static int
has_dt_debug(Elf *elf, GElf_Ehdr *ehdr)
{
int i;
for (i = 0; i < ehdr->e_phnum; i++) {
GElf_Phdr phdr;
GElf_Shdr shdr;
Elf_Scn *scn;
Elf_Data *data;
unsigned int j;
if (gelf_getphdr(elf, i, &phdr) == NULL)
continue;
if (phdr.p_type != PT_DYNAMIC)
continue;
scn = gelf_offscn(elf, phdr.p_offset);
if (gelf_getshdr(scn, &shdr) == NULL)
continue;
if (shdr.sh_type != SHT_DYNAMIC)
continue;
if ((data = elf_getdata(scn, NULL)) == NULL)
continue;
for (j = 0;
j < shdr.sh_size / gelf_fsize(elf, ELF_T_DYN, 1, EV_CURRENT);
j++) {
GElf_Dyn dyn;
if (gelf_getdyn(data, j, &dyn)) {
if (dyn.d_tag == DT_DEBUG)
return 1;
}
}
}
return 0;
}
// Extract the strings associated with the provided `DynamicTag`
// from the DYNAMIC section of the ELF binary.
Try<std::vector<std::string>> GetDynamicStrings(DynamicTag tag) const
{
if (sections.count(SectionType::DYNAMIC) == 0) {
return Error("No DYNAMIC sections found in ELF");
}
if (sections.count(SectionType::DYNAMIC) != 1) {
return Error("Multiple DYNAMIC sections found in ELF");
}
Elf_Scn* dynamic_section = sections.at(SectionType::DYNAMIC)[0];
// Walk through the entries in the dynamic section and look for
// entries with the provided tag. These entries contain offsets to
// strings in the dynamic section's string table. Consequently, we
// also have to look for an entry containing a pointer to the
// dynamic section's string table so we can resolve the strings
// associated with the provided tag later on.
Elf_Data* dynamic_data = elf_getdata(dynamic_section, NULL);
if (dynamic_data == NULL) {
return Error("elf_getdata() failed: " + stringify(elf_errmsg(-1)));
}
Option<uintptr_t> strtab_pointer = None();
std::vector<uintptr_t> strtab_offsets;
for (size_t i = 0; i < dynamic_data->d_size / sizeof(GElf_Dyn); i++) {
GElf_Dyn entry;
if (gelf_getdyn(dynamic_data, i, &entry) == NULL) {
return Error("gelf_getdyn() failed: " + stringify(elf_errmsg(-1)));
}
if ((DynamicTag)entry.d_tag == DynamicTag::STRTAB) {
strtab_pointer = entry.d_un.d_ptr;
}
if ((DynamicTag)entry.d_tag == tag) {
strtab_offsets.push_back(entry.d_un.d_ptr);
}
}
if (strtab_offsets.empty()) {
return std::vector<std::string>();
}
if (strtab_pointer.isNone()) {
return Error("Failed to find string table");
}
// Get a reference to the actual string table so we can index into it.
Elf_Scn* string_table_section = gelf_offscn(elf, strtab_pointer.get());
if (string_table_section == NULL) {
return Error("gelf_offscn() failed: " + stringify(elf_errmsg(-1)));
}
size_t strtab_index = elf_ndxscn(string_table_section);
if (strtab_index == SHN_UNDEF) {
return Error("elf_ndxscn() failed: " + stringify(elf_errmsg(-1)));
}
// Find the strings in the string table from their offsets and return them.
std::vector<std::string> strings;
foreach (uintptr_t offset, strtab_offsets) {
char* string = elf_strptr(elf, strtab_index, offset);
if (string == NULL) {
return Error("elf_strptr() failed: " + stringify(elf_errmsg(-1)));
}
strings.push_back(string);
}
int hook_pltgot(char *exename, unsigned long offset)
{
int fd;
int ret = -1;
Elf *elf;
GElf_Ehdr ehdr;
Elf_Scn *sec;
GElf_Shdr shdr;
Elf_Data *data;
size_t shstr_idx;
size_t i;
bool found = false;
pr_dbg2("opening executable image: %s\n", exename);
fd = open(exename, O_RDONLY);
if (fd < 0)
return -1;
elf_version(EV_CURRENT);
elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
if (gelf_getehdr(elf, &ehdr) == NULL)
goto elf_error;
if (elf_getshdrstrndx(elf, &shstr_idx) < 0)
goto elf_error;
for (i = 0; i < ehdr.e_phnum; i++) {
GElf_Phdr phdr;
if (gelf_getphdr(elf, i, &phdr) == NULL)
goto elf_error;
if (phdr.p_type == PT_LOAD && !found) {
offset -= phdr.p_vaddr;
found = true;
}
if (phdr.p_type != PT_DYNAMIC)
continue;
sec = gelf_offscn(elf, phdr.p_offset);
if (!sec || gelf_getshdr(sec, &shdr) == NULL)
continue;
data = elf_getdata(sec, NULL);
if (data == NULL)
goto elf_error;
if (find_got(data, shdr.sh_size / shdr.sh_entsize, offset) < 0)
goto elf_error;
}
ret = 0;
out:
elf_end(elf);
close(fd);
return ret;
elf_error:
pr_dbg("%s\n", elf_errmsg(elf_errno()));
goto out;
}
