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Support DW_EH_PE_sabsptr and 32-bit elf binaries #436

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Merged
EricRahm merged 3 commits into from
Dec 1, 2025
Merged

Support DW_EH_PE_sabsptr and 32-bit elf binaries #436

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fa62ba9
feat(sabsptr): support for DW_EH_PE_sabsptr
EricRahm Nov 3, 2025
2c552de
Wire up 32-bit support for ReadEncodedPointer
EricRahm Nov 3, 2025
61c7cc7
lit test for 32-bit sabsptr eh_frame value
EricRahm Nov 1, 2025
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4 changes: 2 additions & 2 deletions src/bloaty.h
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Original file line number Diff line number Diff line change
Expand Up @@ -314,8 +314,8 @@ inline void ReadDWARFCompileUnits(const dwarf::File& file, const DualMap& map,
}
void ReadDWARFInlines(const dwarf::File& file, RangeSink* sink,
bool include_line);
void ReadEhFrame(std::string_view contents, RangeSink* sink);
void ReadEhFrameHdr(std::string_view contents, RangeSink* sink);
void ReadEhFrame(std::string_view contents, RangeSink* sink, bool is_64bit);
void ReadEhFrameHdr(std::string_view contents, RangeSink* sink, bool is_64bit);

// Demangle C++ symbols according to the Itanium ABI. The |source| argument
// controls what demangling mode we are using.
Expand Down
13 changes: 9 additions & 4 deletions src/dwarf_constants.h
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Original file line number Diff line number Diff line change
Expand Up @@ -674,10 +674,15 @@ enum PointerEncoding {
DW_EH_PE_udata2 = 0x02,
DW_EH_PE_udata4 = 0x03,
DW_EH_PE_udata8 = 0x04,
DW_EH_PE_sleb128 = 0x09,
DW_EH_PE_sdata2 = 0x0A,
DW_EH_PE_sdata4 = 0x0B,
DW_EH_PE_sdata8 = 0x0C,

// This acts as a flag.
DW_EH_PE_signed = 0x08,

DW_EH_PE_sabsptr = DW_EH_PE_absptr | DW_EH_PE_signed,
DW_EH_PE_sleb128 = DW_EH_PE_uleb128 | DW_EH_PE_signed,
DW_EH_PE_sdata2 = DW_EH_PE_udata2 | DW_EH_PE_signed,
DW_EH_PE_sdata4 = DW_EH_PE_udata4 | DW_EH_PE_signed,
DW_EH_PE_sdata8 = DW_EH_PE_udata8 | DW_EH_PE_signed,
DW_EH_PE_FORMAT_MASK = 0x0f,

DW_EH_PE_pcrel = 0x10,
Expand Down
29 changes: 17 additions & 12 deletions src/eh_frame.cc
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Expand Up @@ -41,6 +41,13 @@ uint64_t ReadEncodedPointer(uint8_t encoding, bool is_64bit, string_view* data,
value = ReadFixed<uint32_t>(data);
}
break;
case DW_EH_PE_sabsptr:
if (is_64bit) {
value = ReadFixed<int64_t>(data);
} else {
value = ReadFixed<int32_t>(data);
}
break;
case DW_EH_PE_uleb128:
value = dwarf::ReadLEB128<uint64_t>(data);
break;
Expand Down Expand Up @@ -124,7 +131,7 @@ uint64_t ReadEncodedPointer(uint8_t encoding, bool is_64bit, string_view* data,
// https://github.com/llvm-mirror/libunwind/blob/master/src/DwarfParser.hpp
// * libgcc
// https://github.com/gcc-mirror/gcc/blob/master/libgcc/unwind-dw2-fde.c
void ReadEhFrame(string_view data, RangeSink* sink) {
void ReadEhFrame(string_view data, RangeSink* sink, bool is_64bit) {
string_view remaining = data;

struct CIEInfo {
Expand Down Expand Up @@ -187,7 +194,7 @@ void ReadEhFrame(string_view data, RangeSink* sink) {
case 'P': {
uint8_t encoding = ReadFixed<uint8_t>(&entry);
cie_info.personality_function =
ReadEncodedPointer(encoding, true, &entry, nullptr, sink);
ReadEncodedPointer(encoding, is_64bit, &entry, nullptr, sink);
break;
}
default:
Expand All @@ -201,14 +208,13 @@ void ReadEhFrame(string_view data, RangeSink* sink) {
THROW("Couldn't find CIE for FDE");
}
const CIEInfo& cie_info = iter->second;
// TODO(haberman): don't hard-code 64-bit.
uint64_t address = ReadEncodedPointer(cie_info.fde_encoding, true, &entry,
uint64_t address = ReadEncodedPointer(cie_info.fde_encoding, is_64bit, &entry,
nullptr, sink);
// TODO(haberman); Technically the FDE addresses could span a
// function/compilation unit? They can certainly span inlines.
/*
uint64_t length =
ReadEncodedPointer(cie_info.fde_encoding & 0xf, true, &entry, sink);
ReadEncodedPointer(cie_info.fde_encoding & 0xf, is_64bit, &entry, sink);
(void)length;

if (cie_info.has_augmentation_length) {
Expand All @@ -217,7 +223,7 @@ void ReadEhFrame(string_view data, RangeSink* sink) {
}

uint64_t lsda =
ReadEncodedPointer(cie_info.lsda_encoding, true, &entry, sink);
ReadEncodedPointer(cie_info.lsda_encoding, is_64bit, &entry, sink);
if (lsda) {
}
*/
Expand All @@ -229,7 +235,7 @@ void ReadEhFrame(string_view data, RangeSink* sink) {

