In my previous post, LLVMintegrated assembler: Improving expressions and relocations delvedinto enhancements made to LLVM's expression resolving and relocationgeneration. This post covers recent refinements to MC, focusing onsections and symbols.

Sections

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class MCSection {
...
  enum SectionVariant {
    SV_COFF = 0,
    SV_ELF,
    SV_GOFF,
    SV_MachO,
    SV_Wasm,
    SV_XCOFF,
    SV_SPIRV,
    SV_DXContainer,
  };

Previously, the MCSection class used an enum calledSectionVariant to differentiate between various object fileformats, such as ELF, Mach-O, and COFF. These subclasses are used incontexts where the section type is known at compile-time, such as inMCStreamer and MCObjectTargetWriter. Thischange eliminates the need for runtime type information (RTTI) checks,simplifying the codebase and improving efficiency.

Additionally, the storage for fragments' fixups (adjustments toaddresses and offsets) has been moved into the MCSectionclass.

Symbols

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class MCSymbol {
protected:
  /// The kind of the symbol.  If it is any value other than unset then this
  /// class is actually one of the appropriate subclasses of MCSymbol.
  enum SymbolKind {
    SymbolKindUnset,
    SymbolKindCOFF,
    SymbolKindELF,
    SymbolKindGOFF,
    SymbolKindMachO,
    SymbolKindWasm,
    SymbolKindXCOFF,
  };

  /// A symbol can contain an Offset, or Value, or be Common, but never more
  /// than one of these.
  enum Contents : uint8_t {
    SymContentsUnset,
    SymContentsOffset,
    SymContentsVariable,
    SymContentsCommon,
    SymContentsTargetCommon, // Index stores the section index
  };

Similar to sections, the MCSymbol class also used adiscriminator enum, SymbolKind, to distinguish between object fileformats. This enum has also been removed.

Furthermore, the MCSymbol class had anenum Contents to specify the kind of symbol. This name wasa bit confusing, so it has been renamed to enum Kind forclarity.

• regular symbol
• equated symbol
• common symbol

A special enumerator, SymContentsTargetCommon, which wasused by AMDGPU for a specific type of common symbol, has also beenremoved. The functionality it provided is now handled by updatingELFObjectWriter to respect the symbol's section index(SHN_AMDGPU_LDS for this special AMDGPU symbol).

The previous blog post LLVMintegrated assembler: Improving expressions and relocationsdescribes other changes:

• The MCSymbol::IsUsed flag was a workaround fordetecting a subset of invalid reassignments and is removed.
• The MCSymbol::IsResolving flag is added to detectcyclic dependencies of equated symbols.