uclibc-ng/ldso/ldso/dl-hash.c

/* vi: set sw=4 ts=4: */
/*
 * Program to load an ELF binary on a linux system, and run it
 * after resolving ELF shared library symbols
 *
 * Copyright (C) 2004 by Joakim Tjernlund <joakim.tjernlund@lumentis.se>
 * Copyright (C) 2000-2004 by Erik Andersen <andersen@codpoet.org>
 * Copyright (c) 1994-2000 Eric Youngdale, Peter MacDonald,
 *				David Engel, Hongjiu Lu and Mitch D'Souza
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. The name of the above contributors may not be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE 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 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.
 */


/* Various symbol table handling functions, including symbol lookup */

/*
 * This is the start of the linked list that describes all of the files present
 * in the system with pointers to all of the symbol, string, and hash tables,
 * as well as all of the other good stuff in the binary.
 */
struct elf_resolve *_dl_loaded_modules = NULL;

/*
 * This is the list of modules that are loaded when the image is first
 * started.  As we add more via dlopen, they get added into other
 * chains.
 */
struct dyn_elf *_dl_symbol_tables = NULL;

/*
 * This is the list of modules that are loaded via dlopen.  We may need
 * to search these for RTLD_GLOBAL files.
 */
struct dyn_elf *_dl_handles = NULL;


/* This is the hash function that is used by the ELF linker to generate the
 * hash table that each executable and library is required to have.  We need
 * it to decode the hash table.  */
unsigned long _dl_elf_hash(const unsigned char *name)
{
	unsigned long hash = 0;
	unsigned long tmp;

	while (*name) {
		hash = (hash << 4) + *name++;
		if ((tmp = hash & 0xf0000000))
			hash ^= tmp >> 24;
		hash &= ~tmp;
	}
	return hash;
}

/* Check to see if a library has already been added to the hash chain.  */
struct elf_resolve *_dl_check_hashed_files(const char *libname)
{
	struct elf_resolve *tpnt;
	int len = _dl_strlen(libname);

	for (tpnt = _dl_loaded_modules; tpnt; tpnt = tpnt->next) {
		if (_dl_strncmp(tpnt->libname, libname, len) == 0 &&
				(tpnt->libname[len] == '\0' || tpnt->libname[len] == '.'))
			return tpnt;
	}

	return NULL;
}

/*
 * We call this function when we have just read an ELF library or executable.
 * We add the relevant info to the symbol chain, so that we can resolve all
 * externals properly.
 */
struct elf_resolve *_dl_add_elf_hash_table(const char *libname,
	char *loadaddr, unsigned long *dynamic_info, unsigned long dynamic_addr,
	unsigned long dynamic_size)
{
	unsigned long *hash_addr;
	struct elf_resolve *tpnt;
	int i;

	if (!_dl_loaded_modules) {
		tpnt = _dl_loaded_modules = (struct elf_resolve *) _dl_malloc(sizeof(struct elf_resolve));
		_dl_memset(tpnt, 0, sizeof(struct elf_resolve));
	} else {
		tpnt = _dl_loaded_modules;
		while (tpnt->next)
			tpnt = tpnt->next;
		tpnt->next = (struct elf_resolve *) _dl_malloc(sizeof(struct elf_resolve));
		_dl_memset(tpnt->next, 0, sizeof(struct elf_resolve));
		tpnt->next->prev = tpnt;
		tpnt = tpnt->next;
	};

	tpnt->next = NULL;
	tpnt->init_flag = 0;
	tpnt->libname = _dl_strdup(libname);
	tpnt->dynamic_addr = (ElfW(Dyn) *)dynamic_addr;
	tpnt->dynamic_size = dynamic_size;
	tpnt->libtype = loaded_file;

	if (dynamic_info[DT_HASH] != 0) {
		hash_addr = (unsigned long *) (intptr_t)(dynamic_info[DT_HASH] + loadaddr);
		tpnt->nbucket = *hash_addr++;
		tpnt->nchain = *hash_addr++;
		tpnt->elf_buckets = hash_addr;
		hash_addr += tpnt->nbucket;
		tpnt->chains = hash_addr;
	}
	tpnt->loadaddr = (ElfW(Addr))loadaddr;
	for (i = 0; i < 24; i++)
		tpnt->dynamic_info[i] = dynamic_info[i];
#ifdef __mips__
	{
		Elf32_Dyn *dpnt = (Elf32_Dyn *) dynamic_addr;

