\n", __func__);
+        return -1;
+    }
+
+    const long start = ftell(f);
+
+    if (start < 0)
+    {
+        LOG("%s: ftell(3) start: %s\n", __func__, strerror(errno));
+        return -1;
+    }
+    else if (check_locals(f, NULL))
+    {
+        LOG("%s: check_locals failed\n", __func__);
+        return -1;
+    }
+
+    const long end = ftell(f);
+
+    if (end < 0)
+    {
+        LOG("%s: ftell(3) end: %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    const unsigned long consumed = end - start;
+
+    if (consumed > body_size)
+    {
+        LOG("%s: exceeded function body size\n", __func__);
+        return -1;
+    }
+    else if (check_body(f, body_size - consumed))
+    {
+        LOG("%s: check_body failed\n", __func__);
+        return -1;
+    }
+
+    *out = start;
+    return 0;
+}
+
+static int run(FILE *const f, const varuint32 idx,
+    struct section_code *const out)
+{
+    varuint32 count;
+
+    if (varuint32_read(f, &count))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return -1;
+    }
+    else if (count > ULONG_MAX - 1)
+    {
+        fprintf(stderr, "%s: count overflow\n", __func__);
+        return -1;
+    }
+
+    for (varuint32 i = 0; i < count; i++)
+    {
+        long start;
+
+        if (check_function_body(f, &start))
+        {
+            LOG("%s: check_function_body failed\n", __func__);
+            return -1;
+        }
+        else if (out && i == idx)
+        {
+            out->start = start;
+            return 0;
+        }
+    }
+
+    return 0;
+}
+
+int section_code_check(const struct section *const s, struct nw_mod *const m,
+    const unsigned long len)
+{
+    FILE *const f = s->f;
+
+    if (m->sections.code)
+    {
+        LOG("%s: ignoring duplicate section\n", __func__);
+        return fseek(f, len, SEEK_CUR);
+    }
+
+    const long start = ftell(f);
+
+    if (start < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+    else if (run(f, 0, NULL))
+    {
+        LOG("%s: run failed\n", __func__);
+        return -1;
+    }
+
+    const long end = ftell(f);
+
+    if (end < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    const unsigned long size = end - start;
+
+    if (size != len)
+    {
+        LOG("%s: size exceeded (%lu expected, got %lu)\n",
+                __func__, len, size);
+        return -1;
+    }
+
+    m->sections.code = start;
+    return 0;
+}
+
+int section_code(const struct section *const s, const struct nw_mod *const m,
+    const varuint32 idx, struct section_code *const out)
+{
+    const long offset = m->sections.code;
+
+    if (offset <= 0)
+    {
+        LOG("%s: code section not found", __func__);
+        return -1;
+    }
+    else if (fseek(s->f, offset, SEEK_SET))
+    {
+        LOG("%s: fseek(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    return run(s->f, idx, out);
+}
+
+int section_code_push(FILE *const f, const long pc, struct nw_frame *const fr)
+{
+    if (fseek(f, pc, SEEK_SET))
+    {
+        LOG("%s: fseek(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+    else if (check_locals(f, fr))
+    {
+        LOG("%s: check_local failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
diff --git a/src/section/common.c b/src/section/common.c
new file mode 100644
index 0000000..b768470
--- /dev/null
+++ b/src/section/common.c
@@ -0,0 +1,150 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/sections.h>
+#include <nw/types.h>
+#include <errno.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+
+int check_resizable_limits(FILE *const f, struct resizable_limits *const r)
+{
+    varuint1 flags;
+    varuint32 initial;
+
+    *r = (const struct resizable_limits){0};
+
+    if (varuint1_read(f, &flags))
+    {
+        LOG("%s: varuint1_read failed\n", __func__);
+        return -1;
+    }
+    else if (varuint32_read(f, &initial))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return -1;
+    }
+
+    if (flags)
+    {
+        varuint32 maximum;
+
+        if (varuint32_read(f, &maximum))
+        {
+            LOG("%s: varuint32_read failed\n", __func__);
+            return -1;
+        }
+
+        r->max = maximum;
+        r->max_available = true;
+    }
+
+    static const unsigned long page_size = 64lu * 1024lu;
+
+    if (initial > UINT32_MAX / page_size)
+    {
+        LOG("%s: initial size (%lu) overflow \n", __func__,
+            (unsigned long)initial);
+        return 1;
+    }
+
+    r->sz = initial * page_size;
+    return 0;
+}
+
+size_t get_type_size(const enum value_type type)
+{
+    static const size_t list[] =
+    {
+        [VALUE_TYPE_I32] = sizeof (int32_t),
+        [VALUE_TYPE_I64] = sizeof (int64_t),
+        [VALUE_TYPE_F32] = sizeof (float),
+        [VALUE_TYPE_F64] = sizeof (double)
+    };
+
+    return list[type];
+}
+
+enum
+{
+    I32 = 0x7f,
+    I64 = 0x7e,
+    F32 = 0x7d,
+    F64 = 0x7c,
+    ANYFUNC = 0x70,
+    FUNC = 0x60,
+    BLOCK_TYPE = 0x40
+};
+
