[DebugLine] Correct debug line emittion #157529

DataCorrupted · 2025-09-08T18:36:55Z

Context

#99710 introduced .loc_label so we can terminate a line sequence. However, it did not advance PC properly. This is problematic for 1-instruction functions as it will have zero-length sequence. The test checked in that PR shows the problem:

# CHECK-LINE-TABLE:                  Address            Line   Column File   ISA Discriminator OpIndex Flags
# CHECK-LINE-TABLE-NEXT:             ------------------ ------ ------ ------ --- ------------- ------- -------------
# CHECK-LINE-TABLE-NEXT: 0x00000028: 05 DW_LNS_set_column (1)
# CHECK-LINE-TABLE-NEXT: 0x0000002a: 00 DW_LNE_set_address (0x0000000000000000)
# CHECK-LINE-TABLE-NEXT: 0x00000035: 01 DW_LNS_copy
# CHECK-LINE-TABLE-NEXT:             0x0000000000000000      1      1      1   0             0       0  is_stmt
# CHECK-LINE-TABLE-NEXT: 0x00000036: 00 DW_LNE_end_sequence
# CHECK-LINE-TABLE-NEXT:             0x0000000000000000      1      1      1   0             0       0  is_stmt end_sequence

Both rows having PC 0x0 is incorrect, and parsers won't be able to parse them. See more explanation why this is wrong in #154851.

Design

This PR attempts to fix this by advancing the PC to the next available Label, and advance to the end of the section if no Label is available.

Implementation

emitDwarfLineEndEntry will advance PC to the CurrLabel
If CurrLabel is null, its probably a fake LineEntry we introduced in [DebugInfo][DWARF] Emit Per-Function Line Table Offsets and End Sequences #110192. In that case look for the next Label
If still not label can be found, use null and emitDwarfLineEndEntry is smart enough to advance PC to the end of the section
Rename LastLabel to PrevLabel, "last" can mean "previous" or "final", this is ambigous.
Updated the tests to emit a correct label.

Note

This fix should render #154986 and #154851 obsolete, they were temporary fixes and don't resolve the root cause.

llvmbot · 2025-09-08T18:37:33Z

@llvm/pr-subscribers-debuginfo

@llvm/pr-subscribers-llvm-mc

Author: Peter Rong (DataCorrupted)

Changes

Context

#99710 introduced .loc_label so we can terminate a line sequence. However, it did not advance PC properly. This is problematic for 1-instruction functions as it will have zero-length sequence. The test checked in that PR shows the problem:

# CHECK-LINE-TABLE:                  Address            Line   Column File   ISA Discriminator OpIndex Flags
# CHECK-LINE-TABLE-NEXT:             ------------------ ------ ------ ------ --- ------------- ------- -------------
# CHECK-LINE-TABLE-NEXT: 0x00000028: 05 DW_LNS_set_column (1)
# CHECK-LINE-TABLE-NEXT: 0x0000002a: 00 DW_LNE_set_address (0x0000000000000000)
# CHECK-LINE-TABLE-NEXT: 0x00000035: 01 DW_LNS_copy
# CHECK-LINE-TABLE-NEXT:             0x0000000000000000      1      1      1   0             0       0  is_stmt
# CHECK-LINE-TABLE-NEXT: 0x00000036: 00 DW_LNE_end_sequence
# CHECK-LINE-TABLE-NEXT:             0x0000000000000000      1      1      1   0             0       0  is_stmt end_sequence

Both rows having PC 0x0 is incorrect, and parsers won't be able to parse them. See more explanation why this is wrong in #154851.

Fix

This PR attempts to fix this by advancing the PC to the next available Label, and advance to the end of the section if no Label is available.

Impl

emitDwarfLineEndEntry will advance PC to the CurrLabel
If CurrLabel is null, its probably a fake LineEntry we introduced in #110192. In that case look for the next Label
If still not label can be found, use null and emitDwarfLineEndEntry is smart enough to advance PC to the end of the section
Rename LastLabel to PrevLabel, "last" can mean "previous" or "final", this is ambigous.
Updated the tests to emit a correct label.

Note

This fix should render #154986 and #154851 obsolete, they were temporary fixes and don't resolve the root cause.

Full diff: https://github.com/llvm/llvm-project/pull/157529.diff

3 Files Affected:

(modified) llvm/lib/MC/MCDwarf.cpp (+20-10)
(modified) llvm/test/DebugInfo/X86/DW_AT_LLVM_stmt_seq_sec_offset.ll (+30-29)
(modified) llvm/test/MC/ELF/debug-loc-label.s (+29-25)

diff --git a/llvm/lib/MC/MCDwarf.cpp b/llvm/lib/MC/MCDwarf.cpp
index e7c0d37e8f99b..e8f000a584839 100644
--- a/llvm/lib/MC/MCDwarf.cpp
+++ b/llvm/lib/MC/MCDwarf.cpp
@@ -181,7 +181,7 @@ void MCDwarfLineTable::emitOne(
 
   unsigned FileNum, LastLine, Column, Flags, Isa, Discriminator;
   bool IsAtStartSeq;
-  MCSymbol *LastLabel;
+  MCSymbol *PrevLabel;
   auto init = [&]() {
     FileNum = 1;
     LastLine = 1;
@@ -189,21 +189,31 @@ void MCDwarfLineTable::emitOne(
     Flags = DWARF2_LINE_DEFAULT_IS_STMT ? DWARF2_FLAG_IS_STMT : 0;
     Isa = 0;
     Discriminator = 0;
-    LastLabel = nullptr;
+    PrevLabel = nullptr;
     IsAtStartSeq = true;
   };
   init();
 
