[DWARFVerifier] Verify that DW_AT_LLVM_stmt_sequence is set correctly #152807

DataCorrupted · 2025-08-08T22:23:03Z

Sometimes DW_AT_LLVM_stmt_sequence won't point to the correct offset. This feature helps us debug when/where it went wrong.

Added a new test and manually tempered with the value to show the intended verification result.

Signed-off-by: Peter Rong <PeterRong@meta.com>

llvmbot · 2025-08-13T22:20:38Z

@llvm/pr-subscribers-debuginfo

Author: Peter Rong (DataCorrupted)

Changes

Patch is 60.80 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/152807.diff

2 Files Affected:

(modified) llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp (+46)
(added) llvm/test/tools/llvm-dwarfdump/verify_stmt_seq.yaml (+1617)

diff --git a/llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp b/llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp
index 8ec3f1729b974..7d6a643560643 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp
@@ -851,6 +851,52 @@ unsigned DWARFVerifier::verifyDebugInfoAttribute(const DWARFDie &Die,
     }
     break;
   }
+  case DW_AT_LLVM_stmt_sequence: {
+    // Make sure the offset in the DW_AT_LLVM_stmt_sequence attribute is valid
+    // and points to a valid sequence start in the line table.
+    auto SectionOffset = AttrValue.Value.getAsSectionOffset();
+    if (!SectionOffset) {
+      ReportError("Invalid DW_AT_LLVM_stmt_sequence encoding",
+                  "DIE has invalid DW_AT_LLVM_stmt_sequence encoding:");
+      break;
+    }
+    if (*SectionOffset >= U->getLineSection().Data.size()) {
+      ReportError(
+          "DW_AT_LLVM_stmt_sequence offset out of bounds",
+          "DW_AT_LLVM_stmt_sequence offset is beyond .debug_line bounds: " +
+              llvm::formatv("{0:x8}", *SectionOffset));
+      break;
+    }
+
+    // Check if the offset points to a valid sequence start
+    const auto *LineTable = DCtx.getLineTableForUnit(U);
+    if (!LineTable) {
+      ReportError("DW_AT_LLVM_stmt_sequence without line table",
+                  "DIE has DW_AT_LLVM_stmt_sequence but compile unit has no "
+                  "line table");
+      break;
+    }
+    bool ValidSequenceOffset = false;
+    // Check if the offset matches any of the sequence start offsets using
+    // binary search
+    auto it = std::lower_bound(LineTable->Sequences.begin(),
+                               LineTable->Sequences.end(), *SectionOffset,
+                               [](const auto &Sequence, const uint64_t Offset) {
+                                 return Sequence.StmtSeqOffset < Offset;
+                               });
+    if (it != LineTable->Sequences.end() &&
+        it->StmtSeqOffset == *SectionOffset) {
+      ValidSequenceOffset = true;
+    }
+
+    if (!ValidSequenceOffset)
+      ReportError(
+          "Invalid DW_AT_LLVM_stmt_sequence offset",
+          "DW_AT_LLVM_stmt_sequence offset " +
+              llvm::formatv("{0:x8}", *SectionOffset) +
+              " does not point to a valid sequence start in the line table");
+    break;
+  }
   default:
     break;
   }
diff --git a/llvm/test/tools/llvm-dwarfdump/verify_stmt_seq.yaml b/llvm/test/tools/llvm-dwarfdump/verify_stmt_seq.yaml
new file mode 100644
index 0000000000000..1873eea9d49f3
--- /dev/null
+++ b/llvm/test/tools/llvm-dwarfdump/verify_stmt_seq.yaml
@@ -0,0 +1,1617 @@
+# Object file copied from llvm/test/tools/dsymutil/ARM/stmt-seq-macho.test
+# Then I manually tempered with some of the value of the attribute
+# I hope there are easier ways to construct tests like this.
+
+# RUN: yaml2obj %s -o verify_stmt_seq.o
+# RUN: not llvm-dwarfdump -verify -debug-info verify_stmt_seq.o | FileCheck %s --check-prefix=CHECK_INVALID
+
+# Line 1326 0XAB
+# CHECK_INVALID: error: DW_AT_LLVM_stmt_sequence offset 0x000000ab does not point to a valid sequence start in the line table
+# Line 1372 0xEEEEE7
+# CHECK_INVALID: error: DW_AT_LLVM_stmt_sequence offset is beyond .debug_line bounds: 0x00eeeee7
+
+# CHECK_INVALID: error: Aggregated error counts:
+# CHECK_INVALID: error: DW_AT_LLVM_stmt_sequence offset out of bounds occurred 1 time(s).
+# CHECK_INVALID: error: Invalid DW_AT_LLVM_stmt_sequence offset occurred 1 time(s).
+
+# CHECK_INVALID-NOT: error:
+--- !mach-o
+IsLittleEndian: true
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[truncated]

clayborg · 2025-08-13T23:31:15Z

llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp

+    auto SectionOffset = AttrValue.Value.getAsSectionOffset();
+    if (!SectionOffset) {
+      ReportError("Invalid DW_AT_LLVM_stmt_sequence encoding",
+                  "DIE has invalid DW_AT_LLVM_stmt_sequence encoding:");


remove the colon from the end of the string since there is no value to show?

