Implement the .reloc directive for WASM

Author: SingleAccretion

llvm/lib/MC/WasmObjectWriter.cpp

@@ -530,8 +530,11 @@ void WasmObjectWriter::recordRelocation(const MCFragment &F,
   // be negative and don't wrap.
   FixedValue = 0;
 
-  unsigned Type =
-      TargetObjectWriter->getRelocType(Target, Fixup, FixupSection, IsLocRel);
+  unsigned Type;
+  if (mc::isRelocRelocation(Fixup.getKind()))
+    Type = Fixup.getKind() - FirstLiteralRelocationKind;
+  else
+    Type = TargetObjectWriter->getRelocType(Target, Fixup, FixupSection, IsLocRel);
 
   // Absolute offset within a section or a function.
   // Currently only supported for metadata sections.

llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyAsmBackend.cpp

@@ -13,6 +13,7 @@
 
 #include "MCTargetDesc/WebAssemblyFixupKinds.h"
 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
+#include "llvm/ADT/StringSwitch.h"
 #include "llvm/MC/MCAsmBackend.h"
 #include "llvm/MC/MCAssembler.h"
 #include "llvm/MC/MCExpr.h"
@@ -36,6 +37,7 @@ class WebAssemblyAsmBackend final : public MCAsmBackend {
       : MCAsmBackend(llvm::endianness::little), Is64Bit(Is64Bit),
         IsEmscripten(IsEmscripten) {}
 
+  std::optional<MCFixupKind> getFixupKind(StringRef Name) const override;
   MCFixupKindInfo getFixupKindInfo(MCFixupKind Kind) const override;
 
   void applyFixup(const MCFragment &, const MCFixup &, const MCValue &Target,
@@ -48,6 +50,17 @@ class WebAssemblyAsmBackend final : public MCAsmBackend {
                     const MCSubtargetInfo *STI) const override;
 };
 
+std::optional<MCFixupKind> WebAssemblyAsmBackend::getFixupKind(StringRef Name) const {
+    unsigned Type = llvm::StringSwitch<unsigned>(Name)
+#define WASM_RELOC(NAME, ID) .Case(#NAME, ID)
+#include "llvm/BinaryFormat/WasmRelocs.def"
+#undef WASM_RELOC
+        .Default(-1u);
+    if (Type != -1u)
+      return static_cast<MCFixupKind>(FirstLiteralRelocationKind + Type);
+    return std::nullopt;
+}
+
 MCFixupKindInfo
 WebAssemblyAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
   const static MCFixupKindInfo Infos[WebAssembly::NumTargetFixupKinds] = {
@@ -61,6 +74,11 @@ WebAssemblyAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
       {"fixup_uleb128_i64", 0, 10 * 8, 0},
   };
 
+  // Fixup kinds from raw relocation types and .reloc directives force
+  // relocations and do not use these fields.
+  if (mc::isRelocation(Kind))
+    return MCAsmBackend::getFixupKindInfo(FK_NONE);
+
   if (Kind < FirstTargetFixupKind)
     return MCAsmBackend::getFixupKindInfo(Kind);