+int get_value_type(const varint7 type, enum value_type *const vtype)
+{
+    static const struct size
+    {
+        varint7 type;
+        enum value_type vtype;
+    } sizes[] =
+    {
+        {.type = I32, .vtype = VALUE_TYPE_I32},
+        {.type = I64, .vtype = VALUE_TYPE_I64},
+        {.type = F32, .vtype = VALUE_TYPE_F32},
+        {.type = F64, .vtype = VALUE_TYPE_F64},
+        /* TODO: check this. */
+        {.type = ANYFUNC, .vtype = VALUE_TYPE_I32},
+        /* TODO: check this. */
+        {.type = FUNC, .vtype = VALUE_TYPE_I32},
+        /* TODO: check this. */
+        {.type = BLOCK_TYPE, .vtype = VALUE_TYPE_I32}
+    };
+
+    for (size_t i = 0; i < sizeof sizes / sizeof *sizes; i++)
+    {
+        const struct size *const s = &sizes[i];
+
+        if (type == s->type)
+        {
+            *vtype = s->vtype;
+            return 0;
+        }
+    }
+
+    LOG("%s: unknown type %#hhx\n", __func__, (char)type);
+    return -1;
+}
+
+static int32_t swap_i32(const int32_t in)
+{
+    const int8_t *const p = (const int8_t *)&in;
+
+    return p[0] | (p[1] << 8) | (p[2] << 16) | (p[3] << 24);
+}
+
+int32_t htoni32(const int32_t in)
+{
+    return swap_i32(in);
+}
+
+int32_t ntohi32(const int32_t in)
+{
+    return swap_i32(in);
+}
+
+const char *value_type_tostr(const enum value_type v)
+{
+    static const char *const s[] =
+    {
+#define X(x) [x] = #x,
+        VALUE_TYPES
+#undef X
+    };
+
+    return s[v];
+}
diff --git a/src/section/custom.c b/src/section/custom.c
new file mode 100644
index 0000000..fe06b74
--- /dev/null
+++ b/src/section/custom.c
@@ -0,0 +1,30 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/sections.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <errno.h>
+#include <stdio.h>
+#include <string.h>
+
+int section_custom_check(const struct section *const s, struct nw_mod *const m,
+    const unsigned long len)
+{
+    FILE *const f = s->f;
+
+    if (fseek(f, len, SEEK_CUR))
+    {
+        LOG("%s: fseek(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    return 0;
+}
diff --git a/src/section/data.c b/src/section/data.c
new file mode 100644
index 0000000..6ea12d6
--- /dev/null
+++ b/src/section/data.c
@@ -0,0 +1,18 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nanowasm/nw.h>
+#include <nw/sections.h>
+#include <nw/types.h>
+
+int section_data_check(const struct section *const s, struct nw_mod *const m,
+    const unsigned long len)
+{
+    return -1;
+}
diff --git a/src/section/element.c b/src/section/element.c
new file mode 100644
index 0000000..39bd5b7
--- /dev/null
+++ b/src/section/element.c
@@ -0,0 +1,17 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/sections.h>
+#include <nanowasm/nw.h>
+
+int section_element_check(const struct section *const s,
+    struct nw_mod *const m, const unsigned long len)
+{
+    return -1;
+}
diff --git a/src/section/export.c b/src/section/export.c
new file mode 100644
index 0000000..0948067
--- /dev/null
+++ b/src/section/export.c
@@ -0,0 +1,161 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/sections.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+
+static int check_string(FILE *const f)
+{
+    varuint32 len;
+
+    if (varuint32_read(f, &len))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return -1;
+    }
+
+    for (varuint32 i = 0; i < len; i++)
+    {
+        uint8_t byte;
+
+        if (!fread(&byte, sizeof byte, 1, f))
+        {
+            LOG("%s: fread(3) failed, feof=%d, ferror=%d\n",
+                __func__, feof(f), ferror(f));
+            return -1;
+        }
+    }
+
+    return 0;
+}
+
+static int check_kind(FILE *const f)
+{
+    uint8_t kind;
+
+    if (!fread(&kind, sizeof kind, 1, f))
+    {
+        LOG("%s: fread(3) failed: feof=%d, ferror=%d\n", __func__,
+            feof(f), ferror(f));
+        return -1;
+    }
+
+    return 0;
+}
+
+static int check_index(FILE *const f)
+{
+    varuint32 index;
+
+    if (varuint32_read(f, &index))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+static int check_export_entry(FILE *const f)
+{
+    if (check_string(f))
+    {
+        LOG("%s: check_string failed\n", __func__);
+        return -1;
+    }
+    else if (check_kind(f))
+    {
+        LOG("%s: check_kind failed\n", __func__);
+        return -1;
+    }
+    else if (check_index(f))
+    {
+        LOG("%s: check_index failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+static int check(FILE *const f, const unsigned long len)
+{
+    const long start = ftell(f);
+    varuint32 count;
+
+    if (start < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+    else if (varuint32_read(f, &count))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return -1;
+    }
+
+    for (varuint32 i = 0; i < count; i++)
+        if (check_export_entry(f))
+        {
+            LOG("%s: check_export_entry failed\n", __func__);
+            return -1;
+        }
+
+    const long end = ftell(f);
+
