Xrasher/engine/platform/android/dlsym-weak.c

/*
 * Copyright (C) 2008, 2009 The Android Open Source Project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *  * Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *  * Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include "build.h"
#if XASH_ANDROID && !XASH_64BIT
#include <string.h>
#include <android/log.h>
#include "linker.h"

static Elf_Sym *soinfo_elf_lookup( const soinfo *si, unsigned hash, const char *name )
{
	const Elf_Sym *symtab = si->symtab;
	const char *strtab = si->strtab;
	unsigned n;

	if( si->nbucket == 0 )
		return NULL;

	for( n = si->bucket[hash % si->nbucket]; n != 0; n = si->chain[n] )
	{
		const Elf_Sym *s = symtab + n;

		if( strcmp( strtab + s->st_name, name ))
			continue;

		/* only concern ourselves with global and weak symbol definitions */
		switch( ELF_ST_BIND( s->st_info ))
		{
		case STB_GLOBAL:
		case STB_WEAK:
			if( s->st_shndx == SHN_UNDEF )
				continue;
			return s;
		}
	}

	return NULL;
}

static unsigned elfhash( const unsigned char *name )
{
	unsigned h = 0;

	while( *name )
	{
		unsigned g;

		h = ( h << 4 ) + *name++;
		g = h & 0xf0000000;
		h ^= g;
		h ^= g >> 24;
	}
	return h;
}

/* This is used by dlsym(3).  It performs symbol lookup only within the
   specified soinfo object and not in any of its dependencies.

   TODO: Only looking in the specified soinfo seems wrong. dlsym(3) says
   that it should do a breadth first search through the dependency
   tree. This agrees with the ELF spec (aka System V Application
   Binary Interface) where in Chapter 5 it discuss resolving "Shared
   Object Dependencies" in breadth first search order.
 */
static Elf_Sym *dlsym_handle_lookup( const soinfo *si, const char *name )
{
	return soinfo_elf_lookup( si, elfhash((const unsigned char *)name ), name );
}

void *dlsym_weak( void *handle, const char *symbol )
{
	soinfo *found = (soinfo *)handle;
	Elf_Sym *sym = dlsym_handle_lookup( found, symbol );

	if( sym != NULL )
		return (void*)( sym->st_value + found->base/*load_bias*/ );

	__android_log_print( ANDROID_LOG_ERROR, "dlsym-weak", "Failed when looking up %s\n", symbol );
	return NULL;
}
#endif // XASH_ANDROID && !XASH_64BIT