[Lldb-commits] [lldb] [lldb] Fix DW_OP_convert type handling (PR #208435)
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Thu Jul 9 04:50:45 PDT 2026
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<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-lldb
Author: firmiana402
<details>
<summary>Changes</summary>
This PR fixes two DW_OP_convert-related issues in LLDB. #<!-- -->208203 #<!-- -->208197
First, a nonzero DW_OP_convert operand must reference a DW_TAG_base_type DIE. LLDB previously accepted any DIE that happened to carry base-type-like size and encoding attributes. This patch rejects non-base-type DIEs before using them as DW_OP_convert target types.
Second, for base types that carry both DW_AT_bit_size and DW_AT_byte_size, LLDB previously derived the conversion width from DW_AT_byte_size * 8. This is incorrect for types such as C _BitInt(31), where DW_AT_bit_size describes the actual value width. This patch prefers DW_AT_bit_size when present and falls back to DW_AT_byte_size otherwise.
## Tests
Extended DWARFExpression.DW_OP_convert coverage to verify:
- non-DW_TAG_base_type DIEs are rejected as DW_OP_convert target types;
- DW_AT_bit_size is preferred over DW_AT_byte_size for conversion width.
---
Full diff: https://github.com/llvm/llvm-project/pull/208435.diff
2 Files Affected:
- (modified) lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp (+5-2)
- (modified) lldb/unittests/Expression/DWARFExpressionTest.cpp (+43-1)
``````````diff
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp b/lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp
index 4b02124e987e8..3fe8bbb8fdf56 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp
@@ -724,11 +724,14 @@ DWARFUnit::GetDIEBitSizeAndSign(uint64_t relative_die_offset) const {
DWARFDIE die = const_cast<DWARFUnit *>(this)->GetDIE(abs_die_offset);
if (!die)
return llvm::createStringError("cannot resolve DW_OP_convert type DIE");
+ if (die.Tag() != DW_TAG_base_type)
+ return llvm::createStringError(
+ "DW_OP_convert type DIE is not a DW_TAG_base_type");
uint64_t encoding =
die.GetAttributeValueAsUnsigned(DW_AT_encoding, DW_ATE_hi_user);
- uint64_t bit_size = die.GetAttributeValueAsUnsigned(DW_AT_byte_size, 0) * 8;
+ uint64_t bit_size = die.GetAttributeValueAsUnsigned(DW_AT_bit_size, 0);
if (!bit_size)
- bit_size = die.GetAttributeValueAsUnsigned(DW_AT_bit_size, 0);
+ bit_size = die.GetAttributeValueAsUnsigned(DW_AT_byte_size, 0) * 8;
if (!bit_size)
return llvm::createStringError("unsupported type size");
bool sign;
diff --git a/lldb/unittests/Expression/DWARFExpressionTest.cpp b/lldb/unittests/Expression/DWARFExpressionTest.cpp
index 75162ca0b5f3e..c5ce2c3ec7afb 100644
--- a/lldb/unittests/Expression/DWARFExpressionTest.cpp
+++ b/lldb/unittests/Expression/DWARFExpressionTest.cpp
@@ -445,6 +445,24 @@ TEST(DWARFExpression, DW_OP_convert) {
Form: DW_FORM_data1
- Attribute: DW_AT_byte_size
Form: DW_FORM_data1
+ - Code: 0x00000003
+ Tag: DW_TAG_enumeration_type
+ Children: DW_CHILDREN_no
+ Attributes:
+ - Attribute: DW_AT_encoding
+ Form: DW_FORM_data1
+ - Attribute: DW_AT_byte_size
+ Form: DW_FORM_data1
+ - Code: 0x00000004
+ Tag: DW_TAG_base_type
+ Children: DW_CHILDREN_no
+ Attributes:
+ - Attribute: DW_AT_encoding
+ Form: DW_FORM_data1
+ - Attribute: DW_AT_byte_size
+ Form: DW_FORM_data1
+ - Attribute: DW_AT_bit_size
+ Form: DW_FORM_data1
debug_info:
- Version: 4
AddrSize: 8
@@ -493,15 +511,28 @@ TEST(DWARFExpression, DW_OP_convert) {
Values:
- Value: 0x000000000000000b # DW_ATE_numeric_string
- Value: 0x0000000000000001
+ # 0x00000020:
+ - AbbrCode: 0x00000003
+ Values:
+ - Value: 0x0000000000000007 # DW_ATE_unsigned
+ - Value: 0x0000000000000004
+ # 0x00000023:
+ - AbbrCode: 0x00000004
+ Values:
+ - Value: 0x0000000000000005 # DW_ATE_signed
+ - Value: 0x0000000000000004
+ - Value: 0x000000000000001f
- AbbrCode: 0x00000000
)";
- // Compile unit relative offsets to each DW_TAG_base_type
+ // Compile unit relative offsets to type DIEs.
uint8_t offs_uint32_t = 0x0000000e;
uint8_t offs_uint64_t = 0x00000011;
uint8_t offs_sint64_t = 0x00000014;
uint8_t offs_uchar = 0x00000017;
uint8_t offs_schar = 0x0000001a;
+ uint8_t offs_enum = 0x00000020;
+ uint8_t offs_sint31_t = 0x00000023;
DWARFExpressionTester t(yamldata, /*cu_index=*/1);
ASSERT_TRUE((bool)t.GetDwarfUnit());
@@ -555,6 +586,11 @@ TEST(DWARFExpression, DW_OP_convert) {
offs_schar, DW_OP_stack_value}),
ExpectScalar(8, 'A', is_signed));
+ // Prefer DW_AT_bit_size over DW_AT_byte_size when both are present.
+ EXPECT_THAT_EXPECTED(t.Eval({DW_OP_const4u, 0x00, 0x00, 0x00, 0x40,
+ DW_OP_convert, offs_sint31_t, DW_OP_stack_value}),
+ ExpectScalar(31, 0x40000000, is_signed));
+
//
// Errors.
//
@@ -575,6 +611,12 @@ TEST(DWARFExpression, DW_OP_convert) {
t.Eval({DW_OP_const1s, 'X', DW_OP_convert, 0x1d}).takeError(),
llvm::Failed());
+ // Not a DW_TAG_base_type.
+ EXPECT_THAT_ERROR(
+ t.Eval({DW_OP_const1s, 'X', DW_OP_convert, offs_enum}).takeError(),
+ llvm::FailedWithMessage(
+ "DW_OP_convert type DIE is not a DW_TAG_base_type"));
+
// A non-zero DIE offset with no DWARF unit.
EXPECT_THAT_ERROR(
Evaluate({DW_OP_const1s, 'X', DW_OP_convert, 0x01}, nullptr, nullptr)
``````````
</details>
https://github.com/llvm/llvm-project/pull/208435
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