[WIP] Always create a MCFragment for Mach-O section.

[JDevlieghere]

Summary

https://bugs.llvm.org/show_bug.cgi?id=38190

[dblaikie]

llvm/lib/MC/MCObjectFileInfo.cpp

955–957

How does this section get deduplicated by the linker? (I don't see the 'Hash' being used here, which is the unique key for the section)

960–964

Similarly here..

969

I assume this is incorrect (given that this function is for the debug_types section (& should be comdat or equivalent) rather than debug_info)?

[JDevlieghere]

llvm/lib/MC/MCObjectFileInfo.cpp

955–957

I can only speak for Darwin, but the linker just ignores debug info. We have dsymutil for deduplication.

969

Yup, this is a typo

[dblaikie]

Posted to the bug with some questions about this direction - or happy to have the conversation here instead.

[JDevlieghere]

The consensus is that we won't support this, at least for now.

llvm/lib/MC/MCContext.cpp

MCSectionMachO *MCContext::getMachOSection(StringRef Segment, StringRef Section,
   if (Entry)
     return Entry;
 
   MCSymbol *Begin = nullptr;
   if (BeginSymName)
     Begin = createTempSymbol(BeginSymName, false);
 
   // Otherwise, return a new section.
-  return Entry = new (MachOAllocator.Allocate()) MCSectionMachO(
+  auto Result = new (MachOAllocator.Allocate()) MCSectionMachO(
              Segment, Section, TypeAndAttributes, Reserved2, Kind, Begin);
+
+  auto *F = new MCDataFragment();
+  Result->getFragmentList().insert(Result->begin(), F);
+  F->setParent(Result);
+  if (Begin)
+    Begin->setFragment(F);
+
+  return Result;
 }
 
 void MCContext::renameELFSection(MCSectionELF *Section, StringRef Name) {
   StringRef GroupName;
   if (const MCSymbol *Group = Section->getGroup())
     GroupName = Group->getName();
 
   unsigned UniqueID = Section->getUniqueID();

llvm/lib/MC/MCObjectFileInfo.cpp

case Triple::Wasm:
     break;
   case Triple::UnknownObjectFormat:
     report_fatal_error("Cannot initialize MC for unknown object file format.");
     break;
   }
 }
 
 MCSection *MCObjectFileInfo::getDwarfTypesSection(uint64_t Hash) const {
+  switch (TT.getObjectFormat()) {
+  case Triple::MachO:
+    return Ctx->getMachOSection("__DWARF", "__debug_types", MachO::S_ATTR_DEBUG,
+                                SectionKind::getMetadata(),
+                                "debug_types_begin");
+  case Triple::COFF:
+
+    return Ctx->getCOFFSection(".debug_types",
+                               COFF::IMAGE_SCN_MEM_DISCARDABLE |
+                                   COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
+                                   COFF::IMAGE_SCN_MEM_READ,
+                               SectionKind::getMetadata(), "debug_types");
+  case Triple::ELF:
     return Ctx->getELFSection(".debug_types", ELF::SHT_PROGBITS, ELF::SHF_GROUP,
                               0, utostr(Hash));
+  case Triple::Wasm:
+    return Ctx->getWasmSection(".debug_info", SectionKind::getMetadata());
+  case Triple::UnknownObjectFormat:
+    report_fatal_error("DWARF types section for unknown object file format.");
+    break;
+  }
 }
 
 MCSection *
 MCObjectFileInfo::getStackSizesSection(const MCSection &TextSec) const {
   if (Env != IsELF)
     return StackSizesSection;
 
   const MCSectionELF &ElfSec = static_cast<const MCSectionELF &>(TextSec);