[BOLT] Ignore AArch64 markers outside their sections. (#74106)
AArch64 uses $d and $x symbols to delimit data embedded in code. However, sometimes we see $d symbols, typically in .eh_frame, with addresses that belong to different sections. These occasionally fall inside .text functions and cause BOLT to stop disassembling, which in turn causes DWARF CFA processing to fail. As a workaround, we just ignore symbols with addresses outside the section they belong to. This behaviour is consistent with objdump and similar tools.
This commit is contained in:
Jacob Bramley
GitHub
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commit
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@ -789,9 +789,44 @@ void RewriteInstance::discoverFileObjects() {
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BinarySection Section(*BC, *cantFail(Sym.getSection()));
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return Section.isAllocatable();
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};
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auto checkSymbolInSection = [this](const SymbolInfo &S) {
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// Sometimes, we encounter symbols with addresses outside their section. If
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// such symbols happen to fall into another section, they can interfere with
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// disassembly. Notably, this occurs with AArch64 marker symbols ($d and $t)
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// that belong to .eh_frame, but end up pointing into .text.
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// As a workaround, we ignore all symbols that lie outside their sections.
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auto Section = cantFail(S.Symbol.getSection());
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// Accept all absolute symbols.
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if (Section == InputFile->section_end())
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return true;
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uint64_t SecStart = Section->getAddress();
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uint64_t SecEnd = SecStart + Section->getSize();
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uint64_t SymEnd = S.Address + ELFSymbolRef(S.Symbol).getSize();
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if (S.Address >= SecStart && SymEnd <= SecEnd)
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return true;
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auto SymType = cantFail(S.Symbol.getType());
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// Skip warnings for common benign cases.
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if (opts::Verbosity < 1 && SymType == SymbolRef::ST_Other)
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return false; // E.g. ELF::STT_TLS.
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auto SymName = S.Symbol.getName();
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auto SecName = cantFail(S.Symbol.getSection())->getName();
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BC->errs() << "BOLT-WARNING: ignoring symbol "
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<< (SymName ? *SymName : "[unnamed]") << " at 0x"
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<< Twine::utohexstr(S.Address) << ", which lies outside "
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<< (SecName ? *SecName : "[unnamed]") << "\n";
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return false;
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};
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for (const SymbolRef &Symbol : InputFile->symbols())
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if (isSymbolInMemory(Symbol))
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SortedSymbols.push_back({cantFail(Symbol.getAddress()), Symbol});
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if (isSymbolInMemory(Symbol)) {
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SymbolInfo SymInfo{cantFail(Symbol.getAddress()), Symbol};
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if (checkSymbolInSection(SymInfo))
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SortedSymbols.push_back(SymInfo);
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}
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auto CompareSymbols = [this](const SymbolInfo &A, const SymbolInfo &B) {
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if (A.Address != B.Address)
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56
bolt/test/AArch64/Inputs/spurious-marker-symbol.yaml
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56
bolt/test/AArch64/Inputs/spurious-marker-symbol.yaml
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@ -0,0 +1,56 @@
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--- !ELF
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FileHeader:
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Class: ELFCLASS64
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Data: ELFDATA2LSB
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Type: ET_EXEC
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Machine: EM_AARCH64
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Entry: 0x2a0000
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ProgramHeaders:
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- Type: PT_PHDR
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Flags: [ PF_R ]
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VAddr: 0x40
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Align: 0x8
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FileSize: 0xa8
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MemSize: 0xa8
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Offset: 0x40
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- Type: PT_LOAD
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Flags: [ PF_R ]
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VAddr: 0x0
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Align: 0x10000
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FileSize: 0xf8
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MemSize: 0xf8
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Offset: 0x0
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- Type: PT_LOAD
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Flags: [ PF_X, PF_R ]
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VAddr: 0x2a0000
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Align: 0x10000
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FirstSec: .text
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LastSec: .ignored
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Sections:
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- Name: .text
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Type: SHT_PROGBITS
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Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
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Address: 0x2a0000
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AddressAlign: 0x4
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Content: 400580d2c0035fd6
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- Name: .ignored
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Type: SHT_PROGBITS
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Flags: [ SHF_ALLOC ]
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Address: 0x2a0008
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AddressAlign: 0x8
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Size: 0x8
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- Name: .eh_frame
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Type: SHT_PROGBITS
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Flags: [ SHF_ALLOC ]
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Address: 0x2a0010
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AddressAlign: 0x8
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Content: 1000000000000000017a520004781e010b0c1f00140000001800000000002a0008000000000e01410e010000
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Symbols:
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- Name: func
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Section: .text
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Value: 0x2a0000
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Size: 0x8
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- Name: '$d.42'
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Section: .ignored
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Value: 0x2a0004
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...
