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tccelf.c
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/*
* ELF file handling for TCC
*
* Copyright (c) 2001-2004 Fabrice Bellard
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include "tcc.h"
/* Define this to get some debug output during relocation processing. */
#undef DEBUG_RELOC
/********************************************************/
/* global variables */
ST_DATA Section *text_section, *data_section, *bss_section; /* predefined sections */
ST_DATA Section *common_section;
ST_DATA Section *cur_text_section; /* current section where function code is generated */
#ifdef CONFIG_TCC_ASM
ST_DATA Section *last_text_section; /* to handle .previous asm directive */
#endif
#ifdef CONFIG_TCC_BCHECK
/* bound check related sections */
ST_DATA Section *bounds_section; /* contains global data bound description */
ST_DATA Section *lbounds_section; /* contains local data bound description */
#endif
/* symbol sections */
ST_DATA Section *symtab_section, *strtab_section;
/* debug sections */
ST_DATA Section *stab_section, *stabstr_section;
/* XXX: avoid static variable */
static int new_undef_sym = 0; /* Is there a new undefined sym since last new_undef_sym() */
/* ------------------------------------------------------------------------- */
ST_FUNC void tccelf_new(TCCState *s)
{
/* no section zero */
dynarray_add(&s->sections, &s->nb_sections, NULL);
/* create standard sections */
text_section = new_section(s, ".text", SHT_PROGBITS, SHF_ALLOC | SHF_EXECINSTR);
data_section = new_section(s, ".data", SHT_PROGBITS, SHF_ALLOC | SHF_WRITE);
bss_section = new_section(s, ".bss", SHT_NOBITS, SHF_ALLOC | SHF_WRITE);
common_section = new_section(s, ".common", SHT_NOBITS, SHF_PRIVATE);
common_section->sh_num = SHN_COMMON;
/* symbols are always generated for linking stage */
symtab_section = new_symtab(s, ".symtab", SHT_SYMTAB, 0,
".strtab",
".hashtab", SHF_PRIVATE);
strtab_section = symtab_section->link;
s->symtab = symtab_section;
/* private symbol table for dynamic symbols */
s->dynsymtab_section = new_symtab(s, ".dynsymtab", SHT_SYMTAB, SHF_PRIVATE,
".dynstrtab",
".dynhashtab", SHF_PRIVATE);
get_sym_attr(s, 0, 1);
}
#ifdef CONFIG_TCC_BCHECK
ST_FUNC void tccelf_bounds_new(TCCState *s)
{
/* create bounds sections */
bounds_section = new_section(s, ".bounds",
SHT_PROGBITS, SHF_ALLOC);
lbounds_section = new_section(s, ".lbounds",
SHT_PROGBITS, SHF_ALLOC);
}
#endif
ST_FUNC void tccelf_stab_new(TCCState *s)
{
stab_section = new_section(s, ".stab", SHT_PROGBITS, 0);
stab_section->sh_entsize = sizeof(Stab_Sym);
stabstr_section = new_section(s, ".stabstr", SHT_STRTAB, 0);
put_elf_str(stabstr_section, "");
stab_section->link = stabstr_section;
/* put first entry */
put_stabs("", 0, 0, 0, 0);
}
static void free_section(Section *s)
{
tcc_free(s->data);
}
ST_FUNC void tccelf_delete(TCCState *s1)
{
int i;
/* free all sections */
for(i = 1; i < s1->nb_sections; i++)
free_section(s1->sections[i]);
dynarray_reset(&s1->sections, &s1->nb_sections);
for(i = 0; i < s1->nb_priv_sections; i++)
free_section(s1->priv_sections[i]);
dynarray_reset(&s1->priv_sections, &s1->nb_priv_sections);
/* free any loaded DLLs */
#ifdef TCC_IS_NATIVE
for ( i = 0; i < s1->nb_loaded_dlls; i++) {
DLLReference *ref = s1->loaded_dlls[i];
