[DebugInfo] Fix emitting DWARF64 .debug_names sections (16/19).

[ikudrin]

Summary

The patch fixes emitting the unit length field in the header of the table and offsets to the entry pool. Note that while the patch changes the common method to emit offsets, in fact, nothing is changed for Apple accelerator tables, because we do not yet support DWARF64 for those targets.

[dblaikie]

llvm/lib/CodeGen/AsmPrinter/AccelTable.cpp

273

Where is this one tested? Is this offset rendered in the dump output at all?

llvm/test/DebugInfo/X86/debug-names-dwarf64.ll

10

I'd probably include the 0x in the match - so the later reference to this match doesn't have to specify the 0x too.

27

Is this a 64 bit offset & should be rendered as such?

[ikudrin]

• Updated the test as suggested.

llvm/lib/CodeGen/AsmPrinter/AccelTable.cpp

273

The line emits offsets to entries. They are rendered in the dump after Entry @. They are not checked in the test directly, but as far as llvm-dwarfdump can interpret the section and find entries with expected information, we assume that the offsets are emitted properly.

llvm/test/DebugInfo/X86/debug-names-dwarf64.ll

27

Took a note for improving llvm-dwarfdump in the future. Right now the offsets are dumped as 32-bit.

[dblaikie]

Looks good, thanks!

llvm/lib/CodeGen/AsmPrinter/AccelTable.cpp

void AccelTableWriter::emitOffsets(const MCSymbol *Base) const {
   uint64_t PrevHash = std::numeric_limits<uint64_t>::max();
   for (size_t i = 0, e = Buckets.size(); i < e; ++i) {
     for (auto *Hash : Buckets[i]) {
       uint32_t HashValue = Hash->HashValue;
       if (SkipIdenticalHashes && PrevHash == HashValue)
         continue;
       PrevHash = HashValue;
       Asm->OutStreamer->AddComment("Offset in Bucket " + Twine(i));
-      Asm->emitLabelDifference(Hash->Sym, Base, sizeof(uint32_t));
+      Asm->emitLabelDifference(Hash->Sym, Base, Asm->getDwarfOffsetByteSize());
     }
   }
 }
 
 void AppleAccelTableWriter::Header::emit(AsmPrinter *Asm) const {
   Asm->OutStreamer->AddComment("Header Magic");
   Asm->emitInt32(Magic);
   Asm->OutStreamer->AddComment("Header Version");

 }
 
 template <typename DataT>
 void Dwarf5AccelTableWriter<DataT>::Header::emit(
     const Dwarf5AccelTableWriter &Ctx) const {
   assert(CompUnitCount > 0 && "Index must have at least one CU.");
 
   AsmPrinter *Asm = Ctx.Asm;
-  Asm->OutStreamer->AddComment("Header: unit length");
-  Asm->emitLabelDifference(Ctx.ContributionEnd, Ctx.ContributionStart,
-                           sizeof(uint32_t));
+  Asm->emitDwarfUnitLength(Ctx.ContributionEnd, Ctx.ContributionStart,
+                           "Header: unit length");
   Asm->OutStreamer->emitLabel(Ctx.ContributionStart);
   Asm->OutStreamer->AddComment("Header: version");
   Asm->emitInt16(Version);
   Asm->OutStreamer->AddComment("Header: padding");
   Asm->emitInt16(Padding);
   Asm->OutStreamer->AddComment("Header: compilation unit count");
   Asm->emitInt32(CompUnitCount);
   Asm->OutStreamer->AddComment("Header: local type unit count");

