Merge pull request #36 from spicyjpeg/dynlink

Dynamic linker, gp-relative addressing, ldscripts and more

4 files changed, 764 insertions, 30 deletions

diff --git a/libpsn00b/psxetc/_dl_resolve_wrapper.s b/libpsn00b/psxetc/_dl_resolve_wrapper.s
new file mode 100644
index 0000000..069ee84
--- /dev/null
+++ b/libpsn00b/psxetc/_dl_resolve_wrapper.s
@@ -0,0 +1,54 @@
+# PSn00bSDK dynamic linker
+# (C) 2021 spicyjpeg - MPL licensed
+#
+# This function is called by the lazy loader stubs generated by GCC in the
+# .plt/.MIPS.stubs section when attempting to call a GOT entry whose address
+# hasn't yet been resolved. The generated stubs conform to the MIPS ABI and
+# uses the following registers to pass the following parameters:
+# - $t7 = address the resolved function should return to (i.e. $ra of the
+#   caller that triggered the stub)
+# - $t8 = index of the function in the .dynsym symbol table
+# - $t9 = _dl_resolve_wrapper itself's address
+
+.set		noreorder
+.section	.text
+
+.global	_dl_resolve_wrapper
+.type	_dl_resolve_wrapper, @function
+_dl_resolve_wrapper:
+	# Push the registers we're going to use onto the stack.
+	addiu $sp, -16
+	sw    $a0,  0($sp)
+	sw    $a1,  4($sp)
+	sw    $v0,  8($sp)
+	sw    $t7, 12($sp) # (will be restored directly to $ra)
+
+	# Figure out where the DLL's struct is. dlinit() places a pointer to the
+	# struct in the second GOT entry, so it's just a matter of indexing the GOT
+	# using GP. Then call _dl_resolve_helper with the struct and $t8 as
+	# arguments, and store the return value into $t0.
+	lw    $a0, -0x7fec($gp) # sizeof(uint32_t) - 0x7ff0 (see dll.ld)
+	move  $a1, $t8
+
+	jal   _dl_resolve_helper
+	addiu $sp, -8 # (branch delay)
+	addiu $sp, 8
+
+	move  $t0, $v0
+
+	# Restore registers from the stack and tail-call the function at the
+	# address returned by the resolver. This will cause the resolved function
+	# to run and return directly to the code that called the stub.
+	lw    $a0,  0($sp)
+	lw    $a1,  4($sp)
+	lw    $v0,  8($sp)
+	lw    $ra, 12($sp)
+	addiu $sp, 16
+
+	jr    $t0
+	nop
+
+.global _dl_credits
+.type _dl_credits, @object
+_dl_credits:
+	.asciiz "psxetc runtime dynamic linker by spicyjpeg\n"
diff --git a/libpsn00b/psxetc/dl.c b/libpsn00b/psxetc/dl.c
new file mode 100644
index 0000000..1485183
--- /dev/null
+++ b/libpsn00b/psxetc/dl.c
@@ -0,0 +1,665 @@
+/*
+ * PSn00bSDK dynamic linker
+ * (C) 2021 spicyjpeg - MPL licensed
+ *
+ * The bulk of this code is MIPS-specific but not PS1-specific, so the whole
+ * dynamic linker could be ported to other MIPS platforms that do not have one
+ * in their OS/SDK (e.g. N64, PIC32 microcontrollers). Note that, despite the
+ * various ELF references, I did *not* implement a full ELF file parser: this
+ * implementation just expects all library files to begin with several metadata
+ * sections (.dynamic, .dynsym, .hash, .dynstr) laid out in a fixed order. Use
+ * the dll.ld linker script to generate compatible libraries.