   // Loop through each MCDwarfLineEntry and encode the dwarf line number table.
   bool EndEntryEmitted = false;
-  for (const MCDwarfLineEntry &LineEntry : LineEntries) {
-    MCSymbol *Label = LineEntry.getLabel();
+  for (auto It = LineEntries.begin(); It != LineEntries.end(); ++It) {
+    auto LineEntry = *It;
+    MCSymbol *CurrLabel = LineEntry.getLabel();
     const MCAsmInfo *asmInfo = MCOS->getContext().getAsmInfo();
 
     if (LineEntry.LineStreamLabel) {
       if (!IsAtStartSeq) {
-        MCOS->emitDwarfLineEndEntry(Section, LastLabel,
-                                    /*EndLabel =*/LastLabel);
+        auto *Label = CurrLabel;
+        auto NextIt = It + 1;
+        // LineEntry with a null Label is probably a fake LineEntry we added
+        // when `-emit-func-debug-line-table-offsets` in order to terminate the
+        // sequence. Look for the next Label if possible, otherwise we will set
+        // the PC to the end of the section.
+        if (!Label && NextIt != LineEntries.end()) {
+          Label = NextIt->getLabel();
+        }
+        MCOS->emitDwarfLineEndEntry(Section, PrevLabel,
+                                    /*EndLabel =*/Label);
         init();
       }
       MCOS->emitLabel(LineEntry.LineStreamLabel, LineEntry.StreamLabelDefLoc);
@@ -211,7 +221,7 @@ void MCDwarfLineTable::emitOne(
     }
 
     if (LineEntry.IsEndEntry) {
-      MCOS->emitDwarfAdvanceLineAddr(INT64_MAX, LastLabel, Label,
+      MCOS->emitDwarfAdvanceLineAddr(INT64_MAX, PrevLabel, CurrLabel,
                                      asmInfo->getCodePointerSize());
       init();
       EndEntryEmitted = true;
@@ -258,12 +268,12 @@ void MCDwarfLineTable::emitOne(
     // At this point we want to emit/create the sequence to encode the delta in
     // line numbers and the increment of the address from the previous Label
     // and the current Label.
-    MCOS->emitDwarfAdvanceLineAddr(LineDelta, LastLabel, Label,
+    MCOS->emitDwarfAdvanceLineAddr(LineDelta, PrevLabel, CurrLabel,
                                    asmInfo->getCodePointerSize());
 
     Discriminator = 0;
     LastLine = LineEntry.getLine();
-    LastLabel = Label;
+    PrevLabel = CurrLabel;
     IsAtStartSeq = false;
   }
 
@@ -273,7 +283,7 @@ void MCDwarfLineTable::emitOne(
   // does not track ranges nor terminate the line table. In that case,
   // conservatively use the section end symbol to end the line table.
   if (!EndEntryEmitted && !IsAtStartSeq)
-    MCOS->emitDwarfLineEndEntry(Section, LastLabel);
+    MCOS->emitDwarfLineEndEntry(Section, PrevLabel);
 }
 
 void MCDwarfLineTable::endCurrentSeqAndEmitLineStreamLabel(MCStreamer *MCOS,
diff --git a/llvm/test/DebugInfo/X86/DW_AT_LLVM_stmt_seq_sec_offset.ll b/llvm/test/DebugInfo/X86/DW_AT_LLVM_stmt_seq_sec_offset.ll
index 58f6495924b90..10059b7b30c20 100644
--- a/llvm/test/DebugInfo/X86/DW_AT_LLVM_stmt_seq_sec_offset.ll
+++ b/llvm/test/DebugInfo/X86/DW_AT_LLVM_stmt_seq_sec_offset.ll
@@ -14,38 +14,39 @@
 ; STMT_SEQ:       DW_AT_LLVM_stmt_sequence [DW_FORM_sec_offset]	(0x00000043)
 ; STMT_SEQ:   DW_AT_name {{.*}}func01
 ; STMT_SEQ:   DW_TAG_subprogram [[[ABBREV_CODE2]]]
-; STMT_SEQ:       DW_AT_LLVM_stmt_sequence [DW_FORM_sec_offset]	(0x00000056)
+; STMT_SEQ:       DW_AT_LLVM_stmt_sequence [DW_FORM_sec_offset]	(0x00000058)
 ; STMT_SEQ:   DW_AT_name {{.*}}main
 