if ( ref->handle )
# ifdef _WIN32
FreeLibrary((HMODULE)ref->handle);
# else
dlclose(ref->handle);
# endif
}
#endif
/* free loaded dlls array */
dynarray_reset(&s1->loaded_dlls, &s1->nb_loaded_dlls);
tcc_free(s1->sym_attrs);
}
ST_FUNC Section *new_section(TCCState *s1, const char *name, int sh_type, int sh_flags)
{
Section *sec;
sec = tcc_mallocz(sizeof(Section) + strlen(name));
strcpy(sec->name, name);
sec->sh_type = sh_type;
sec->sh_flags = sh_flags;
switch(sh_type) {
case SHT_HASH:
case SHT_REL:
case SHT_RELA:
case SHT_DYNSYM:
case SHT_SYMTAB:
case SHT_DYNAMIC:
sec->sh_addralign = 4;
break;
case SHT_STRTAB:
sec->sh_addralign = 1;
break;
default:
sec->sh_addralign = PTR_SIZE; /* gcc/pcc default alignment */
break;
}
if (sh_flags & SHF_PRIVATE) {
dynarray_add(&s1->priv_sections, &s1->nb_priv_sections, sec);
} else {
sec->sh_num = s1->nb_sections;
dynarray_add(&s1->sections, &s1->nb_sections, sec);
}
return sec;
}
ST_FUNC Section *new_symtab(TCCState *s1,
const char *symtab_name, int sh_type, int sh_flags,
const char *strtab_name,
const char *hash_name, int hash_sh_flags)
{
Section *symtab, *strtab, *hash;
int *ptr, nb_buckets;
symtab = new_section(s1, symtab_name, sh_type, sh_flags);
symtab->sh_entsize = sizeof(ElfW(Sym));
strtab = new_section(s1, strtab_name, SHT_STRTAB, sh_flags);
put_elf_str(strtab, "");
symtab->link = strtab;
put_elf_sym(symtab, 0, 0, 0, 0, 0, NULL);
nb_buckets = 1;
hash = new_section(s1, hash_name, SHT_HASH, hash_sh_flags);
hash->sh_entsize = sizeof(int);
symtab->hash = hash;
hash->link = symtab;
ptr = section_ptr_add(hash, (2 + nb_buckets + 1) * sizeof(int));
ptr[0] = nb_buckets;
ptr[1] = 1;
memset(ptr + 2, 0, (nb_buckets + 1) * sizeof(int));
return symtab;
}
/* realloc section and set its content to zero */
ST_FUNC void section_realloc(Section *sec, unsigned long new_size)
{
unsigned long size;
unsigned char *data;
size = sec->data_allocated;
if (size == 0)
size = 1;
while (size < new_size)
size = size * 2;
data = tcc_realloc(sec->data, size);
memset(data + sec->data_allocated, 0, size - sec->data_allocated);
sec->data = data;
sec->data_allocated = size;
}
/* reserve at least 'size' bytes aligned per 'align' in section
'sec' from current offset, and return the aligned offset */
ST_FUNC size_t section_add(Section *sec, addr_t size, int align)
{
size_t offset, offset1;
offset = (sec->data_offset + align - 1) & -align;
offset1 = offset + size;
if (sec->sh_type != SHT_NOBITS && offset1 > sec->data_allocated)
section_realloc(sec, offset1);
sec->data_offset = offset1;
if (align > sec->sh_addralign)
sec->sh_addralign = align;
return offset;
}
/* reserve at least 'size' bytes in section 'sec' from
sec->data_offset. */
ST_FUNC void *section_ptr_add(Section *sec, addr_t size)
{
size_t offset = section_add(sec, size, 1);
return sec->data + offset;
}
/* reserve at least 'size' bytes from section start */
ST_FUNC void section_reserve(Section *sec, unsigned long size)
{
if (size > sec->data_allocated)
section_realloc(sec, size);
if (size > sec->data_offset)
sec->data_offset = size;
}
/* return a reference to a section, and create it if it does not
exists */
ST_FUNC Section *find_section(TCCState *s1, const char *name)
{
Section *sec;
int i;
for(i = 1; i < s1->nb_sections; i++) {
sec = s1->sections[i];