+    if (end < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    const unsigned long size = end - start;
+
+    if (size != len)
+    {
+        LOG("%s: size exceeded (%lu expected, got %lu)\n",
+                __func__, len, size);
+        return -1;
+    }
+
+    return 0;
+}
+
+int section_export_check(const struct section *const s, struct nw_mod *const m,
+    const unsigned long len)
+{
+    FILE *const f = s->f;
+
+    if (m->sections.export)
+    {
+        LOG("%s: ignoring duplicate section\n", __func__);
+        return fseek(f, len, SEEK_CUR);
+    }
+
+    const long offset = ftell(f);
+
+    if (offset < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+    else if (check(f, len))
+    {
+        LOG("%s: check failed\n", __func__);
+        return -1;
+    }
+
+    m->sections.export = offset;
+    return 0;
+}
diff --git a/src/section/function.c b/src/section/function.c
new file mode 100644
index 0000000..3ffed36
--- /dev/null
+++ b/src/section/function.c
@@ -0,0 +1,127 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/sections.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <errno.h>
+#include <limits.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+
+static int run(FILE *const f, const varuint32 idx,
+    struct section_function *const out)
+{
+    varuint32 count;
+
+    if (varuint32_read(f, &count))
+    {
+        LOG("%s: varuint32_read count failed\n", __func__);
+        return -1;
+    }
+    else if (count > ULONG_MAX - 1)
+    {
+        fprintf(stderr, "%s: count overflow\n", __func__);
+        return -1;
+    }
+
+    for (varuint32 i = 0; i < count; i++)
+    {
+        varuint32 type;
+
+        if (varuint32_read(f, &type))
+        {
+            LOG("%s: varuint32_read type failed\n", __func__);
+            return -1;
+        }
+        else if (out && i == idx)
+        {
+            out->type = type;
+            out->nreturn = count;
+            return 0;
+        }
+    }
+
+    if (out)
+    {
+        LOG("%s: could not find function index %ju\n", __func__,
+            (uintmax_t)idx);
+        return -1;
+    }
+
+    return 0;
+}
+
+int section_function_check(const struct section *const s,
+    struct nw_mod *const m, const unsigned long len)
+{
+    FILE *const f = s->f;
+
+    if (m->sections.function)
+    {
+        LOG("%s: ignoring duplicate section\n", __func__);
+        return fseek(f, len, SEEK_CUR);
+    }
+
+    const long start = ftell(f);
+
+    if (start < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+    else if (run(f, 0, NULL))
+    {
+        LOG("%s: run failed\n", __func__);
+        return -1;
+    }
+
+    const long end = ftell(f);
+
+    if (end < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    const unsigned long size = end - start;
+
+    if (size != len)
+    {
+        LOG("%s: size exceeded (%lu expected, got %lu)\n",
+                __func__, len, size);
+        return -1;
+    }
+
+    m->sections.function = start;
+    return 0;
+}
+
+int section_function(const struct section *const s,
+    const struct nw_mod *const m, const varuint32 idx,
+    struct section_function *const f)
+{
+    const long offset = m->sections.function;
+
+    if (offset <= 0)
+    {
+        LOG("%s: function section not found", __func__);
+        return -1;
+    }
+    else if (fseek(s->f, offset, SEEK_SET))
+    {
+        LOG("%s: fseek(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    return run(s->f, idx, f);
+}
diff --git a/src/section/global.c b/src/section/global.c
new file mode 100644
index 0000000..eff2e0b
--- /dev/null
+++ b/src/section/global.c
@@ -0,0 +1,346 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/sections.h>
+#include <nanowasm/nw.h>
+#include <nw/interp.h>
+#include <nw/types.h>
+#include <errno.h>
+#include <stdio.h>
+#include <string.h>
+
+struct global_type
+{
+    bool mutable;
+    enum value_type type;
+
+    union global_value
+    {
+        int32_t i32;
+        int64_t i64;
+        float f32;
+        double f64;
+    } value;
+};
+
+static int get_i32(const struct nw_interp *const i,
+    union global_value *const value)
+{
+    if (i->stack_i != sizeof value->i32)
+    {
+        LOG("%s: expected %zu used stack bytes, got %zu\n",
+            __func__, i->stack_i, sizeof value->i32);
+        return -1;
+    }
+
+    value->i32 = *(const int32_t *)i->cfg.stack.buf;
+    return 0;
+}
+
+static int get_i64(const struct nw_interp *const i,
+    union global_value *const value)
+{
+    if (i->stack_i != sizeof value->i64)
+    {
+        LOG("%s: expected %zu used stack bytes, got %zu\n",
+            __func__, i->stack_i, sizeof value->i64);
+        return -1;
+    }
+
+    value->i64 = *(const int64_t *)i->cfg.stack.buf;
+    return 0;
+}
+
+static int get_f32(const struct nw_interp *const i,
+    union global_value *const value)
+{
+    if (i->stack_i != sizeof value->f32)
+    {
+        LOG("%s: expected %zu used stack bytes, got %zu\n",
+            __func__, i->stack_i, sizeof value->f32);