clayborg · 2025-08-13T23:35:56Z

llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp

+    if (*SectionOffset >= U->getLineSection().Data.size()) {
+      ReportError(
+          "DW_AT_LLVM_stmt_sequence offset out of bounds",
+          "DW_AT_LLVM_stmt_sequence offset is beyond .debug_line bounds: " +


This should probably check if the DW_AT_LLVM_stmt_sequence is inside the current line table only? The .debug_line section conttains multiple line tables, each one has a prologue and then N sequences. We want to make sure the *SectionOffset is after the prologue and before the end of all sequences. Each line table prologue contains:

dwarfdump --debug-line a.out.dSYM -v a.out.dSYM/Contents/Resources/DWARF/a.out: file format Mach-O arm64 .debug_line contents: debug_line[0x00000000] Line table prologue: total_length: 0x00000055 format: DWARF32 version: 5 address_size: 8 seg_select_size: 0 prologue_length: 0x00000037

The total_length tells us where the this line table's data ends. And the prologue_length tells us where the prologue ends. So we want to make sure that the *SectionOffset is between the end of the prologue and the and of the current line table, not the entire .debug_line section

I added a test for out of range (of the intended line table) test

clayborg · 2025-08-13T23:37:00Z

llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp

+          "Invalid DW_AT_LLVM_stmt_sequence offset",
+          "DW_AT_LLVM_stmt_sequence offset " +
+              llvm::formatv("{0:x8}", *SectionOffset) +
+              " does not point to a valid sequence start in the line table");


Maybe change "valid sequence start" to "valid sequence offset"?

clayborg · 2025-08-13T23:39:06Z

llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp

+    // Make sure the offset in the DW_AT_LLVM_stmt_sequence attribute is valid
+    // and points to a valid sequence start in the line table.
+    auto SectionOffset = AttrValue.Value.getAsSectionOffset();
+    if (!SectionOffset) {


We should add a test for this case

I added a test for " invalid DW_AT_LLVM_stmt_sequence encoding"

ellishg · 2025-08-18T16:46:23Z

llvm/test/tools/llvm-dwarfdump/verify_stmt_seq.yaml

+# Then manually tempered with some of the value of the attribute
+# I hope there are easier ways to construct tests like this.
+
+# RUN: yaml2obj %p/Inputs/verify_stmt_seq.yaml -o verify_stmt_seq.o


Since the yaml input is only used in one test, we should use split-file to inline it here

That input is thousands lines long, I'd prefer to keep them separate, or loading it could take unnecessarily long (especially on web pages)

The yaml file is shorter than llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp above

ellishg · 2025-08-18T16:47:37Z

llvm/test/tools/llvm-dwarfdump/verify_stmt_seq.yaml

+# CHECK_INVALID-NEXT: error: Invalid DW_AT_LLVM_stmt_sequence encoding occurred 1 time(s).
+# CHECK_INVALID-NEXT: error: Invalid DW_AT_LLVM_stmt_sequence offset occurred 1 time(s).
+
+# CHECK_INVALID-NOT: error:


You can add --implicit-check-not=error: to make sure no other error lines exist

ellishg · 2025-08-18T16:49:30Z

llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp

+    if (it != LineTable->Sequences.end() &&
+        it->StmtSeqOffset == *SectionOffset) {
+      ValidSequenceOffset = true;
+    }


Suggested change

if (it != LineTable->Sequences.end() &&

it->StmtSeqOffset == *SectionOffset) {

ValidSequenceOffset = true;

}

ValidSequenceOffset = it != LineTable->Sequences.end() && it->StmtSeqOffset == *SectionOffset;

alx32 · 2025-08-20T04:09:36Z

llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp

+    uint64_t LineTableStart = *StmtListOffset;
+    uint64_t PrologueLength = LineTable->Prologue.PrologueLength;
+    uint64_t TotalLength = LineTable->Prologue.TotalLength;
+    uint64_t LineTableEnd =


Can we extract (LineTable->Prologue.getFormParams().Format == dwarf::DWARF64 ? 12 : 4) to a constant ?