llvm/test/DebugInfo/X86/debug-names-dwarf64.ll

+; This checks that .debug_names can be generated in the DWARF64 format.
+
+; RUN: llc -mtriple=x86_64 -dwarf64 -accel-tables=Dwarf -dwarf-version=5 -filetype=obj %s -o %t
+; RUN: llvm-dwarfdump -debug-info -debug-names %t | FileCheck %s
+; RUN: llvm-dwarfdump -debug-names -verify %t | FileCheck --check-prefix=VERIFY %s
+
+; CHECK:     .debug_info contents:
+; CHECK-NEXT: 0x00000000:     Compile Unit: {{.+}}, format = DWARF64,
+; CHECK:      [[VARDIE:.+]]:  DW_TAG_variable
+; CHECK-NEXT:                   DW_AT_name ("foo")
+; CHECK:      [[TYPEDIE:.+]]: DW_TAG_base_type
+; CHECK-NEXT:                   DW_AT_name ("int")
+
+; CHECK:      .debug_names contents:
+; CHECK-NEXT: Name Index @ 0x0 {
+; CHECK-NEXT:   Header {
+; CHECK:          Format: DWARF64
+; CHECK-NEXT:     Version: 5
+; CHECK-NEXT:     CU count: 1
+; CHECK-NEXT:     Local TU count: 0
+; CHECK-NEXT:     Foreign TU count: 0
+; CHECK-NEXT:     Bucket count: 2
+; CHECK-NEXT:     Name count: 2
+; CHECK:        }
+; CHECK-NEXT:   Compilation Unit offsets [
+; CHECK-NEXT:     CU[0]: 0x00000000
+; CHECK-NEXT:   ]
+; CHECK-NEXT:   Abbreviations [
+; CHECK-NEXT:     Abbreviation 0x34 {
+; CHECK-NEXT:       Tag: DW_TAG_variable
+; CHECK-NEXT:       DW_IDX_die_offset: DW_FORM_ref4
+; CHECK-NEXT:     }
+; CHECK-NEXT:     Abbreviation 0x24 {
+; CHECK-NEXT:       Tag: DW_TAG_base_type
+; CHECK-NEXT:       DW_IDX_die_offset: DW_FORM_ref4
+; CHECK-NEXT:     }
+; CHECK-NEXT:   ]
+; CHECK-NEXT:   Bucket 0 [
+; CHECK-NEXT:     Name 1 {
+; CHECK-NEXT:       Hash: 0xB888030
+; CHECK-NEXT:       String: {{.+}} "int"
+; CHECK-NEXT:       Entry @ {{.+}} {
+; CHECK-NEXT:         Abbrev: 0x24
+; CHECK-NEXT:         Tag: DW_TAG_base_type
+; CHECK-NEXT:         DW_IDX_die_offset: [[TYPEDIE]]
+; CHECK-NEXT:       }
+; CHECK-NEXT:     }
+; CHECK-NEXT:   ]
+; CHECK-NEXT:   Bucket 1 [
+; CHECK-NEXT:     Name 2 {
+; CHECK-NEXT:       Hash: 0xB887389
+; CHECK-NEXT:       String: {{.+}} "foo"
+; CHECK-NEXT:       Entry @ {{.+}} {
+; CHECK-NEXT:         Abbrev: 0x34
+; CHECK-NEXT:         Tag: DW_TAG_variable
+; CHECK-NEXT:         DW_IDX_die_offset: [[VARDIE]]
+; CHECK-NEXT:       }
+; CHECK-NEXT:     }
+; CHECK-NEXT:   ]
+; CHECK-NEXT: }
+
+; VERIFY: No errors.
+
+; IR generated and reduced from:
+; $ cat foo.c
+; int foo;
+; $ clang -g -gpubnames -S -emit-llvm foo.c -o foo.ll
+
+target triple = "x86_64-unknown-linux-gnu"
+
+@foo = dso_local global i32 0, align 4, !dbg !0
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!7, !8, !9}
+!llvm.ident = !{!10}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "foo", scope: !2, file: !3, line: 1, type: !6, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 12.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5, splitDebugInlining: false)
+!3 = !DIFile(filename: "foo.c", directory: "/tmp")
+!4 = !{}
+!5 = !{!0}
+!6 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!7 = !{i32 7, !"Dwarf Version", i32 4}
+!8 = !{i32 2, !"Debug Info Version", i32 3}
+!9 = !{i32 1, !"wchar_size", i32 4}
+!10 = !{!"clang version 12.0.0"}