if (!strcmp(name, sec->name))
return sec;
}
/* sections are created as PROGBITS */
return new_section(s1, name, SHT_PROGBITS, SHF_ALLOC);
}
/* ------------------------------------------------------------------------- */
ST_FUNC int put_elf_str(Section *s, const char *sym)
{
int offset, len;
char *ptr;
len = strlen(sym) + 1;
offset = s->data_offset;
ptr = section_ptr_add(s, len);
memcpy(ptr, sym, len);
return offset;
}
/* elf symbol hashing function */
static unsigned long elf_hash(const unsigned char *name)
{
unsigned long h = 0, g;
while (*name) {
h = (h << 4) + *name++;
g = h & 0xf0000000;
if (g)
h ^= g >> 24;
h &= ~g;
}
return h;
}
/* rebuild hash table of section s */
/* NOTE: we do factorize the hash table code to go faster */
static void rebuild_hash(Section *s, unsigned int nb_buckets)
{
ElfW(Sym) *sym;
int *ptr, *hash, nb_syms, sym_index, h;
unsigned char *strtab;
strtab = s->link->data;
nb_syms = s->data_offset / sizeof(ElfW(Sym));
s->hash->data_offset = 0;
ptr = section_ptr_add(s->hash, (2 + nb_buckets + nb_syms) * sizeof(int));
ptr[0] = nb_buckets;
ptr[1] = nb_syms;
ptr += 2;
hash = ptr;
memset(hash, 0, (nb_buckets + 1) * sizeof(int));
ptr += nb_buckets + 1;
sym = (ElfW(Sym) *)s->data + 1;
for(sym_index = 1; sym_index < nb_syms; sym_index++) {
if (ELFW(ST_BIND)(sym->st_info) != STB_LOCAL) {
h = elf_hash(strtab + sym->st_name) % nb_buckets;
*ptr = hash[h];
hash[h] = sym_index;
} else {
*ptr = 0;
}
ptr++;
sym++;
}
}
/* return the symbol number */
ST_FUNC int put_elf_sym(Section *s, addr_t value, unsigned long size,
int info, int other, int shndx, const char *name)
{
int name_offset, sym_index;
int nbuckets, h;
ElfW(Sym) *sym;
Section *hs;
sym = section_ptr_add(s, sizeof(ElfW(Sym)));
if (name)
name_offset = put_elf_str(s->link, name);
else
name_offset = 0;
/* XXX: endianness */
sym->st_name = name_offset;
sym->st_value = value;
sym->st_size = size;
sym->st_info = info;
sym->st_other = other;
sym->st_shndx = shndx;
sym_index = sym - (ElfW(Sym) *)s->data;
hs = s->hash;
if (hs) {
int *ptr, *base;
ptr = section_ptr_add(hs, sizeof(int));
base = (int *)hs->data;
/* only add global or weak symbols */
if (ELFW(ST_BIND)(info) != STB_LOCAL) {
/* add another hashing entry */
nbuckets = base[0];
h = elf_hash((unsigned char *) name) % nbuckets;
*ptr = base[2 + h];
base[2 + h] = sym_index;
base[1]++;
/* we resize the hash table */
hs->nb_hashed_syms++;
if (hs->nb_hashed_syms > 2 * nbuckets) {
rebuild_hash(s, 2 * nbuckets);
}
} else {
*ptr = 0;
base[1]++;
}
}
return sym_index;
}
/* find global ELF symbol 'name' and return its index. Return 0 if not
found. */
ST_FUNC int find_elf_sym(Section *s, const char *name)
{
ElfW(Sym) *sym;
Section *hs;
int nbuckets, sym_index, h;
const char *name1;
hs = s->hash;
if (!hs)
return 0;
nbuckets = ((int *)hs->data)[0];
h = elf_hash((unsigned char *) name) % nbuckets;
sym_index = ((int *)hs->data)[2 + h];
while (sym_index != 0) {
sym = &((ElfW(Sym) *)s->data)[sym_index];
name1 = (char *) s->link->data + sym->st_name;
if (!strcmp(name, name1))
return sym_index;
sym_index = ((int *)hs->data)[2 + nbuckets + sym_index];
}
return 0;
}
/* return elf symbol value, signal error if 'err' is nonzero */
ST_FUNC addr_t get_elf_sym_addr(TCCState *s, const char *name, int err)
{
int sym_index;
ElfW(Sym) *sym;
