[clang][RISCV] Introduce command line options for RISC-V Zicfilp CFI

This patch enables the following command line flags for RISC-V targets:

+ `-fcf-protection=branch` turns on forward-edge control-flow integrity conditioning
+ `-mcf-branch-label-scheme=unlabeled|func-sig` selects the label scheme used in the forward-edge CFI conditioning

5 files changed, 92 insertions, 0 deletions

diff --git a/clang/lib/Basic/TargetInfo.cpp b/clang/lib/Basic/TargetInfo.cpp
index 29f5cd1..9219533 100644
--- a/clang/lib/Basic/TargetInfo.cpp
+++ b/clang/lib/Basic/TargetInfo.cpp
@@ -198,6 +198,22 @@ TargetInfo::checkCFProtectionBranchSupported(DiagnosticsEngine &Diags) const {
   return false;
 }
 
+CFBranchLabelSchemeKind TargetInfo::getDefaultCFBranchLabelScheme() const {
+  // if this hook is called, the target should override it to return a
+  // non-default scheme
+  llvm::report_fatal_error("not implemented");
+}
+
+bool TargetInfo::checkCFBranchLabelSchemeSupported(
+    const CFBranchLabelSchemeKind Scheme, DiagnosticsEngine &Diags) const {
+  if (Scheme != CFBranchLabelSchemeKind::Default)
+    Diags.Report(diag::err_opt_not_valid_on_target)
+        << (Twine("mcf-branch-label-scheme=") +
+            getCFBranchLabelSchemeFlagVal(Scheme))
+               .str();
+  return false;
+}
+
 bool
 TargetInfo::checkCFProtectionReturnSupported(DiagnosticsEngine &Diags) const {
   Diags.Report(diag::err_opt_not_valid_on_target) << "cf-protection=return";
diff --git a/clang/lib/Basic/Targets/RISCV.h b/clang/lib/Basic/Targets/RISCV.h
index 351ef21..bf40edb 100644
--- a/clang/lib/Basic/Targets/RISCV.h
+++ b/clang/lib/Basic/Targets/RISCV.h
@@ -134,6 +134,28 @@ public:
 
   bool validateGlobalRegisterVariable(StringRef RegName, unsigned RegSize,
                                       bool &HasSizeMismatch) const override;
+
+  bool checkCFProtectionBranchSupported(DiagnosticsEngine &) const override {
+    // Always generate Zicfilp lpad insns
+    // Non-zicfilp CPUs would read them as NOP
+    return true;
+  }
+
+  CFBranchLabelSchemeKind getDefaultCFBranchLabelScheme() const override {
+    return CFBranchLabelSchemeKind::FuncSig;
+  }
+
+  bool
+  checkCFBranchLabelSchemeSupported(const CFBranchLabelSchemeKind Scheme,
+                                    DiagnosticsEngine &Diags) const override {
+    switch (Scheme) {
+    case CFBranchLabelSchemeKind::Default:
+    case CFBranchLabelSchemeKind::Unlabeled:
+    case CFBranchLabelSchemeKind::FuncSig:
+      return true;
+    }
+    return TargetInfo::checkCFBranchLabelSchemeSupported(Scheme, Diags);
+  }
 };
 class LLVM_LIBRARY_VISIBILITY RISCV32TargetInfo : public RISCVTargetInfo {
 public:
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index d53d479..2381fa9 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -1164,6 +1164,16 @@ void CodeGenModule::Release() {
     // Indicate that we want to instrument branch control flow protection.
     getModule().addModuleFlag(llvm::Module::Min, "cf-protection-branch",
                               1);
+
+    auto Scheme = CodeGenOpts.getCFBranchLabelScheme();
+    if (Target.checkCFBranchLabelSchemeSupported(Scheme, getDiags())) {
+      if (Scheme == CFBranchLabelSchemeKind::Default)
+        Scheme = Target.getDefaultCFBranchLabelScheme();
+      getModule().addModuleFlag(
+          llvm::Module::Error, "cf-branch-label-scheme",
+          llvm::MDString::get(getLLVMContext(),
+                              getCFBranchLabelSchemeFlagVal(Scheme)));
+    }
   }
 