+        return -1;
+    }
+
+    value->f32 = *(const float *)i->cfg.stack.buf;
+    return 0;
+}
+
+static int get_f64(const struct nw_interp *const i,
+    union global_value *const value)
+{
+    if (i->stack_i != sizeof value->f64)
+    {
+        LOG("%s: expected %zu used stack bytes, got %zu\n",
+            __func__, i->stack_i, sizeof value->f64);
+        return -1;
+    }
+
+    value->f64 = *(const double *)i->cfg.stack.buf;
+    return 0;
+}
+
+static int get_value(const struct nw_interp *const i,
+    const enum value_type type, union global_value *const value)
+{
+    static int (*const get[])(const struct nw_interp *, union global_value *) =
+    {
+        [VALUE_TYPE_I32] = get_i32,
+        [VALUE_TYPE_I64] = get_i64,
+        [VALUE_TYPE_F32] = get_f32,
+        [VALUE_TYPE_F64] = get_f64
+    };
+
+    if (get[type](i, value))
+    {
+        LOG("%s: get failed with type %d\n", __func__, type);
+        return -1;
+    }
+
+    return 0;
+}
+
+static int check_global_type(FILE *const f, struct global_type *const g)
+{
+    const struct nw_interp_cfg cfg =
+    {
+        .stack = NW_BUF(sizeof (union global_value))
+    };
+
+    struct nw_interp i;
+    enum value_type vtype;
+    varint7 content_type;
+    varuint1 mutability;
+    union global_value value;
+
+    if (varint7_read(f, &content_type))
+    {
+        LOG("%s: varint7_read failed\n", __func__);
+        return -1;
+    }
+    else if (get_value_type(content_type, &vtype))
+    {
+        LOG("%s: get_value_type failed\n", __func__);
+        return -1;
+    }
+    else if (varuint1_read(f, &mutability))
+    {
+        LOG("%s: varuint1_read failed\n", __func__);
+        return -1;
+    }
+    else if (interp_start(&cfg, f, &i))
+    {
+        LOG("%s: interp_start failed\n", __func__);
+        return -1;
+    }
+    else if (interp_run_limited(&i, &interp_initexpr_set))
+    {
+        LOG("%s: interp_run failed\n", __func__);
+        return -1;
+    }
+    else if (get_value(&i, vtype, &value))
+    {
+        LOG("%s: get_value failed\n", __func__);
+        return -1;
+    }
+
+    *g = (const struct global_type)
+    {
+        .mutable = mutability,
+        .type = vtype,
+        .value = value
+    };
+
+    return 0;
+}
+
+static int set_i32(struct nw_interp *const i, void *const dst,
+    const struct global_type *const g)
+{
+    *(int32_t *)dst = g->value.i32;
+    return 0;
+}
+
+static int set_i64(struct nw_interp *const i, void *const dst,
+    const struct global_type *const g)
+{
+    *(int64_t *)dst = g->value.i64;
+    return 0;
+}
+
+static int set_f32(struct nw_interp *const i, void *const dst,
+    const struct global_type *const g)
+{
+    *(float *)dst = g->value.f32;
+    return 0;
+}
+
+static int set_f64(struct nw_interp *const i, void *const dst,
+    const struct global_type *const g)
+{
+    *(double *)dst = g->value.f64;
+    return 0;
+}
+
+static int add_global(struct nw_interp *const i,
+    const struct global_type *const g)
+{
+    const struct nw_gframe f =
+    {
+        .mutable = g->mutable,
+        .type = g->type
+    };
+
+    const size_t sz = sizeof f + get_type_size(g->type),
+        max = i->cfg.global.n;
+
+    if (max < sz || i->global_i > max - sz)
+    {
+        LOG("%s: global memory overflow\n", __func__);
+        i->exception = "global memory overflow";
+        return -1;
+    }
+
+    void *const buf = (char *)i->cfg.global.buf + i->global_i;
+    struct nw_gframe *const dst = buf;
+
+    if (i->gfp)
+        i->gfp->next = dst;
+
+    *dst = f;
+
+    static int (*const set[])(struct nw_interp *, void *,
+        const struct global_type *) =
+    {
+        [VALUE_TYPE_I32] = set_i32,
+        [VALUE_TYPE_I64] = set_i64,
+        [VALUE_TYPE_F32] = set_f32,
+        [VALUE_TYPE_F64] = set_f64
+    };
+
+    if (set[g->type](i, dst + 1, g))
+    {
+        LOG("%s: set failed with type %d\n", __func__, g->type);
+        return -1;
+    }
+
+    i->global_i += sz;
+    i->gfp = dst;
+    return 0;
+}
+
+static int check_global_types(FILE *const f,
+    struct nw_interp *const in)
+{
+    varuint32 count;
+
+    if (varuint32_read(f, &count))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return -1;
+    }
+
+    for (varuint32 i = 0; i < count; i++)
+    {
+        struct global_type g;
+
+        if (check_global_type(f, &g))
+        {
+            LOG("%s: check_global_type\n", __func__);
+            return -1;
+        }
+        else if (in && add_global(in, &g))
+        {
+            LOG("%s: add_global failed\n", __func__);
+            return -1;
+        }
+    }
+
+    return 0;
+}
+
+static int check(FILE *const f, const unsigned long len)
+{
+    const long start = ftell(f);
+
+    if (start < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+    else if (check_global_types(f, NULL))
+    {
+        LOG("%s: check_global_types failed\n", __func__);
+        return -1;
+    }
+
+    const long end = ftell(f);