sym_index = find_elf_sym(s->symtab, name);
sym = &((ElfW(Sym) *)s->symtab->data)[sym_index];
if (!sym_index || sym->st_shndx == SHN_UNDEF) {
if (err)
tcc_error("%s not defined", name);
return 0;
}
return sym->st_value;
}
/* return elf symbol value */
LIBTCCAPI void *tcc_get_symbol(TCCState *s, const char *name)
{
return (void*)(uintptr_t)get_elf_sym_addr(s, name, 0);
}
#if defined TCC_IS_NATIVE || defined TCC_TARGET_PE
/* return elf symbol value or error */
ST_FUNC void* tcc_get_symbol_err(TCCState *s, const char *name)
{
return (void*)(uintptr_t)get_elf_sym_addr(s, name, 1);
}
#endif
/* add an elf symbol : check if it is already defined and patch
it. Return symbol index. NOTE that sh_num can be SHN_UNDEF. */
ST_FUNC int set_elf_sym(Section *s, addr_t value, unsigned long size,
int info, int other, int shndx, const char *name)
{
ElfW(Sym) *esym;
int sym_bind, sym_index, sym_type, esym_bind;
unsigned char sym_vis, esym_vis, new_vis;
sym_bind = ELFW(ST_BIND)(info);
sym_type = ELFW(ST_TYPE)(info);
sym_vis = ELFW(ST_VISIBILITY)(other);
sym_index = find_elf_sym(s, name);
esym = &((ElfW(Sym) *)s->data)[sym_index];
if (sym_index && esym->st_value == value && esym->st_size == size
&& esym->st_info == info && esym->st_other == other
&& esym->st_shndx == shndx)
return sym_index;
if (sym_bind != STB_LOCAL) {
/* we search global or weak symbols */
if (!sym_index)
goto do_def;
if (esym->st_shndx != SHN_UNDEF) {
esym_bind = ELFW(ST_BIND)(esym->st_info);
/* propagate the most constraining visibility */
/* STV_DEFAULT(0)<STV_PROTECTED(3)<STV_HIDDEN(2)<STV_INTERNAL(1) */
esym_vis = ELFW(ST_VISIBILITY)(esym->st_other);
if (esym_vis == STV_DEFAULT) {
new_vis = sym_vis;
} else if (sym_vis == STV_DEFAULT) {
new_vis = esym_vis;
} else {
new_vis = (esym_vis < sym_vis) ? esym_vis : sym_vis;
}
esym->st_other = (esym->st_other & ~ELFW(ST_VISIBILITY)(-1))
| new_vis;
other = esym->st_other; /* in case we have to patch esym */
if (shndx == SHN_UNDEF) {
/* ignore adding of undefined symbol if the
corresponding symbol is already defined */
} else if (sym_bind == STB_GLOBAL && esym_bind == STB_WEAK) {
/* global overrides weak, so patch */
goto do_patch;
} else if (sym_bind == STB_WEAK && esym_bind == STB_GLOBAL) {
/* weak is ignored if already global */
} else if (sym_bind == STB_WEAK && esym_bind == STB_WEAK) {
/* keep first-found weak definition, ignore subsequents */
} else if (sym_vis == STV_HIDDEN || sym_vis == STV_INTERNAL) {
/* ignore hidden symbols after */
} else if ((esym->st_shndx == SHN_COMMON
|| esym->st_shndx == bss_section->sh_num)
&& (shndx < SHN_LORESERVE
&& shndx != bss_section->sh_num)) {
/* data symbol gets precedence over common/bss */
goto do_patch;
} else if (shndx == SHN_COMMON || shndx == bss_section->sh_num) {
/* data symbol keeps precedence over common/bss */
} else if (s == tcc_state->dynsymtab_section) {
/* we accept that two DLL define the same symbol */
} else {
#if 0
printf("new_bind=%x new_shndx=%x new_vis=%x old_bind=%x old_shndx=%x old_vis=%x\n",
sym_bind, shndx, new_vis, esym_bind, esym->st_shndx, esym_vis);
#endif
tcc_error_noabort("'%s' defined twice", name);
}
} else {
do_patch:
esym->st_info = ELFW(ST_INFO)(sym_bind, sym_type);
esym->st_shndx = shndx;
new_undef_sym = 1;
esym->st_value = value;
esym->st_size = size;
esym->st_other = other;
