[PATCH] D17736: [SSP, 1/2] Refactor to support customizable stack guard load from IR level.

[Tim Shen via llvm-commits]

timshen updated this revision to Diff 49788.
timshen added a comment.

tl;dr: because we have a million code paths. :)

The customization point in backends is the opcode LOAD_STACK_GUARD. It already exists for other reasons, but suitable for our purpose.

Previously we have two code paths to handle SSP, SelectionDAG path and IR path.

To customize stack guard loading in IR SSP, we need llvm.stackguardvalue. It lowers to LOAD_STACK_GUARD directly.

To customize stack guard loading in SelectionDAG, llvm.stackprotectorcheck has to take a value, so it doesn't have to be an address (e.g. could be a llvm.stackguardvalue call). To not break existing user code (it's documented) and tests, I created llvm.stackprotectorcheckvalue instead. llvm.stackprotectorcheck is not generated by LLVM anymore. See http://lists.llvm.org/pipermail/llvm-dev/2016-February/095760.html. We may want to delete llvm.stackprotectorcheck?

I haven't push all generic stack guard loading (typically loading the global variable __stack_chk_guard) to the backends. Once we push them all down, we can remove target-independent code path that deals with global variables. But we still need these two intrinsics for supporting both SelectionDAG and IR approach.

I added some comments for these two intrinsics.


http://reviews.llvm.org/D17736

Files:
  include/llvm/IR/Intrinsics.td
  include/llvm/Target/TargetLowering.h
  lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
  lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
  lib/CodeGen/StackProtector.cpp
  lib/CodeGen/TargetLoweringBase.cpp
  lib/Target/X86/X86ISelLowering.cpp
  lib/Target/X86/X86ISelLowering.h

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