Support -fstack-clash-protection for x86

Implement protection against the stack clash attack [0] through inline stack
probing.

Probe stack allocation every PAGE_SIZE during frame lowering or dynamic
allocation to make sure the page guard, if any, is touched when touching the
stack, in a similar manner to GCC[1].

This extends the existing `probe-stack' mechanism with a special value `inline-asm'.
Technically the former uses function call before stack allocation while this
patch provides inlined stack probes and chunk allocation.

Only implemented for x86.

[0] https://www.qualys.com/2017/06/19/stack-clash/stack-clash.txt
[1] https://gcc.gnu.org/ml/gcc-patches/2017-07/msg00556.html

This a recommit of 39f50da2a357a8f685b3540246c5d762734e035f with proper LiveIn
declaration, better option handling and more portable testing.

Differential Revision: https://reviews.llvm.org/D68720

1 files changed, 2 insertions, 3 deletions

diff --git a/llvm/lib/Target/X86/X86CallFrameOptimization.cpp b/llvm/lib/Target/X86/X86CallFrameOptimization.cpp
index f8faa57..467d243 100644
--- a/llvm/lib/Target/X86/X86CallFrameOptimization.cpp
+++ b/llvm/lib/Target/X86/X86CallFrameOptimization.cpp
@@ -162,14 +162,13 @@ bool X86CallFrameOptimization::isLegal(MachineFunction &MF) {
   // memory for arguments.
   unsigned FrameSetupOpcode = TII->getCallFrameSetupOpcode();
   unsigned FrameDestroyOpcode = TII->getCallFrameDestroyOpcode();
-  bool UseStackProbe =
-      !STI->getTargetLowering()->getStackProbeSymbolName(MF).empty();
+  bool EmitStackProbeCall = STI->getTargetLowering()->hasStackProbeSymbol(MF);
   unsigned StackProbeSize = STI->getTargetLowering()->getStackProbeSize(MF);
   for (MachineBasicBlock &BB : MF) {
     bool InsideFrameSequence = false;
     for (MachineInstr &MI : BB) {
       if (MI.getOpcode() == FrameSetupOpcode) {
-        if (TII->getFrameSize(MI) >= StackProbeSize && UseStackProbe)
+        if (TII->getFrameSize(MI) >= StackProbeSize && EmitStackProbeCall)
           return false;
         if (InsideFrameSequence)
           return false;