 ;; Check the entire line sequence to see that it's correct
-; STMT_SEQ:                   Address            Line   Column File   ISA Discriminator OpIndex Flags
-; STMT_SEQ-NEXT:              ------------------ ------ ------ ------ --- ------------- ------- -------------
-; STMT_SEQ-NEXT:  0x00000043: 04 DW_LNS_set_file (0)
-; STMT_SEQ-NEXT:  0x00000045: 05 DW_LNS_set_column (9)
-; STMT_SEQ-NEXT:  0x00000047: 0a DW_LNS_set_prologue_end
-; STMT_SEQ-NEXT:  0x00000048: 00 DW_LNE_set_address (0x00000000)
-; STMT_SEQ-NEXT:  0x0000004f: 16 address += 0,  line += 4,  op-index += 0
-; STMT_SEQ-NEXT:              0x0000000000000000      5      9      0   0             0       0  is_stmt prologue_end
-; STMT_SEQ-NEXT:  0x00000050: 05 DW_LNS_set_column (3)
-; STMT_SEQ-NEXT:  0x00000052: 67 address += 6,  line += 1,  op-index += 0
-; STMT_SEQ-NEXT:              0x0000000000000006      6      3      0   0             0       0  is_stmt
-; STMT_SEQ-NEXT:  0x00000053: 00 DW_LNE_end_sequence
-; STMT_SEQ-NEXT:              0x0000000000000006      6      3      0   0             0       0  is_stmt end_sequence
-; STMT_SEQ-NEXT:  0x00000056: 04 DW_LNS_set_file (0)
-; STMT_SEQ-NEXT:  0x00000058: 00 DW_LNE_set_address (0x00000008)
-; STMT_SEQ-NEXT:  0x0000005f: 03 DW_LNS_advance_line (10)
-; STMT_SEQ-NEXT:  0x00000061: 01 DW_LNS_copy
-; STMT_SEQ-NEXT:              0x0000000000000008     10      0      0   0             0       0  is_stmt
-; STMT_SEQ-NEXT:  0x00000062: 05 DW_LNS_set_column (10)
-; STMT_SEQ-NEXT:  0x00000064: 0a DW_LNS_set_prologue_end
-; STMT_SEQ-NEXT:  0x00000065: 83 address += 8,  line += 1,  op-index += 0
-; STMT_SEQ-NEXT:              0x0000000000000010     11     10      0   0             0       0  is_stmt prologue_end
-; STMT_SEQ-NEXT:  0x00000066: 05 DW_LNS_set_column (3)
-; STMT_SEQ-NEXT:  0x00000068: 9f address += 10,  line += 1,  op-index += 0
-; STMT_SEQ-NEXT:              0x000000000000001a     12      3      0   0             0       0  is_stmt
-; STMT_SEQ-NEXT:  0x00000069: 02 DW_LNS_advance_pc (addr += 5, op-index += 0)
-; STMT_SEQ-NEXT:  0x0000006b: 00 DW_LNE_end_sequence
-; STMT_SEQ-NEXT:              0x000000000000001f     12      3      0   0             0       0  is_stmt end_sequence
+; STMT_SEQ:                  Address            Line   Column File   ISA Discriminator OpIndex Flags
+; STMT_SEQ-NEXT:             ------------------ ------ ------ ------ --- ------------- ------- -------------
+; STMT_SEQ-NEXT: 0x00000043: 04 DW_LNS_set_file (0)
+; STMT_SEQ-NEXT: 0x00000045: 05 DW_LNS_set_column (9)
+; STMT_SEQ-NEXT: 0x00000047: 0a DW_LNS_set_prologue_end
+; STMT_SEQ-NEXT: 0x00000048: 00 DW_LNE_set_address (0x00000000)
+; STMT_SEQ-NEXT: 0x0000004f: 16 address += 0,  line += 4,  op-index += 0
+; STMT_SEQ-NEXT:             0x0000000000000000      5      9      0   0             0       0  is_stmt prologue_end
+; STMT_SEQ-NEXT: 0x00000050: 05 DW_LNS_set_column (3)
+; STMT_SEQ-NEXT: 0x00000052: 67 address += 6,  line += 1,  op-index += 0
+; STMT_SEQ-NEXT:             0x0000000000000006      6      3      0   0             0       0  is_stmt
+; STMT_SEQ-NEXT: 0x00000053: 02 DW_LNS_advance_pc (addr += 2, op-index += 0)
+; STMT_SEQ-NEXT: 0x00000055: 00 DW_LNE_end_sequence
+; STMT_SEQ-NEXT:             0x0000000000000008      6      3      0   0             0       0  is_stmt end_sequence
+; STMT_SEQ-NEXT: 0x00000058: 04 DW_LNS_set_file (0)
+; STMT_SEQ-NEXT: 0x0000005a: 00 DW_LNE_set_address (0x00000008)
+; STMT_SEQ-NEXT: 0x00000061: 03 DW_LNS_advance_line (10)
+; STMT_SEQ-NEXT: 0x00000063: 01 DW_LNS_copy
+; STMT_SEQ-NEXT:             0x0000000000000008     10      0      0   0             0       0  is_stmt
+; STMT_SEQ-NEXT: 0x00000064: 05 DW_LNS_set_column (10)
+; STMT_SEQ-NEXT: 0x00000066: 0a DW_LNS_set_prologue_end
+; STMT_SEQ-NEXT: 0x00000067: 83 address += 8,  line += 1,  op-index += 0
+; STMT_SEQ-NEXT:             0x0000000000000010     11     10      0   0             0       0  is_stmt prologue_end
+; STMT_SEQ-NEXT: 0x00000068: 05 DW_LNS_set_column (3)
+; STMT_SEQ-NEXT: 0x0000006a: 9f address += 10,  line += 1,  op-index += 0
+; STMT_SEQ-NEXT:             0x000000000000001a     12      3      0   0             0       0  is_stmt
+; STMT_SEQ-NEXT: 0x0000006b: 02 DW_LNS_advance_pc (addr += 5, op-index += 0)
+; STMT_SEQ-NEXT: 0x0000006d: 00 DW_LNE_end_sequence
+; STMT_SEQ-NEXT:             0x000000000000001f     12      3      0   0             0       0  is_stmt end_sequence
 
