[MC][X86] Make .reloc support arbitrary relocation types

Generalizes D62014 (R_386_NONE/R_X86_64_NONE).

Unlike ARM (D76746) and AArch64 (D76754), we cannot delete FK_NONE from
getFixupKindSize because FK_NONE is still used by R_386_TLS_DESC_CALL/R_X86_64_TLSDESC_CALL.

llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp

@@ -646,13 +646,23 @@ void X86AsmBackend::emitInstructionEnd(MCObjectStreamer &OS, const MCInst &Inst)
 
 Optional<MCFixupKind> X86AsmBackend::getFixupKind(StringRef Name) const {
   if (STI.getTargetTriple().isOSBinFormatELF()) {
+    unsigned Type;
     if (STI.getTargetTriple().getArch() == Triple::x86_64) {
-      if (Name == "R_X86_64_NONE")
-        return FK_NONE;
+      Type = llvm::StringSwitch<unsigned>(Name)
+#define ELF_RELOC(X, Y) .Case(#X, Y)
+#include "llvm/BinaryFormat/ELFRelocs/x86_64.def"
+#undef ELF_RELOC
+                 .Default(-1u);
     } else {
-      if (Name == "R_386_NONE")
-        return FK_NONE;
+      Type = llvm::StringSwitch<unsigned>(Name)
+#define ELF_RELOC(X, Y) .Case(#X, Y)
+#include "llvm/BinaryFormat/ELFRelocs/i386.def"
+#undef ELF_RELOC
+                 .Default(-1u);
     }
+    if (Type == -1u)
+      return None;
+    return static_cast<MCFixupKind>(FirstLiteralRelocationKind + Type);
   }
   return MCAsmBackend::getFixupKind(Name);
 }
@@ -670,6 +680,11 @@ const MCFixupKindInfo &X86AsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
       {"reloc_branch_4byte_pcrel", 0, 32, MCFixupKindInfo::FKF_IsPCRel},
   };
 
+  // Fixup kinds from .reloc directive are like R_386_NONE/R_X86_64_NONE. They
+  // do not require any extra processing.
+  if (Kind >= FirstLiteralRelocationKind)
+    return MCAsmBackend::getFixupKindInfo(FK_NONE);
+
   if (Kind < FirstTargetFixupKind)
     return MCAsmBackend::getFixupKindInfo(Kind);
 
@@ -682,7 +697,7 @@ const MCFixupKindInfo &X86AsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
 bool X86AsmBackend::shouldForceRelocation(const MCAssembler &,
                                           const MCFixup &Fixup,
                                           const MCValue &) {
-  return Fixup.getKind() == FK_NONE;
+  return Fixup.getKind() >= FirstLiteralRelocationKind;
 }
 
 static unsigned getFixupKindSize(unsigned Kind) {
@@ -724,7 +739,10 @@ void X86AsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
                                MutableArrayRef<char> Data,
                                uint64_t Value, bool IsResolved,
                                const MCSubtargetInfo *STI) const {
-  unsigned Size = getFixupKindSize(Fixup.getKind());
+  unsigned Kind = Fixup.getKind();
+  if (Kind >= FirstLiteralRelocationKind)
+    return;
+  unsigned Size = getFixupKindSize(Kind);
 
   assert(Fixup.getOffset() + Size <= Data.size() && "Invalid fixup offset!");
 

llvm/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp

@@ -317,8 +317,10 @@ static unsigned getRelocType32(MCContext &Ctx,
 unsigned X86ELFObjectWriter::getRelocType(MCContext &Ctx, const MCValue &Target,
                                           const MCFixup &Fixup,
                                           bool IsPCRel) const {
-  MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
   MCFixupKind Kind = Fixup.getKind();
+  if (Kind >= FirstLiteralRelocationKind)
+    return Kind - FirstLiteralRelocationKind;
+  MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
   X86_64RelType Type = getType64(Kind, Modifier, IsPCRel);
   if (getEMachine() == ELF::EM_X86_64)
     return getRelocType64(Ctx, Fixup.getLoc(), Modifier, Type, IsPCRel, Kind);

llvm/test/MC/X86/reloc-directive-elf-32.s

@@ -7,12 +7,18 @@
 # PRINT:      .reloc 2, R_386_NONE, .data
 # PRINT-NEXT: .reloc 1, R_386_NONE, foo+4
 # PRINT-NEXT: .reloc 0, R_386_NONE, 8
+# PRINT-NEXT: .reloc 0, R_386_32, .data+2
+# PRINT-NEXT: .reloc 0, R_386_IRELATIVE, foo+3
+# PRINT-NEXT: .reloc 0, R_386_GOT32X, 5
 
 # X86 relocations use the Elf32_Rel format. Addends are neither stored in the
 # relocation entries nor applied in the referenced locations.
 # CHECK:      0x2 R_386_NONE .data 0x0
 # CHECK-NEXT: 0x1 R_386_NONE foo 0x0
 # CHECK-NEXT: 0x0 R_386_NONE - 0x0
+# CHECK-NEXT: 0x0 R_386_32 .data 0x0
+# CHECK-NEXT: 0x0 R_386_IRELATIVE foo 0x0
+# CHECK-NEXT: 0x0 R_386_GOT32X - 0x0
 
 # HEX: 0x00000000 00000000 00000000
 
@@ -23,6 +29,9 @@
   .reloc 2, R_386_NONE, .data
   .reloc 1, R_386_NONE, foo+4
   .reloc 0, R_386_NONE, 8
+  .reloc 0, R_386_32, .data+2
+  .reloc 0, R_386_IRELATIVE, foo+3
+  .reloc 0, R_386_GOT32X, 5
 
 .data
 .globl foo

llvm/test/MC/X86/reloc-directive-elf-64.s

@@ -6,10 +6,16 @@
 # PRINT:      .reloc 2, R_X86_64_NONE, .data
 # PRINT-NEXT: .reloc 1, R_X86_64_NONE, foo+4
 # PRINT-NEXT: .reloc 0, R_X86_64_NONE, 8
+# PRINT-NEXT: .reloc 0, R_X86_64_64, .data+2
+# PRINT-NEXT: .reloc 0, R_X86_64_GOTPCRELX, foo+3
+# PRINT-NEXT: .reloc 0, R_X86_64_REX_GOTPCRELX, 5
 
 # CHECK:      0x2 R_X86_64_NONE .data 0x0
 # CHECK-NEXT: 0x1 R_X86_64_NONE foo 0x4
 # CHECK-NEXT: 0x0 R_X86_64_NONE - 0x8
+# CHECK-NEXT: 0x0 R_X86_64_64 .data 0x2
+# CHECK-NEXT: 0x0 R_X86_64_GOTPCRELX foo 0x3
+# CHECK-NEXT: 0x0 R_X86_64_REX_GOTPCRELX - 0x5
 
 .text
   ret
@@ -18,6 +24,9 @@
   .reloc 2, R_X86_64_NONE, .data
   .reloc 1, R_X86_64_NONE, foo+4
   .reloc 0, R_X86_64_NONE, 8
+  .reloc 0, R_X86_64_64, .data+2
+  .reloc 0, R_X86_64_GOTPCRELX, foo+3
+  .reloc 0, R_X86_64_REX_GOTPCRELX, 5
 
 .data
 .globl foo