+ *
+ * Most of the stuff implemented here, despite looking like black magic, is
+ * actually well-documented across several PDFs scattered around the internet:
+ * - http://www.sco.com/developers/devspecs/gabi41.pdf
+ * - http://math-atlas.sourceforge.net/devel/assembly/mipsabi32.pdf
+ * - http://flint.cs.yale.edu/cs422/doc/ELF_Format.pdf
+ *
+ * TODO:
+ * - Clean up duplicated code, especially hash-table-related loops
+ * - Fix bugs and improve allocation checks
+ * - Find a way to predict the smallest ELF hash table size for a certain set
+ *   of entries
+ */
+
+#include <sys/types.h>
+#include <stdio.h>
+#include <malloc.h>
+#include <ctype.h>
+#include <elf.h>
+#include <dlfcn.h>
+#include <string.h>
+#include <psxapi.h>
+
+/* Compile options */
+
+// Uncomment before building to enable debug logging (via printf()).
+#define DEBUG
+
+// Comment before building to disable functions that rely on BIOS file APIs,
+// i.e. DL_LoadSymbolMap() and dlopen().
+#define USE_FILE_API
+
+/* Private types */
+
+typedef struct {
+	uint32_t hash;
+	void     *ptr;
+} MapEntry;
+
+typedef enum {
+	ERR_NONE,
+	ERR_FILE,
+	ERR_FILE_MALLOC,
+	ERR_FILE_READ,
+	ERR_NO_MAP,
+	ERR_MAP_MALLOC,
+	ERR_NO_SYMBOLS,
+	ERR_DLL_NULL,
+	ERR_DLL_MALLOC,
+	ERR_DLL_FORMAT,
+	ERR_NO_FILE_API,
+	ERR_MAP_SYMBOL,
+	ERR_DLL_SYMBOL
+} ErrorCode;
+
+/* Data */
+
+static const char *const DL_ERROR_MESSAGES[] = {
+	"Unable to find file",
+	"Unable to allocate buffer to load file into",
+	"Failed to read file",
+	"No symbol map has been loaded yet",
+	"Unable to allocate symbol map structures",
+	"No symbols found in symbol map",
+	"Unable to initialize DLL from null pointer",
+	"Unable to allocate DLL metadata structures",
+	"Unsupported DLL type or format",
+	"psxetc has been built without file support",
+	"Symbol not found in symbol map",
+	"Symbol not found in DLL"
+};
+
+static ErrorCode _error_code       = ERR_NONE;
+static uint32_t  *_map_hash_table  = 0;
+static MapEntry  *_map_entry_table = 0;
+
+// Accessed by _dl_resolve_helper, stores the pointer to the current resolver
+// function. Can be changed using DL_SetResolveCallback().
+void *(*_dl_resolve_callback)(DLL *, const char *) = 0;
+
+/* Private utilities */
+
+#ifdef DEBUG
+#define _LOG(...) printf(__VA_ARGS__)
+#define _ERROR(code, ret) { \
+	_LOG("psxetc: ERROR! %s\n", DL_ERROR_MESSAGES[code - 1]); \
+	_error_code = code; \
+	return ret; \
+}
+#else
+#define _LOG(...)
+#define _ERROR(code, ret) { \
+	_error_code = code; \
+	return ret; \
+}
+#endif
+
+void _dl_resolve_wrapper(void);
+
+// Called by _dl_resolve_wrapper() (which is in turn called by GCC stubs) to
+// resolve a function.
+void *_dl_resolve_helper(DLL *dll, uint32_t index) {
+	Elf32_Sym  *sym   = &(dll->symtab[index]);
+	const char *_name = &(dll->strtab[sym->st_name]);
+	void       *address;
+
+	if (_dl_resolve_callback)
+		address = _dl_resolve_callback(dll, _name);
+	else