 ; generated from:
 ; clang -Oz -g -S -emit-llvm test.c -o test.ll
diff --git a/llvm/test/MC/ELF/debug-loc-label.s b/llvm/test/MC/ELF/debug-loc-label.s
index 6b5d04777bef4..4200b1192107b 100644
--- a/llvm/test/MC/ELF/debug-loc-label.s
+++ b/llvm/test/MC/ELF/debug-loc-label.s
@@ -17,43 +17,47 @@
 # CHECK-LINE-TABLE-NEXT: 0x0000002a: 00 DW_LNE_set_address (0x0000000000000000)
 # CHECK-LINE-TABLE-NEXT: 0x00000035: 01 DW_LNS_copy
 # CHECK-LINE-TABLE-NEXT:             0x0000000000000000      1      1      1   0             0       0  is_stmt
-# CHECK-LINE-TABLE-NEXT: 0x00000036: 00 DW_LNE_end_sequence
-# CHECK-LINE-TABLE-NEXT:             0x0000000000000000      1      1      1   0             0       0  is_stmt end_sequence
-# CHECK-LINE-TABLE-NEXT: 0x00000039: 05 DW_LNS_set_column (2)
-# CHECK-LINE-TABLE-NEXT: 0x0000003b: 00 DW_LNE_set_address (0x0000000000000008)
-# CHECK-LINE-TABLE-NEXT: 0x00000046: 01 DW_LNS_copy
+# CHECK-LINE-TABLE-NEXT: 0x00000036: 02 DW_LNS_advance_pc (addr += 8, op-index += 0)
+# CHECK-LINE-TABLE-NEXT: 0x00000038: 00 DW_LNE_end_sequence
+# CHECK-LINE-TABLE-NEXT:             0x0000000000000008      1      1      1   0             0       0  is_stmt end_sequence
+# CHECK-LINE-TABLE-NEXT: 0x0000003b: 05 DW_LNS_set_column (2)
+# CHECK-LINE-TABLE-NEXT: 0x0000003d: 00 DW_LNE_set_address (0x0000000000000008)
+# CHECK-LINE-TABLE-NEXT: 0x00000048: 01 DW_LNS_copy
 # CHECK-LINE-TABLE-NEXT:             0x0000000000000008      1      2      1   0             0       0  is_stmt
-# CHECK-LINE-TABLE-NEXT: 0x00000047: 00 DW_LNE_end_sequence
-# CHECK-LINE-TABLE-NEXT:             0x0000000000000008      1      2      1   0             0       0  is_stmt end_sequence
-# CHECK-LINE-TABLE-NEXT: 0x0000004a: 05 DW_LNS_set_column (3)
-# CHECK-LINE-TABLE-NEXT: 0x0000004c: 00 DW_LNE_set_address (0x0000000000000010)
-# CHECK-LINE-TABLE-NEXT: 0x00000057: 01 DW_LNS_copy
+# CHECK-LINE-TABLE-NEXT: 0x00000049: 02 DW_LNS_advance_pc (addr += 8, op-index += 0)
+# CHECK-LINE-TABLE-NEXT: 0x0000004b: 00 DW_LNE_end_sequence
+# CHECK-LINE-TABLE-NEXT:             0x0000000000000010      1      2      1   0             0       0  is_stmt end_sequence
+# CHECK-LINE-TABLE-NEXT: 0x0000004e: 05 DW_LNS_set_column (3)
+# CHECK-LINE-TABLE-NEXT: 0x00000050: 00 DW_LNE_set_address (0x0000000000000010)
+# CHECK-LINE-TABLE-NEXT: 0x0000005b: 01 DW_LNS_copy
 # CHECK-LINE-TABLE-NEXT:             0x0000000000000010      1      3      1   0             0       0  is_stmt
-# CHECK-LINE-TABLE-NEXT: 0x00000058: 00 DW_LNE_end_sequence
-# CHECK-LINE-TABLE-NEXT:             0x0000000000000010      1      3      1   0             0       0  is_stmt end_sequence
-# CHECK-LINE-TABLE-NEXT: 0x0000005b: 05 DW_LNS_set_column (4)
-# CHECK-LINE-TABLE-NEXT: 0x0000005d: 00 DW_LNE_set_address (0x0000000000000018)
-# CHECK-LINE-TABLE-NEXT: 0x00000068: 01 DW_LNS_copy
+# CHECK-LINE-TABLE-NEXT: 0x0000005c: 02 DW_LNS_advance_pc (addr += 8, op-index += 0)
+# CHECK-LINE-TABLE-NEXT: 0x0000005e: 00 DW_LNE_end_sequence
+# CHECK-LINE-TABLE-NEXT:             0x0000000000000018      1      3      1   0             0       0  is_stmt end_sequence
+# CHECK-LINE-TABLE-NEXT: 0x00000061: 05 DW_LNS_set_column (4)
+# CHECK-LINE-TABLE-NEXT: 0x00000063: 00 DW_LNE_set_address (0x0000000000000018)
+# CHECK-LINE-TABLE-NEXT: 0x0000006e: 01 DW_LNS_copy
 # CHECK-LINE-TABLE-NEXT:             0x0000000000000018      1      4      1   0             0       0  is_stmt
-# CHECK-LINE-TABLE-NEXT: 0x00000069: 05 DW_LNS_set_column (5)
-# CHECK-LINE-TABLE-NEXT: 0x0000006b: 01 DW_LNS_copy
+# CHECK-LINE-TABLE-NEXT: 0x0000006f: 05 DW_LNS_set_column (5)
+# CHECK-LINE-TABLE-NEXT: 0x00000071: 01 DW_LNS_copy
 # CHECK-LINE-TABLE-NEXT:             0x0000000000000018      1      5      1   0             0       0  is_stmt
-# CHECK-LINE-TABLE-NEXT: 0x0000006c: 00 DW_LNE_end_sequence
-# CHECK-LINE-TABLE-NEXT:             0x0000000000000018      1      5      1   0             0       0  is_stmt end_sequence
+# CHECK-LINE-TABLE-NEXT: 0x00000072: 02 DW_LNS_advance_pc (addr += 8, op-index += 0)
+# CHECK-LINE-TABLE-NEXT: 0x00000074: 00 DW_LNE_end_sequence
+# CHECK-LINE-TABLE-NEXT:             0x0000000000000020      1      5      1   0             0       0  is_stmt end_sequence
 