alx32 · 2025-08-20T04:15:44Z

llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp

+    ValidSequenceOffset =
+        it != LineTable->Sequences.end() && it->StmtSeqOffset == *SectionOffset;
+
+    if (!ValidSequenceOffset)


Could this give invalid errors? I think that for sequence extraction we have our own logic to detect the sequences because the built-in parser's sequence detection is incomplete. See:

llvm-project/llvm/lib/DWARFLinker/Classic/DWARFLinker.cpp

Line 2412 in 9ae0bd2

// The DWARF parser's discovery of sequences can be incomplete. To

So we can have valid offsets pointing to sequences that are not detected by the DWARF parser, even if they are actually valid sequences.

built-in parser's sequence detection is incomplete

I feel like that's something we should spend more time on fixing.

But I've updated the logic to take that into consideration as well

Instead of patching the same logic in verifier and linker, I've managed to find the real reason some sequence is not detected:

A sequence is only valid when LowPC < HighPC, which normally is true since no sequence has only one instruction. This is not true for thunks created by ICF, which only contains one branch instruction.

llvm-project/llvm/include/llvm/DebugInfo/DWARF/DWARFDebugLine.h

Line 224 in b3baa4d

return !Empty && (LowPC < HighPC) && (FirstRowIndex < LastRowIndex);

This logic is essentially wrong, since the HighPC was added to the sequence by:

llvm-project/llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp

Lines 582 to 590 in b3baa4d

if (Row.EndSequence) {

// Record the end of instruction sequence.

Sequence.HighPC = Row.Address.Address;

Sequence.LastRowIndex = RowNumber + 1;

Sequence.SectionIndex = Row.Address.SectionIndex;

if (Sequence.isValid())

LineTable->appendSequence(Sequence);

Sequence.reset();

}

But not be considered to be as part of this sequence:

llvm-project/llvm/include/llvm/DebugInfo/DWARF/DWARFDebugLine.h

Lines 227 to 230 in b3baa4d

bool containsPC(object::SectionedAddress PC) const {

return SectionIndex == PC.SectionIndex &&

(LowPC <= PC.Address && PC.Address < HighPC);

}

My proposed fix is to strip the extra sequence matching logic here (it is hard to find a Row's offset to start with) and in the linker, and update how the Sequence is defined. Essentially, it should be [LowPC, HighPC] (right inclusive) rather than right exclusive. Let me start a discussion with another PR, if we can change HighPC, both problems will be solved.

Unfortunately, #154851 enabling single-instruction sequence seems to cause more problem than it solved. I've invested a day on this and I'll add special logic here, but in the future it should go away.

See discussion on #154986 / #110192 , if the sequence can't be parsed, the line table is ill formed, and we should not bend verifier for it.

I plan to fix that in #154986, if not other approach.

DataCorrupted · 2025-08-29T17:33:06Z

llvm/test/tools/llvm-dwarfdump/verify_stmt_seq.yaml

+# 0xd3 would be a valid offset, if the line table wan't ill formed with two rows having the same PC (0x8c).
+# CHECK_INVALID: error: DW_AT_LLVM_stmt_sequence offset 0x000000d3 does not point to a valid sequence offset in the line table
+# CHECK_INVALID: DW_AT_LLVM_stmt_sequence [DW_FORM_sec_offset]     (0x000000d3)
+
+# CHECK_DEBUG_LINE:      0x000000d3: 05 DW_LNS_set_column (85)
+# CHECK_DEBUG_LINE-NEXT: 0x000000d5: 0a DW_LNS_set_prologue_end
+# CHECK_DEBUG_LINE-NEXT: 0x000000d6: 00 DW_LNE_set_address (0x000000000000008c)
+# CHECK_DEBUG_LINE-NEXT: 0x000000e1: 03 DW_LNS_advance_line (30)
+# CHECK_DEBUG_LINE-NEXT: 0x000000e3: 01 DW_LNS_copy
+# CHECK_DEBUG_LINE-NEXT:             0x000000000000008c     30     85      1   0             0       0  is_stmt prologue_end
+# CHECK_DEBUG_LINE-NEXT: 0x000000e4: 00 DW_LNE_end_sequence
+# CHECK_DEBUG_LINE-NEXT:             0x000000000000008c     30     85      1   0             0       0  is_stmt end_sequence


@dwblaikie If we agreed that this line table is wrong and needs to be fixed (#154986), on the verifier side I'll just say these type of offsets are invalid.

Incorrect issue/PR reference? The linked one seems unrelated.