+		address = DL_GetSymbolByName(_name);
+
+	if (!address) {
+		_LOG("psxetc: FATAL! Can't resolve %s, locking up\n", _name);
+		while (1)
+			__asm__ volatile("nop");
+	}
+
+	// Patch the GOT entry to "cache" the resolved address. This can probably
+	// be implemented in a faster way, but this thing is already too complex.
+	for (uint32_t i = 0; i < dll->got_length; i++) {
+		if (dll->got[2 + i] == (uint32_t) sym->st_value) {
+			dll->got[2 + i] = (uint32_t) address;
+			break;
+		}
+	}
+
+	return address;
+}
+
+// Implementation of the weird obscure hashing function used in the ELF .hash
+// section. Not sure how collision-prone this is.
+// https://en.wikipedia.org/wiki/PJW_hash_function
+static uint32_t _elf_hash(const char *str) {
+	uint32_t value = 0;
+
+	while (*str) {
+		value <<= 4;
+		value  += (uint32_t) *(str++);
+
+		uint32_t nibble = value & 0xf0000000;
+		if (nibble)
+			value ^= nibble >> 24;
+
+		value &= ~nibble;
+	}
+
+	return value;
+}
+
+#ifdef USE_FILE_API
+static uint8_t *_load_file(const char *filename, size_t *size_output) {
+	int32_t fd = open(filename, 1);
+	if (fd < 0)
+		_ERROR(ERR_FILE, 0);
+
+	// Extract file size from the file's associated control block.
+	// https://problemkaputt.de/psx-spx.htm#biosmemorymap
+	FCB    *fcb = (FCB *) *((FCB **) 0x80000140);
+	size_t size = fcb[fd].filesize;
+
+	uint8_t *buffer = malloc(size);
+	if (!buffer)
+		_ERROR(ERR_FILE_MALLOC, 0);
+
+	_LOG("psxetc: Loading %s (%d bytes)..", filename, size);
+
+	for (uint32_t offset = 0; offset < size; ) {
+		int32_t length = read(fd, &(buffer[offset]), 0x800);
+
+		if (length <= 0) {
+			close(fd);
+			free(buffer);
+			_ERROR(ERR_FILE_READ, 0);
+		}
+
+		_LOG(".");
+		offset += length;
+	}
+
+	close(fd);
+	_LOG(" done\n");
+
+	if (size_output)
+		*size_output = size;
+	return buffer;
+}
+#endif
+
+/* Symbol map loading/parsing API */
+
+int32_t DL_ParseSymbolMap(const char *ptr, size_t size) {
+	DL_UnloadSymbolMap();
+
+	// Perform a quick scan over the entire map text and count the number of
+	// newlines. This allows us to (over)estimate the number of entries and
+	// allocate a sufficiently large hash/entry table.
+	uint32_t entries = 0;
+	for (uint32_t pos = 0; pos < size; pos++) {
+		if (ptr[pos] == '\n')
+			entries++;
+	}
+
+	// TODO: find a way to calculate the optimal number of hash table "buckets"
+	// in order to minimize hash table size
+	uint32_t nbucket = entries;
+	_LOG("psxetc: Predicted %d entries, %d hash buckets\n", entries, nbucket);
+
+	// Allocate an entry table to store parsed symbols in, and an associated
+	// hash table (same format as .hash section, with 8-byte header).
+	_map_hash_table  = malloc(sizeof(uint32_t) * (2 + nbucket + entries));
+	_map_entry_table = malloc(sizeof(MapEntry) * entries);
+	if (!_map_hash_table || !_map_entry_table)
+		_ERROR(ERR_MAP_MALLOC, -1);
+
+	_map_hash_table[0] = nbucket;
+	_map_hash_table[1] = entries;
+	for (uint32_t i = 0; i < (nbucket + entries); i++)
