Support R_X86_64_PC8 and R_X86_64_PC16.

[ruiu]

Summary

We found that we need R_X86_64_PC8 and R_X86_64_PC16, so is the patch.
They are defined by the x86-64 ELF ABI standard.

[grimar]

LGTM with a nit.

lld/test/ELF/x86-64-pcrel.s

8

You want to use llvm-objdump, not GNU objdump.

lld/ELF/Arch/X86_64.cpp

case R_X86_64_TLSLD:
     return R_TLSLD_PC;
   case R_X86_64_TLSGD:
     return R_TLSGD_PC;
   case R_X86_64_SIZE32:
   case R_X86_64_SIZE64:
     return R_SIZE;
   case R_X86_64_PLT32:
     return R_PLT_PC;
+  case R_X86_64_PC8:
+  case R_X86_64_PC16:
   case R_X86_64_PC32:
   case R_X86_64_PC64:
     return R_PC;
   case R_X86_64_GOT32:
   case R_X86_64_GOT64:
     return R_GOT_FROM_END;
   case R_X86_64_GOTPCREL:
   case R_X86_64_GOTPCRELX:
void X86_64<ELFT>::relaxTlsLdToLe(uint8_t *Loc, RelType Type,
   error(getErrorLocation(Loc - 3) +
         "expected R_X86_64_PLT32 or R_X86_64_GOTPCRELX after R_X86_64_TLSLD");
 }
 
 template <class ELFT>
 void X86_64<ELFT>::relocateOne(uint8_t *Loc, RelType Type, uint64_t Val) const {
   switch (Type) {
   case R_X86_64_8:
+  case R_X86_64_PC8:
     checkUInt(Loc, Val, 8, Type);
     *Loc = Val;
     break;
   case R_X86_64_16:
+  case R_X86_64_PC16:
     checkUInt(Loc, Val, 16, Type);
     write16le(Loc, Val);
     break;
   case R_X86_64_32:
     checkUInt(Loc, Val, 32, Type);
     write32le(Loc, Val);
     break;
   case R_X86_64_32S:

lld/test/ELF/x86-64-pcrel.s

+// REQUIRES: x86
+
+// This is a test for R_X86_64_PC8 and R_X86_64_PC16.
+
+// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t1.o
+// RUN: echo '.globl foo; foo:' | llvm-mc -filetype=obj -triple=x86_64-pc-linux - -o %t2.o
+// RUN: ld.lld -o %t.exe %t1.o %t2.o
+// RUN: objdump -s %t.exe | FileCheck %s
+
+// CHECK: Contents of section .text:
+// CHECK: 2000cccc cccccccc cccccccc cccccccc
+// CHECK: 20cccccc cccccccc cccccccc cccccccc
+
+.globl _start
+_start:
+
+.word foo - _start
+.fill 14,1,0xcc
+
+.byte foo - _start
+.fill 15,1,0xcc