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CarlosAlbertoEncisoCarlosAlbertoEnciso
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[llvm-debuginfo-analyzer] Fix crash with WebAssembly dead code (llvm#141616)
llvm#136772 Incorrect handling of 'tombstone' value for WebAssembly. llvm-debuginfo-analyzer already uses the tombstone approach to identify dead code. Currently, the tombstone value is evaluated as std::numeric_limits<uint64_t>::max(). Which is wrong as it does not take into account the 'Address Byte Size' from the Compile Unit header.
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‎llvm/include/llvm/DebugInfo/LogicalView/Core/LVObject.h

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@@ -84,6 +84,14 @@ using LVTypes = SmallVector<LVType *, 8>;
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using LVOffsets = SmallVector<LVOffset, 8>;
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// The following DWARF documents detail the 'tombstone' concept:
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// https://dwarfstd.org/issues/231013.1.html
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// https://dwarfstd.org/issues/200609.1.html
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//
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// The value of the largest representable address offset (for example,
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// 0xffffffff when the size of an address is 32 bits).
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//
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// -1 (0xffffffff) => Valid tombstone
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const LVAddress MaxAddress = std::numeric_limits<uint64_t>::max();
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enum class LVBinaryType { NONE, ELF, COFF };

‎llvm/include/llvm/DebugInfo/LogicalView/Readers/LVDWARFReader.h

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@@ -58,6 +58,9 @@ class LVDWARFReader final : public LVBinaryReader {
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bool FoundLowPC = false;
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bool FoundHighPC = false;
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// The value is updated for each Compile Unit that is processed.
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std::optional<LVAddress> TombstoneAddress;
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// Cross references (Elements).
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using LVElementSet = std::unordered_set<LVElement *>;
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struct LVElementEntry {
@@ -127,6 +130,12 @@ class LVDWARFReader final : public LVBinaryReader {
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LVAddress getCUHighAddress() const { return CUHighAddress; }
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void setCUHighAddress(LVAddress Address) { CUHighAddress = Address; }
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void setTombstoneAddress(LVAddress Address) { TombstoneAddress = Address; }
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LVAddress getTombstoneAddress() const {
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assert(TombstoneAddress && "Unset tombstone value");
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return TombstoneAddress.value();
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}
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const LVSymbols &GetSymbolsWithLocations() const {
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return SymbolsWithLocations;
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}

‎llvm/lib/DebugInfo/LogicalView/Readers/LVDWARFReader.cpp

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@@ -214,10 +214,11 @@ void LVDWARFReader::processOneAttribute(const DWARFDie &Die,
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}
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}
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if (FoundLowPC) {
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if (CurrentLowPC == MaxAddress)
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if (CurrentLowPC == getTombstoneAddress())
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CurrentElement->setIsDiscarded();
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// Consider the case of WebAssembly.
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CurrentLowPC += WasmCodeSectionOffset;
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else
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// Consider the case of WebAssembly.
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CurrentLowPC += WasmCodeSectionOffset;
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if (CurrentElement->isCompileUnit())
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setCUBaseAddress(CurrentLowPC);
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}
@@ -271,7 +272,8 @@ void LVDWARFReader::processOneAttribute(const DWARFDie &Die,
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DWARFAddressRangesVector Ranges = RangesOrError.get();
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for (DWARFAddressRange &Range : Ranges) {
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// This seems to be a tombstone for empty ranges.
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if (Range.LowPC == Range.HighPC)
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if ((Range.LowPC == Range.HighPC) ||
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(Range.LowPC = getTombstoneAddress()))
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continue;
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// Store the real upper limit for the address range.
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if (UpdateHighAddress && Range.HighPC > 0)
@@ -629,6 +631,11 @@ Error LVDWARFReader::createScopes() {
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: DwarfContext->dwo_compile_units();
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for (const std::unique_ptr<DWARFUnit> &CU : CompileUnits) {
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// Take into account the address byte size for a correct 'tombstone'
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// value identification.
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setTombstoneAddress(
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dwarf::computeTombstoneAddress(CU->getAddressByteSize()));
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// Deduction of index used for the line records.
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//
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// For the following test case: test.cpp