#154986 and #110192, updated.

llvm/test/tools/llvm-dwarfdump/verify_stmt_seq.yaml

drodriguez · 2025-08-29T18:07:57Z

llvm/test/tools/llvm-dwarfdump/verify_stmt_seq.yaml

+# 0xd3 would be a valid offset, if the line table wan't ill formed with two rows having the same PC (0x8c).
+# CHECK_INVALID: error: DW_AT_LLVM_stmt_sequence offset 0x000000d3 does not point to a valid sequence offset in the line table
+# CHECK_INVALID: DW_AT_LLVM_stmt_sequence [DW_FORM_sec_offset]     (0x000000d3)
+
+# CHECK_DEBUG_LINE:      0x000000d3: 05 DW_LNS_set_column (85)
+# CHECK_DEBUG_LINE-NEXT: 0x000000d5: 0a DW_LNS_set_prologue_end
+# CHECK_DEBUG_LINE-NEXT: 0x000000d6: 00 DW_LNE_set_address (0x000000000000008c)
+# CHECK_DEBUG_LINE-NEXT: 0x000000e1: 03 DW_LNS_advance_line (30)
+# CHECK_DEBUG_LINE-NEXT: 0x000000e3: 01 DW_LNS_copy
+# CHECK_DEBUG_LINE-NEXT:             0x000000000000008c     30     85      1   0             0       0  is_stmt prologue_end
+# CHECK_DEBUG_LINE-NEXT: 0x000000e4: 00 DW_LNE_end_sequence
+# CHECK_DEBUG_LINE-NEXT:             0x000000000000008c     30     85      1   0             0       0  is_stmt end_sequence


Incorrect issue/PR reference? The linked one seems unrelated.

llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp

2. Bug fix on where line table starts

DataCorrupted added 2 commits August 8, 2025 15:22

[DWARFVerifier] Verify that DW_AT_LLVM_stmt_sequence is set correctly

cedce21

Signed-off-by: Peter Rong <PeterRong@meta.com>

add t est

e1a4ed7

Signed-off-by: Peter Rong <PeterRong@meta.com>

DataCorrupted requested review from mbucko, alx32 and clayborg August 11, 2025 22:16

[DWARF] Fix incorrect offset

c8f2305

Signed-off-by: Peter Rong <PeterRong@meta.com>

DataCorrupted marked this pull request as ready for review August 13, 2025 22:20

llvmbot added the debuginfo label Aug 13, 2025

clayborg requested changes Aug 13, 2025

View reviewed changes

clayborg reviewed Aug 13, 2025

View reviewed changes

DataCorrupted added 2 commits August 14, 2025 11:14

Address Review

5715526

Split input and test

01a59eb

DataCorrupted requested a review from JDevlieghere as a code owner August 14, 2025 18:19

Revert unrelated change

8fc1a3b

DataCorrupted requested review from ellishg and kyulee-com August 18, 2025 16:38

ellishg reviewed Aug 18, 2025

View reviewed changes

address comments

41a9fbf

alx32 reviewed Aug 20, 2025

View reviewed changes

DataCorrupted added 2 commits August 20, 2025 17:22

Address comments

dc053bc

Not testing

c7461d3

This was referenced Aug 21, 2025

[NFC][DebugInfo] Allow single instruction sequence in line table to make symbolication of merged functions easier #154851

Draft

[ICF] Add a NOP after branch in ICF thunk to improve debugability #154986

Draft

DataCorrupted added 2 commits August 28, 2025 16:13

We should not bend if the line table is wrong

25bbe1a

Demostrate where Debug line is wrong

c463b7e

DataCorrupted force-pushed the DWARFVerifier branch from ce9c629 to c463b7e Compare August 28, 2025 23:14

DataCorrupted requested a review from dwblaikie August 29, 2025 17:31

DataCorrupted commented Aug 29, 2025

View reviewed changes

drodriguez reviewed Aug 29, 2025

View reviewed changes

1. Address comment

03f6b8b

2. Bug fix on where line table starts

	if (Row.EndSequence) {
	// Record the end of instruction sequence.
	Sequence.HighPC = Row.Address.Address;
	Sequence.LastRowIndex = RowNumber + 1;
	Sequence.SectionIndex = Row.Address.SectionIndex;
	if (Sequence.isValid())
	LineTable->appendSequence(Sequence);
	Sequence.reset();
	}

	bool containsPC(object::SectionedAddress PC) const {
	return SectionIndex == PC.SectionIndex &&
	(LowPC <= PC.Address && PC.Address < HighPC);
	}

[DWARFVerifier] Verify that DW_AT_LLVM_stmt_sequence is set correctly #152807

Are you sure you want to change the base?

[DWARFVerifier] Verify that DW_AT_LLVM_stmt_sequence is set correctly #152807

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DataCorrupted commented Aug 8, 2025 •

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