Handle undefined weak hidden symbols on all architectures

[• rafael]

Summary

We were handling the non-hidden case in lib/Target/TargetMachine.cpp, but the hidden case was handled in architecture dependent code and only X86_64 and AArch64 were covered.

While it is true that some code sequences in some ABIs might be able to produce the correct value at runtime, that doesn't seem to be the common case.

I left the AArch64 code in place since it also forces a got access for non-pic code. It is not clear if that is needed, but it is probably better to change that in another commit.

[• rafael]

ping

[rnk]

lgtm, thanks!

[• rafael]

r316799.

lib/Target/TargetMachine.cpp

   if (TT.isOSBinFormatCOFF() || (TT.isOSWindows() && TT.isOSBinFormatMachO()))
     return true;
 
+  // Most PIC code sequences that assume that a symbol is local cannot
+  // 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())
+    return false;
+
   if (GV && (GV->hasLocalLinkage() || !GV->hasDefaultVisibility()))
     return true;
 

       return true;
 
     bool IsTLS = GV && GV->isThreadLocal();
-    bool IsAccessViaCopyRelocs = Options.MCOptions.MCPIECopyRelocations && GV &&
-                                 isa<GlobalVariable>(GV) &&
-                                 !GV->hasExternalWeakLinkage();
+    bool IsAccessViaCopyRelocs =
+        Options.MCOptions.MCPIECopyRelocations && GV && isa<GlobalVariable>(GV);
     Triple::ArchType Arch = TT.getArch();
     bool IsPPC =
         Arch == Triple::ppc || Arch == Triple::ppc64 || Arch == Triple::ppc64le;

lib/Target/X86/X86Subtarget.cpp

   return X86II::MO_GOTOFF;
 }
 
-static bool shouldAssumeGlobalReferenceLocal(const X86Subtarget *ST,
-                                             const TargetMachine &TM,
-                                             const Module &M,
-                                             const GlobalValue *GV) {
-  if (!TM.shouldAssumeDSOLocal(M, GV))
-    return false;
-  // A weak reference can end up being 0. If the code can be more that 4g away
-  // from zero and we are using the small code model we have to treat it as non
-  // local.
-  if (GV && GV->hasExternalWeakLinkage() &&
-      TM.getCodeModel() == CodeModel::Small && TM.isPositionIndependent() &&
-      ST->is64Bit() && ST->isTargetELF())
-    return false;
-  return true;
-}
-
 unsigned char X86Subtarget::classifyGlobalReference(const GlobalValue *GV,
                                                     const Module &M) const {
   // Large model never uses stubs.

     }
   }
 
-  if (shouldAssumeGlobalReferenceLocal(this, TM, M, GV))
+  if (TM.shouldAssumeDSOLocal(M, GV))
     return classifyLocalReference(GV);
 
   if (isTargetCOFF())

test/CodeGen/X86/global-access-pie-copyrelocs.ll

   ret i32* @e
 }
 
+; ExternalWeak hidden Linkage
+@he = extern_weak hidden global i32, align 4
+
+define i32* @my_access_global_he() #0 {
+; X32-LABEL: my_access_global_he:
+; X32:       addl $_GLOBAL_OFFSET_TABLE_{{.*}}, %eax
+; X32:       movl he@GOT(%eax), %eax
+; X64-LABEL: my_access_global_he:
+; X64:       movq he@GOTPCREL(%rip), %rax
+  ret i32* @he
+}
+
+
 ; External Linkage, only declaration, store a value.
 
 define i32 @my_access_global_store_d() #0 {

test/CodeGen/X86/weak-undef.ll

 ; CHECK: bar1:
 ; CHECK: movq foo1@GOTPCREL(%rip), %rax
 ; I386: bar1:
-; I386: leal foo1@GOTOFF(%eax), %eax
+; I386: movl foo1@GOT(%eax), %eax
 
 @foo2 = external hidden global i32, align 4
 define i32* @bar2() {

 ; CHECK: bar5:
 ; CHECK: movq foo5@GOTPCREL(%rip), %rax
 ; I386: bar5:
-; I386: leal foo5@GOTOFF(%eax), %eax
+; I386: movl foo5@GOT(%eax), %eax
 
 declare external hidden i32 @foo6()
 define i32()* @bar6() {