[WebAssembly] Don't crash when gnu-style pubnames are requested

[loladiro]

Summary

Julia started emitting these after upgrading to LLVM8, causing crashes
in LLVM when targetting WebAssembly. I'm not entirely convinced that
these sections are useful for WebAssembly since the wasm debugging
story isn't entirely fleshed out yet, but at least we shouldn't crash
here while we figure out the right answer.

[sbc100]

I have be working on CL that does basically a superset of this to support -gsplit-dwarf. But maybe can land this first.

llvm/test/DebugInfo/WebAssembly/gnu-public-names-tu.ll

2

How does -generate-type-units related to clang option -ggnu-pubnames

Can this test case be reduced to something more minimal?

[sbc100]

(sorry.. I wrote those comments a while back and forgot to hit send)..

[loladiro]

In D71156#1782580, @sbc100 wrote:

I have be working on CL that does basically a superset of this to support -gsplit-dwarf. But maybe can land this first.

I'm happy to just leave this as is and carry locally until your CL is done.

llvm/lib/MC/MCObjectFileInfo.cpp

void MCObjectFileInfo::initWasmMCObjectFileInfo(const Triple &T) {
   DwarfAddrSection = Ctx->getWasmSection(".debug_addr", SectionKind::getMetadata());
   DwarfCUIndexSection = Ctx->getWasmSection(".debug_cu_index", SectionKind::getMetadata());
   DwarfTUIndexSection = Ctx->getWasmSection(".debug_tu_index", SectionKind::getMetadata());
   DwarfInfoSection =
       Ctx->getWasmSection(".debug_info", SectionKind::getMetadata());
   DwarfFrameSection = Ctx->getWasmSection(".debug_frame", SectionKind::getMetadata());
   DwarfPubNamesSection = Ctx->getWasmSection(".debug_pubnames", SectionKind::getMetadata());
   DwarfPubTypesSection = Ctx->getWasmSection(".debug_pubtypes", SectionKind::getMetadata());
+  DwarfGnuPubNamesSection = Ctx->getWasmSection(".debug_gnu_pubnames", SectionKind::getMetadata());
+  DwarfGnuPubTypesSection = Ctx->getWasmSection(".debug_gnu_pubtypes", SectionKind::getMetadata());
 
   // Wasm use data section for LSDA.
   // TODO Consider putting each function's exception table in a separate
   // section, as in -function-sections, to facilitate lld's --gc-section.
   LSDASection = Ctx->getWasmSection(".rodata.gcc_except_table",
                                     SectionKind::getReadOnlyWithRel());
 
   // TODO: Define more sections.

llvm/test/DebugInfo/WebAssembly/gnu-public-names-tu.ll

+; RUN: llc -mtriple=wasm32-unknown-unknown -generate-type-units -filetype=obj < %s | llvm-dwarfdump -v - | FileCheck %s
+
+; Generated from:
+
+; namespace ns {
+; struct foo {
+; };
+; }
+; struct bar {
+;   ns::foo f;
+; };
+; bar b;
+
+; CHECK-LABEL: .debug_gnu_pubnames contents:
+; CHECK-LABEL: debug_gnu_pubtypes contents:
+
+%struct.bar = type { %"struct.ns::foo" }
+%"struct.ns::foo" = type { i8 }
+
+@b = global %struct.bar zeroinitializer, align 1, !dbg !0
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!11, !12}
+!llvm.ident = !{!13}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "b", scope: !2, file: !3, line: 8, type: !6, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "clang version 5.0.0 (trunk 293904) (llvm/trunk 293908)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5, nameTableKind: GNU)
+!3 = !DIFile(filename: "type.cpp", directory: "/tmp/dbginfo")
+!4 = !{}
+!5 = !{!0}
+!6 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "bar", file: !3, line: 5, size: 8, elements: !7, identifier: "_ZTS3bar")
+!7 = !{!8}
+!8 = !DIDerivedType(tag: DW_TAG_member, name: "f", scope: !6, file: !3, line: 6, baseType: !9, size: 8)
+!9 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "foo", scope: !10, file: !3, line: 2, size: 8, elements: !4, identifier: "_ZTSN2ns3fooE")
+!10 = !DINamespace(name: "ns", scope: null)
+!11 = !{i32 2, !"Dwarf Version", i32 4}
+!12 = !{i32 2, !"Debug Info Version", i32 3}
+!13 = !{!"clang version 5.0.0 (trunk 293904) (llvm/trunk 293908)"}