+		_map_hash_table[2 + i] = 0xffffffff;
+
+	// Go again through the symbol map and fill in the hash table.
+	uint32_t index = 0;
+	for (uint32_t pos = 0; (pos < size) && ptr[pos]; pos++) {
+		char     name[64];
+		char     type_string[2];
+		uint64_t address64;
+		size_t   _size;
+
+		// e.g. "main T ffffffff80000000 100 ...\n"
+		int32_t parsed = sscanf(
+			&(ptr[pos]),
+			"%63s %1s %Lx %x",
+			name,
+			type_string,
+			&address64,
+			&_size // Optional, unused (yet)
+		);
+
+		if (parsed >= 3) {
+			// Drop the upper 32 bits of the address (for some reason MIPS nm
+			// insists on printing 64-bit addresses... wtf) and normalize the
+			// type letter to upper case, then check if the entry is valid and
+			// non-null.
+			void     *address = (void *) address64;
+			char     _type    = toupper(type_string[0]);
+			uint32_t hash     = _elf_hash(name);
+			uint32_t hash_mod = hash % nbucket;
+
+			if (address && (
+				(_type == 'T') || // .text
+				(_type == 'R') || // .rodata
+				(_type == 'D') || // .data
+				(_type == 'B')    // .bss
+			)) {
+				_LOG(
+					"psxetc: Map sym: %08x,%08x [%c %s]\n",
+					address,
+					_size,
+					_type,
+					name
+				);
+
+				MapEntry *entry = &(_map_entry_table[index]);
+				entry->hash     = hash;
+				entry->ptr      = address;
+
+				// Append a reference to the entry to the hash table's chain
+				// for the current hash_mod. I can't explain this properly.
+				uint32_t *hash_entry = &(_map_hash_table[2 + hash_mod]);
+				while (*hash_entry != 0xffffffff)
+					hash_entry = &(_map_hash_table[2 + nbucket + *hash_entry]);
+
+				*hash_entry = index;
+				index++;
+			}
+		}
+
+		// Skip the line by advancing the pointer until a newline is found. The
+		// for loop will then skip the newline itself.
+		while ((pos < size) && (ptr[pos] != '\n'))
+			pos++;
+	}
+
+	_LOG("psxetc: Parsed %d symbols from map\n", entries);
+	if (!entries)
+		_ERROR(ERR_NO_SYMBOLS, -1);
+
+	return entries;
+}
+
+int32_t DL_LoadSymbolMap(const char *filename) {
+#ifdef USE_FILE_API
+	size_t size;
+	char   *ptr = _load_file(filename, &size);
+	if (!ptr)
+		return -1;
+
+	int32_t entries = DL_ParseSymbolMap(ptr, size);
+	free(ptr);
+
+	return entries;
+#else
+	_ERROR(ERR_NO_FILE_API, -1);
+#endif
+}
+
+void DL_UnloadSymbolMap(void) {
+	if (!_map_hash_table)
+		return;
+
+	free(_map_hash_table);
+	free(_map_entry_table);
+	_map_hash_table = 0;
+}
+
+void *DL_GetSymbolByName(const char *name) {
+	if (!_map_hash_table)
+		_ERROR(ERR_NO_MAP, 0);
+
+	// https://docs.oracle.com/cd/E23824_01/html/819-0690/chapter6-48031.html
+	uint32_t nbucket  = _map_hash_table[0];
+	uint32_t hash     = _elf_hash(name);
+	uint32_t hash_mod = hash % nbucket;
+
+	// Go through the hash table's chain until the symbol hash matches the one
+	// calculated.
+	for (uint32_t i = _map_hash_table[2 + hash_mod]; i;) {
+		MapEntry *entry = &(_map_entry_table[i]);
+
