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Copy pathlinker.c
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588 lines (528 loc) · 15.9 KB
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#include "linker.h"
Section* symtab_section;
Section* strtab_section;
Section* hash_section;
Section* dynsymtab_section;
Section* bss_section;
static int new_undef_sym = 0; /* Is there a new undefined sym since last new_undef_sym() */
typedef struct Sections {
size_t size;
size_t allocated;
Section** sec;
}Sections;
Sections* Secs;
/* realloc section and set its content to zero */
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 = realloc(sec->data, size);
memset(data + sec->data_allocated, 0, size - sec->data_allocated);
sec->data = data;
sec->data_allocated = size;
}
/* 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;
}
/* reserve at least 'size' bytes in section 'sec' from
sec->data_offset. */
void *section_ptr_add(Section *sec, unsigned long size)
{
unsigned long offset, offset1;
offset = sec->data_offset;
offset1 = offset + size;
if (offset1 > sec->data_allocated)
section_realloc(sec, offset1);
sec->data_offset = offset1;
return sec->data + offset;
}
static void *load_data(int fd, unsigned long file_offset, unsigned long size)
{
void *data;
data = malloc(size);
lseek(fd, file_offset, SEEK_SET);
read(fd, data, size);
return data;
}
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;
}
/* 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;
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++;
}
}
Section *new_section(Sections* ss, const char *name, int sh_type, int sh_flags)
{
Section *sec;
sec = malloc(sizeof(Section) + strlen(name));
memset(sec, 0, 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 = 32; /* default conservative alignment */
break;
}
if (ss->size >= ss->allocated) {
int i = ss->allocated + 10;
ss->sec = realloc(ss->sec, i * sizeof(Section *));
ss->allocated = i;
}
sec->sh_num = ss->size;
ss->sec[ss->size] = sec;
ss->size += 1;
return sec;
}
/* find global ELF symbol 'name' and return its index. Return 0 if not
found. */
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(name) % nbuckets;
sym_index = ((int *)hs->data)[2 + h];
while (sym_index != 0) {
sym = &((ElfW(Sym) *)s->data)[sym_index];
name1 = 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 the symbol number */
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(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;
}
#define SHN_UNDEF 0 /* Undefined section */
int add_elf_sym(Section *s, addr_t value, unsigned long size,
int info, int other, int sh_num, 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);
if (sym_bind != STB_LOCAL) {
/* we search global or weak symbols */
sym_index = find_elf_sym(s, name);
if (!sym_index)
goto do_def;
esym = &((ElfW(Sym) *)s->data)[sym_index];
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 (sh_num == 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
&& (sh_num < SHN_LORESERVE || sh_num == SHN_COMMON)) {
/* gr: Happens with 'tcc ... -static tcctest.c' on e.g. Ubuntu 6.01
No idea if this is the correct solution ... */
goto do_patch;
} else if (s == dynsymtab_section) {
/* we accept that two DLL define the same symbol */
} else {
assert(0 && "'%s' defined twice");
}
} else {
do_patch:
esym->st_info = ELFW(ST_INFO)(sym_bind, sym_type);
esym->st_shndx = sh_num;
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,
