/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#define LOG_TAG "Corkscrew"
//#define LOG_NDEBUG 0
#include <corkscrew/symbol_table.h>
#include <stdbool.h>
#include <stdlib.h>
#include <elf.h>
#include <fcntl.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <cutils/log.h>
static bool is_elf(Elf32_Ehdr* e) {
return (e->e_ident[EI_MAG0] == ELFMAG0 &&
e->e_ident[EI_MAG1] == ELFMAG1 &&
e->e_ident[EI_MAG2] == ELFMAG2 &&
e->e_ident[EI_MAG3] == ELFMAG3);
}
// Compare function for qsort
static int qcompar(const void *a, const void *b) {
const symbol_t* asym = (const symbol_t*)a;
const symbol_t* bsym = (const symbol_t*)b;
if (asym->start > bsym->start) return 1;
if (asym->start < bsym->start) return -1;
return 0;
}
// Compare function for bsearch
static int bcompar(const void *key, const void *element) {
uintptr_t addr = *(const uintptr_t*)key;
const symbol_t* symbol = (const symbol_t*)element;
if (addr < symbol->start) return -1;
if (addr >= symbol->end) return 1;
return 0;
}
symbol_table_t* load_symbol_table(const char *filename) {
symbol_table_t* table = NULL;
ALOGV("Loading symbol table from '%s'.", filename);
int fd = open(filename, O_RDONLY);
if (fd < 0) {
goto out;
}
struct stat sb;
if (fstat(fd, &sb)) {
goto out_close;
}
size_t length = sb.st_size;
char* base = mmap(NULL, length, PROT_READ, MAP_PRIVATE, fd, 0);
if (base == MAP_FAILED) {
goto out_close;
}
// Parse the file header
Elf32_Ehdr *hdr = (Elf32_Ehdr*)base;
if (!is_elf(hdr)) {
goto out_close;
}
Elf32_Shdr *shdr = (Elf32_Shdr*)(base + hdr->e_shoff);
// Search for the dynamic symbols section
int sym_idx = -1;
int dynsym_idx = -1;
for (Elf32_Half i = 0; i < hdr->e_shnum; i++) {
if (shdr[i].sh_type == SHT_SYMTAB) {
sym_idx = i;
}
if (shdr[i].sh_type == SHT_DYNSYM) {
dynsym_idx = i;
}
}
if (dynsym_idx == -1 && sym_idx == -1) {
goto out_unmap;
}
table = malloc(sizeof(symbol_table_t));
if(!table) {
goto out_unmap;
}
table->num_symbols = 0;
Elf32_Sym *dynsyms = NULL;
int dynnumsyms = 0;
char *dynstr = NULL;
if (dynsym_idx != -1) {
dynsyms = (Elf32_Sym*)(base + shdr[dynsym_idx].sh_offset);
dynnumsyms = shdr[dynsym_idx].sh_size / shdr[dynsym_idx].sh_entsize;
int dynstr_idx = shdr[dynsym_idx].sh_link;
dynstr = base + shdr[dynstr_idx].sh_offset;
}
Elf32_Sym *syms = NULL;
int numsyms = 0;
char *str = NULL;
if (sym_idx != -1) {
syms = (Elf32_Sym*)(base + shdr[sym_idx].sh_offset);
numsyms = shdr[sym_idx].sh_size / shdr[sym_idx].sh_entsize;
int str_idx = shdr[sym_idx].sh_link;
str = base + shdr[str_idx].sh_offset;
}
int dynsymbol_count = 0;
if (dynsym_idx != -1) {
// Iterate through the dynamic symbol table, and count how many symbols
// are actually defined
for (int i = 0; i < dynnumsyms; i++) {
if (dynsyms[i].st_shndx != SHN_UNDEF) {
dynsymbol_count++;
}
}
}
size_t symbol_count = 0;
if (sym_idx != -1) {
// Iterate through the symbol table, and count how many symbols
// are actually defined
for (int i = 0; i < numsyms; i++) {
if (syms[i].st_shndx != SHN_UNDEF
&& str[syms[i].st_name]
&& syms[i].st_value
&& syms[i].st_size) {
symbol_count++;
}
}
}
// Now, create an entry in our symbol table structure for each symbol...
table->num_symbols += symbol_count + dynsymbol_count;
table->symbols = malloc(table->num_symbols * sizeof(symbol_t));
if (!table->symbols) {
free(table);
table = NULL;
goto out_unmap;
}
size_t symbol_index = 0;
if (dynsym_idx != -1) {
// ...and populate them
for (int i = 0; i < dynnumsyms; i++) {
if (dynsyms[i].st_shndx != SHN_UNDEF) {
table->symbols[symbol_index].name = strdup(dynstr + dynsyms[i].st_name);
table->symbols[symbol_index].start = dynsyms[i].st_value;
table->symbols[symbol_index].end = dynsyms[i].st_value + dynsyms[i].st_size;
ALOGV(" [%d] '%s' 0x%08x-0x%08x (DYNAMIC)",
symbol_index, table->symbols[symbol_index].name,
table->symbols[symbol_index].start, table->symbols[symbol_index].end);
symbol_index += 1;
}
}
}
if (sym_idx != -1) {
// ...and populate them
for (int i = 0; i < numsyms; i++) {
if (syms[i].st_shndx != SHN_UNDEF
&& str[syms[i].st_name]
&& syms[i].st_value
&& syms[i].st_size) {
table->symbols[symbol_index].name = strdup(str + syms[i].st_name);
table->symbols[symbol_index].start = syms[i].st_value;
table->symbols[symbol_index].end = syms[i].st_value + syms[i].st_size;
ALOGV(" [%d] '%s' 0x%08x-0x%08x",
symbol_index, table->symbols[symbol_index].name,
table->symbols[symbol_index].start, table->symbols[symbol_index].end);
symbol_index += 1;
}
}
}
// Sort the symbol table entries, so they can be bsearched later
qsort(table->symbols, table->num_symbols, sizeof(symbol_t), qcompar);
out_unmap:
munmap(base, length);
out_close:
close(fd);
out:
return table;
}
void free_symbol_table(symbol_table_t* table) {
if (table) {
for (size_t i = 0; i < table->num_symbols; i++) {
free(table->symbols[i].name);
}
free(table->symbols);
free(table);
}
}
const symbol_t* find_symbol(const symbol_table_t* table, uintptr_t addr) {
if (!table) return NULL;
return (const symbol_t*)bsearch(&addr, table->symbols, table->num_symbols,
sizeof(symbol_t), bcompar);
}