[safestack] Fast access to the unsafe stack pointer on AArch64/Android.

Android libc provides a fixed TLS slot for the unsafe stack pointer,
and this change implements direct access to that slot on AArch64 via
__builtin_thread_pointer() + offset.

This change also moves more code into TargetLowering and its
target-specific subclasses to get rid of target-specific codegen
in SafeStackPass.

This change does not touch the ARM backend because ARM lowers
builting_thread_pointer as aeabi_read_tp, which is not available
on Android.

The previous iteration of this change was reverted in r250461. This
version leaves the generic, compiler-rt based implementation in
SafeStack.cpp instead of moving it to TargetLoweringBase in order to
allow testing without a TargetMachine.

llvm-svn: 251324

1 files changed, 13 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/TargetLoweringBase.cpp b/llvm/lib/CodeGen/TargetLoweringBase.cpp
index 7250fdc9385..ece2e395c3d 100644
--- a/llvm/lib/CodeGen/TargetLoweringBase.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringBase.cpp
@@ -1662,6 +1662,19 @@ TargetLoweringBase::getTypeLegalizationCost(const DataLayout &DL,
   }
 }
 
+Value *TargetLoweringBase::getSafeStackPointerLocation(IRBuilder<> &IRB) const {
+  if (!TM.getTargetTriple().isAndroid())
+    return nullptr;
+
+  // Android provides a libc function to retrieve the address of the current
+  // thread's unsafe stack pointer.
+  Module *M = IRB.GetInsertBlock()->getParent()->getParent();
+  Type *StackPtrTy = Type::getInt8PtrTy(M->getContext());
+  Value *Fn = M->getOrInsertFunction("__safestack_pointer_address",
+                                     StackPtrTy->getPointerTo(0), nullptr);
+  return IRB.CreateCall(Fn);
+}
+
 //===----------------------------------------------------------------------===//
 //  Loop Strength Reduction hooks
 //===----------------------------------------------------------------------===//