sh_num, name);
}
return sym_index;
}
int load_object_file(int fd, unsigned long file_offset) {
ElfW(Ehdr) ehdr;
ElfW(Shdr) *shdr, *sh;
ElfW(Sym) *sym, *symtab;
SectionMergeInfo *sm_table, *sm;
unsigned char *strsec, *strtab;
int i, j, nb_syms, offset;
int size, sym_index;
char *sh_name, *name;
Section *s;
int *old_to_new_syms;
int stab_index;
int stabstr_index;
int offseti;
ElfW_Rel *rel, *rel_end;
if (read(fd, &ehdr, sizeof(ehdr)) != sizeof(ehdr))
assert(0);
if (ehdr.e_ident[0] != ELFMAG0 ||
ehdr.e_ident[1] != ELFMAG1 ||
ehdr.e_ident[2] != ELFMAG2 ||
ehdr.e_ident[3] != ELFMAG3)
assert(0);
/* test if object file */
if (ehdr.e_type != ET_REL)
assert(0);
/* test CPU specific stuff */
if (ehdr.e_ident[5] != ELFDATA2LSB ||
ehdr.e_machine != TARGET) {
assert(0);
return -1;
}
/* read sections */
shdr = load_data(fd, file_offset + ehdr.e_shoff,
sizeof(ElfW(Shdr)) * ehdr.e_shnum);
sm_table = malloc(sizeof(SectionMergeInfo) * ehdr.e_shnum);
/* load section names */
sh = &shdr[ehdr.e_shstrndx];
strsec = load_data(fd, file_offset + sh->sh_offset, sh->sh_size);
symtab = NULL;
for(i = 1; i < ehdr.e_shnum; i++) {
sh = &shdr[i];
if (sh->sh_type == SHT_SYMTAB) {
if (symtab) {
assert(0);
}
nb_syms = sh->sh_size / sizeof(ElfW(Sym));
symtab = load_data(fd, file_offset + sh->sh_offset, sh->sh_size);
sm_table[i].s = symtab_section;
/* now load strtab */
sh = &shdr[sh->sh_link];
strtab = load_data(fd, file_offset + sh->sh_offset, sh->sh_size);
}
}
/* now examine each section and try to merge its content with the
ones in memory */
for(i = 1; i < ehdr.e_shnum; i++) {
/* no need to examine section name strtab */
if (i == ehdr.e_shstrndx)
continue;
sh = &shdr[i];
sh_name = strsec + sh->sh_name;
/* ignore sections types we do not handle */
if (sh->sh_type != SHT_PROGBITS &&
sh->sh_type != SHT_RELX &&
sh->sh_type != SHT_NOBITS &&
sh->sh_type != SHT_PREINIT_ARRAY &&
sh->sh_type != SHT_INIT_ARRAY &&
sh->sh_type != SHT_FINI_ARRAY &&
strcmp(sh_name, ".stabstr")
)
continue;
if (sh->sh_addralign < 1)
sh->sh_addralign = 1;
/* find corresponding section, if any */
for(j = 1; j < Secs->size;j++) {
s = Secs->sec[j];
if (!strcmp(s->name, sh_name)) {
if (!strncmp(sh_name, ".gnu.linkonce",
sizeof(".gnu.linkonce") - 1)) {
/* if a 'linkonce' section is already present, we
do not add it again. It is a little tricky as
symbols can still be defined in
it. */
sm_table[i].link_once = 1;
goto next;
} else {
goto found;
}
}
}
/* not found: create new section */
s = new_section(Secs, sh_name, sh->sh_type, sh->sh_flags);
/* take as much info as possible from the section. sh_link and
sh_info will be updated later */
s->sh_addralign = sh->sh_addralign;
s->sh_entsize = sh->sh_entsize;
sm_table[i].new_section = 1;
found:
if (sh->sh_type != s->sh_type) {
assert(0);
}
/* align start of section */
offset = s->data_offset;
if (0 == strcmp(sh_name, ".stab")) {
stab_index = i;
assert(0 && "what's this");
goto no_align;
}
if (0 == strcmp(sh_name, ".stabstr")) {
stabstr_index = i;
goto no_align;
}
size = sh->sh_addralign - 1;
offset = (offset + size) & ~size;
if (sh->sh_addralign > s->sh_addralign)
s->sh_addralign = sh->sh_addralign;
s->data_offset = offset;
no_align:
sm_table[i].offset = offset;
sm_table[i].s = s;
/* concatenate sections */
size = sh->sh_size;
if (sh->sh_type != SHT_NOBITS) {
unsigned char *ptr;
lseek(fd, file_offset + sh->sh_offset, SEEK_SET);
ptr = section_ptr_add(s, size);