+
+    if (end < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    const unsigned long size = end - start;
+
+    if (size != len)
+    {
+        LOG("%s: size exceeded (%lu expected, got %lu)\n",
+            __func__, len, size);
+        return -1;
+    }
+
+    return 0;
+}
+
+int section_global_check(const struct section *const s, struct nw_mod *const m,
+    const unsigned long len)
+{
+    FILE *const f = s->f;
+
+    if (m->sections.global)
+    {
+        LOG("%s: ignoring duplicate section\n", __func__);
+        return fseek(f, len, SEEK_CUR);
+    }
+
+    const long offset = ftell(f);
+
+    if (offset < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+    else if (check(f, len))
+    {
+        LOG("%s: check failed\n", __func__);
+        return -1;
+    }
+
+    m->sections.global = offset;
+    return 0;
+}
+
+int section_global_push(FILE *const f, const struct nw_mod *const m,
+    struct nw_interp *const i)
+{
+    if (fseek(f, m->sections.global, SEEK_SET))
+    {
+        LOG("%s: fseek(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+    else if (check_global_types(f, i))
+    {
+        LOG("%s: check_global_types failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
diff --git a/src/section/import.c b/src/section/import.c
new file mode 100644
index 0000000..5dd708e
--- /dev/null
+++ b/src/section/import.c
@@ -0,0 +1,274 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/sections.h>
+#include <nw/fstring.h>
+#include <nw/log.h>
+#include <nw/types.h>
+#include <errno.h>
+#include <inttypes.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+static int dump_import_name(FILE *const f, const varuint32 len)
+{
+    for (varuint32 i = 0; i < len; i++)
+    {
+        uint8_t byte;
+
+        if (!fread(&byte, sizeof byte, 1, f))
+        {
+            LOG("%s: fread(3) failed, feof=%d, ferror=%d\n",
+                __func__, feof(f), ferror(f));
+            return -1;
+        }
+
+        LOG("%c", (char)byte);
+    }
+
+    return 0;
+}
+
+static int check_module_string(const struct nw_mod_cfg *const cfg,
+    FILE *const f)
+{
+    varuint32 len;
+
+    if (varuint32_read(f, &len))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return -1;
+    }
+
+    for (size_t i = 0; i < cfg->n_imports; i++)
+    {
+        const struct nw_import *const im = &cfg->imports[i];
+        const char *const mod = im->module;
+
+        if (strlen(mod) == len)
+        {
+            const long offset = ftell(f);
+
+            if (offset < 0)
+            {
+                LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+                return -1;
+            }
+            else if (!fstrcmp(mod, f, true))
+                return 0;
+            else if (fseek(f, offset, SEEK_SET))
+            {
+                LOG("%s: fseek(3): %s\n", __func__, strerror(errno));
+                return -1;
+            }
+        }
+    }
+
+    LOG("%s: required imported module ", __func__);
+    dump_import_name(f, len);
+    LOG(" not found\n");
+    return -1;
+}
+
+static int check_field_string(const struct nw_mod_cfg *const cfg,
+    FILE *const f)
+{
+    varuint32 len;
+
+    if (varuint32_read(f, &len))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return -1;
+    }
+
+    for (size_t i = 0; i < cfg->n_imports; i++)
+    {
+        const struct nw_import *const im = &cfg->imports[i];
+        const char *const field = im->field;
+
+        if (strlen(field) == len)
+        {
+            const long offset = ftell(f);
+
+            if (offset < 0)
+            {
+                LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+                return -1;
+            }
+            else if (!fstrcmp(field, f, true))
+                return 0;
+            else if (fseek(f, offset, SEEK_SET))
+            {
+                LOG("%s: fseek(3): %s\n", __func__, strerror(errno));
+                return -1;
+            }
+        }
+    }
+
+    LOG("%s: required imported field ", __func__);
+    dump_import_name(f, len);
+    LOG(" not found\n");
+    return -1;
+}
+
+static int check_function_kind(FILE *const f)
+{
+    varuint32 type;
+
+    if (varuint32_read(f, &type))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+static int check_table_kind(FILE *const f)
+{
+    varint7 type;
+
+    if (varint7_read(f, &type))
+    {
+        LOG("%s: varint7_read failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+static int check_memory_kind(FILE *const f)
+{
+    /* TODO. */
+    return -1;
+}
+
+static int check_global_kind(FILE *const f)
+{
+    /* TODO. */
+    return -1;
+}
+
+static int check_import_entry(const struct nw_mod_cfg *const cfg,
+    FILE *const f)
+{
+    if (check_module_string(cfg, f))
+    {
+        LOG("%s: check_module_string failed\n", __func__);
+        return -1;
+    }
+    else if (check_field_string(cfg, f))
+    {
+        LOG("%s: check_field_string failed\n", __func__);
+        return -1;