 # CHECK-SYM:      Symbol table '.symtab' contains 9 entries:
 # CHECK-SYM-NEXT:    Num:    Value          Size Type    Bind   Vis       Ndx Name
 # CHECK-SYM-NEXT:      0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT   UND
 # CHECK-SYM-NEXT:      1: 0000000000000000     0 FILE    LOCAL  DEFAULT   ABS test.c
 # CHECK-SYM-NEXT:      2: 0000000000000000     0 SECTION LOCAL  DEFAULT     2 .text
-# CHECK-SYM-NEXT:      3: 0000000000000039     0 NOTYPE  LOCAL  DEFAULT     3 my_label_02
-# CHECK-SYM-NEXT:      4: 000000000000004a     0 NOTYPE  LOCAL  DEFAULT     3 my_label_03
-# CHECK-SYM-NEXT:      5: 000000000000005b     0 NOTYPE  LOCAL  DEFAULT     3 my_label_04
-# CHECK-SYM-NEXT:      6: 000000000000004a     0 NOTYPE  LOCAL  DEFAULT     3 my_label_03.1
-# CHECK-SYM-NEXT:      7: 000000000000006f     0 NOTYPE  LOCAL  DEFAULT     3 my_label_05
+# CHECK-SYM-NEXT:      3: 000000000000003b     0 NOTYPE  LOCAL  DEFAULT     3 my_label_02
+# CHECK-SYM-NEXT:      4: 000000000000004e     0 NOTYPE  LOCAL  DEFAULT     3 my_label_03
+# CHECK-SYM-NEXT:      5: 0000000000000061     0 NOTYPE  LOCAL  DEFAULT     3 my_label_04
+# CHECK-SYM-NEXT:      6: 000000000000004e     0 NOTYPE  LOCAL  DEFAULT     3 my_label_03.1
+# CHECK-SYM-NEXT:      7: 0000000000000077     0 NOTYPE  LOCAL  DEFAULT     3 my_label_05
 # CHECK-SYM-NEXT:      8: 0000000000000000     0 FUNC    GLOBAL DEFAULT     2 foo
 
-# CHECK-OFFSETS: 0000 39000000 4a000000 5b000000
+# CHECK-OFFSETS: 0000 3b000000 4e000000 61000000
 
 	.text
 	.file	"test.c"

DataCorrupted · 2025-09-08T18:37:53Z

cc @nocchijiang , I can't tag you as a reviewer somehow

DataCorrupted · 2025-09-08T20:31:14Z

@rastogishubham / @adrian-prantl You mentioned a bug in #110192, which wasn't really fixed there. This PR fixed the issue, but I wonder if it will work fine with your fork. Let me know if you have any comments.