+		if (hash == entry->hash) {
+			_LOG("psxetc: Map lookup [%s = %08x]\n", name, entry->ptr);
+			return entry->ptr;
+		}
+
+		i = _map_hash_table[2 + nbucket + i];
+	}
+
+	_ERROR(ERR_MAP_SYMBOL, 0);
+}
+
+void DL_SetResolveCallback(void *(*callback)(DLL *, const char *)) {
+	_dl_resolve_callback = callback;
+}
+
+/* Library loading and linking API */
+
+DLL *dlinit(void *ptr, size_t size, DL_ResolveMode mode) {
+	if (!ptr)
+		_ERROR(ERR_DLL_NULL, 0);
+
+	DLL *dll = malloc(sizeof(DLL));
+	if (!dll)
+		_ERROR(ERR_DLL_MALLOC, 0);
+
+	dll->ptr        = ptr;
+	dll->malloc_ptr = 0;
+	dll->size       = size;
+	_LOG("psxetc: Initializing DLL at %08x\n", ptr);
+
+	// Interpret the key-value pairs in the .dynamic section to obtain info
+	// about all the other sections. The pairs are null-terminated, which makes
+	// parsing trivial.
+	uint32_t local_got_len = 0;
+	uint32_t first_got_sym = 0;
+
+	for (Elf32_Dyn *dyn = (Elf32_Dyn *) ptr; dyn->d_tag; dyn++) {
+		_LOG("psxetc: .dynamic %08x=%08x ", dyn->d_tag, dyn->d_un.d_val);
+
+		switch (dyn->d_tag) {
+			// Offset of .got section
+			case DT_PLTGOT:
+				_LOG("[PLTGOT]\n");
+
+				dll->got = (void *) (ptr + dyn->d_un.d_val);
+				break;
+
+			// Offset of .hash section
+			case DT_HASH:
+				_LOG("[HASH]\n");
+
+				dll->hash = (void *) (ptr + dyn->d_un.d_val);
+				break;
+
+			// Offset of .dynstr (NOT .strtab) section
+			case DT_STRTAB:
+				_LOG("[STRTAB]\n");
+
+				dll->strtab = (void *) (ptr + dyn->d_un.d_val);
+				break;
+
+			// Offset of .dynsym (NOT .symtab) section
+			case DT_SYMTAB:
+				_LOG("[SYMTAB]\n");
+
+				dll->symtab = (void *) (ptr + dyn->d_un.d_val);
+				break;
+
+			// Length of .dynstr section
+			//case DT_STRSZ:
+				//_LOG("[STRSZ]\n");
+				//break;
+
+			// Length of each .dynsym entry
+			case DT_SYMENT:
+				_LOG("[SYMENT]\n");
+
+				// Only 16-byte symbol table entries are supported.
+				if (dyn->d_un.d_val != sizeof(Elf32_Sym)) {
+					free(dll);
+					_ERROR(ERR_DLL_FORMAT, 0);
+				}
+				break;
+
+			// MIPS ABI (?) version
+			case DT_MIPS_RLD_VERSION:
+				_LOG("[MIPS_RLD_VERSION]\n");
+
+				// Versions other than 1 are unsupported (do they even exist?).
+				if (dyn->d_un.d_val != 1) {
+					free(dll);
+					_ERROR(ERR_DLL_FORMAT, 0);
+				}
+				break;
+
+			// DLL/ABI flags
+			case DT_MIPS_FLAGS:
+				_LOG("[MIPS_FLAGS]\n");
+
+				// Shortcut pointers (whatever they are) are not supported.
+				if (dyn->d_un.d_val & RHF_QUICKSTART) {
+					free(dll);
+					_ERROR(ERR_DLL_FORMAT, 0);
+				}
+				break;
+
+			// Number of local (not to resolve) GOT entries
+			case DT_MIPS_LOCAL_GOTNO:
+				_LOG("[MIPS_LOCAL_GOTNO]\n");
+
+				local_got_len = dyn->d_un.d_val;
+				break;
+
+			// Base address DLL was compiled for
+			case DT_MIPS_BASE_ADDRESS:
+				_LOG("[MIPS_BASE_ADDRESS]\n");
+
+				// Base addresses other than zero are not supported. It would
+				// be easy enough to support them, but why?
+				if (dyn->d_un.d_val) {