}
} else {
do_def:
sym_index = put_elf_sym(s, value, size,
ELFW(ST_INFO)(sym_bind, sym_type), other,
shndx, name);
}
return sym_index;
}
/* put relocation */
ST_FUNC void put_elf_reloca(Section *symtab, Section *s, unsigned long offset,
int type, int symbol, addr_t addend)
{
char buf[256];
Section *sr;
ElfW_Rel *rel;
sr = s->reloc;
if (!sr) {
/* if no relocation section, create it */
snprintf(buf, sizeof(buf), REL_SECTION_FMT, s->name);
/* if the symtab is allocated, then we consider the relocation
are also */
sr = new_section(tcc_state, buf, SHT_RELX, symtab->sh_flags);
sr->sh_entsize = sizeof(ElfW_Rel);
sr->link = symtab;
sr->sh_info = s->sh_num;
s->reloc = sr;
}
rel = section_ptr_add(sr, sizeof(ElfW_Rel));
rel->r_offset = offset;
rel->r_info = ELFW(R_INFO)(symbol, type);
#if SHT_RELX == SHT_RELA
rel->r_addend = addend;
#else
if (addend)
tcc_error("non-zero addend on REL architecture");
#endif
}
ST_FUNC void put_elf_reloc(Section *symtab, Section *s, unsigned long offset,
int type, int symbol)
{
put_elf_reloca(symtab, s, offset, type, symbol, 0);
}
/* Remove relocations for section S->reloc starting at oldrelocoffset
that are to the same place, retaining the last of them. As side effect
the relocations are sorted. Possibly reduces the number of relocs. */
ST_FUNC void squeeze_multi_relocs(Section *s, size_t oldrelocoffset)
{
Section *sr = s->reloc;
ElfW_Rel *r, *dest;
ssize_t a;
ElfW(Addr) addr;
if (oldrelocoffset + sizeof(*r) >= sr->data_offset)
return;
/* The relocs we're dealing with are the result of initializer parsing.
So they will be mostly in order and there aren't many of them.
Secondly we need a stable sort (which qsort isn't). We use
a simple insertion sort. */
for (a = oldrelocoffset + sizeof(*r); a < sr->data_offset; a += sizeof(*r)) {
ssize_t i = a - sizeof(*r);
addr = ((ElfW_Rel*)(sr->data + a))->r_offset;
for (; i >= (ssize_t)oldrelocoffset &&
((ElfW_Rel*)(sr->data + i))->r_offset > addr; i -= sizeof(*r)) {
ElfW_Rel tmp = *(ElfW_Rel*)(sr->data + a);
*(ElfW_Rel*)(sr->data + a) = *(ElfW_Rel*)(sr->data + i);
*(ElfW_Rel*)(sr->data + i) = tmp;
}
}
r = (ElfW_Rel*)(sr->data + oldrelocoffset);
dest = r;
for (; r < (ElfW_Rel*)(sr->data + sr->data_offset); r++) {
if (dest->r_offset != r->r_offset)
dest++;
*dest = *r;
}
sr->data_offset = (unsigned char*)dest - sr->data + sizeof(*r);
}
/* put stab debug information */
ST_FUNC void put_stabs(const char *str, int type, int other, int desc,
unsigned long value)
{
Stab_Sym *sym;
sym = section_ptr_add(stab_section, sizeof(Stab_Sym));
if (str) {
sym->n_strx = put_elf_str(stabstr_section, str);
} else {
sym->n_strx = 0;
}
sym->n_type = type;
sym->n_other = other;
sym->n_desc = desc;
sym->n_value = value;
}
ST_FUNC void put_stabs_r(const char *str, int type, int other, int desc,
unsigned long value, Section *sec, int sym_index)
{
put_stabs(str, type, other, desc, value);
put_elf_reloc(symtab_section, stab_section,
stab_section->data_offset - sizeof(unsigned int),
R_DATA_32, sym_index);
}
ST_FUNC void put_stabn(int type, int other, int desc, int value)
{
put_stabs(NULL, type, other, desc, value);
}
ST_FUNC void put_stabd(int type, int other, int desc)
{
put_stabs(NULL, type, other, desc, 0);
}
ST_FUNC struct sym_attr *get_sym_attr(TCCState *s1, int index, int alloc)
{
int n;
