#include <algorithm>
#include <memory>
+#include <utility>
+#include <fcntl.h>
#include <cstdlib>
#define DW_LANG_Objc DW_LANG_ObjC /* fix spelling error in older dwarf.h */
#include <dwarf.h>
}
}
+/** Get the build-id (NT_GNU_BUILD_ID) from the ELF file
+ *
+ * This build-id may is used to locate an external debug (DWARF) file
+ * for this ELF file.
+ *
+ * @param elf libelf handle for an ELF file
+ * @return build-id for this ELF file (or an empty vector if none is found)
+ */
+static
+std::vector<char> get_build_id(Elf* elf)
+{
+ size_t phnum;
+ if (elf_getphdrnum (elf, &phnum) != 0)
+ xbt_die("Could not read program headers");
+
+ // Iterate over the program headers and find the PT_NOTE ones:
+ for (size_t i = 0; i < phnum; ++i) {
+ GElf_Phdr phdr_temp;
+ GElf_Phdr *phdr = gelf_getphdr(elf, i, &phdr_temp);
+ if (phdr->p_type != PT_NOTE)
+ continue;
+
+ Elf_Data* data = elf_getdata_rawchunk(elf, phdr->p_offset, phdr->p_filesz, ELF_T_NHDR);
+
+ // Iterate over the notes and find the NT_GNU_BUILD_ID one:
+ size_t pos = 0;
+ while (1) {
+ GElf_Nhdr nhdr;
+ size_t name_pos;
+ size_t desc_pos;
+ pos = gelf_getnote(data, pos, &nhdr, &name_pos, &desc_pos);
+ // A note is identified by a name "GNU" and a integer type within
+ // the namespace defined by this name (here NT_GNU_BUILD_ID):
+ if (nhdr.n_type == NT_GNU_BUILD_ID
+ && nhdr.n_namesz == sizeof("GNU")
+ && memcmp((char*) data->d_buf + name_pos, "GNU", sizeof("GNU")) == 0) {
+
+ // Found the NT_GNU_BUILD_ID note:
+ char* start = (char*) data->d_buf + desc_pos;
+ char* end = (char*) start + nhdr.n_descsz;
+ return std::vector<char>(start, end);
+
+ }
+ }
+
+ }
+ return std::vector<char>();
+}
+
+static char hexdigits[16] = {
+ '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
+ 'a', 'b', 'c', 'd', 'e', 'f'
+};
+
+/** Binary data to hexadecimal */
+static inline
+std::array<char, 2> to_hex(std::uint8_t byte)
+{
+ // Horrid double braces!
+ // Apparently, this is needed in C++11 (not in C++14).
+ return { { hexdigits[byte >> 4], hexdigits[byte & 0xF] } };
+}
+
+/** Binary data to hexadecimal */
+static
+std::string to_hex(const char* data, std::size_t count)
+{
+ std::string res;
+ res.resize(2*count);
+ for (std::size_t i = 0; i < count; i++) {
+ std::array<char, 2> hex_byte = to_hex(data[i]);
+ for (int j = 0; j < 2; ++j)
+ res[2 * i + j] = hex_byte[j];
+ }
+ return std::move(res);
+}
+
+/** Binary data to hexadecimal */
+static
+std::string to_hex(std::vector<char> const& data)
+{
+ return to_hex(data.data(), data.size());
+}
+
+/** Base directories for external debug files */
+const char* debug_paths[] = {
+ "/usr/lib/debug/",
+ "/usr/local/lib/debug/",
+};
+
+/** Locate an external debug file from the NT_GNU_BUILD_ID
+ *
+ * This is one of the mechanisms used for
+ * [separate debug files](https://sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-Files.html).
+ */
+static
+std::string find_by_build_id(std::vector<char> id)
+{
+ std::string filename;
+ for (const char* debug_path : debug_paths) {
+ filename = debug_path;
+ filename += ".build-id/" + to_hex(id.data(), 1) + '/'
+ + to_hex(id.data() + 1, id.size() - 1) + ".debug";
+ XBT_DEBUG("Checking debug file: %s", filename.c_str());
+ if (access(filename.c_str(), F_OK) == 0)
+ return std::move(filename);
+ }
+ return std::string();
+}
+
/** \brief Populate the debugging informations of the given ELF object
*
* Read the DWARf information of the EFFL object and populate the
if (elf_version(EV_CURRENT) == EV_NONE)
xbt_die("libelf initialization error");
+ // Open the ELF file:
int fd = open(info->file_name.c_str(), O_RDONLY);
if (fd < 0)
xbt_die("Could not open file %s", info->file_name.c_str());
if (kind != ELF_K_ELF)
xbt_die("Not an ELF file 2");
+ // Remember if this is a `ET_EXEC` (fixed location) or `ET_DYN` (relocatable):
Elf64_Half type = get_type(elf);
if (type == ET_EXEC)
info->flags |= simgrid::mc::ObjectInformation::Executable;
+ // Read DWARF debug information in the file:
Dwarf* dwarf = dwarf_begin_elf (elf, DWARF_C_READ, nullptr);
- // Dwarf *dwarf = dwarf_begin(fd, DWARF_C_READ);
if (dwarf != nullptr) {
read_dwarf_info(info, dwarf);
dwarf_end(dwarf);
- dwarf = nullptr;
+ elf_end(elf);
+ close(fd);
+ return;
}
- else
- xbt_die("Missing debugging information in %s\n"
- "Your program and its dependencies must have debugging information.\n"
- "You might want to recompile with -g or install the suitable debugging package.\n",
- info->file_name.c_str());
+ dwarf_end(dwarf);
+
+ // If there was no DWARF in the file, try to find it in a separate file
+ // with NT_GNU_BUILD_ID:
+ std::vector<char> build_id = get_build_id(elf);
+ if (!build_id.empty()) {
+ elf_end(elf);
+ close(fd);
+
+ // Find the debug file using the build id:
+ std::string debug_file = find_by_build_id(build_id);
+ if (debug_file.empty()) {
+ std::string hex = to_hex(build_id);
+ xbt_die(
+ "Missing debug info for %s with build-id %s\n"
+ "You might want to install the suitable debugging package.\n",
+ info->file_name.c_str(), hex.c_str());
+ }
+
+ // Load the DWARF info from this file:
+ XBT_DEBUG("Load DWARF for %s from %s",
+ info->file_name.c_str(), debug_file.c_str());
+ fd = open(debug_file.c_str(), O_RDONLY);
+ if (fd < 0)
+ xbt_die("Could not open file %s", debug_file.c_str());
+ Dwarf* dwarf = dwarf_begin(fd, DWARF_C_READ);
+ if (dwarf == nullptr)
+ xbt_die("No DWARF info in %s for %s",
+ debug_file.c_str(), info->file_name.c_str());
+ read_dwarf_info(info, dwarf);
+ dwarf_end(dwarf);
+ close(fd);
+ return;
+ }
+
+ // TODO, try to find DWARF info using debug-link.
+ // Is this method really used anywhere?
- elf_end(elf);
- close(fd);
+ xbt_die("Debugging information not found for %s\n"
+ "Try recompiling with -g\n",
+ info->file_name.c_str());
}
// ***** Functions index