…ries (#133079) When hitting a sanitizer breakpoint, LLDB currently displays the frame in the sanitizer dylib (which we usually don't have debug-info for), which isn't very helpful to the user. A more helpful frame to display would be the first frame not in the sanitizer library (we have a [similar heuristic when we trap inside libc++](#108825)). This patch does just that, by implementing the `GetSuggestedStackFrameIndex` API Depends on #133078

Signed-off-by: Peter Rong <[email protected]>

DataCorrupted · 2025-09-10T19:41:15Z

@dwblaikie Can I get a quick review pls?

dwblaikie

shrug I'm not especially familiar with this code, but the resulting changes seem OK & doesn't seem too invasive...

DataCorrupted · 2025-09-12T17:33:46Z

@dwblaikie Confirming the tests are correct is a huge help to us. Thanks!

llvm-ci · 2025-09-12T17:43:54Z

LLVM Buildbot has detected a new failure on builder ml-opt-rel-x86-64 running on ml-opt-rel-x86-64-b1 while building llvm at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/185/builds/25273

Here is the relevant piece of the build log for the reference

Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: DebugInfo/ARM/stmt_seq_macho.test' FAILED ********************
Exit Code: 127

Command Output (stdout):
--
# RUN: at line 1
split-file /b/ml-opt-rel-x86-64-b1/llvm-project/llvm/test/DebugInfo/ARM/stmt_seq_macho.test /b/ml-opt-rel-x86-64-b1/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp
# executed command: split-file /b/ml-opt-rel-x86-64-b1/llvm-project/llvm/test/DebugInfo/ARM/stmt_seq_macho.test /b/ml-opt-rel-x86-64-b1/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp
# RUN: at line 3
clang++ --target=arm64-apple-macos11    /b/ml-opt-rel-x86-64-b1/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp/stmt_seq_macho.cpp -o /b/ml-opt-rel-x86-64-b1/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp/stmt_seq_macho.o    -g -Oz -gdwarf-4 -c -mno-outline    -mllvm -emit-func-debug-line-table-offsets    -fdebug-compilation-dir=/private/tmp/stmt_seq    -fno-unwind-tables -fno-exceptions
# executed command: clang++ --target=arm64-apple-macos11 /b/ml-opt-rel-x86-64-b1/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp/stmt_seq_macho.cpp -o /b/ml-opt-rel-x86-64-b1/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp/stmt_seq_macho.o -g -Oz -gdwarf-4 -c -mno-outline -mllvm -emit-func-debug-line-table-offsets -fdebug-compilation-dir=/private/tmp/stmt_seq -fno-unwind-tables -fno-exceptions
# .---command stderr------------
# | 'clang++': command not found
# `-----------------------------
# error: command failed with exit status: 127

--

********************

llvm-ci · 2025-09-12T17:44:13Z

LLVM Buildbot has detected a new failure on builder ml-opt-dev-x86-64 running on ml-opt-dev-x86-64-b2 while building llvm at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/137/builds/25430

Here is the relevant piece of the build log for the reference

Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: DebugInfo/ARM/stmt_seq_macho.test' FAILED ********************
Exit Code: 127

Command Output (stdout):
--
# RUN: at line 1
split-file /b/ml-opt-dev-x86-64-b1/llvm-project/llvm/test/DebugInfo/ARM/stmt_seq_macho.test /b/ml-opt-dev-x86-64-b1/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp
# executed command: split-file /b/ml-opt-dev-x86-64-b1/llvm-project/llvm/test/DebugInfo/ARM/stmt_seq_macho.test /b/ml-opt-dev-x86-64-b1/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp
# RUN: at line 3
clang++ --target=arm64-apple-macos11    /b/ml-opt-dev-x86-64-b1/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp/stmt_seq_macho.cpp -o /b/ml-opt-dev-x86-64-b1/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp/stmt_seq_macho.o    -g -Oz -gdwarf-4 -c -mno-outline    -mllvm -emit-func-debug-line-table-offsets    -fdebug-compilation-dir=/private/tmp/stmt_seq    -fno-unwind-tables -fno-exceptions
# executed command: clang++ --target=arm64-apple-macos11 /b/ml-opt-dev-x86-64-b1/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp/stmt_seq_macho.cpp -o /b/ml-opt-dev-x86-64-b1/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp/stmt_seq_macho.o -g -Oz -gdwarf-4 -c -mno-outline -mllvm -emit-func-debug-line-table-offsets -fdebug-compilation-dir=/private/tmp/stmt_seq -fno-unwind-tables -fno-exceptions
# .---command stderr------------
# | 'clang++': command not found
# `-----------------------------
# error: command failed with exit status: 127

--

********************

llvm-ci · 2025-09-12T17:44:32Z

LLVM Buildbot has detected a new failure on builder ml-opt-devrel-x86-64 running on ml-opt-devrel-x86-64-b1 while building llvm at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/175/builds/25273

