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support for separate debug info: build-ids #9

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73 changes: 61 additions & 12 deletions elf_parser.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,8 @@
// SOFTWARE.

#include "elf_parser.hpp"
#include <sys/stat.h>
#include <cstring>
using namespace elf_parser;

std::vector<section_t> Elf_parser::get_sections() {
Expand Down Expand Up @@ -80,23 +82,53 @@ std::vector<symbol_t> Elf_parser::get_symbols() {
// get headers for offsets
Elf64_Ehdr *ehdr = (Elf64_Ehdr*)m_mmap_program;
Elf64_Shdr *shdr = (Elf64_Shdr*)(m_mmap_program + ehdr->e_shoff);

// get build-id
char *build_id_buf = nullptr;
std::string buildId;
// get strtab
char *sh_strtab_p = nullptr;
for(auto &sec: secs) {
if((sec.section_type == "SHT_STRTAB") && (sec.section_name == ".strtab")){
sh_strtab_p = (char*)m_mmap_program + sec.section_offset;
break;
}
}

// get dynstr
char *sh_dynstr_p = nullptr;
for(auto &sec: secs) {
if((sec.section_type == "SHT_STRTAB") && (sec.section_name == ".dynstr")){
sh_dynstr_p = (char*)m_mmap_program + sec.section_offset;
break;
for (auto &sec : secs) {
if ((sec.section_type == "SHT_NOTE") &&
(sec.section_name == ".note.gnu.build-id")) {
build_id_buf =
reinterpret_cast<char *>(m_mmap_program) + sec.section_offset;

Elf64_Nhdr *nhdr64 = reinterpret_cast<Elf64_Nhdr *>(build_id_buf);

uint64_t n_namesz = nhdr64->n_namesz;
uint64_t n_descsz = nhdr64->n_descsz;
uint64_t n_type = nhdr64->n_type;
char *n_data = build_id_buf + sizeof(Elf64_Nhdr);

if (std::strcmp(n_data, ELF_NOTE_GNU) == 0 &&
n_type == NT_GNU_BUILD_ID) {
const char *hex_digits = "0123456789abcdef";
unsigned char *build_id;

build_id = (unsigned char *)n_data + n_namesz;
for (int i = 0; i < n_descsz; i++) {
buildId.push_back(hex_digits[(build_id[i] >> 4) & 0xf]);
buildId.push_back(hex_digits[(build_id[i] >> 0) & 0xf]);
}
}
}

if ((sec.section_type == "SHT_STRTAB") &&
(sec.section_name == ".strtab")) {
sh_strtab_p =
reinterpret_cast<char *>(m_mmap_program) + sec.section_offset;
}

if ((sec.section_type == "SHT_STRTAB") &&
(sec.section_name == ".dynstr")) {
sh_dynstr_p =
reinterpret_cast<char *>(m_mmap_program) + sec.section_offset;
}
if (build_id_buf && sh_strtab_p && sh_dynstr_p) {
break;
}
}

std::vector<symbol_t> symbols;
Expand Down Expand Up @@ -127,6 +159,23 @@ std::vector<symbol_t> Elf_parser::get_symbols() {
symbols.push_back(symbol);
}
}

if (buildId.length() > 0) {
/* Look for separate debug info: build-ids */
std::string debug_file =
std::string("/usr/lib/debug/.build-id/" + buildId.substr(0, 2) + "/" +
buildId.substr(2, std::string::npos) + ".debug");

if (m_program_path != debug_file) {
struct stat buffer;
if (stat(debug_file.c_str(), &buffer) == 0) {
Elf_parser dp(debug_file.c_str());
auto debug_syms = dp.get_symbols();
symbols.insert(symbols.end(), debug_syms.begin(), debug_syms.end());
}
}
}

return symbols;
}

Expand Down
8 changes: 7 additions & 1 deletion elf_parser.hpp
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -63,10 +63,16 @@ typedef struct {
std::intptr_t relocation_plt_address;
} relocation_t;

// Note header for ELF64.
struct Elf64_Nhdr {
Elf64_Word n_namesz;
Elf64_Word n_descsz;
Elf64_Word n_type;
};

class Elf_parser {
public:
Elf_parser (std::string &program_path): m_program_path{program_path} {
Elf_parser (const std::string &program_path): m_program_path{program_path} {
load_memory_map();
}
std::vector<section_t> get_sections();
Expand Down