[PATCH] D29086: Restore visibility attribute for OpenBSD's stack guard

[Stefan Kempf via Phabricator via llvm-commits]

sisnkemp created this revision.

This diff is from Philip Guenther (guenther at openbsd.org)
and got committed to the OpenBSD tree, see http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/gnu/llvm/lib/CodeGen/TargetLoweringBase.cpp?rev=1.3&content-type=text/x-cvsweb-markup
and http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/gnu/llvm/lib/CodeGen/TargetLoweringBase.cpp.diff?r1=1.2&r2=1.3&f=h

This repairs my previous patch (https://reviews.llvm.org/rL279449) that
missed the fact that removing visibility diff results accesses to
the stack protector look like this:

two loads
=========

movq __guard_local at GOTPCREL(%rip), %rbx
movq (%rbx), %rax

But better is one load only, which is what Philip's diff achieves
movq __guard_local(%rip), %rax


https://reviews.llvm.org/D29086

Files:
  lib/CodeGen/TargetLoweringBase.cpp


Index: lib/CodeGen/TargetLoweringBase.cpp
===================================================================
--- lib/CodeGen/TargetLoweringBase.cpp
+++ lib/CodeGen/TargetLoweringBase.cpp
@@ -1873,7 +1873,10 @@
   if (getTargetMachine().getTargetTriple().isOSOpenBSD()) {
     Module &M = *IRB.GetInsertBlock()->getParent()->getParent();
     PointerType *PtrTy = Type::getInt8PtrTy(M.getContext());
-    return M.getOrInsertGlobal("__guard_local", PtrTy);
+    Constant *C = M.getOrInsertGlobal("__guard_local", PtrTy);
+    if (GlobalVariable *G = dyn_cast_or_null<GlobalVariable>(C))
+      G->setVisibility(GlobalValue::HiddenVisibility);
+    return C;
   }
   return nullptr;
 }


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