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61
bolt/test/AArch64/spurious-marker-symbol.test
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61
bolt/test/AArch64/spurious-marker-symbol.test
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@ -0,0 +1,61 @@
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// Check that marker symbols ($d, $x) denoting data embedded in code are ignored
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// if they fall outside their respective sections.
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// RUN: yaml2obj %S/Inputs/spurious-marker-symbol.yaml -o %t.exe
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// RUN: llvm-bolt %t.exe -o %t.bolt 2>&1 | FileCheck %s
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// CHECK: 1 out of 1 functions were overwritten
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// RUN: llvm-objdump -j .text -d %t.bolt | FileCheck %s -check-prefix=CHECK-DISASM
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// CHECK-DISASM: func
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// CHECK-DISASM: 2a0000: d2800540 mov
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// CHECK-DISASM: 2a0004: d65f03c0 ret
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// The YAML encodes the following assembly and debug information:
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.text
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.globl func
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.type func, %function
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func:
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mov x0, #42
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// $d.42: (symbol in .ignored, with an address in .text)
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ret
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// .eh_frame contains minimal DWARF with a CFA operation on the `ret`. BOLT
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// should ignore the spurious `$d.42`. If it doesn't, then it will stop
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// disassembling after the `mov` and will fail to process the second
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// DW_CFA_def_cfa_offset.
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//
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// CIE
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// length: 00000010
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// CIE_id: 00000000
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// version: 01
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// augmentation:
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// "zR" 7a 52 00
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// - read augmentation data
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// - read FDE pointer encoding
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// code_alignment_factor: 04
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// data_alignment_factor: 78 (-8)
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// return_address_register: 1e (r30 / lr)
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//
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// augmentation data:
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// length: 01
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// FDE pointers are absptr+sdata4 0b
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//
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// initial_instructions:
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// DW_CFA_def_cfa (31, 0): 0c 1f 00
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//
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// Encoding: 10000000'00000000'01'7a5200'04'78'1e'10'0b'0c1f00
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//
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// FDE
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// length: 00000014
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// CIE_pointer: 00000018 (backwards offset from here to CIE)
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// initial_location: 002a0000 (`func` as absptr+sdata4)
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// address_range: 00000008
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// augmentation data:
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// length: 00
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// instructions:
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// DW_CFA_def_cfa_offset (1) 0e 01
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// DW_CFA_advance_loc (1) 41 (`ret` at 0x2a0004)
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// DW_CFA_def_cfa_offset (1) 0e 01 Fails unless $d.42 is ignored.
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// DW_CFA_nop 00 00
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//
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// Encoding: 14000000'18000000'00002a00'08000000'000e0141'0e010000
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@ -199,7 +199,7 @@ public:
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Expected<SymbolRef::Type> getType() const;
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/// Get section this symbol is defined in reference to. Result is
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/// end_sections() if it is undefined or is an absolute symbol.
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/// section_end() if it is undefined or is an absolute symbol.
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Expected<section_iterator> getSection() const;
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const ObjectFile *getObject() const;
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