// See documentation here:
// http://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/ehframechpt.html#EHFRAME
void ReadEhFrameHdr(string_view data, RangeSink* sink) {
void ReadEhFrameHdr(string_view data, RangeSink* sink, bool is_64bit) {
const char* base = data.data();
uint8_t version = ReadFixed<uint8_t>(&data);
uint8_t eh_frame_ptr_enc = ReadFixed<uint8_t>(&data);
Expand All @@ -240,12 +246,11 @@ void ReadEhFrameHdr(string_view data, RangeSink* sink) {
THROWF("Unknown eh_frame_hdr version: $0", version);
}

// TODO(haberman): don't hard-code 64-bit.
uint64_t eh_frame_ptr =
ReadEncodedPointer(eh_frame_ptr_enc, true, &data, base, sink);
ReadEncodedPointer(eh_frame_ptr_enc, is_64bit, &data, base, sink);
(void)eh_frame_ptr;
uint64_t fde_count =
ReadEncodedPointer(fde_count_enc, true, &data, base, sink);
ReadEncodedPointer(fde_count_enc, is_64bit, &data, base, sink);

if (table_enc == DW_EH_PE_omit) {
return;
Expand All @@ -254,8 +259,8 @@ void ReadEhFrameHdr(string_view data, RangeSink* sink) {
for (uint64_t i = 0; i < fde_count; i++) {
string_view entry_data = data;
uint64_t initial_location =
ReadEncodedPointer(table_enc, true, &data, base, sink);
uint64_t fde_addr = ReadEncodedPointer(table_enc, true, &data, base, sink);
ReadEncodedPointer(table_enc, is_64bit, &data, base, sink);
uint64_t fde_addr = ReadEncodedPointer(table_enc, is_64bit, &data, base, sink);
entry_data.remove_suffix(data.size());
sink->AddFileRangeForVMAddr("dwarf_fde_table", initial_location,
entry_data);
Expand Down
4 changes: 2 additions & 2 deletions src/elf.cc
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Expand Up @@ -1022,9 +1022,9 @@ static void ReadELFTables(const InputFile& file, RangeSink* sink) {
// fde entries from there). But these section names should be
// standard enough that this approach works also.
if (section.GetName() == ".eh_frame") {
ReadEhFrame(section.contents(), sink);
ReadEhFrame(section.contents(), sink, elf.is_64bit());
} else if (section.GetName() == ".eh_frame_hdr") {
ReadEhFrameHdr(section.contents(), sink);
ReadEhFrameHdr(section.contents(), sink, elf.is_64bit());
}
}
});
Expand Down
53 changes: 53 additions & 0 deletions tests/elf/sections/eh-frame-signed.test
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Original file line number Diff line number Diff line change
@@ -0,0 +1,53 @@
# RUN: %yaml2obj %s -o %t.o
# RUN: %bloaty -d symbols %t.o | %FileCheck %s

--- !ELF
FileHeader:
Class: ELFCLASS32
Data: ELFDATA2LSB
Type: ET_REL
Machine: EM_386
Sections:
- Name: .text
Type: SHT_PROGBITS
Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
Address: 0x1000
Size: 0x100
- Name: .eh_frame
Type: SHT_PROGBITS
Flags: [ SHF_ALLOC ]
AddressAlign: 4
# CIE Details:
# 10000000 # Length (16 bytes)
# 00000000 # CIE ID (0)
# 01 # Version (1)
# 7A5200 # Augmentation String: "zR"
# 01 # Code Alignment Factor (1)
# 7C # Data Alignment Factor (-4)
# 08 # Return Address Register (8)
# 01 # Augmentation Data Length (1)
# 08 # Augmentation Data (FDE Encoding: DW_EH_PE_signed = 0x08)
# 000000 # Padding (DW_CFA_nop)
# FDE Details:
# 0C000000 # Length (12 bytes)
# 18000000 # CIE Pointer (offset 24 backwards from here -> points to CIE at 0)
# 00100000 # PC Begin (0x1000, encoded as DW_EH_PE_signed 32-bit)
# 00010000 # PC Range (0x100, assuming same encoding)
Content: 1000000000000000017A5200017C0801080000000C000000180000000010000000010000

Symbols:
- Name: foo
Type: STT_FUNC
Section: .text
Value: 0x1000
Size: 0x100

# CHECK: FILE SIZE VM SIZE
# CHECK-NEXT: -------------- --------------
# CHECK-NEXT: 41.7% 277 87.7% 256 foo
# CHECK-NEXT: 36.1% 240 0.0% 0 [ELF Section Headers]
# CHECK-NEXT: 7.8% 52 0.0% 0 [ELF Header]
# CHECK-NEXT: 6.5% 43 0.0% 0 [section .shstrtab]
# CHECK-NEXT: 5.4% 36 12.3% 36 [section .eh_frame]
# CHECK-NEXT: 2.4% 16 0.0% 0 [section .symtab]
# CHECK-NEXT: 100.0% 664 100.0% 292 TOTAL