Here is the relevant piece of the build log for the reference

Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: DebugInfo/ARM/stmt_seq_macho.test' FAILED ********************
Exit Code: 127

Command Output (stdout):
--
# RUN: at line 1
split-file /b/ml-opt-devrel-x86-64-b1/llvm-project/llvm/test/DebugInfo/ARM/stmt_seq_macho.test /b/ml-opt-devrel-x86-64-b1/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp
# executed command: split-file /b/ml-opt-devrel-x86-64-b1/llvm-project/llvm/test/DebugInfo/ARM/stmt_seq_macho.test /b/ml-opt-devrel-x86-64-b1/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp
# RUN: at line 3
clang++ --target=arm64-apple-macos11    /b/ml-opt-devrel-x86-64-b1/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp/stmt_seq_macho.cpp -o /b/ml-opt-devrel-x86-64-b1/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp/stmt_seq_macho.o    -g -Oz -gdwarf-4 -c -mno-outline    -mllvm -emit-func-debug-line-table-offsets    -fdebug-compilation-dir=/private/tmp/stmt_seq    -fno-unwind-tables -fno-exceptions
# executed command: clang++ --target=arm64-apple-macos11 /b/ml-opt-devrel-x86-64-b1/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp/stmt_seq_macho.cpp -o /b/ml-opt-devrel-x86-64-b1/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp/stmt_seq_macho.o -g -Oz -gdwarf-4 -c -mno-outline -mllvm -emit-func-debug-line-table-offsets -fdebug-compilation-dir=/private/tmp/stmt_seq -fno-unwind-tables -fno-exceptions
# .---command stderr------------
# | 'clang++': command not found
# `-----------------------------
# error: command failed with exit status: 127

--

********************

llvm-ci · 2025-09-12T17:45:40Z

LLVM Buildbot has detected a new failure on builder lld-x86_64-ubuntu-fast running on as-builder-4 while building llvm at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/33/builds/22944

Here is the relevant piece of the build log for the reference

Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: DebugInfo/ARM/stmt_seq_macho.test' FAILED ********************
Exit Code: 127

Command Output (stdout):
--
# RUN: at line 1
split-file /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/DebugInfo/ARM/stmt_seq_macho.test /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp
# executed command: split-file /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/DebugInfo/ARM/stmt_seq_macho.test /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp
# RUN: at line 3
clang++ --target=arm64-apple-macos11    /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp/stmt_seq_macho.cpp -o /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp/stmt_seq_macho.o    -g -Oz -gdwarf-4 -c -mno-outline    -mllvm -emit-func-debug-line-table-offsets    -fdebug-compilation-dir=/private/tmp/stmt_seq    -fno-unwind-tables -fno-exceptions
# executed command: clang++ --target=arm64-apple-macos11 /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp/stmt_seq_macho.cpp -o /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/test/DebugInfo/ARM/Output/stmt_seq_macho.test.tmp/stmt_seq_macho.o -g -Oz -gdwarf-4 -c -mno-outline -mllvm -emit-func-debug-line-table-offsets -fdebug-compilation-dir=/private/tmp/stmt_seq -fno-unwind-tables -fno-exceptions
# .---command stderr------------
# | 'clang++': command not found
# `-----------------------------
# error: command failed with exit status: 127

--

********************

This reverts commit 84f431c.

Reverts #157529 Sorry, I missed that the missed that the LLVM test was using clang - layering dictates thats not OK. Please readjust the test case to work like the existing test coverage (or perhaps the existing test coverage is sufficient?) and post a new PR.

Reverts llvm/llvm-project#157529 Sorry, I missed that the missed that the LLVM test was using clang - layering dictates thats not OK. Please readjust the test case to work like the existing test coverage (or perhaps the existing test coverage is sufficient?) and post a new PR.

This reverts commit aabf18d. #157529 included a test that used clang, which doesn't exists in some CI. #158343 reverts it. This PR reapplies the original patch with the incorrect test removed. ### Context #99710 introduced `.loc_label` so we can terminate a line sequence. However, it did not advance PC properly. This is problematic for 1-instruction functions as it will have zero-length sequence. The test checked in that PR shows the problem: ``` # CHECK-LINE-TABLE: Address Line Column File ISA Discriminator OpIndex Flags # CHECK-LINE-TABLE-NEXT: ------------------ ------ ------ ------ --- ------------- ------- ------------- # CHECK-LINE-TABLE-NEXT: 0x00000028: 05 DW_LNS_set_column (1) # CHECK-LINE-TABLE-NEXT: 0x0000002a: 00 DW_LNE_set_address (0x0000000000000000) # CHECK-LINE-TABLE-NEXT: 0x00000035: 01 DW_LNS_copy # CHECK-LINE-TABLE-NEXT: 0x0000000000000000 1 1 1 0 0 0 is_stmt # CHECK-LINE-TABLE-NEXT: 0x00000036: 00 DW_LNE_end_sequence # CHECK-LINE-TABLE-NEXT: 0x0000000000000000 1 1 1 0 0 0 is_stmt end_sequence ``` Both rows having PC 0x0 is incorrect, and parsers won't be able to parse them. See more explanation why this is wrong in #154851. ### Design This PR attempts to fix this by advancing the PC to the next available Label, and advance to the end of the section if no Label is available. ### Implementation - `emitDwarfLineEndEntry` will advance PC to the `CurrLabel` - If `CurrLabel` is null, its probably a fake LineEntry we introduced in #110192. In that case look for the next Label - If still not label can be found, use `null` and `emitDwarfLineEndEntry` is smart enough to advance PC to the end of the section - Rename `LastLabel` to `PrevLabel`, "last" can mean "previous" or "final", this is ambigous. - Updated the tests to emit a correct label. ### Note This fix should render #154986 and #154851 obsolete, they were temporary fixes and don't resolve the root cause.