+					free(dll);
+					_ERROR(ERR_DLL_FORMAT, 0);
+				}
+				break;
+
+			// Number of symbol table entries
+			case DT_MIPS_SYMTABNO:
+				_LOG("[MIPS_SYMTABNO]\n");
+
+				dll->symbol_count = dyn->d_un.d_val;
+				break;
+
+			// Index of first unresolved symbol table entry
+			//case DT_MIPS_UNREFEXTNO:
+				//_LOG("[MIPS_UNREFEXTNO]\n");
+				//break;
+
+			// Index of first symbol table entry which has a matching GOT entry
+			case DT_MIPS_GOTSYM:
+				_LOG("[MIPS_GOTSYM]\n");
+
+				first_got_sym = dyn->d_un.d_val;
+				break;
+
+			// Number of pages the GOT is split into (does not apply to PS1)
+			//case DT_MIPS_HIPAGENO:
+				//_LOG("[MIPS_HIPAGENO]\n");
+				//break;
+
+			default:
+				_LOG("[ignored]\n");
+		}
+	}
+
+	// Calculate the number of GOT entries (and symbols, if MIPS_SYMTABNO was
+	// not found in the .dynamic section).
+	//dll->symbol_count = \
+		((uint32_t) dll->hash - (uint32_t) dll->symtab) / sizeof(Elf32_Sym);
+	//dll->got_length = \
+		((uint32_t) ptr + size - (uint32_t) dll->got) / sizeof(uint32_t) - 2;
+
+	dll->got_length = local_got_len + (dll->symbol_count - first_got_sym) - 2;
+	_LOG(
+		"psxetc: %d symbols, %d GOT entries\n",
+		dll->symbol_count,
+		dll->got_length
+	);
+
+	// Relocate the DLL by adding its base address to all pointers in the GOT
+	// except the first two, which are reserved. The first entry in particular
+	// is a pointer to the lazy resolver, called by auto-generated stubs when a
+	// function is first used. got[1] is normally unused, but here we'll set it
+	// to the DLL's metadata struct so we can look that up when resolving
+	// functions (see _dl_resolve_wrapper()).
+	dll->got[0] = (uint32_t) &_dl_resolve_wrapper;
+	dll->got[1] = (uint32_t) dll;
+
+	for (uint32_t i = 0; i < dll->got_length; i++)
+		dll->got[2 + i] += (uint32_t) ptr;
+
+	// Fix addresses in the symbol table.
+	// TODO: clean this shit up
+	uint32_t got_offset = first_got_sym;
+
+	for (uint32_t i = 0; i < dll->symbol_count; i++) {
+		Elf32_Sym  *sym   = &(dll->symtab[i]);
+		const char *_name = &(dll->strtab[sym->st_name]);
+
+		if (!sym->st_value)
+			continue;
+
+		sym->st_value += (uint32_t) ptr;
+		_LOG(
+			"psxetc: DLL sym: %08x,%08x [%s]\n",
+			sym->st_value,
+			sym->st_size,
+			_name
+		);
+
+		// If RTLD_NOW was passed, resolve GOT entries ahead of time by
+		// cross-referencing them with the symbol table.
+		if (mode != RTLD_NOW)
+			continue;
+
+		for (uint32_t j = got_offset; j < dll->got_length; j++) {
+			if (dll->got[2 + j] != (uint32_t) sym->st_value)
+				continue;
+
+			got_offset = j;
+
+			// If the symbol is undefined (st_shndx = 0) and is either a
+			// variable or a function, resolve it immediately.
+			// TODO: linking of external variables needs more testing
+			if (!(sym->st_shndx) && (
+				ELF32_ST_TYPE(sym->st_info) == STT_OBJECT ||
+				ELF32_ST_TYPE(sym->st_info) == STT_FUNC
+			)) {
+				dll->got[2 + j] = (uint32_t) _dl_resolve_callback(dll, _name);
