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#include <stdlib.h>
#include <fcntl.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include "symbol_table.h"
#include <linux/elf.h>
// Compare func for qsort
static int qcompar(const void *a, const void *b)
{
return ((struct symbol*)a)->addr - ((struct symbol*)b)->addr;
}
// Compare func for bsearch
static int bcompar(const void *addr, const void *element)
{
struct symbol *symbol = (struct symbol*)element;
if((unsigned int)addr < symbol->addr) {
return -1;
}
if((unsigned int)addr - symbol->addr >= symbol->size) {
return 1;
}
return 0;
}
/*
* Create a symbol table from a given file
*
* Parameters:
* filename - Filename to process
*
* Returns:
* A newly-allocated SymbolTable structure, or NULL if error.
* Free symbol table with symbol_table_free()
*/
struct symbol_table *symbol_table_create(const char *filename)
{
struct symbol_table *table = NULL;
// Open the file, and map it into memory
struct stat sb;
int length;
char *base;
int fd = open(filename, O_RDONLY);
if(fd < 0) {
goto out;
}
fstat(fd, &sb);
length = sb.st_size;
base = mmap(NULL, length, PROT_READ, MAP_PRIVATE, fd, 0);
if(!base) {
goto out_close;
}
// Parse the file header
Elf32_Ehdr *hdr = (Elf32_Ehdr*)base;
Elf32_Shdr *shdr = (Elf32_Shdr*)(base + hdr->e_shoff);
// Search for the dynamic symbols section
int dynsym_idx = -1;
int i;
for(i = 0; i < hdr->e_shnum; i++) {
if(shdr[i].sh_type == SHT_DYNSYM ) {
dynsym_idx = i;
}
}
if(dynsym_idx == -1) {
goto out_unmap;
}
Elf32_Sym *dynsyms = (Elf32_Sym*)(base + shdr[dynsym_idx].sh_offset);
int numsyms = shdr[dynsym_idx].sh_size / shdr[dynsym_idx].sh_entsize;
table = malloc(sizeof(struct symbol_table));
if(!table) {
goto out_unmap;
}
table->num_symbols = 0;
// Iterate through the dynamic symbol table, and count how many symbols
// are actually defined
for(i = 0; i < numsyms; i++) {
if(dynsyms[i].st_shndx != SHN_UNDEF) {
table->num_symbols++;
}
}
int dynstr_idx = shdr[dynsym_idx].sh_link;
char *dynstr = base + shdr[dynstr_idx].sh_offset;
// Now, create an entry in our symbol table structure for each symbol...
table->symbols = malloc(table->num_symbols * sizeof(struct symbol));
if(!table->symbols) {
free(table);
table = NULL;
goto out_unmap;
}
// ...and populate them
int j = 0;
for(i = 0; i < numsyms; i++) {
if(dynsyms[i].st_shndx != SHN_UNDEF) {
table->symbols[j].name = strdup(dynstr + dynsyms[i].st_name);
table->symbols[j].addr = dynsyms[i].st_value;
table->symbols[j].size = dynsyms[i].st_size;
j++;
}
}
// Sort the symbol table entries, so they can be bsearched later
qsort(table->symbols, table->num_symbols, sizeof(struct symbol), qcompar);
out_unmap:
munmap(base, length);
out_close:
close(fd);
out:
return table;
}
/*
* Free a symbol table
*
* Parameters:
* table - Table to free
*/
void symbol_table_free(struct symbol_table *table)
{
int i;
if(!table) {
return;
}
for(i=0; i<table->num_symbols; i++) {
free(table->symbols[i].name);
}
free(table->symbols);
free(table);
}
/*
* Search for an address in the symbol table
*
* Parameters:
* table - Table to search in
* addr - Address to search for.
*
* Returns:
* A pointer to the Symbol structure corresponding to the
* symbol which contains this address, or NULL if no symbol
* contains it.
*/
const struct symbol *symbol_table_lookup(struct symbol_table *table, unsigned int addr)
{
if(!table) {
return NULL;
}
return bsearch((void*)addr, table->symbols, table->num_symbols, sizeof(struct symbol), bcompar);
}
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