struct sym_attr *tab;
if (index >= s1->nb_sym_attrs) {
if (!alloc)
return s1->sym_attrs;
/* find immediately bigger power of 2 and reallocate array */
n = 1;
while (index >= n)
n *= 2;
tab = tcc_realloc(s1->sym_attrs, n * sizeof(*s1->sym_attrs));
s1->sym_attrs = tab;
memset(s1->sym_attrs + s1->nb_sym_attrs, 0,
(n - s1->nb_sym_attrs) * sizeof(*s1->sym_attrs));
s1->nb_sym_attrs = n;
}
return &s1->sym_attrs[index];
}
/* Browse each elem of type <type> in section <sec> starting at elem <startoff>
using variable <elem> */
#define for_each_elem(sec, startoff, elem, type) \
for (elem = (type *) sec->data + startoff; \
elem < (type *) (sec->data + sec->data_offset); elem++)
/* In an ELF file symbol table, the local symbols must appear below
the global and weak ones. Since TCC cannot sort it while generating
the code, we must do it after. All the relocation tables are also
modified to take into account the symbol table sorting */
static void sort_syms(TCCState *s1, Section *s)
{
int *old_to_new_syms;
ElfW(Sym) *new_syms;
int nb_syms, i;
ElfW(Sym) *p, *q;
ElfW_Rel *rel;
Section *sr;
int type, sym_index;
nb_syms = s->data_offset / sizeof(ElfW(Sym));
new_syms = tcc_malloc(nb_syms * sizeof(ElfW(Sym)));
old_to_new_syms = tcc_malloc(nb_syms * sizeof(int));
/* first pass for local symbols */
p = (ElfW(Sym) *)s->data;
q = new_syms;
for(i = 0; i < nb_syms; i++) {
if (ELFW(ST_BIND)(p->st_info) == STB_LOCAL) {
old_to_new_syms[i] = q - new_syms;
*q++ = *p;
}
p++;
}
/* save the number of local symbols in section header */
if( s->sh_size ) /* this 'if' makes IDA happy */
s->sh_info = q - new_syms;
/* then second pass for non local symbols */
p = (ElfW(Sym) *)s->data;
for(i = 0; i < nb_syms; i++) {
if (ELFW(ST_BIND)(p->st_info) != STB_LOCAL) {
old_to_new_syms[i] = q - new_syms;
*q++ = *p;
}
p++;
}
/* we copy the new symbols to the old */
memcpy(s->data, new_syms, nb_syms * sizeof(ElfW(Sym)));
tcc_free(new_syms);
/* now we modify all the relocations */
for(i = 1; i < s1->nb_sections; i++) {
sr = s1->sections[i];
if (sr->sh_type == SHT_RELX && sr->link == s) {
for_each_elem(sr, 0, rel, ElfW_Rel) {
sym_index = ELFW(R_SYM)(rel->r_info);
type = ELFW(R_TYPE)(rel->r_info);
sym_index = old_to_new_syms[sym_index];
rel->r_info = ELFW(R_INFO)(sym_index, type);
}
}
}
tcc_free(old_to_new_syms);
}
/* relocate common symbols in the .bss section */
ST_FUNC void relocate_common_syms(void)
{
ElfW(Sym) *sym;
for_each_elem(symtab_section, 1, sym, ElfW(Sym)) {
if (sym->st_shndx == SHN_COMMON) {
/* symbol alignment is in st_value for SHN_COMMONs */
sym->st_value = section_add(bss_section, sym->st_size,
sym->st_value);
sym->st_shndx = bss_section->sh_num;
}
}
}
/* relocate symbol table, resolve undefined symbols if do_resolve is
true and output error if undefined symbol. */
ST_FUNC void relocate_syms(TCCState *s1, Section *symtab, int do_resolve)
{
ElfW(Sym) *sym;
int sym_bind, sh_num;
const char *name;
for_each_elem(symtab, 1, sym, ElfW(Sym)) {
sh_num = sym->st_shndx;
if (sh_num == SHN_UNDEF) {
name = (char *) strtab_section->data + sym->st_name;
/* Use ld.so to resolve symbol for us (for tcc -run) */
if (do_resolve) {
#if defined TCC_IS_NATIVE && !defined TCC_TARGET_PE
void *addr = dlsym(RTLD_DEFAULT, name);
if (addr) {
sym->st_value = (addr_t) addr;
#ifdef DEBUG_RELOC
