[lld-macho] Support X86_64_RELOC_GOT

[int3]

Summary

As far as I can tell, it's identical to _GOT_LOAD. llvm-mc has the following
comment explaining why _GOT exists:

// x86_64 distinguishes movq foo@GOTPCREL so that the linker can
// rewrite the movq to an leaq at link time if the symbol ends up in
// the same linkage unit.

Depends on D80855.

[MaskRay]

IIUC, X86_64_RELOC_GOT is the non-relaxable form of X86_64_RELOC_GOT_LOAD. We don't relax X86_64_RELOC_GOT_LOAD currently, so the two should have same processing now.

[int3]

@MaskRay yup that's my understanding too

[smeenai]

We should add a TODO to handle linker relaxation.

[int3]

add TODO

lld/MachO/Arch/X86_64.cpp

case X86_64_RELOC_BRANCH:
     // relocation will actually be generated.
     validateLength(mb, sec, rel, {2});
     break;
   case X86_64_RELOC_SIGNED:
   case X86_64_RELOC_SIGNED_1:
   case X86_64_RELOC_SIGNED_2:
   case X86_64_RELOC_SIGNED_4:
   case X86_64_RELOC_GOT_LOAD:
+  case X86_64_RELOC_GOT:
     if (!rel.r_pcrel)
       fatal(getErrorLocation(mb, sec, rel) + ": relocations of type " +
             std::to_string(rel.r_type) + " must be pcrel");
     validateLength(mb, sec, rel, {2});
     break;
   case X86_64_RELOC_UNSIGNED:
     if (rel.r_pcrel)
       fatal(getErrorLocation(mb, sec, rel) + ": relocations of type " +

 void X86_64::relocateOne(uint8_t *loc, const Reloc &r, uint64_t val) const {
   switch (r.type) {
   case X86_64_RELOC_BRANCH:
   case X86_64_RELOC_SIGNED:
   case X86_64_RELOC_SIGNED_1:
   case X86_64_RELOC_SIGNED_2:
   case X86_64_RELOC_SIGNED_4:
   case X86_64_RELOC_GOT_LOAD:
+  case X86_64_RELOC_GOT:
     // These types are only used for pc-relative relocations, so offset by 4
     // since the RIP has advanced by 4 at this point. This is only valid when
     // r_length = 2, which is enforced by validateLength().
     val -= 4;
     break;
   case X86_64_RELOC_UNSIGNED:
     break;
   default:
void X86_64::writeStubHelperEntry(uint8_t *buf, const DylibSymbol &sym,
   write32le(buf + 1, sym.lazyBindOffset);
   writeRipRelative(buf, entryAddr, sizeof(stubHelperEntry),
                    in.stubHelper->addr);
 }
 
 void X86_64::prepareDylibSymbolRelocation(DylibSymbol &sym, uint8_t type) {
   switch (type) {
   case X86_64_RELOC_GOT_LOAD:
+    // TODO: implement mov -> lea relaxation for non-dynamic symbols
+  case X86_64_RELOC_GOT:
     in.got->addEntry(sym);
     break;
   case X86_64_RELOC_BRANCH:
     in.stubs->addEntry(sym);
     break;
-  case X86_64_RELOC_GOT:
-    fatal("TODO: Unhandled dylib symbol relocation X86_64_RELOC_GOT");
   default:
     llvm_unreachable("Unexpected dylib relocation type");
   }
 }
 
 uint64_t X86_64::getDylibSymbolVA(const DylibSymbol &sym, uint8_t type) const {
   switch (type) {
   case X86_64_RELOC_GOT_LOAD:
+  case X86_64_RELOC_GOT:
     return in.got->addr + sym.gotIndex * WordSize;
   case X86_64_RELOC_BRANCH:
     return in.stubs->addr + sym.stubsIndex * sizeof(stub);
-  case X86_64_RELOC_GOT:
-    fatal("TODO: Unhandled dylib symbol relocation X86_64_RELOC_GOT");
   default:
     llvm_unreachable("Unexpected dylib relocation type");
   }
 }
 
 X86_64::X86_64() {
   cpuType = CPU_TYPE_X86_64;
   cpuSubtype = CPU_SUBTYPE_X86_64_ALL;

lld/test/MachO/dylink.s

 # RUN: llvm-strip %t/libhello.dylib
 # RUN: llvm-strip %t/libgoodbye.dylib
 # RUN: llvm-nm %t/libhello.dylib 2>&1 | FileCheck %s --check-prefix=NOSYM
 # RUN: llvm-nm %t/libgoodbye.dylib 2>&1 | FileCheck %s --check-prefix=NOSYM
 # NOSYM: no symbols
 
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t/dylink.o
 # RUN: lld -flavor darwinnew -o %t/dylink -Z -L%t -lhello -lgoodbye %t/dylink.o
-# RUN: llvm-objdump --bind -d %t/dylink | FileCheck %s
+# RUN: llvm-objdump --bind -d --no-show-raw-insn %t/dylink | FileCheck %s
 
 # CHECK: movq [[#%u, HELLO_OFF:]](%rip), %rsi
 # CHECK-NEXT: [[#%x, HELLO_RIP:]]:
 
 # CHECK: movq [[#%u, HELLO_ITS_ME_OFF:]](%rip), %rsi
 # CHECK-NEXT: [[#%x, HELLO_ITS_ME_RIP:]]:
 
-# CHECK: movq [[#%u, GOODBYE_OFF:]](%rip), %rsi
-# CHECK-NEXT: [[#%x, GOODBYE_RIP:]]:
+# CHECK: pushq [[#%u, GOODBYE_OFF:]](%rip)
+# CHECK-NEXT: [[#%x, GOODBYE_RIP:]]: popq %rsi
 
 # CHECK-LABEL: Bind table:
 # CHECK-DAG: __DATA_CONST __got 0x{{0*}}[[#%x, HELLO_RIP + HELLO_OFF]]               pointer 0 libhello   _hello_world
 # CHECK-DAG: __DATA_CONST __got 0x{{0*}}[[#%x, HELLO_ITS_ME_RIP + HELLO_ITS_ME_OFF]] pointer 0 libhello   _hello_its_me
 # CHECK-DAG: __DATA_CONST __got 0x{{0*}}[[#%x, GOODBYE_RIP + GOODBYE_OFF]]           pointer 0 libgoodbye _goodbye_world
 
 .section __TEXT,__text
 .globl _main
 
 _main:
   movl $0x2000004, %eax # write() syscall
   mov $1, %rdi # stdout
   movq _hello_world@GOTPCREL(%rip), %rsi
   mov $13, %rdx # length of str
   syscall
 
   movl $0x2000004, %eax # write() syscall
   mov $1, %rdi # stdout
   movq _hello_its_me@GOTPCREL(%rip), %rsi
   mov $15, %rdx # length of str
   syscall
 
   movl $0x2000004, %eax # write() syscall
   mov $1, %rdi # stdout
-  movq _goodbye_world@GOTPCREL(%rip), %rsi
+  pushq _goodbye_world@GOTPCREL(%rip)
+  popq %rsi
   mov $15, %rdx # length of str
   syscall
   mov $0, %rax
   ret