[X86] Support modifier @PLTOFF for R_X86_64_PLTOFF64

[MaskRay]

Summary

gcc -mcmodel=large can emit @PLTOFF.

[grimar]

LGTM

llvm/include/llvm/MC/MCExpr.h

enum VariantKind : uint16_t {
     VK_PAGEOFF,
     VK_GOTPAGE,
     VK_GOTPAGEOFF,
     VK_SECREL,
     VK_SIZE,    // symbol@SIZE
     VK_WEAKREF, // The link between the symbols in .weakref foo, bar
 
     VK_X86_ABS8,
+    VK_X86_PLTOFF,
 
     VK_ARM_NONE,
     VK_ARM_GOT_PREL,
     VK_ARM_TARGET1,
     VK_ARM_TARGET2,
     VK_ARM_PREL31,
     VK_ARM_SBREL,  // symbol(sbrel)
     VK_ARM_TLSLDO, // symbol(tlsldo)

llvm/lib/MC/MCExpr.cpp

StringRef MCSymbolRefExpr::getVariantKindName(VariantKind Kind) {
   case VK_PAGE: return "PAGE";
   case VK_PAGEOFF: return "PAGEOFF";
   case VK_GOTPAGE: return "GOTPAGE";
   case VK_GOTPAGEOFF: return "GOTPAGEOFF";
   case VK_SECREL: return "SECREL32";
   case VK_SIZE: return "SIZE";
   case VK_WEAKREF: return "WEAKREF";
   case VK_X86_ABS8: return "ABS8";
+  case VK_X86_PLTOFF: return "PLTOFF";
   case VK_ARM_NONE: return "none";
   case VK_ARM_GOT_PREL: return "GOT_PREL";
   case VK_ARM_TARGET1: return "target1";
   case VK_ARM_TARGET2: return "target2";
   case VK_ARM_PREL31: return "prel31";
   case VK_ARM_SBREL: return "sbrel";
   case VK_ARM_TLSLDO: return "tlsldo";
   case VK_ARM_TLSDESCSEQ: return "tlsdescseq";
return StringSwitch<VariantKind>(Name.lower())
     .Case("page", VK_PAGE)
     .Case("pageoff", VK_PAGEOFF)
     .Case("gotpage", VK_GOTPAGE)
     .Case("gotpageoff", VK_GOTPAGEOFF)
     .Case("imgrel", VK_COFF_IMGREL32)
     .Case("secrel32", VK_SECREL)
     .Case("size", VK_SIZE)
     .Case("abs8", VK_X86_ABS8)
+    .Case("pltoff", VK_X86_PLTOFF)
     .Case("l", VK_PPC_LO)
     .Case("h", VK_PPC_HI)
     .Case("ha", VK_PPC_HA)
     .Case("high", VK_PPC_HIGH)
     .Case("higha", VK_PPC_HIGHA)
     .Case("higher", VK_PPC_HIGHER)
     .Case("highera", VK_PPC_HIGHERA)
     .Case("highest", VK_PPC_HIGHEST)

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

 }
 
 static void checkIs32(MCContext &Ctx, SMLoc Loc, X86_64RelType Type) {
   if (Type != RT64_32)
     Ctx.reportError(Loc,
                     "32 bit reloc applied to a field with a different size");
 }
 
+static void checkIs64(MCContext &Ctx, SMLoc Loc, X86_64RelType Type) {
+  if (Type != RT64_64)
+    Ctx.reportError(Loc,
+                    "64 bit reloc applied to a field with a different size");
+}
+
 static unsigned getRelocType64(MCContext &Ctx, SMLoc Loc,
                                MCSymbolRefExpr::VariantKind Modifier,
                                X86_64RelType Type, bool IsPCRel,
                                MCFixupKind Kind) {
   switch (Modifier) {
   default:
     llvm_unreachable("Unimplemented");
   case MCSymbolRefExpr::VK_None:
default:
       return ELF::R_X86_64_GOTPCREL;
     case X86::reloc_riprel_4byte_relax:
       return ELF::R_X86_64_GOTPCRELX;
     case X86::reloc_riprel_4byte_relax_rex:
     case X86::reloc_riprel_4byte_movq_load:
       return ELF::R_X86_64_REX_GOTPCRELX;
     }
     llvm_unreachable("unexpected relocation type!");
+  case MCSymbolRefExpr::VK_X86_PLTOFF:
+    checkIs64(Ctx, Loc, Type);
+    return ELF::R_X86_64_PLTOFF64;
   }
 }
 
 enum X86_32RelType { RT32_NONE, RT32_32, RT32_16, RT32_8 };
 
 static X86_32RelType getType32(X86_64RelType T) {
   switch (T) {
   case RT64_NONE:

llvm/test/MC/X86/pltoff.s

+# RUN: llvm-mc -triple=x86_64 %s | FileCheck %s --check-prefix=ASM
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %s -o %t
+# RUN: llvm-objdump -d -r %t | FileCheck %s --check-prefix=OBJ
+
+# RUN: not llvm-mc -filetype=obj -triple=x86_64 --defsym ERR=1 %s -o /dev/null 2>&1 | FileCheck %s --check-prefix=ERR
+
+# ASM:      movabsq $puts@PLTOFF, %rax
+# OBJ:      movabsq $0, %rax
+# OBJ-NEXT:   0000000000000002: R_X86_64_PLTOFF64 puts{{$}}
+
+movabsq $puts@PLTOFF, %rax
+
+.ifdef ERR
+# ERR: {{.*}}.s:[[#@LINE+1]]:1: error: 64 bit reloc applied to a field with a different size
+movl $puts@PLTOFF, %eax
+.endif