Android support for SafeStack.

Add two new ways of accessing the unsafe stack pointer:

* At a fixed offset from the thread TLS base. This is very similar to
  StackProtector cookies, but we plan to extend it to other backends
  (ARM in particular) soon. Bionic-side implementation here:
  https://android-review.googlesource.com/170988.
* Via a function call, as a fallback for platforms that provide
  neither a fixed TLS slot, nor a reasonable TLS implementation (i.e.
  not emutls).

This is a re-commit of a change in r248357 that was reverted in
r248358.

llvm-svn: 248405

2 files changed, 11 insertions, 1 deletions

diff --git a/llvm/include/llvm/Target/TargetLowering.h b/llvm/include/llvm/Target/TargetLowering.h
index caf28d2b118..64e0ee55030 100644
--- a/llvm/include/llvm/Target/TargetLowering.h
+++ b/llvm/include/llvm/Target/TargetLowering.h
@@ -995,6 +995,14 @@ public:
     return false;
   }
 
+  /// Return true if the target stores SafeStack pointer at a fixed offset in
+  /// some non-standard address space, and populates the address space and
+  /// offset as appropriate.
+  virtual bool getSafeStackPointerLocation(unsigned & /*AddressSpace*/,
+                                           unsigned & /*Offset*/) const {
+    return false;
+  }
+
   /// Returns true if a cast between SrcAS and DestAS is a noop.
   virtual bool isNoopAddrSpaceCast(unsigned SrcAS, unsigned DestAS) const {
     return false;
diff --git a/llvm/include/llvm/Transforms/Instrumentation.h b/llvm/include/llvm/Transforms/Instrumentation.h
index da4c0782cb9..cfe6b432895 100644
--- a/llvm/include/llvm/Transforms/Instrumentation.h
+++ b/llvm/include/llvm/Transforms/Instrumentation.h
@@ -34,6 +34,8 @@ inline void *getDFSanRetValTLSPtrForJIT() {
 
 namespace llvm {
 
+class TargetMachine;
+
 /// Instrumentation passes often insert conditional checks into entry blocks.
 /// Call this function before splitting the entry block to move instructions
 /// that must remain in the entry block up before the split point. Static
@@ -143,7 +145,7 @@ FunctionPass *createBoundsCheckingPass();
 
 /// \brief This pass splits the stack into a safe stack and an unsafe stack to
 /// protect against stack-based overflow vulnerabilities.
-FunctionPass *createSafeStackPass();
+FunctionPass *createSafeStackPass(const TargetMachine *TM = nullptr);
 
 } // End llvm namespace