printf ("relocate_sym: %s -> 0x%lx\n", name, sym->st_value);
#endif
goto found;
}
#endif
/* if dynamic symbol exist, it will be used in relocate_section */
} else if (s1->dynsym && find_elf_sym(s1->dynsym, name))
goto found;
/* XXX: _fp_hw seems to be part of the ABI, so we ignore
it */
if (!strcmp(name, "_fp_hw"))
goto found;
/* only weak symbols are accepted to be undefined. Their
value is zero */
sym_bind = ELFW(ST_BIND)(sym->st_info);
if (sym_bind == STB_WEAK)
sym->st_value = 0;
else
tcc_error_noabort("undefined symbol '%s'", name);
} else if (sh_num < SHN_LORESERVE) {
/* add section base */
sym->st_value += s1->sections[sym->st_shndx]->sh_addr;
}
found: ;
}
}
/* relocate a given section (CPU dependent) by applying the relocations
in the associated relocation section */
ST_FUNC void relocate_section(TCCState *s1, Section *s)
{
Section *sr = s->reloc;
ElfW_Rel *rel;
ElfW(Sym) *sym;
int type, sym_index;
unsigned char *ptr;
addr_t tgt, addr;
relocate_init(sr);
for_each_elem(sr, 0, rel, ElfW_Rel) {
ptr = s->data + rel->r_offset;
sym_index = ELFW(R_SYM)(rel->r_info);
sym = &((ElfW(Sym) *)symtab_section->data)[sym_index];
type = ELFW(R_TYPE)(rel->r_info);
tgt = sym->st_value;
#if SHT_RELX == SHT_RELA
tgt += rel->r_addend;
#endif
addr = s->sh_addr + rel->r_offset;
relocate(s1, rel, type, ptr, addr, tgt);
}
/* if the relocation is allocated, we change its symbol table */
if (sr->sh_flags & SHF_ALLOC)
sr->link = s1->dynsym;
}
/* relocate relocation table in 'sr' */
static void relocate_rel(TCCState *s1, Section *sr)
{
Section *s;
ElfW_Rel *rel;
s = s1->sections[sr->sh_info];
for_each_elem(sr, 0, rel, ElfW_Rel)
rel->r_offset += s->sh_addr;
}
/* count the number of dynamic relocations so that we can reserve
their space */
static int prepare_dynamic_rel(TCCState *s1, Section *sr)
{
ElfW_Rel *rel;
int sym_index, type, count;
count = 0;
for_each_elem(sr, 0, rel, ElfW_Rel) {
sym_index = ELFW(R_SYM)(rel->r_info);
type = ELFW(R_TYPE)(rel->r_info);
switch(type) {
#if defined(TCC_TARGET_I386)
case R_386_32:
if (!get_sym_attr(s1, sym_index, 0)->dyn_index
&& ((ElfW(Sym)*)symtab_section->data + sym_index)->st_shndx == SHN_UNDEF) {
/* don't fixup unresolved (weak) symbols */
rel->r_info = ELFW(R_INFO)(sym_index, R_386_RELATIVE);
break;
}
#elif defined(TCC_TARGET_X86_64)
case R_X86_64_32:
case R_X86_64_32S:
case R_X86_64_64:
#endif
count++;
break;
#if defined(TCC_TARGET_I386)
case R_386_PC32:
#elif defined(TCC_TARGET_X86_64)
case R_X86_64_PC32:
#endif
if (get_sym_attr(s1, sym_index, 0)->dyn_index)
count++;
break;
default:
break;
}
}
if (count) {
/* allocate the section */
sr->sh_flags |= SHF_ALLOC;
sr->sh_size = count * sizeof(ElfW_Rel);
}
return count;
}
static void build_got(TCCState *s1)
{
/* if no got, then create it */
s1->got = new_section(s1, ".got", SHT_PROGBITS, SHF_ALLOC | SHF_WRITE);
s1->got->sh_entsize = 4;
set_elf_sym(symtab_section, 0, 4, ELFW(ST_INFO)(STB_GLOBAL, STT_OBJECT),
0, s1->got->sh_num, "_GLOBAL_OFFSET_TABLE_");
/* keep space for _DYNAMIC pointer and two dummy got entries */
section_ptr_add(s1->got, 3 * PTR_SIZE);
}
/* Create a GOT and (for function call) a PLT entry corresponding to a symbol
in s1->symtab. When creating the dynamic symbol table entry for the GOT
relocation, use 'size' and 'info' for the corresponding symbol metadata.
