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#include "elf_got.h"
#include <string.h>
#if defined(OBJFORMAT_ELF)
/*
* Check if we need a global offset table slot for a
* given symbol
*/
bool
needGotSlot(Elf_Sym * symbol) {
/* using global here should give an upper bound */
/* I don't believe we need to relocate STB_LOCAL
* symbols via the GOT; however I'm unsure about
* STB_WEAK.
*
* Any more restrictive filter here would result
* in a smaller GOT, which is preferrable.
*/
return ELF_ST_BIND(symbol->st_info) == STB_GLOBAL
|| ELF_ST_BIND(symbol->st_info) == STB_WEAK;
}
bool
makeGot(ObjectCode * oc) {
size_t got_slots = 0;
/* we need to find all symbol tables (elf can have multiple)
* and need to iterate over all symbols, to check how many
* got slots we need at most
*/
ASSERT( oc->info != NULL );
ASSERT( oc->info->sectionHeader != NULL );
for(int i=0; i < oc->n_sections; i++) {
if(SHT_SYMTAB == oc->info->sectionHeader[i].sh_type) {
Elf_Sym *symTab =
(Elf_Sym*)((uint8_t*)oc->info->elfHeader
+ oc->info->sectionHeader[i].sh_offset);
size_t n_symbols = oc->info->sectionHeader[i].sh_size
/ sizeof(Elf_Sym);
for(size_t j=0; j < n_symbols; j++) {
if(needGotSlot(&symTab[j])) {
got_slots += 1;
}
}
}
}
if(got_slots > 0) {
oc->info->got_size = got_slots * sizeof(void *);
void * mem = mmap(NULL, oc->info->got_size,
PROT_READ | PROT_WRITE,
MAP_ANON | MAP_PRIVATE,
-1, 0);
if (mem == MAP_FAILED) {
errorBelch("MAP_FAILED. errno=%d", errno);
return EXIT_FAILURE;
}
oc->info->got_start = (void*)mem;
/* update got_addr */
size_t slot = 0;
for(ElfSymbolTable *symTab = oc->info->symbolTables;
symTab != NULL; symTab = symTab->next) {
for(size_t i=0; i < symTab->n_symbols; i++)
if(needGotSlot(symTab->symbols[i].elf_sym))
symTab->symbols[i].got_addr
= (uint8_t *)oc->info->got_start
+ (slot++ * sizeof(void*));
}
}
return EXIT_SUCCESS;
}
bool
fillGot(ObjectCode * oc) {
/* fill the GOT table */
for(ElfSymbolTable *symTab = oc->info->symbolTables;
symTab != NULL; symTab = symTab->next) {
for(size_t i=0; i < symTab->n_symbols; i++) {
ElfSymbol * symbol = &symTab->symbols[i];
if(needGotSlot(symbol->elf_sym)) {
/* no type are undefined symbols */
if( STT_NOTYPE == ELF_ST_TYPE(symbol->elf_sym->st_info)
|| STB_WEAK == ELF_ST_BIND(symbol->elf_sym->st_info)) {
if(0x0 == symbol->addr) {
symbol->addr = lookupSymbol_(symbol->name);
if(0x0 == symbol->addr) {
if(0 == strncmp(symbol->name,"_GLOBAL_OFFSET_TABLE_",21)) {
symbol->addr = oc->info->got_start;
} else {
errorBelch("Failed to lookup symbol: %s\n",
symbol->name);
return EXIT_FAILURE;
}
}
} else {
// we already have the address.
}
} /* else it was defined somewhere in the same object, and
* we should have the address already.
*/
if(0x0 == symbol->addr) {
errorBelch(
"Something went wrong! Symbol %s has null address.\n",
symbol->name);
return EXIT_FAILURE;
}
if(0x0 == symbol->got_addr) {
errorBelch("Not good either!");
return EXIT_FAILURE;
}
*(void**)symbol->got_addr = symbol->addr;
}
}
}
// We are done initializing the GOT; freeze it.
if(mprotect(oc->info->got_start, oc->info->got_size, PROT_READ) != 0) {
sysErrorBelch("unable to protect memory");
}
return EXIT_SUCCESS;
}
bool
verifyGot(ObjectCode * oc) {
for(ElfSymbolTable *symTab = oc->info->symbolTables;
symTab != NULL; symTab = symTab->next) {
for(size_t i=0; i < symTab->n_symbols; i++) {
ElfSymbol * symbol = &symTab->symbols[i];
if(symbol->got_addr) {
ASSERT((void*)(*(void**)symbol->got_addr)
== (void*)symbol->addr);
}
ASSERT(0 == ((uintptr_t)symbol->addr & 0xffff000000000000));
}
}
return EXIT_SUCCESS;
}
void
freeGot(ObjectCode * oc) {
// munmap(oc->info->got_start, oc->info->got_size);
oc->info->got_start = 0x0;
oc->info->got_size = 0;
}
#endif
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