+    }
+
+    uint8_t kind;
+
+    if (!fread(&kind, sizeof kind, 1, f))
+    {
+        LOG("%s: fread(3) failed, feof=%d, ferror=%d\n",
+            __func__, feof(f), ferror(f));
+        return -1;
+    }
+
+    static int (*const fn[])(FILE *) =
+    {
+        [NW_KIND_FUNCTION] = check_function_kind,
+        [NW_KIND_TABLE] = check_table_kind,
+        [NW_KIND_MEMORY] = check_memory_kind,
+        [NW_KIND_GLOBAL] = check_global_kind
+    };
+
+    if (kind >= sizeof fn / sizeof *fn)
+    {
+        LOG("%s: unexpected kind %#" PRIx8 "\n", __func__, kind);
+        return -1;
+    }
+
+    return fn[kind](f);
+}
+
+static int check(const struct nw_mod_cfg *const cfg, FILE *const f,
+    const unsigned long len)
+{
+    const long start = ftell(f);
+
+    if (start < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    varuint32 count;
+
+    if (varuint32_read(f, &count))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return -1;
+    }
+
+    for (varuint32 i = 0; i < count; i++)
+        if (check_import_entry(cfg, f))
+        {
+            LOG("%s: check_import_entry failed\n", __func__);
+            return -1;
+        }
+
+    const long end = ftell(f);
+
+    if (end < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    const unsigned long size = end - start;
+
+    if (size != len)
+    {
+        LOG("%s: size exceeded (%lu expected, got %lu)\n",
+                __func__, len, size);
+        return -1;
+    }
+
+    return 0;
+}
+
+int section_import_check(const struct section *const s, struct nw_mod *m,
+    const unsigned long len)
+{
+    const struct nw_mod_cfg *const cfg = s->cfg;
+    FILE *const f = s->f;
+
+    if (m->sections.import)
+    {
+        LOG("%s: ignoring duplicate section\n", __func__);
+        return fseek(f, len, SEEK_CUR);
+    }
+
+    const long offset = ftell(f);
+
+    if (offset < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+    else if (check(cfg, f, len))
+    {
+        LOG("%s: check failed\n", __func__);
+        return -1;
+    }
+
+    m->sections.import = offset;
+    return 0;
+}
diff --git a/src/section/memory.c b/src/section/memory.c
new file mode 100644
index 0000000..0de5b4c
--- /dev/null
+++ b/src/section/memory.c
@@ -0,0 +1,102 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/sections.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <errno.h>
+#include <stdio.h>
+#include <string.h>
+
+static int check_memory_type(FILE *const f, struct resizable_limits *const r)
+{
+    return check_resizable_limits(f, r);
+}
+
+static int check(FILE *const f, const unsigned long len,
+    struct resizable_limits *const r)
+{
+    const long start = ftell(f);
+
+    if (start < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    varuint32 count;
+
+    if (varuint32_read(f, &count))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return 1;
+    }
+    else if (count > 1)
+    {
+        LOG("%s: only 1 memory allowed\n", __func__);
+        return 1;
+    }
+
+    for (varuint32 i = 0; i < count; i++)
+        if (check_memory_type(f, r))
+        {
+            LOG("%s: check_memory_type failed\n", __func__);
+            return -1;
+        }
+
+    const long end = ftell(f);
+
+    if (end < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    const unsigned long size = end - start;
+
+    if (size != len)
+    {
+        LOG("%s: size exceeded (%lu expected, got %lu)\n",
+                __func__, len, size);
+        return -1;
+    }
+
+    return 0;
+}
+
+int section_memory_check(const struct section *const s, struct nw_mod *const m,
+    const unsigned long len)
+{
+    FILE *const f = s->f;
+
+    if (m->sections.memory)
+    {
+        LOG("%s: ignoring duplicate section\n", __func__);
+        return fseek(f, len, SEEK_CUR);
+    }
+
+    const long offset = ftell(f);
+    struct resizable_limits r;
+
+    if (offset < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+    else if (check(f, len, &r))
+    {
+        LOG("%s: check failed\n", __func__);
+        return -1;
+    }
+
+    m->heap_len = r.sz;
+    m->sections.memory = offset;
+    return 0;
+}
diff --git a/src/section/start.c b/src/section/start.c
new file mode 100644
index 0000000..dd44652
--- /dev/null
+++ b/src/section/start.c
@@ -0,0 +1,18 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/sections.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+
+int section_start_check(const struct section *const s, struct nw_mod *const m,
+    const unsigned long len)
+{
+    return -1;
+}
diff --git a/src/section/table.c b/src/section/table.c
new file mode 100644
index 0000000..15fc619
--- /dev/null
+++ b/src/section/table.c
@@ -0,0 +1,112 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/sections.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <errno.h>
+#include <stdio.h>
+#include <string.h>
+
+static int check_table_type(FILE *const f)
+{
+    enum {ANYFUNC = 0x70};
+    varint7 elem_type;
+
