[PATCH] D42009: Use a got to access a hidden weak undefined on MachO

[Rafael Avila de Espindola via Phabricator via llvm-commits]

espindola created this revision.
espindola added reviewers: rnk, mehdi_amini.
Herald added a subscriber: hiraditya.

Trying to link

__attribute__((weak, visibility("hidden"))) extern int foo;
int *main(void) {

  return &foo;

}

on OS X fails with

final section layout:

  __TEXT/__text addr=0x100000FAB, size=0x0000000D, fileOffset=0x00000FAB, type=1
  __TEXT/__unwind_info addr=0x100000FB8, size=0x00000048, fileOffset=0x00000FB8, type=22

ld: 32-bit RIP relative reference out of range (-4294971318 max is +/-2GB): from _main (0x100000FAB) to _foo at 0x00001000 (0x00000000) in '_main' from test.o for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

The problem being that 0 cannot be computed as a fixed difference from %rip. Exactly the same issue exists on ELF and we can use the same solution.


https://reviews.llvm.org/D42009

Files:
  llvm/lib/Target/TargetMachine.cpp
  llvm/test/CodeGen/X86/hidden-vis-3.ll


Index: llvm/test/CodeGen/X86/hidden-vis-3.ll
===================================================================
--- llvm/test/CodeGen/X86/hidden-vis-3.ll
+++ llvm/test/CodeGen/X86/hidden-vis-3.ll
@@ -10,7 +10,7 @@
 ; X32: movl _y, %eax
 
 ; X64: _t:
-; X64: movl _y(%rip), %eax
+; X64: movq _y at GOTPCREL(%rip), %rax
 
 	%0 = load i32, i32* @x, align 4		; <i32> [#uses=1]
 	%1 = load i32, i32* @y, align 4		; <i32> [#uses=1]
Index: llvm/lib/Target/TargetMachine.cpp
===================================================================
--- llvm/lib/Target/TargetMachine.cpp
+++ llvm/lib/Target/TargetMachine.cpp
@@ -141,9 +141,7 @@
   // produce a 0 if it turns out the symbol is undefined. While this
   // is ABI and relocation depended, it seems worth it to handle it
   // here.
-  // FIXME: this is probably not ELF specific.
-  if (GV && isPositionIndependent() && TT.isOSBinFormatELF() &&
-      GV->hasExternalWeakLinkage())
+  if (GV && isPositionIndependent() && GV->hasExternalWeakLinkage())
     return false;
 
   if (GV && !GV->hasDefaultVisibility())


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