First commit

14 files changed, 1986 insertions, 0 deletions

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);
+}