+
+				if (!dll->got[2 + j]) {
+					free(dll);
+					_ERROR(ERR_MAP_SYMBOL, 0);
+				}
+			}
+
+			break;
+		}
+	}
+
+	EnterCriticalSection();
+	FlushCache();
+	ExitCriticalSection();
+
+	// Call the DLL's global constructors. This is the same thing we'd do in
+	// _start() for regular executables, but we have to do it outside of the
+	// DLL as there's no _start() or even a defined entry point within the
+	// DLL itself.
+	const uint32_t *ctor_list = dlsym(dll, "__CTOR_LIST__");
+	if (ctor_list) {
+		for (uint32_t i = ((uint32_t) ctor_list[0]); i >= 1; i--) {
+			void (*ctor)(void) = (void (*)(void)) ctor_list[i];
+			DL_CALL(ctor);
+		}
+	}
+
+	return dll;
+}
+
+DLL *dlopen(const char *filename, DL_ResolveMode mode) {
+#ifdef USE_FILE_API
+	size_t size;
+	char   *ptr = _load_file(filename, &size);
+	if (!ptr)
+		return 0;
+
+	DLL *dll = dlinit(ptr, size, mode);
+	if (dll)
+		dll->malloc_ptr = dll->ptr;
+	else
+		free(ptr);
+
+	return dll;
+#else
+	_ERROR(ERR_NO_FILE_API, 0);
+#endif
+}
+
+void dlclose(DLL *dll) {
+	if (dll == RTLD_DEFAULT)
+		return;
+
+	if (dll->ptr) {
+		// Call the DLL's global destructors.
+		const uint32_t *dtor_list = dlsym(dll, "__DTOR_LIST__");
+		if (dtor_list) {
+			for (uint32_t i = 0; i < ((uint32_t) dtor_list[0]); i++) {
+				void (*dtor)(void) = (void (*)(void)) dtor_list[i + 1];
+				DL_CALL(dtor);
+			}
+		}
+	}
+
+	// If the DLL is associated to a buffer allocated by dlopen(), free that
+	// buffer.
+	if (dll->malloc_ptr)
+		free(dll->malloc_ptr);
+
+	free(dll);
+}
+
+void *dlsym(DLL *dll, const char *name) {
+	if (dll == RTLD_DEFAULT)
+		return DL_GetSymbolByName(name);
+		//return _dl_resolve_callback(RTLD_DEFAULT, name);
+
+	// https://docs.oracle.com/cd/E23824_01/html/819-0690/chapter6-48031.html
+	const uint32_t *hash_table = dll->hash;
+	uint32_t       nbucket     = hash_table[0];
+	uint32_t       hash_mod    = _elf_hash(name) % nbucket;
+
+	// Go through the hash table's chain until the symbol name matches the one
+	// provided.
+	for (uint32_t i = hash_table[2 + hash_mod]; i;) {
+		Elf32_Sym  *sym   = &(dll->symtab[i]);
+		const char *_name = &(dll->strtab[sym->st_name]);
+
+		if (!strcmp(name, _name)) {
+			_LOG("psxetc: DLL lookup [%s = %08x]\n", name, sym->st_value);
+			return sym->st_value;
+		}
+
+		i = hash_table[2 + nbucket + i];
+	}
+
+	_ERROR(ERR_DLL_SYMBOL, 0);
+}
+
+const char *const dlerror(void) {
+	uint32_t last = _error_code;
+	_error_code   = ERR_NONE;
+
+	if (last)
+		return DL_ERROR_MESSAGES[last - 1];
+
+	return 0;
+}
diff --git a/libpsn00b/psxetc/makefile b/libpsn00b/psxetc/makefile
index cc12944..84bb64b 100644
--- a/libpsn00b/psxetc/makefile
+++ b/libpsn00b/psxetc/makefile
@@ -1,46 +1,59 @@
-# Run using make (Linux) or gmake (BSD)
+# PSn00bSDK library makefile
 # Part of the PSn00bSDK Project
-# 2019 - 2020 Lameguy64 / Meido-Tek Productions
+# 2019 - 2021 Lameguy64 / Meido-Tek Productions
 
