[RISCV][Zicfilp] Enable Zicfilp CFI compiler behaviors by looking at module flags

llvm/include/llvm/Support/RISCVISAUtils.h

@@ -14,7 +14,9 @@
 #define LLVM_SUPPORT_RISCVISAUTILS_H
 
 #include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/StringSwitch.h"
 #include "llvm/Support/Compiler.h"
+#include <cassert>
 #include <map>
 #include <string>
 
@@ -43,6 +45,23 @@ struct ExtensionComparator {
 typedef std::map<std::string, ExtensionVersion, ExtensionComparator>
     OrderedExtensionMap;
 
+enum class ZicfilpLabelSchemeKind {
+  Invalid,
+  Unlabeled,
+  FuncSig,
+};
+
+// See clang::getCFBranchLabelSchemeFlagVal() for possible CFBranchLabelScheme
+inline ZicfilpLabelSchemeKind
+getZicfilpLabelScheme(const StringRef CFBranchLabelScheme) {
+  const auto Ret = StringSwitch<ZicfilpLabelSchemeKind>(CFBranchLabelScheme)
+                       .Case("unlabeled", ZicfilpLabelSchemeKind::Unlabeled)
+                       .Case("func-sig", ZicfilpLabelSchemeKind::FuncSig)
+                       .Default(ZicfilpLabelSchemeKind::Invalid);
+  assert(Ret != ZicfilpLabelSchemeKind::Invalid);
+  return Ret;
+}
+
 } // namespace RISCVISAUtils
 
 } // namespace llvm

llvm/lib/Target/RISCV/RISCVIndirectBranchTracking.cpp

@@ -19,11 +19,14 @@
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Support/RISCVISAUtils.h"
 
 #define DEBUG_TYPE "riscv-indrect-branch-tracking"
 #define PASS_NAME "RISC-V Indirect Branch Tracking"
 
 using namespace llvm;
+using namespace llvm::RISCVISAUtils;
 
 cl::opt<uint32_t> PreferredLandingPadLabel(
     "riscv-landing-pad-label", cl::ReallyHidden,
@@ -64,9 +67,25 @@ static void emitLpad(MachineBasicBlock &MBB, const RISCVInstrInfo *TII,
 bool RISCVIndirectBranchTracking::runOnMachineFunction(MachineFunction &MF) {
   const auto &Subtarget = MF.getSubtarget<RISCVSubtarget>();
   const RISCVInstrInfo *TII = Subtarget.getInstrInfo();
-  if (!Subtarget.hasStdExtZicfilp())
+
+  const Module *const M = MF.getFunction().getParent();
+  if (!M)
+    return false;
+  if (const Metadata *const Flag = M->getModuleFlag("cf-protection-branch");
+      !Flag || mdconst::extract<ConstantInt>(Flag)->isZero())
     return false;
 
+  StringRef CFBranchLabelScheme;
+  if (const Metadata *const MD = M->getModuleFlag("cf-branch-label-scheme"))
+    CFBranchLabelScheme = cast<MDString>(MD)->getString();
+  else
+    report_fatal_error("missing cf-branch-label-scheme module flag");
+
+  const ZicfilpLabelSchemeKind Scheme =
+      getZicfilpLabelScheme(CFBranchLabelScheme);
+  if (Scheme != ZicfilpLabelSchemeKind::Unlabeled)
+    report_fatal_error("unsupported cf-branch-label-scheme module flag");
+
   uint32_t FixedLabel = 0;
   if (PreferredLandingPadLabel.getNumOccurrences() > 0) {
     if (!isUInt<20>(PreferredLandingPadLabel))

llvm/test/CodeGen/RISCV/lpad.ll

@@ -289,3 +289,8 @@ define void @interrupt() "interrupt"="machine" {
 ; FIXED-ONE-NEXT:    mret
   ret void
 }
+
+!llvm.module.flags = !{!0, !1}
+
+!0 = !{i32 8, !"cf-protection-branch", i32 1}
+!1 = !{i32 1, !"cf-branch-label-scheme", !"unlabeled"}