+    if (varint7_read(f, &elem_type))
+    {
+        LOG("%s: varint7_read failed\n", __func__);
+        return -1;
+    }
+    else if (elem_type != ANYFUNC)
+    {
+        LOG("%s: expected %x, got %x", __func__, ANYFUNC,
+            (int)elem_type);
+        return -1;
+    }
+
+    /* TODO: what to do with this? */
+    struct resizable_limits r;
+
+    return check_resizable_limits(f, &r);
+}
+
+static int check(FILE *const f, const unsigned long len)
+{
+    const long start = ftell(f);
+
+    if (start < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    varuint32 count;
+
+    if (varuint32_read(f, &count))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return -1;
+    }
+
+    for (varuint32 i = 0; i < count; i++)
+        if (check_table_type(f))
+        {
+            LOG("%s: check_table_type failed\n", __func__);
+            return -1;
+        }
+
+    const long end = ftell(f);
+
+    if (end < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    const unsigned long size = end - start;
+
+    if (size != len)
+    {
+        LOG("%s: size exceeded (%lu expected, got %lu)\n",
+                __func__, len, size);
+        return -1;
+    }
+
+    return 0;
+}
+
+int section_table_check(const struct section *const s, struct nw_mod *const m,
+    const unsigned long len)
+{
+    FILE *const f = s->f;
+
+    if (m->sections.table)
+    {
+        LOG("%s: ignoring duplicate section\n", __func__);
+        return fseek(f, len, SEEK_CUR);
+    }
+
+    const long offset = ftell(f);
+
+    if (offset < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+    else if (check(f, len))
+    {
+        LOG("%s: check failed\n", __func__);
+        return -1;
+    }
+
+    m->sections.table = offset;
+    return 0;
+}
diff --git a/src/section/type.c b/src/section/type.c
new file mode 100644
index 0000000..0bf7a06
--- /dev/null
+++ b/src/section/type.c
@@ -0,0 +1,180 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/log.h>
+#include <nw/sections.h>
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <errno.h>
+#include <stdio.h>
+#include <string.h>
+
+static int check_value_type(FILE *const f, enum value_type *const vtype)
+{
+    varint7 value_type;
+
+    if (varint7_read(f, &value_type))
+    {
+        LOG("%s: varint7_read failed\n", __func__);
+        return -1;
+    }
+    else if (vtype && get_value_type(value_type, vtype))
+    {
+        LOG("%s: get_value_type failed\n", __func__);
+        return -1;
+    }
+
+    return 0;
+}
+
+static int check_func_type(FILE *const f, struct retval *const r)
+{
+    varint7 form;
+    varuint32 param_count;
+
+    if (varint7_read(f, &form))
+    {
+        LOG("%s: varint7_read failed\n", __func__);
+        return -1;
+    }
+    else if (varuint32_read(f, &param_count))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return -1;
+    }
+
+    for (varuint32 i = 0; i < param_count; i++)
+        if (check_value_type(f, NULL))
+        {
+            LOG("%s: check_value_type failed\n", __func__);
+            return -1;
+        }
+
+    varuint1 return_count;
+    enum value_type vtype;
+
+    if (varuint1_read(f, &return_count))
+    {
+        LOG("%s: varuint1_read failed\n", __func__);
+        return -1;
+    }
+    else if (return_count && check_value_type(f, &vtype))
+    {
+        LOG("%s: check_value_type 2 failed\n", __func__);
+        return -1;
+    }
+
+    *r = (const struct retval)
+    {
+        .returns = return_count,
+        .type = vtype
+    };
+
+    return 0;
+}
+
+static int run(FILE *const f, const unsigned long len, const varuint32 idx,
+    struct nw_frame *const fr)
+{
+    const long start = ftell(f);
+    varuint32 count;
+
+    if (start < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+    else if (varuint32_read(f, &count))
+    {
+        LOG("%s: varuint32_read failed\n", __func__);
+        return -1;
+    }
+
+    for (varuint32 i = 0; i < count; i++)
+    {
+        struct retval r;
+
+        if (check_func_type(f, &r))
+        {
+            LOG("%s: check_func_type failed\n", __func__);
+            return -1;
+        }
+        else if (fr && i == idx)
+        {
+            fr->retval = r;
+            return 0;
+        }
+    }
+
+    const long end = ftell(f);
+
+    if (end < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    const unsigned long size = end - start;
+
+    if (size != len)
+    {
+        LOG("%s: size exceeded (%lu expected, got %lu)\n",
+                __func__, len, size);
+        return -1;
+    }
+
+    return 0;
+}
+
+int section_type_check(const struct section *const s, struct nw_mod *const m,
+    const unsigned long len)
+{
+    FILE *const f = s->f;
+
+    if (m->sections.type)
+    {
+        LOG("%s: ignoring duplicate section\n", __func__);
+        return fseek(f, len, SEEK_CUR);
+    }
+
+    const long offset = ftell(f);
+
+    if (offset < 0)
+    {
+        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+    else if (run(f, len, 0, NULL))
