[DebugInfo] Emit skeleton to avoid mismatching inlining flags

[ecnelises]

This actually reverts 4181205.

The original commit omits unit with all symbols inlined into current one, which leads to crash when a module using split-dwarf inlined a function from another module with mismatched split-dwarf-inlining option. This revert guarantees that DIEs are created in both DWO and the skeleton sections whenever split-dwarf is active.

[llvmbot]

@llvm/pr-subscribers-debuginfo

Author: Qiu Chaofan (ecnelises)

Changes

This actually reverts 4181205.

The original commit omits unit with all symbols inlined into current one, which leads to crash when a module using split-dwarf inlined a function from another module with mismatched split-dwarf-inlining option. This revert guarantees that DIEs are created in both DWO and the skeleton sections whenever split-dwarf is active.

---

Full diff: https://github.com/llvm/llvm-project/pull/153568.diff

2 Files Affected:

• (modified) llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp (+8-12)
• (modified) llvm/test/DebugInfo/X86/split-dwarf-omit-empty.ll (+1-1)

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index c27f100775625..afa8511981e23 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -558,18 +558,14 @@ void DwarfDebug::constructAbstractSubprogramScopeDIE(DwarfCompileUnit &SrcCU,
 
   // Find the subprogram's DwarfCompileUnit in the SPMap in case the subprogram
   // was inlined from another compile unit.
-  if (useSplitDwarf() && !shareAcrossDWOCUs() && !SP->getUnit()->getSplitDebugInlining())
-    // Avoid building the original CU if it won't be used
-    SrcCU.constructAbstractSubprogramScopeDIE(Scope);
-  else {
-    auto &CU = getOrCreateDwarfCompileUnit(SP->getUnit());
-    if (auto *SkelCU = CU.getSkeleton()) {
-      (shareAcrossDWOCUs() ? CU : SrcCU)
-          .constructAbstractSubprogramScopeDIE(Scope);
-      if (CU.getCUNode()->getSplitDebugInlining())
-        SkelCU->constructAbstractSubprogramScopeDIE(Scope);
-    } else
-      CU.constructAbstractSubprogramScopeDIE(Scope);
+  auto &CU = getOrCreateDwarfCompileUnit(SP->getUnit());
+  if (auto *SkelCU = CU.getSkeleton()) {
+    (shareAcrossDWOCUs() ? CU : SrcCU)
+        .constructAbstractSubprogramScopeDIE(Scope);
+    if (CU.getCUNode()->getSplitDebugInlining())
+      SkelCU->constructAbstractSubprogramScopeDIE(Scope);
+  } else {
+    CU.constructAbstractSubprogramScopeDIE(Scope);
   }
 }
 
diff --git a/llvm/test/DebugInfo/X86/split-dwarf-omit-empty.ll b/llvm/test/DebugInfo/X86/split-dwarf-omit-empty.ll
index f4cee1ec78b1d..95aae44b679d5 100644
--- a/llvm/test/DebugInfo/X86/split-dwarf-omit-empty.ll
+++ b/llvm/test/DebugInfo/X86/split-dwarf-omit-empty.ll
@@ -38,7 +38,7 @@ entry:
 !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 5.0.0 (trunk 304054) (llvm/trunk 304080)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false)
 !1 = !DIFile(filename: "a.cpp", directory: "/usr/local/google/home/blaikie/dev/scratch")
 !2 = !{}
-!3 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !4, producer: "clang version 5.0.0 (trunk 304054) (llvm/trunk 304080)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false)
+!3 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !4, producer: "clang version 5.0.0 (trunk 304054) (llvm/trunk 304080)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: true)
 !4 = !DIFile(filename: "b.cpp", directory: "/usr/local/google/home/blaikie/dev/scratch")
 !5 = !{!"clang version 5.0.0 (trunk 304054) (llvm/trunk 304080)"}
 !6 = !{i32 2, !"Dwarf Version", i32 4}

[dwblaikie]

Hrm - could you describe this a bit more verbosely/with an example perhaps? I can't quite picture it straight-off.

Example of a case where the previous optimization continues to apply - and an example where this bug shows up.

Are there any false positives/false negatives? (do we end up producing empty CUs under certain circumstances with this new patch applied?)

[ecnelises]

hi @dwblaikie

This comes from a real-world thin-lto case which triggers a crash: A static library containing bitcode files were compiled with debug info but split-inlining is false. The library is linked into final application builtin with -gsplit-dwarf (split-inlining=true).

In such case, when a function from the bitcode archive is inlined, compiler sees splitDebugInlining is false in the original CU, so incorrectly skips emitting an abstract origin DIE for that function into the skeleton. However, the application's CU requires the skeleton DIE to generate its own entry for inlined_subroutine, then crash happens. My added testcase shows the crash:

Assertion failed: (OriginDIE && "Unable to find original DIE for an inlined subprogram."), function constructInlinedScopeDIE, file DwarfCompileUnit.cpp, line 741.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
1.	Running pass 'Function Pass Manager' on module 'llvm/test/DebugInfo/X86/split-dwarf-inline.ll'.
2.	Running pass 'X86 Assembly Printer' on function '@caller_func'
Stack dump without symbol names (ensure you have llvm-symbolizer in your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point to it):
0  llc                      0x0000000106252104 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 56
1  llc                      0x000000010624fe90 llvm::sys::RunSignalHandlers() + 172
2  llc                      0x0000000106252bfc SignalHandler(int, __siginfo*, void*) + 360
3  libsystem_platform.dylib 0x000000019bdf16a4 _sigtramp + 56
4  libsystem_pthread.dylib  0x000000019bdb788c pthread_kill + 296
5  libsystem_c.dylib        0x000000019bcc0a3c abort + 124
6  libsystem_c.dylib        0x000000019bcbfc70 err + 0
7  llc                      0x0000000106fdd0c8 llvm::DwarfCompileUnit::constructInlinedScopeDIE(llvm::LexicalScope*, llvm::DIE&) (.cold.9) + 0
8  llc                      0x0000000105404234 llvm::DwarfCompileUnit::constructInlinedScopeDIE(llvm::LexicalScope*, llvm::DIE&) + 704
9  llc                      0x0000000105403ee8 llvm::DwarfCompileUnit::constructScopeDIE(llvm::LexicalScope*, llvm::DIE&) + 88
10 llc                      0x0000000105405174 llvm::DwarfCompileUnit::createAndAddScopeChildren(llvm::LexicalScope*, llvm::DIE&) + 3868
11 llc                      0x0000000105407314 llvm::DwarfCompileUnit::constructSubprogramScopeDIE(llvm::DISubprogram const*, llvm::LexicalScope*, llvm::MCSymbol*) + 80
12 llc                      0x0000000105419f70 llvm::DwarfDebug::endFunctionImpl(llvm::MachineFunction const*) + 1672
13 llc                      0x00000001053f942c llvm::DebugHandlerBase::endFunction(llvm::MachineFunction const*) + 64
14 llc                      0x00000001053dea40 llvm::AsmPrinter::emitFunctionBody() + 14580
15 llc                      0x0000000104d2efec llvm::X86AsmPrinter::runOnMachineFunction(llvm::MachineFunction&) + 396
16 llc                      0x000000010563a714 llvm::MachineFunctionPass::runOnFunction(llvm::Function&) + 784
17 llc                      0x0000000105a8f338 llvm::FPPassManager::runOnFunction(llvm::Function&) + 656
18 llc                      0x0000000105a9649c llvm::FPPassManager::runOnModule(llvm::Module&) + 60
19 llc                      0x0000000105a8fbec llvm::legacy::PassManagerImpl::run(llvm::Module&) + 1528