PPC64: Constant initializers with dynamic relocations go in .data.rel.ro.

[oota-llvm.git] / lib / Target / PowerPC / PPCTargetObjectFile.cpp

diff --git a/lib/Target/PowerPC/PPCTargetObjectFile.cpp b/lib/Target/PowerPC/PPCTargetObjectFile.cpp
new file mode 100644 (file)
index 0000000..b374b59
--- /dev/null
+++ b/lib/Target/PowerPC/PPCTargetObjectFile.cpp
@@ -0,0 +1,57 @@
+//===-- PPCTargetObjectFile.cpp - PPC Object Info -------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "PPCTargetObjectFile.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCExpr.h"
+#include "llvm/MC/MCSectionELF.h"
+#include "llvm/Target/Mangler.h"
+
+using namespace llvm;
+
+void
+PPC64LinuxTargetObjectFile::
+Initialize(MCContext &Ctx, const TargetMachine &TM) {
+  TargetLoweringObjectFileELF::Initialize(Ctx, TM);
+  InitializeELF(TM.Options.UseInitArray);
+}
+
+const MCSection * PPC64LinuxTargetObjectFile::
+SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
+                       Mangler *Mang, const TargetMachine &TM) const {
+
+  const MCSection *DefaultSection = 
+    TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind, Mang, TM);
+
+  if (DefaultSection != ReadOnlySection)
+    return DefaultSection;
+
+  // Here override isReadOnly() to isReadOnlyWithRel() for PPC64 SVR4 ABI
+  // when we have a constant that contains global relocations.  This is
+  // necessary because of this ABI's handling of pointers to functions in
+  // a shared library.  The address of a function is actually the address
+  // of a function descriptor, which resides in the .opd section.  Generated
+  // code uses the descriptor directly rather than going via the GOT as some
+  // other ABIs do, which means that initialized function pointers must
+  // reference the descriptor.  The linker must convert copy relocs of
+  // pointers to functions in shared libraries into dynamic relocations,
+  // because of an ordering problem with initialization of copy relocs and
+  // PLT entries.  The dynamic relocation will be initialized by the dynamic
+  // linker, so we must use the DataRelRO section instead of ReadOnlySection.
+  // For more information, see the description of ELIMINATE_COPY_RELOCS in
+  // GNU ld.
+  const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
+
+  if (GVar && GVar->isConstant() &&
+      (GVar->getInitializer()->getRelocationInfo() ==
+       Constant::GlobalRelocations))
+    return DataRelROSection;
+
+  return DefaultSection;
+}