[asan] Enable -asan-use-private-alias on Darwin/Mach-O, add test for ODR false positive with LTO

[kubamracek]

Summary

The '-asan-use-private-alias’ option (disabled by default) option is currently only enabled for Linux and ELF, but it also works on Darwin and Mach-O. This option also fixes a known problem with LTO on Darwin (https://github.com/google/sanitizers/issues/647). This patch enables the support for Darwin (but still keeps it off by default) and adds the LTO test case.

[m.ostapenko]

I'm really glad that you found this useful! I'm not good with Darwin and Mach-OS, so could you tell me whether it has something similar to -fvisibility=hidden stuff?

[kubamracek]

In D24292#536037, @m.ostapenko wrote:

I'm really glad that you found this useful! I'm not good with Darwin and Mach-OS, so could you tell me whether it has something similar to -fvisibility=hidden stuff?

-fvisibility=hidden works on Darwin, as far as I know.

[m.ostapenko]

Ok with me, thanks! Kostya, Evgenii, do you mind?

[eugenis]

Not at all.

llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp

if (!MD.SourceLoc.empty()) {
       SourceLoc = ConstantExpr::getPointerCast(SourceLocGlobal, IntptrTy);
     } else {
       SourceLoc = ConstantInt::get(IntptrTy, 0);
     }
 
     Constant *ODRIndicator = ConstantExpr::getNullValue(IRB.getInt8PtrTy());
     GlobalValue *InstrumentedGlobal = NewGlobal;
 
-    bool CanUsePrivateAliases = TargetTriple.isOSBinFormatELF();
+    bool CanUsePrivateAliases =
+        TargetTriple.isOSBinFormatELF() || TargetTriple.isOSBinFormatMachO();
     if (CanUsePrivateAliases && ClUsePrivateAliasForGlobals) {
       // Create local alias for NewGlobal to avoid crash on ODR between
       // instrumented and non-instrumented libraries.
       auto *GA = GlobalAlias::create(GlobalValue::InternalLinkage,
                                      NameForGlobal + M.getName(), NewGlobal);
 
       // With local aliases, we need to provide another externally visible
       // symbol __odr_asan_XXX to detect ODR violation.