[llvm][DebugInfo] Add support for DW_OP_GNU_implicit_pointer #142913
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@llvm/pr-subscribers-llvm-binary-utilities @llvm/pr-subscribers-debuginfo Author: Thrrreeee (Thrrreeee) ChangesThis patch introduces support for the DWARF operation Full diff: https://github.com/llvm/llvm-project/pull/142913.diff 4 Files Affected:
diff --git a/llvm/include/llvm/BinaryFormat/Dwarf.def b/llvm/include/llvm/BinaryFormat/Dwarf.def
index e52324a8ebc12..b1b406cbebf97 100644
--- a/llvm/include/llvm/BinaryFormat/Dwarf.def
+++ b/llvm/include/llvm/BinaryFormat/Dwarf.def
@@ -887,6 +887,8 @@ HANDLE_DW_OP(0xed, WASM_location, -1, -1, 0, WASM)
HANDLE_DW_OP(0xee, WASM_location_int, -1, -1, 0, WASM)
// Historic and not implemented in LLVM.
HANDLE_DW_OP(0xf0, APPLE_uninit, -1, -1, 0, APPLE)
+// The GNU implicit pointer extension.
+HANDLE_DW_OP(0xf2, GNU_implicit_pointer, 2, 0, 5, GNU)
// The GNU entry value extension.
HANDLE_DW_OP(0xf3, GNU_entry_value, 2, 0, 0, GNU)
HANDLE_DW_OP(0xf8, PGI_omp_thread_num, -1, -1, 0, PGI)
diff --git a/llvm/lib/DebugInfo/DWARF/DWARFExpression.cpp b/llvm/lib/DebugInfo/DWARF/DWARFExpression.cpp
index 2ae5ff3efc8c5..17e816a1e4552 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFExpression.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFExpression.cpp
@@ -104,6 +104,8 @@ static std::vector<Desc> getOpDescriptions() {
Descriptions[DW_OP_GNU_addr_index] = Desc(Op::Dwarf4, Op::SizeLEB);
Descriptions[DW_OP_GNU_const_index] = Desc(Op::Dwarf4, Op::SizeLEB);
Descriptions[DW_OP_GNU_entry_value] = Desc(Op::Dwarf4, Op::SizeLEB);
+ Descriptions[DW_OP_GNU_implicit_pointer] =
+ Desc(Op::Dwarf4, Op::SizeRefAddr, Op::SignedSizeLEB);
// This Description acts as a marker that getSubOpDesc must be called
// to fetch the final Description for the operation. Each such final
// Description must share the same first SizeSubOpLEB operand.
diff --git a/llvm/lib/DebugInfo/LogicalView/Core/LVLocation.cpp b/llvm/lib/DebugInfo/LogicalView/Core/LVLocation.cpp
index 3c078d8ee74b8..7c1a025e9a4b9 100644
--- a/llvm/lib/DebugInfo/LogicalView/Core/LVLocation.cpp
+++ b/llvm/lib/DebugInfo/LogicalView/Core/LVLocation.cpp
@@ -284,6 +284,7 @@ std::string LVOperation::getOperandsDWARFInfo() {
case dwarf::DW_OP_implicit_value:
Stream << "TODO: DW_OP_implicit_value";
break;
+ case dwarf::DW_OP_GNU_implicit_pointer:
case dwarf::DW_OP_implicit_pointer:
Stream << "implicit_pointer DIE offset " << hexString(Operands[0]) << " "
<< int(Operands[1]);
diff --git a/llvm/test/tools/llvm-dwarfdump/X86/DW_OP_GNU_implicit_pointer.yaml b/llvm/test/tools/llvm-dwarfdump/X86/DW_OP_GNU_implicit_pointer.yaml
new file mode 100644
index 0000000000000..56dcbc036cbbb
--- /dev/null
+++ b/llvm/test/tools/llvm-dwarfdump/X86/DW_OP_GNU_implicit_pointer.yaml
@@ -0,0 +1,87 @@
+# Test that we can decode `DW_OP_GNU_implicit_pointer` (0xf2)
+# RUN: yaml2obj %s | llvm-dwarfdump - | FileCheck %s
+
+# CHECK: DW_TAG_variable
+# CHECK-NEXT: DW_AT_location (DW_OP_GNU_implicit_pointer 0x2a +4)
+
+--- !ELF
+FileHeader:
+ Class: ELFCLASS64
+ Data: ELFDATA2LSB
+ Type: ET_DYN
+ Machine: EM_X86_64
+DWARF:
+ debug_abbrev:
+ - Table:
+ - Code: 0x00000001
+ Tag: DW_TAG_compile_unit