+    {
+        LOG("%s: check failed\n", __func__);
+        return -1;
+    }
+
+    m->sections.type = offset;
+    return 0;
+}
+
+int section_type_push(FILE *const f, const struct nw_mod *const m,
+    const varuint32 idx, struct nw_frame *const fr)
+{
+    const long offset = m->sections.type;
+
+    if (offset <= 0)
+    {
+        LOG("%s: function section not found", __func__);
+        return -1;
+    }
+    else if (fseek(f, offset, SEEK_SET))
+    {
+        LOG("%s: fseek(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    return run(f, 0, idx, fr);
+}
diff --git a/src/start.c b/src/start.c
new file mode 100644
index 0000000..c22bddf
--- /dev/null
+++ b/src/start.c
@@ -0,0 +1,81 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nanowasm/nw.h>
+#include <nw/interp.h>
+#include <nw/log.h>
+#include <nw/search.h>
+#include <nw/sections.h>
+#include <errno.h>
+#include <stdio.h>
+#include <string.h>
+
+int nw_start(const struct nw_inst_cfg *const icfg, struct nw_inst *const i)
+{
+    int ret = -1;
+    const struct nw_mod *const m = icfg->interp.m;
+    const struct nw_mod_cfg *const mcfg = &m->cfg;
+    FILE *const f = fopen(mcfg->path, "rb");
+    struct search_fn fn;
+    struct nw_frame fr = {0};
+
+    *i = (const struct nw_inst){0};
+
+    if (!f)
+    {
+        LOG("%s: fopen(3) %s: %s\n", __func__, mcfg->path, strerror(errno));
+        goto end;
+    }
+    else if (m->sections.start)
+    {
+        /* TODO. */
+    }
+    else if (interp_start(&icfg->interp, f, &i->interp))
+    {
+        LOG("%s: interp_start failed\n", __func__);
+        goto end;
+    }
+    else if (search_exported_fn("_start", m, f, &fn))
+    {
+        LOG("%s: search_exported_fn failed\n", __func__);
+        goto end;
+    }
+    else if (section_global_push(f, m, &i->interp))
+    {
+        LOG("%s: section_global_push failed\n", __func__);
+        goto end;
+    }
+    else if (section_type_push(f, m, fn.index, &fr))
+    {
+        LOG("%s: section_type_push failed\n", __func__);
+        goto end;
+    }
+    else if (section_code_push(f, fn.start, &fr))
+    {
+        LOG("%s: section_code_push failed\n", __func__);
+        goto end;
+    }
+    else if (interp_push(&i->interp, &fr))
+    {
+        LOG("%s: interp_push failed\n", __func__);
+        goto end;
+    }
+
+    ret = 0;
+
+end:
+
+    if (ret && f && fclose(f))
+    {
+        LOG("%s: fclose(3) %s: %s\n", __func__, mcfg->path, strerror(errno));
+        ret = -1;
+    }
+
+    return ret;
+}
diff --git a/src/stop.c b/src/stop.c
new file mode 100644
index 0000000..1d5d604
--- /dev/null
+++ b/src/stop.c
@@ -0,0 +1,27 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nanowasm/nw.h>
+#include <nw/log.h>
+#include <errno.h>
+#include <stdio.h>
+#include <string.h>
+
+int nw_stop(struct nw_inst *const i)
+{
+    struct nw_interp *const in = &i->interp;
+
+    if (in->f && fclose(in->f))
+    {
+        LOG("%s: fclose(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    return 0;
+}
diff --git a/src/types.c b/src/types.c
new file mode 100644
index 0000000..88c883e
--- /dev/null
+++ b/src/types.c
@@ -0,0 +1,89 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/leb128.h>
+#include <nw/types.h>
+#include <stdio.h>
+
+int varuint1_read(FILE *const f, varuint1 *const out)
+{
+    unsigned long long value;
+
+    if (leb128_read_unsigned(f, 1, &value))
+        return -1;
+
+    *out = value;
+    return 0;
+}
+
+int varint7_read(FILE *const f, varint7 *const out)
+{
+    long long value;
+
+    if (leb128_read_signed(f, 7, &value))
+        return -1;
+
+    *out = value;
+    return 0;
+}
+
+int varuint7_read(FILE *const f, varuint7 *const out)
+{
+    unsigned long long value;
+
+    if (leb128_read_unsigned(f, 7, &value))
+        return -1;
+
+    *out = value;
+    return 0;
+}
+
+int varuint32_read(FILE *const f, varuint32 *out)
+{
+    unsigned long long value;
+
+    if (leb128_read_unsigned(f, 32, &value))
+        return -1;
+
+    *out = value;
+    return 0;
+}
+
+int varint32_read(FILE *const f, varint32 *const out)
+{
+    long long value;
+
+    if (leb128_read_signed(f, 32, &value))
+        return -1;
+
+    *out = value;
+    return 0;
+}
+
+int varuint64_read(FILE *const f, varuint64 *const out)
+{
+    unsigned long long value;
+
+    if (leb128_read_unsigned(f, 64, &value))
+        return -1;
+
+    *out = value;
+    return 0;
+}
+
+int varint64_read(FILE *const f, varint64 *const out)
+{
+    long long value;
+
+    if (leb128_read_signed(f, 64, &value))
+        return -1;
+
+    *out = value;
+    return 0;
+}
diff --git a/src/unload.c b/src/unload.c
new file mode 100644
index 0000000..5b5ef9b
--- /dev/null
+++ b/src/unload.c
@@ -0,0 +1,19 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nanowasm/nw.h>
+#include <nw/types.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+
+void nw_unload(struct nw_mod *const m)
+{
+    free(m);
+}