…#158379) This reverts commit aabf18d. llvm#157529 included a test that used clang, which doesn't exists in some CI. llvm#158343 reverts it. This PR reapplies the original patch with the incorrect test removed. ### Context llvm#99710 introduced `.loc_label` so we can terminate a line sequence. However, it did not advance PC properly. This is problematic for 1-instruction functions as it will have zero-length sequence. The test checked in that PR shows the problem: ``` # CHECK-LINE-TABLE: Address Line Column File ISA Discriminator OpIndex Flags # CHECK-LINE-TABLE-NEXT: ------------------ ------ ------ ------ --- ------------- ------- ------------- # CHECK-LINE-TABLE-NEXT: 0x00000028: 05 DW_LNS_set_column (1) # CHECK-LINE-TABLE-NEXT: 0x0000002a: 00 DW_LNE_set_address (0x0000000000000000) # CHECK-LINE-TABLE-NEXT: 0x00000035: 01 DW_LNS_copy # CHECK-LINE-TABLE-NEXT: 0x0000000000000000 1 1 1 0 0 0 is_stmt # CHECK-LINE-TABLE-NEXT: 0x00000036: 00 DW_LNE_end_sequence # CHECK-LINE-TABLE-NEXT: 0x0000000000000000 1 1 1 0 0 0 is_stmt end_sequence ``` Both rows having PC 0x0 is incorrect, and parsers won't be able to parse them. See more explanation why this is wrong in llvm#154851. ### Design This PR attempts to fix this by advancing the PC to the next available Label, and advance to the end of the section if no Label is available. ### Implementation - `emitDwarfLineEndEntry` will advance PC to the `CurrLabel` - If `CurrLabel` is null, its probably a fake LineEntry we introduced in llvm#110192. In that case look for the next Label - If still not label can be found, use `null` and `emitDwarfLineEndEntry` is smart enough to advance PC to the end of the section - Rename `LastLabel` to `PrevLabel`, "last" can mean "previous" or "final", this is ambigous. - Updated the tests to emit a correct label. ### Note This fix should render llvm#154986 and llvm#154851 obsolete, they were temporary fixes and don't resolve the root cause.

DataCorrupted requested review from MaskRay, rastogishubham, ellishg, dwblaikie, kyulee-com and alx32 September 8, 2025 18:36

llvmbot added debuginfo llvm:mc Machine (object) code labels Sep 8, 2025

DataCorrupted force-pushed the CorrectLineTable branch from 26b397e to 444bfe3 Compare September 8, 2025 20:15

DataCorrupted requested a review from adrian-prantl September 8, 2025 20:31

DataCorrupted mentioned this pull request Sep 8, 2025

[lldb][Instrumentation] Set selected frame to outside sanitizer libraries #133079

Merged

DataCorrupted added 3 commits September 8, 2025 16:30

[DebugLine] Correct debug line emittion

dbbf529

Signed-off-by: Peter Rong <[email protected]>

Format test to reduce diff size

ba688a8

Signed-off-by: Peter Rong <[email protected]>

Add a test for macho

34bf79b

DataCorrupted force-pushed the CorrectLineTable branch from 268e9ac to 34bf79b Compare September 8, 2025 23:30

DataCorrupted added 2 commits September 8, 2025 20:31

Verify metadata

a3a64e6

Update test

5445f54

This was referenced Sep 9, 2025

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

Closed

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

Closed

DataCorrupted mentioned this pull request Sep 10, 2025

[DWARFVerifier] Verify that DW_AT_LLVM_stmt_sequence is set correctly #152807

Open

dwblaikie approved these changes Sep 12, 2025

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DataCorrupted merged commit 84f431c into llvm:main Sep 12, 2025
9 checks passed

dwblaikie added a commit that referenced this pull request Sep 12, 2025

Revert "[DebugLine] Correct debug line emittion (#157529)"

1ff8b74

This reverts commit 84f431c.

dwblaikie mentioned this pull request Sep 12, 2025

Revert "[DebugLine] Correct debug line emittion" #158343

Merged

This was referenced Sep 12, 2025

[DebugInfo] Rm a test in #157529 #158353

Closed

[DebugInfo] Fix test introduced in #157529 #158352

Closed

DataCorrupted mentioned this pull request Sep 12, 2025

Reapply "[DebugLine] Correct debug line emittion" (#158343) #158379

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