Returns the offset of the GOT or (if any) PLT entry. */
static struct sym_attr * put_got_entry(TCCState *s1, int dyn_reloc_type,
unsigned long size,
int info, int sym_index)
{
int need_plt_entry;
const char *name;
ElfW(Sym) *sym;
struct sym_attr *attr;
unsigned got_offset;
char plt_name[100];
int len;
need_plt_entry = (dyn_reloc_type == R_JMP_SLOT);
attr = get_sym_attr(s1, sym_index, 1);
/* In case a function is both called and its address taken 2 GOT entries
are created, one for taking the address (GOT) and the other for the PLT
entry (PLTGOT). */
if (need_plt_entry ? attr->plt_offset : attr->got_offset)
return attr;
/* create the GOT entry */
got_offset = s1->got->data_offset;
section_ptr_add(s1->got, PTR_SIZE);
/* Create the GOT relocation that will insert the address of the object or
function of interest in the GOT entry. This is a static relocation for
memory output (dlsym will give us the address of symbols) and dynamic
relocation otherwise (executable and DLLs). The relocation should be
done lazily for GOT entry with *_JUMP_SLOT relocation type (the one
associated to a PLT entry) but is currently done at load time for an
unknown reason. */
sym = &((ElfW(Sym) *) symtab_section->data)[sym_index];
name = (char *) symtab_section->link->data + sym->st_name;
if (s1->dynsym) {
if (ELFW(ST_BIND)(sym->st_info) == STB_LOCAL) {
/* Hack alarm. We don't want to emit dynamic symbols
and symbol based relocs for STB_LOCAL symbols, but rather
want to resolve them directly. At this point the symbol
values aren't final yet, so we must defer this. We will later
have to create a RELATIVE reloc anyway, so we misuse the
relocation slot to smuggle the symbol reference until
fill_local_got_entries. Not that the sym_index is
relative to symtab_section, not s1->dynsym! Nevertheless
we use s1->dyn_sym so that if this is the first call
that got->reloc is correctly created. Also note that
RELATIVE relocs are not normally created for the .got,
so the types serves as a marker for later (and is retained
also for the final output, which is okay because then the
got is just normal data). */
put_elf_reloc(s1->dynsym, s1->got, got_offset, R_RELATIVE,
sym_index);
} else {
if (0 == attr->dyn_index)
attr->dyn_index = set_elf_sym(s1->dynsym, sym->st_value, size,
info, 0, sym->st_shndx, name);
put_elf_reloc(s1->dynsym, s1->got, got_offset, dyn_reloc_type,
attr->dyn_index);
}
} else {
put_elf_reloc(symtab_section, s1->got, got_offset, dyn_reloc_type,
sym_index);
}
if (need_plt_entry) {
if (!s1->plt) {
s1->plt = new_section(s1, ".plt", SHT_PROGBITS,
SHF_ALLOC | SHF_EXECINSTR);
s1->plt->sh_entsize = 4;
}
attr->plt_offset = create_plt_entry(s1, got_offset, attr);
/* create a symbol 'sym@plt' for the PLT jump vector */
len = strlen(name);
if (len > sizeof plt_name - 5)
len = sizeof plt_name - 5;
memcpy(plt_name, name, len);
strcpy(plt_name + len, "@plt");
attr->plt_sym = put_elf_sym(s1->symtab, attr->plt_offset, sym->st_size,
ELFW(ST_INFO)(STB_GLOBAL, STT_FUNC), 0, s1->plt->sh_num, plt_name);
} else {
attr->got_offset = got_offset;
}
return attr;
}
/* build GOT and PLT entries */
ST_FUNC void build_got_entries(TCCState *s1)
{
Section *s;
ElfW_Rel *rel;
ElfW(Sym) *sym;
int i, type, gotplt_entry, reloc_type, sym_index;
struct sym_attr *attr;
for(i = 1; i < s1->nb_sections; i++) {
s = s1->sections[i];
if (s->sh_type != SHT_RELX)
continue;
/* no need to handle got relocations */
if (s->link != symtab_section)
continue;
for_each_elem(s, 0, rel, ElfW_Rel) {
type = ELFW(R_TYPE)(rel->r_info);
gotplt_entry = gotplt_entry_type(type);
sym_index = ELFW(R_SYM)(rel->r_info);
sym = &((ElfW(Sym) *)symtab_section->data)[sym_index];
if (gotplt_entry == NO_GOTPLT_ENTRY) {
continue;
}
/* Automatically create PLT/GOT [entry] if it is an undefined
reference (resolved at runtime), or the symbol is absolute,
probably created by tcc_add_symbol, and thus on 64-bit
targets might be too far from application code. */
if (gotplt_entry == AUTO_GOTPLT_ENTRY) {