+ Children: DW_CHILDREN_yes
+ Attributes:
+ - Attribute: DW_AT_language
+ Form: DW_FORM_data2
+ - Attribute: DW_AT_low_pc
+ Form: DW_FORM_addr
+ - Attribute: DW_AT_high_pc
+ Form: DW_FORM_data4
+ - Code: 0x00000002
+ Tag: DW_TAG_subprogram
+ Children: DW_CHILDREN_yes
+ Attributes:
+ - Attribute: DW_AT_low_pc
+ Form: DW_FORM_addr
+ - Attribute: DW_AT_high_pc
+ Form: DW_FORM_data4
+ - Attribute: DW_AT_frame_base
+ Form: DW_FORM_exprloc
+ - Code: 0x00000003
+ Tag: DW_TAG_formal_parameter
+ Children: DW_CHILDREN_no
+ Attributes:
+ - Attribute: DW_AT_location
+ Form: DW_FORM_exprloc
+ - Code: 0x00000004
+ Tag: DW_TAG_variable
+ Children: DW_CHILDREN_no
+ Attributes:
+ - Attribute: DW_AT_location
+ Form: DW_FORM_exprloc
+ debug_info:
+ - Length: 52
+ Version: 5
+ UnitType: DW_UT_compile
+ AbbrOffset: 0
+ AddrSize: 8
+ Entries:
+ - AbbrCode: 0x00000001
+ Values:
+ - Value: 0x000000000000000C
+ - Value: 0x0000000100000F50
+ - Value: 0x0000000000000034
+ - AbbrCode: 0x00000002
+ Values:
+ - Value: 0x0000000100000F50
+ - Value: 0x0000000000000034
+ - Value: 0x0000000000000001
+ BlockData:
+ - 0x56
+ - AbbrCode: 0x00000003
+ Values:
+ - Value: 0x0000000000000002
+ BlockData:
+ - 0x91
+ - 0x78
+ - AbbrCode: 0x00000004
+ Values:
+ - Value: 0x0000000000000006
+ BlockData:
+ - 0xf2 # DW_OP_GNU_implicit_pointer
+ - 0x2a # Section offset of parameter in the previous entry
+ - 0x00
+ - 0x00
+ - 0x00
+ - 0x04 # Pointer references location 4 bytes into value of previous entry
+ - AbbrCode: 0x00000000
+ Values:
+ - AbbrCode: 0x00000000
+ Values:
+...
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✅ With the latest revision this PR passed the C/C++ code formatter. |
Michael137
changed the title
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Hi @Michael137, |
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Please fix up the formatting identified by https://github.com/llvm/llvm-project/actions/runs/15470488440/job/43561147116?pr=142913 (& we'll see if the presubmit checks find anything else) |
Thanks for pointing that out! I've checked the formatting locally with clang-format, and it completed without reporting any issues on my end. Reviewing the CI log (thanks for the link!), it does look like clang-format itself might have encountered an issue and terminated abnormally. Would it be possible to re-trigger the presubmit checks to see if it passes on a subsequent run? Of course, if any genuine formatting errors are identified, I'll address them promptly. |
This patch introduces support for the DWARF operation
DW_OP_GNU_implicit_pointer(value 0xf3) within LLVM's DWARF parsing and expression evaluation infrastructure. This GNU extension is used to describe the location of a variable that is itself a pointer, where the value of this pointer is stored at an address derived from another DWARF location expression plus a constant offset.Motivation:
Compilers like GCC use
DW_OP_GNU_implicit_pointerto represent the location of certain variables.Without support for this opcode, debuggers like LLDB (and other tools relying on LLVM's DWARF libraries) cannot correctly resolve the location of such variables, leading to an inability to inspect their values or an incorrect debugging experience.