		while(dpnt->d_tag) {
			if (dpnt->d_tag == DT_MIPS_GOTSYM)
				tpnt->mips_gotsym = dpnt->d_un.d_val;
			if (dpnt->d_tag == DT_MIPS_LOCAL_GOTNO)
				tpnt->mips_local_gotno = dpnt->d_un.d_val;
			if (dpnt->d_tag == DT_MIPS_SYMTABNO)
				tpnt->mips_symtabno = dpnt->d_un.d_val;
			dpnt++;
		}
	}
#endif
	return tpnt;
}


/*
 * This function resolves externals, and this is either called when we process
 * relocations or when we call an entry in the PLT table for the first time.
 */
char *_dl_find_hash(const char *name, struct dyn_elf *rpnt1,
		    int type_class)
{
	struct elf_resolve *tpnt;
	int si;
	int pass;
	char *strtab;
	Elf32_Sym *symtab;
	unsigned long elf_hash_number, hn;
	char *weak_result;
	struct dyn_elf *rpnt;
	const ElfW(Sym) *sym;

	weak_result = 0;
	elf_hash_number = _dl_elf_hash(name);

	/*
	 * The passes are so that we can first search the regular symbols
	 * for whatever module was specified, and then search anything
	 * loaded with RTLD_GLOBAL.  When pass is 1, it means we are just
	 * starting the first dlopened module, and anything above that
	 * is just the next one in the chain.
	 */
	if (rpnt1 == NULL)
		rpnt1 = _dl_symbol_tables;

	for (pass = 0; (1 == 1); pass++) {

		/*
		 * If we are just starting to search for RTLD_GLOBAL, setup
		 * the pointer for the start of the search.
		 */
		if (pass == 1)
			rpnt1 = _dl_handles;

		/*
		 * Anything after this, we need to skip to the next module.
		 */
		else if (pass >= 2)
			rpnt1 = rpnt1->next_handle;

		/*
		 * Make sure we still have a module.
		 */
			if (rpnt1 == NULL)
				break;

		for (rpnt = rpnt1; rpnt; rpnt = rpnt->next) {
			tpnt = rpnt->dyn;

			/* Don't search the executable when resolving a copy reloc. */
			if ((type_class &  ELF_RTYPE_CLASS_COPY) && tpnt->libtype == elf_executable)
				continue;

			/*
			 * Avoid calling .urem here.
			 */
			do_rem(hn, elf_hash_number, tpnt->nbucket);
			symtab = (Elf32_Sym *) (intptr_t) (tpnt->dynamic_info[DT_SYMTAB] + tpnt->loadaddr);
			strtab = (char *) (tpnt->dynamic_info[DT_STRTAB] + tpnt->loadaddr);

			for (si = tpnt->elf_buckets[hn]; si != STN_UNDEF; si = tpnt->chains[si]) {
				sym = &symtab[si];

				if (sym->st_value == 0)
					continue;
				if (ELF32_ST_TYPE(sym->st_info) > STT_FUNC)
					continue;
				if (type_class & (sym->st_shndx == SHN_UNDEF))
					continue;
				if (_dl_strcmp(strtab + sym->st_name, name) != 0)
					continue;

				switch (ELF32_ST_BIND(sym->st_info)) {
					case STB_WEAK:
#ifndef __LIBDL_SHARED__
/* 
Due to a special hack in libdl.c, one must handle the _dl_ symbols
according to the OLD weak symbol scheme. This stuff can be deleted
once that hack has been fixed.
*/

						if(_dl_symbol((char *)name)) {
						if (!weak_result)
							weak_result = (char *)tpnt->loadaddr + sym->st_value;
						break;
						}
#endif
					case STB_GLOBAL:
						return (char*)tpnt->loadaddr + sym->st_value;
					default:	/* Local symbols not handled here */
						break;
				}
			}
		}
	}
	return weak_result;
}