   if (CodeGenOpts.FunctionReturnThunks)
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index a2e403e..cbcc3b8 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -7016,6 +7016,10 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   if (Arg *A = Args.getLastArg(options::OPT_fcf_protection_EQ)) {
     CmdArgs.push_back(
         Args.MakeArgString(Twine("-fcf-protection=") + A->getValue()));
+
+    if (Arg *SA = Args.getLastArg(options::OPT_mcf_branch_label_scheme_EQ))
+      CmdArgs.push_back(Args.MakeArgString(Twine("-mcf-branch-label-scheme=") +
+                                           SA->getValue()));
   }
 
   if (Arg *A = Args.getLastArg(options::OPT_mfunction_return_EQ))
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index efd8525..6c09843 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -1688,6 +1688,18 @@ void CompilerInvocationBase::GenerateCodeGenArgs(const CodeGenOptions &Opts,
   else if (Opts.CFProtectionBranch)
     GenerateArg(Consumer, OPT_fcf_protection_EQ, "branch");
 
+  if (Opts.CFProtectionBranch) {
+    switch (Opts.getCFBranchLabelScheme()) {
+    case CFBranchLabelSchemeKind::Default:
+      break;
+#define CF_BRANCH_LABEL_SCHEME(Kind, FlagVal)                                  \
+  case CFBranchLabelSchemeKind::Kind:                                          \
+    GenerateArg(Consumer, OPT_mcf_branch_label_scheme_EQ, #FlagVal);           \
+    break;
+#include "clang/Basic/CFProtectionOptions.def"
+    }
+  }
+
   if (Opts.FunctionReturnThunks)
     GenerateArg(Consumer, OPT_mfunction_return_EQ, "thunk-extern");
 
@@ -2022,6 +2034,22 @@ bool CompilerInvocation::ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args,
       Diags.Report(diag::err_drv_invalid_value) << A->getAsString(Args) << Name;
   }
 
+  if (Opts.CFProtectionBranch && T.isRISCV()) {
+    if (const Arg *A = Args.getLastArg(OPT_mcf_branch_label_scheme_EQ)) {
+      const auto Scheme =
+          llvm::StringSwitch<CFBranchLabelSchemeKind>(A->getValue())
+#define CF_BRANCH_LABEL_SCHEME(Kind, FlagVal)                                  \
+  .Case(#FlagVal, CFBranchLabelSchemeKind::Kind)
+#include "clang/Basic/CFProtectionOptions.def"
+              .Default(CFBranchLabelSchemeKind::Default);
+      if (Scheme != CFBranchLabelSchemeKind::Default)
+        Opts.setCFBranchLabelScheme(Scheme);
+      else
+        Diags.Report(diag::err_drv_invalid_value)
+            << A->getAsString(Args) << A->getValue();
+    }
+  }
+
   if (const Arg *A = Args.getLastArg(OPT_mfunction_return_EQ)) {
     auto Val = llvm::StringSwitch<llvm::FunctionReturnThunksKind>(A->getValue())
                    .Case("keep", llvm::FunctionReturnThunksKind::Keep)
@@ -3952,6 +3980,18 @@ bool CompilerInvocation::ParseLangArgs(LangOptions &Opts, ArgList &Args,
     }
   }
 
+  if (Opts.CFProtectionBranch) {
+    if (const Arg *A = Args.getLastArg(OPT_mcf_branch_label_scheme_EQ)) {
+      const auto Scheme =
+          llvm::StringSwitch<CFBranchLabelSchemeKind>(A->getValue())
+#define CF_BRANCH_LABEL_SCHEME(Kind, FlagVal)                                  \
+  .Case(#FlagVal, CFBranchLabelSchemeKind::Kind)
+#include "clang/Basic/CFProtectionOptions.def"
+              .Default(CFBranchLabelSchemeKind::Default);
+      Opts.setCFBranchLabelScheme(Scheme);
+    }
+  }
+
   if ((Args.hasArg(OPT_fsycl_is_device) || Args.hasArg(OPT_fsycl_is_host)) &&
       !Args.hasArg(OPT_sycl_std_EQ)) {
     // If the user supplied -fsycl-is-device or -fsycl-is-host, but failed to