read(fd, ptr, size);
} else {
s->data_offset += size;
}
next: ;
}
/* //gr relocate stab strings */
/* if (stab_index && stabstr_index) { */
/* Stab_Sym *a, *b; */
/* unsigned o; */
/* s = sm_table[stab_index].s; */
/* a = (Stab_Sym *)(s->data + sm_table[stab_index].offset); */
/* b = (Stab_Sym *)(s->data + s->data_offset); */
/* o = sm_table[stabstr_index].offset; */
/* while (a < b) */
/* a->n_strx += o, a++; */
/* } */
/* second short pass to update sh_link and sh_info fields of new
sections */
for(i = 1; i < ehdr.e_shnum; i++) {
s = sm_table[i].s;
if (!s || !sm_table[i].new_section)
continue;
sh = &shdr[i];
if (sh->sh_link > 0)
s->link = sm_table[sh->sh_link].s;
if (sh->sh_type == SHT_RELX) {
s->sh_info = sm_table[sh->sh_info].s->sh_num;
/* update backward link */
Secs->sec[s->sh_info]->reloc = s;
}
}
sm = sm_table;
/* resolve symbols */
old_to_new_syms = malloc(nb_syms * sizeof(int));
sym = symtab + 1;
for(i = 1; i < nb_syms; i++, sym++) {
if (sym->st_shndx != SHN_UNDEF &&
sym->st_shndx < SHN_LORESERVE) {
sm = &sm_table[sym->st_shndx];
if (sm->link_once) {
/* if a symbol is in a link once section, we use the
already defined symbol. It is very important to get
correct relocations */
if (ELFW(ST_BIND)(sym->st_info) != STB_LOCAL) {
name = strtab + sym->st_name;
sym_index = find_elf_sym(symtab_section, name);
if (sym_index)
old_to_new_syms[i] = sym_index;
}
continue;
}
/* if no corresponding section added, no need to add symbol */
if (!sm->s)
continue;
/* convert section number */
sym->st_shndx = sm->s->sh_num;
/* offset value */
sym->st_value += sm->offset;
}
/* add symbol */
name = strtab + sym->st_name;
sym_index = add_elf_sym(symtab_section, sym->st_value, sym->st_size,
sym->st_info, sym->st_other,
sym->st_shndx, name);
old_to_new_syms[i] = sym_index;
}
/* third pass to patch relocation entries */
for(i = 1; i < ehdr.e_shnum; i++) {
s = sm_table[i].s;
if (!s)
continue;
sh = &shdr[i];
offset = sm_table[i].offset;
switch(s->sh_type) {
case SHT_RELX:
/* take relocation offset information */
offseti = sm_table[sh->sh_info].offset;
rel_end = (ElfW_Rel *)(s->data + s->data_offset);
for(rel = (ElfW_Rel *)(s->data + offset);
rel < rel_end;
rel++) {
int type;
unsigned sym_index;
/* convert symbol index */
type = ELFW(R_TYPE)(rel->r_info);
sym_index = ELFW(R_SYM)(rel->r_info);
/* NOTE: only one symtab assumed */
if (sym_index >= nb_syms)
goto invalid_reloc;
sym_index = old_to_new_syms[sym_index];
/* ignore link_once in rel section. */
if (!sym_index && !sm->link_once
) {
invalid_reloc:
assert(0);
}
rel->r_info = ELFW(R_INFO)(sym_index, type);
/* offset the relocation offset */
rel->r_offset += offseti;
}
break;
default:
break;
}
}
}
int main(int argc, char ** argv) {
int i = 0;
Secs = malloc(sizeof(struct Sections));
Secs->allocated = 0;
Secs->size = 0;
symtab_section = new_section(Secs, ".symtab", SHT_SYMTAB, SHF_ALLOC);
strtab_section = new_section(Secs, ".strtab", SHT_STRTAB, SHF_ALLOC);
hash_section = new_section(Secs, ".hash", SHT_HASH, SHF_ALLOC);
bss_section = new_section(Secs, ".bss", SHT_NOBITS, SHF_ALLOC);
symtab_section->link = strtab_section;
symtab_section->hash = hash_section;
int *data = section_ptr_add(hash_section, sizeof(int) * 3);
data[0] = 1;
add_elf_sym(symtab_section, 0, 0, 0, 0,
0, "");
for (i = 1; i < argc; i++) {
int fd = open(argv[i], O_RDONLY);
load_object_file(fd, 0);
}
printf("section size = %lu\n", Secs->size);
}