-include ../../template/psn00bsdk-setup.mk
+## Settings
 
-TARGET	= libpsxetc.a
+PSN00BSDK_LIBS	?= ..
 
-CFILES	= $(notdir $(wildcard ./*.c))
-AFILES	= $(notdir $(wildcard ./*.s))
-OFILES	= $(addprefix build/,$(CFILES:.c=.o) $(AFILES:.s=.o))
+include ../../psn00bsdk-setup.mk
 
-CFLAGS	= -g -O2 -msoft-float -fno-builtin -nostdlib -fdata-sections \
-		  -ffunction-sections -Wa,--strip-local-absolute
-AFLAGS	= -g -msoft-float -strip-local-absolute
+# Project target name
+TARGET	= libpsxetc.a
 
-INCLUDE = -I../include
+## Files
 
-ifndef PSN00BSDK_LIBS
+# Searches for C, C++ and S (assembler) files in local directory
+CFILES	= $(notdir $(wildcard *.c))
+CXXFILES= $(notdir $(wildcard *.cxx))
+AFILES	= $(notdir $(wildcard *.s))
 
-PSN00BSDK_LIBS	= ..
+# Create names for object files
+OFILES	= $(addprefix build/,$(CFILES:.c=.o)) \
+	$(addprefix build/,$(CXXFILES:.cxx=.o)) \
+	$(addprefix build/,$(AFILES:.s=.o))
 
-endif
+# Project specific includes and libraries
+# (use -I for include dirs, -L for library dirs, -l for static libraries)
+INCLUDE	+=
+LIBDIRS	+=
+LIBS	+=
 
-all: $(TARGET)
+## Build rules
 
-$(TARGET): $(OFILES)
-	$(AR) cr $(TARGET) $(OFILES)
-	$(RANLIB) $(TARGET)
+all: build/$(TARGET)
+
+build/$(TARGET): $(OFILES)
+	@mkdir -p $(dir $@)
+	$(AR) crs $@ $(OFILES)
 
 build/%.o: %.c
 	@mkdir -p $(dir $@)
-	$(CC) $(CFLAGS) $(INCLUDE) -c $< -o $@
+	$(CC) $(CFLAGS_LIB) $(INCLUDE) -c $< -o $@
+
+build/%.o: %.cxx
+	@mkdir -p $(dir $@)
+	$(CXX) $(CPPFLAGS_LIB) $(INCLUDE) -c $< -o $@
 	
 build/%.o: %.s
 	@mkdir -p $(dir $@)
-	$(AS) $(AFLAGS) $(INCLUDE) $< -o $@
+	$(CC) $(AFLAGS_LIB) $(INCLUDE) -c $< -o $@
 
 install:
 ifneq ($(PSN00BSDK_LIBS), "..")
 	@mkdir -p $(PSN00BSDK_LIBS)
 endif
-	cp $(TARGET) $(PSN00BSDK_LIBS)/$(TARGET)
-
+	cp build/$(TARGET) $(PSN00BSDK_LIBS)/$(TARGET)
+	
 clean:
-	rm -Rf build $(TARGET)
+	rm -rf build
diff --git a/libpsn00b/psxetc/readme.txt b/libpsn00b/psxetc/readme.txt
index f2e7649..24645f7 100644
--- a/libpsn00b/psxetc/readme.txt
+++ b/libpsn00b/psxetc/readme.txt
@@ -1,18 +1,20 @@
 PSX Misc library, part of PSn00bSDK
-2019 Lameguy64 / Meido-Tek Productions
+2021 Lameguy64 / Meido-Tek Productions
 
 Licensed under Mozilla Public License
 
-Open source implementation of the ETC library. Doesn't really provide much
-aside from some debug font stuff at the moment.
-
+Open source implementation of the ETC library. Currently provides the interrupt
+and DMA callback dispatchers (used by other libraries) as well as the DL_* and
+dl* functions for dynamic library loading (original, not present in the official
+SDK but similar to the standard dlopen() API).
 
 Library developer(s):
 
 	Lameguy64
-	
-	
+	spicyjpeg
+
 Library header(s):
 
 	psxetc.h
-	
+	dlfcn.h
+	elf.h (used internally)