[clang] [RISCV] Implement shadow stack on shadow stack mode with Zicfiss. (PR #68075)

[Craig Topper via cfe-commits]

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@@ -106,9 +111,14 @@ static void emitSCSEpilogue(MachineFunction &MF, MachineBasicBlock &MBB,
           CSI, [&](CalleeSavedInfo &CSR) { return CSR.getReg() == RAReg; }))
     return;
 
+  const RISCVInstrInfo *TII = STI.getInstrInfo();
+  if (STI.hasFeature(RISCV::FeatureStdExtZicfiss)) {
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topperc wrote:

> > Do we need an enable other than just the feature being in -march? The shadow stack pointer has to be set up when the application starts.
> 
> The hardware shadow stack support in this pr needs `-fsanitize=shadow-call-stack` now.

What if we're compiling for a platform that only uses the software shadow stack and does not support the hardware shadow stack even if the CPU supports it?

https://github.com/llvm/llvm-project/pull/68075