[DwarfDebug] Prioritise DWARF filename in debuginfo over MC Target Options

[cbeuw]

Summary

The value of splitDebugFilename in DICompileUnit is currently ignored when
emitting the dwo name into an object file. The path supplied in
MCOptions.SplitDwarfFile is used both as a real path to write the split
dwo content, and as the value of DW_AT_[GNU_]dwo_name emitted into the object
file.

Instead, the filename specified in DICompileUnit should be the one emitted so
long as it has been specified. Additionally, since MCOptions.SplitDwarfFile
points to a real path, this may lead to inconsistent compilation results when
doing remote/distributed builds.

MCOptions.SplitDwarfFile remains to be used as the real path to write the
dwo file, but splitDebugFilename in DICompileUnit is emitted when specified,
and otherwise falls back to emit MCOptions.SplitDwarfFile as-is

[cbeuw]

Fix an llvm-dwp test

[cbeuw]

Fix line endings

[dblaikie]

I /think/ this is the wrong direction.

"split dwarf file" is meant to be the name that goes in the dwo_name
"split dwarf output" is the name of the actual output file, and doesn't have to be the same as the "split dwarf file".

I guess currently this is only exposed in -cc1/llc/etc, and not in the clang driver (the only thing that causes split dwarf file/output to differ.

At the LLVM level in this patch, if you want the physical file to be something other than SplitDwarfFile, then that can be achieved by creating a different/non-null raw_pwrite_stream for the DwoOS parameter here: https://github.com/llvm/llvm-project/blob/bebfbfd4a82573e27171b4adf239c9804fa6d656/clang/lib/CodeGen/BackendUtil.cpp#L1075

[cbeuw]

Indeed I was mistaken about the effect of SplitDwarfFile in MCOptions. It does not dictate the actual output path if DwoOS is specified. The thing I was working on was rustc and it does open DwoOS separately and passes it in like clang.

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

for (const auto &P : CUMap) {
 
     bool HasSplitUnit = SkCU && !TheCU.getUnitDie().children().empty();
 
     if (HasSplitUnit) {
       dwarf::Attribute attrDWOName = getDwarfVersion() >= 5
                                          ? dwarf::DW_AT_dwo_name
                                          : dwarf::DW_AT_GNU_dwo_name;
       finishUnitAttributes(TheCU.getCUNode(), TheCU);
-      TheCU.addString(TheCU.getUnitDie(), attrDWOName,
-                      Asm->TM.Options.MCOptions.SplitDwarfFile);
-      SkCU->addString(SkCU->getUnitDie(), attrDWOName,
-                      Asm->TM.Options.MCOptions.SplitDwarfFile);
+      StringRef embeddedDWOName = TheCU.getCUNode()->getSplitDebugFilename();
+      if (embeddedDWOName.empty()) {
+        embeddedDWOName = Asm->TM.Options.MCOptions.SplitDwarfFile;
+      }
+      TheCU.addString(TheCU.getUnitDie(), attrDWOName, embeddedDWOName);
+      SkCU->addString(SkCU->getUnitDie(), attrDWOName, embeddedDWOName);
       // Emit a unique identifier for this CU.
       uint64_t ID =
           DIEHash(Asm, &TheCU).computeCUSignature(DWOName, TheCU.getUnitDie());
       if (getDwarfVersion() >= 5) {
         TheCU.setDWOId(ID);
         SkCU->setDWOId(ID);
       } else {
         TheCU.addUInt(TheCU.getUnitDie(), dwarf::DW_AT_GNU_dwo_id,

llvm/test/DebugInfo/X86/debug-macinfo-split-dwarf.ll

 
 attributes #0 = { noinline nounwind optnone uwtable }
 attributes #1 = { nounwind readnone speculatable willreturn }
 
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!21, !22, !23}
 !llvm.ident = !{!24}
 
-!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 10.0.0", isOptimized: false, runtimeVersion: 0, splitDebugFilename: "debug-macro-split-dwarf.dwo", emissionKind: FullDebug, enums: !2, macros: !3, nameTableKind: GNU)
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 10.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, macros: !3, nameTableKind: GNU)
 !1 = !DIFile(filename: "debug-macro-split-dwarf.c", directory: "/", checksumkind: CSK_MD5, checksum: "e74d0fa8f714535c1bac6da2ffbbd898")
 !2 = !{}
 !3 = !{!4, !14, !15, !16, !17, !18, !19, !20}
 !4 = !DIMacroFile(file: !1, nodes: !5)
 !5 = !{!6, !10}
 !6 = !DIMacroFile(line: 1, file: !7, nodes: !8)
 !7 = !DIFile(filename: "./1.h", directory: "/", checksumkind: CSK_MD5, checksum: "6185a3a5ae6eb7d1fd2692718f9d95e5")
 !8 = !{!9}

llvm/test/DebugInfo/dwo-different-name.ll

+; RUN: %llc_dwarf %s -filetype=obj -o %t --split-dwarf-file from-mc-options.dwo
+; RUN: llvm-dwarfdump -debug-info %t | FileCheck %s
+; REQUIRES: default_triple, object-emission
+;
+; CHECK: DW_AT_GNU_dwo_name ("from-debuginfo.dwo")
+; CHECK-NOT: DW_AT_GNU_dwo_name ("from-mc-options.dwo")
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "Clang", isOptimized: false, runtimeVersion: 2, splitDebugFilename: "from-debuginfo.dwo", emissionKind: FullDebug, enums: !2, globals: !2, retainedTypes: !5)
+!1 = !DIFile(filename: "<stdin>", directory: "/")
+!2 = !{}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{!6}
+!6 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)

llvm/test/tools/llvm-dwp/X86/absolute_paths.test

 define void @banana() !dbg !8 {
   ret void, !dbg !12
 }
 
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!3, !4, !5, !6}
 !llvm.ident = !{!7}
 
-!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 11.0.1", isOptimized: true, runtimeVersion: 0, splitDebugFilename: "test.dwo", emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: GNU)
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 11.0.1", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: GNU)
 !1 = !DIFile(filename: "/tmp/test.c", directory: "/tmp")
 !2 = !{}
 !3 = !{i32 7, !"Dwarf Version", i32 4}
 !4 = !{i32 2, !"Debug Info Version", i32 3}
 !5 = !{i32 1, !"wchar_size", i32 4}
 !6 = !{i32 7, !"PIC Level", i32 2}
 !7 = !{!"clang version 11.0.1"}
 !8 = distinct !DISubprogram(name: "banana", scope: !9, file: !9, line: 1, type: !10, scopeLine: 1, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
 !9 = !DIFile(filename: "test.c", directory: "/tmp")
 !10 = !DISubroutineType(types: !11)
 !11 = !{null}
 !12 = !DILocation(line: 1, column: 20, scope: !8)