From 372bfc86105728732fc115af46223d7a4e49f8d9 Mon Sep 17 00:00:00 2001 From: Benjamin Barenblat Date: Thu, 29 Jun 2023 13:05:51 -0700 Subject: Fix symbolization on PowerPC ELF v1 The big-endian PowerPC ELF ABI (ppc64 in Debian) relies on function descriptors mapped in a non-executable segment. Make sure that segment is scanned during symbolization. Also correct bounds computation for that segment. PiperOrigin-RevId: 544440302 Change-Id: Ic05532aa35ae9efa127028318640ee7cdeeecc5f --- absl/debugging/symbolize_elf.inc | 52 +++++++++++++++++++++++++--------------- 1 file changed, 33 insertions(+), 19 deletions(-) diff --git a/absl/debugging/symbolize_elf.inc b/absl/debugging/symbolize_elf.inc index 0fee89f2..30638cb2 100644 --- a/absl/debugging/symbolize_elf.inc +++ b/absl/debugging/symbolize_elf.inc @@ -658,8 +658,10 @@ static bool ShouldPickFirstSymbol(const ElfW(Sym) & symbol1, } // Return true if an address is inside a section. -static bool InSection(const void *address, const ElfW(Shdr) * section) { - const char *start = reinterpret_cast(section->sh_addr); +static bool InSection(const void *address, ptrdiff_t relocation, + const ElfW(Shdr) * section) { + const char *start = reinterpret_cast( + section->sh_addr + static_cast(relocation)); size_t size = static_cast(section->sh_size); return start <= address && address < (start + size); } @@ -699,8 +701,8 @@ static ABSL_ATTRIBUTE_NOINLINE FindSymbolResult FindSymbol( // starting address. However, we do not always want to use the real // starting address because we sometimes want to symbolize a function // pointer into the .opd section, e.g. FindSymbol(&foo,...). - const bool pc_in_opd = - kPlatformUsesOPDSections && opd != nullptr && InSection(pc, opd); + const bool pc_in_opd = kPlatformUsesOPDSections && opd != nullptr && + InSection(pc, relocation, opd); const bool deref_function_descriptor_pointer = kPlatformUsesOPDSections && opd != nullptr && !pc_in_opd; @@ -740,7 +742,7 @@ static ABSL_ATTRIBUTE_NOINLINE FindSymbolResult FindSymbol( #endif if (deref_function_descriptor_pointer && - InSection(original_start_address, opd)) { + InSection(original_start_address, /*relocation=*/0, opd)) { // The opd section is mapped into memory. Just dereference // start_address to get the first double word, which points to the // function entry. @@ -1336,7 +1338,7 @@ static bool MaybeInitializeObjFile(ObjFile *obj) { const int phnum = obj->elf_header.e_phnum; const int phentsize = obj->elf_header.e_phentsize; auto phoff = static_cast(obj->elf_header.e_phoff); - size_t num_executable_load_segments = 0; + size_t num_interesting_load_segments = 0; for (int j = 0; j < phnum; j++) { ElfW(Phdr) phdr; if (!ReadFromOffsetExact(obj->fd, &phdr, sizeof(phdr), phoff)) { @@ -1345,23 +1347,35 @@ static bool MaybeInitializeObjFile(ObjFile *obj) { return false; } phoff += phentsize; - constexpr int rx = PF_X | PF_R; - if (phdr.p_type != PT_LOAD || (phdr.p_flags & rx) != rx) { - // Not a LOAD segment, or not executable code. + +#if defined(__powerpc__) && !(_CALL_ELF > 1) + // On the PowerPC ELF v1 ABI, function pointers actually point to function + // descriptors. These descriptors are stored in an .opd section, which is + // mapped read-only. We thus need to look at all readable segments, not + // just the executable ones. + constexpr int interesting = PF_R; +#else + constexpr int interesting = PF_X | PF_R; +#endif + + if (phdr.p_type != PT_LOAD + || (phdr.p_flags & interesting) != interesting) { + // Not a LOAD segment, not executable code, and not a function + // descriptor. continue; } - if (num_executable_load_segments < obj->phdr.size()) { - memcpy(&obj->phdr[num_executable_load_segments++], &phdr, sizeof(phdr)); + if (num_interesting_load_segments < obj->phdr.size()) { + memcpy(&obj->phdr[num_interesting_load_segments++], &phdr, sizeof(phdr)); } else { ABSL_RAW_LOG( - WARNING, "%s: too many executable LOAD segments: %zu >= %zu", - obj->filename, num_executable_load_segments, obj->phdr.size()); + WARNING, "%s: too many interesting LOAD segments: %zu >= %zu", + obj->filename, num_interesting_load_segments, obj->phdr.size()); break; } } - if (num_executable_load_segments == 0) { - // This object has no "r-x" LOAD segments. That's unexpected. - ABSL_RAW_LOG(WARNING, "%s: no executable LOAD segments", obj->filename); + if (num_interesting_load_segments == 0) { + // This object has no interesting LOAD segments. That's unexpected. + ABSL_RAW_LOG(WARNING, "%s: no interesting LOAD segments", obj->filename); return false; } } @@ -1389,8 +1403,8 @@ const char *Symbolizer::GetUncachedSymbol(const void *pc) { // X in the file will have a start address of [true relocation]+X. relocation = static_cast(start_addr - obj->offset); - // Note: some binaries have multiple "rx" LOAD segments. We must - // find the right one. + // Note: some binaries have multiple LOAD segments that can contain + // function pointers. We must find the right one. ElfW(Phdr) *phdr = nullptr; for (size_t j = 0; j < obj->phdr.size(); j++) { ElfW(Phdr) &p = obj->phdr[j]; @@ -1400,7 +1414,7 @@ const char *Symbolizer::GetUncachedSymbol(const void *pc) { ABSL_RAW_CHECK(p.p_type == PT_NULL, "unexpected p_type"); break; } - if (pc < reinterpret_cast(start_addr + p.p_memsz)) { + if (pc < reinterpret_cast(start_addr + p.p_vaddr + p.p_memsz)) { phdr = &p; break; } -- cgit v1.2.3