‎llvm/test/tools/llvm-debuginfo-analyzer/WebAssembly/wasm-32bit-tombstone.s

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@@ -0,0 +1,107 @@
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# REQUIRES: x86-registered-target
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# Test that DWARF tombstones are correctly detected/respected in wasm
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# 32 bit object files.
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# The test case was produced by the following steps:
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#
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# // test-clang.cpp
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# void foo() {
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# }
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#
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# 1) clang --target=wasm32 -S -g test-clang.cpp
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# -o Inputs/wasm-32bit-tombstone.s
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#
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# 2) Creating a single function, tombstoning it in the assembly, by
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# manually changing the DW_AT_low_pc for the DW_TAG_subprogram:
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# .Lfunc_begin0 to 0xffffffff to mark the function as dead code:
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#
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# .int8 2 # Abbrev [2] 0x26:0x1b DW_TAG_subprogram
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# .int32 .Lfunc_begin0 # DW_AT_low_pc <---------
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# .int32 .Lfunc_end0-.Lfunc_begin0 # DW_AT_high_pc
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# .int8 2 # Abbrev [2] 0x26:0x1b DW_TAG_subprogram
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# .int32 0xffffffff # DW_AT_low_pc <---------
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# .int32 .Lfunc_end0-.Lfunc_begin0 # DW_AT_high_pc
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# RUN: llvm-mc -arch=wasm32 -filetype=obj \
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# RUN: %p/wasm-32bit-tombstone.s \
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# RUN: -o %t.wasm-32bit-tombstone.wasm
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# RUN: llvm-debuginfo-analyzer --select-elements=Discarded \
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# RUN: --print=elements \
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# RUN: %t.wasm-32bit-tombstone.wasm 2>&1 | \
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# RUN: FileCheck --strict-whitespace -check-prefix=ONE %s
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# ONE: Logical View:
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# ONE-NEXT: {File} '{{.*}}wasm-32bit-tombstone.wasm'
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# ONE-EMPTY:
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# ONE-NEXT: {CompileUnit} 'test-clang.cpp'
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# ONE-NEXT: {Function} not_inlined 'foo' -> 'void'
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# RUN: llvm-dwarfdump --debug-info %t.wasm-32bit-tombstone.wasm | \
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# RUN: FileCheck %s --check-prefix=TWO
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# TWO: DW_TAG_subprogram
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# TWO-NEXT: DW_AT_low_pc (dead code)
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# TWO-NEXT: DW_AT_high_pc
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# TWO-NEXT: DW_AT_name ("foo")
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.text
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.file "test-clang.cpp"
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.functype _Z3foov () -> ()
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.section .text._Z3foov,"",@
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_Z3foov: # @_Z3foov
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.Lfunc_begin0:
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.functype _Z3foov () -> ()
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return
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end_function
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.Lfunc_end0:
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# -- End function
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.section .debug_abbrev,"",@
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.int8 1 # Abbreviation Code
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.int8 17 # DW_TAG_compile_unit
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.int8 1 # DW_CHILDREN_yes
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.int8 3 # DW_AT_name
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.int8 14 # DW_FORM_strp
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.int8 17 # DW_AT_low_pc
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.int8 1 # DW_FORM_addr
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.int8 18 # DW_AT_high_pc
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.int8 6 # DW_FORM_data4
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.int8 0 # EOM(1)
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.int8 0 # EOM(2)
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.int8 2 # Abbreviation Code
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.int8 46 # DW_TAG_subprogram
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.int8 0 # DW_CHILDREN_no
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.int8 17 # DW_AT_low_pc
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.int8 1 # DW_FORM_addr
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.int8 18 # DW_AT_high_pc
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.int8 6 # DW_FORM_data4
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.int8 3 # DW_AT_name
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.int8 14 # DW_FORM_strp
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.int8 0 # EOM(1)
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.int8 0 # EOM(2)
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.int8 0 # EOM(3)
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.section .debug_info,"",@
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.Lcu_begin0:
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.int32 .Ldebug_info_end0-.Ldebug_info_start0 # Length of Unit
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.Ldebug_info_start0:
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.int16 4 # DWARF version number
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.int32 .debug_abbrev0 # Offset Into Abbrev. Section
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.int8 4 # Address Size (in bytes)
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.int8 1 # Abbrev [1] 0xb:0x37 DW_TAG_compile_unit
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.int32 .Linfo_string1 # DW_AT_name
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.int32 .Lfunc_begin0 # DW_AT_low_pc
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.int32 .Lfunc_end0-.Lfunc_begin0 # DW_AT_high_pc
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.int8 2 # Abbrev [2] 0x26:0x1b DW_TAG_subprogram
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.int32 0xffffffff # DW_AT_low_pc
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.int32 .Lfunc_end0-.Lfunc_begin0 # DW_AT_high_pc
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.int32 .Linfo_string4 # DW_AT_name
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.int8 0 # End Of Children Mark
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.Ldebug_info_end0:
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.section .debug_str,"S",@
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.Linfo_string1:
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.asciz "test-clang.cpp" # string offset=176
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.Linfo_string4:
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.asciz "foo" # string offset=241
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.ident "clang version 19.0.0"

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