[RISCV] Separate HW/SW shadow stack on RISC-V (#112478)

This patch follows #112477.
Previously `-fsanitize=shadow-call-stack` (which get transform to
`Attribute::ShadowCallStack`) is used for enable both hardware and
software shadow stack, and another option `-force-sw-shadow-stack` is
needed if the user wants to use the software shadow stack where hardware
software shadow stack could be supported. It decouples both by using the
string attribute `hw-shadow-stack` to distinguish from the software
shadow stack attribute.

Author: jaidTw

llvm/lib/Target/RISCV/RISCVFrameLowering.cpp

@@ -67,10 +67,14 @@ static const std::pair<MCPhysReg, int8_t> FixedCSRFIMap[] = {
 static void emitSCSPrologue(MachineFunction &MF, MachineBasicBlock &MBB,
                             MachineBasicBlock::iterator MI,
                             const DebugLoc &DL) {
-  if (!MF.getFunction().hasFnAttribute(Attribute::ShadowCallStack))
+  const auto &STI = MF.getSubtarget<RISCVSubtarget>();
+  bool HasHWShadowStack = MF.getFunction().hasFnAttribute("hw-shadow-stack") &&
+                          STI.hasStdExtZicfiss();
+  bool HasSWShadowStack =
+      MF.getFunction().hasFnAttribute(Attribute::ShadowCallStack);
+  if (!HasHWShadowStack && !HasSWShadowStack)
     return;
 
-  const auto &STI = MF.getSubtarget<RISCVSubtarget>();
   const llvm::RISCVRegisterInfo *TRI = STI.getRegisterInfo();
   Register RAReg = TRI->getRARegister();
 
@@ -82,7 +86,7 @@ static void emitSCSPrologue(MachineFunction &MF, MachineBasicBlock &MBB,
     return;
 
   const RISCVInstrInfo *TII = STI.getInstrInfo();
-  if (!STI.hasForcedSWShadowStack() && STI.hasStdExtZicfiss()) {
+  if (HasHWShadowStack) {
     BuildMI(MBB, MI, DL, TII->get(RISCV::SSPUSH)).addReg(RAReg);
     return;
   }
@@ -129,10 +133,14 @@ static void emitSCSPrologue(MachineFunction &MF, MachineBasicBlock &MBB,
 static void emitSCSEpilogue(MachineFunction &MF, MachineBasicBlock &MBB,
                             MachineBasicBlock::iterator MI,
                             const DebugLoc &DL) {
-  if (!MF.getFunction().hasFnAttribute(Attribute::ShadowCallStack))
+  const auto &STI = MF.getSubtarget<RISCVSubtarget>();
+  bool HasHWShadowStack = MF.getFunction().hasFnAttribute("hw-shadow-stack") &&
+                          STI.hasStdExtZicfiss();
+  bool HasSWShadowStack =
+      MF.getFunction().hasFnAttribute(Attribute::ShadowCallStack);
+  if (!HasHWShadowStack && !HasSWShadowStack)
     return;
 
-  const auto &STI = MF.getSubtarget<RISCVSubtarget>();
   Register RAReg = STI.getRegisterInfo()->getRARegister();
 
   // See emitSCSPrologue() above.
@@ -142,7 +150,7 @@ static void emitSCSEpilogue(MachineFunction &MF, MachineBasicBlock &MBB,
     return;
 
   const RISCVInstrInfo *TII = STI.getInstrInfo();
-  if (!STI.hasForcedSWShadowStack() && STI.hasStdExtZicfiss()) {
+  if (HasHWShadowStack) {
     BuildMI(MBB, MI, DL, TII->get(RISCV::SSPOPCHK)).addReg(RAReg);
     return;
   }