[Clang] Introduce -fcf-branch-label-scheme=unlabeled|func-sig

This flag controls the scheme of the labels of landing pad insns. Landing pad
insns are special insns that mark the targets of indirect jumps. In RISC-V
Zicfilp extension, its landing pad insn further encodes a field of `label',
which can be used to limit the sources of indirect jumps to those that set up a
matching label according to a `scheme' selected at compile time. This flag
controls the selection of that `scheme'. It's named `-fcf-branch-label-scheme`
since the generation of landing pad insns is turned on by
`-fcf-protection=branch`.

Author: mylai-mtk

clang/include/clang/Basic/CFProtectionOptions.h

@@ -0,0 +1,22 @@
+//===--- CFProtectionOptions.h ----------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file defines constants for -fcf-protection and other related flags.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_BASIC_CFPROTECTIONOPTIONS_H
+#define LLVM_CLANG_BASIC_CFPROTECTIONOPTIONS_H
+
+namespace clang {
+
+enum class CFBranchLabelSchemeKind { Default, Unlabeled, FuncSig };
+
+} // namespace clang
+
+#endif // #ifndef LLVM_CLANG_BASIC_CFPROTECTIONOPTIONS_H

clang/include/clang/Basic/CodeGenOptions.def

@@ -110,6 +110,8 @@ CODEGENOPT(CFProtectionReturn , 1, 0) ///< if -fcf-protection is
                                       ///< set to full or return.
 CODEGENOPT(CFProtectionBranch , 1, 0) ///< if -fcf-protection is
                                       ///< set to full or branch.
+ENUM_CODEGENOPT(CFBranchLabelScheme, CFBranchLabelSchemeKind, 2,
+    CFBranchLabelSchemeKind::Default) ///< if -mcf-branch-label-scheme is set.
 CODEGENOPT(FunctionReturnThunks, 1, 0) ///< -mfunction-return={keep|thunk-extern}
 CODEGENOPT(IndirectBranchCSPrefix, 1, 0) ///< if -mindirect-branch-cs-prefix
                                          ///< is set.

clang/include/clang/Basic/CodeGenOptions.h

@@ -13,6 +13,7 @@
 #ifndef LLVM_CLANG_BASIC_CODEGENOPTIONS_H
 #define LLVM_CLANG_BASIC_CODEGENOPTIONS_H
 
+#include "clang/Basic/CFProtectionOptions.h"
 #include "clang/Basic/PointerAuthOptions.h"
 #include "clang/Basic/Sanitizers.h"
 #include "clang/Basic/XRayInstr.h"

clang/include/clang/Basic/LangOptions.def

@@ -364,6 +364,8 @@ BENIGN_LANGOPT(CompatibilityQualifiedIdBlockParamTypeChecking, 1, 0,
 LANGOPT(ObjCDisableDirectMethodsForTesting, 1, 0,
         "Disable recognition of objc_direct methods")
 LANGOPT(CFProtectionBranch , 1, 0, "Control-Flow Branch Protection enabled")
+ENUM_LANGOPT(CFBranchLabelScheme, CFBranchLabelSchemeKind, 2, CFBranchLabelSchemeKind::Default,
+             "Control-Flow Branch Protection Label Scheme")
 LANGOPT(FakeAddressSpaceMap , 1, 0, "OpenCL fake address space map")
 ENUM_LANGOPT(AddressSpaceMapMangling , AddrSpaceMapMangling, 2, ASMM_Target, "OpenCL address space map mangling mode")
 LANGOPT(IncludeDefaultHeader, 1, 0, "Include default header file for OpenCL")

clang/include/clang/Basic/LangOptions.h

@@ -14,6 +14,7 @@
 #ifndef LLVM_CLANG_BASIC_LANGOPTIONS_H
 #define LLVM_CLANG_BASIC_LANGOPTIONS_H
 
+#include "clang/Basic/CFProtectionOptions.h"
 #include "clang/Basic/CommentOptions.h"
 #include "clang/Basic/LLVM.h"
 #include "clang/Basic/LangStandard.h"
@@ -73,6 +74,7 @@ class LangOptionsBase {
 public:
   using Visibility = clang::Visibility;
   using RoundingMode = llvm::RoundingMode;
+  using CFBranchLabelSchemeKind = clang::CFBranchLabelSchemeKind;
 
   enum GCMode { NonGC, GCOnly, HybridGC };
   enum StackProtectorMode { SSPOff, SSPOn, SSPStrong, SSPReq };

clang/include/clang/Basic/TargetInfo.h

@@ -16,6 +16,7 @@
 
 #include "clang/Basic/AddressSpaces.h"
 #include "clang/Basic/BitmaskEnum.h"
+#include "clang/Basic/CFProtectionOptions.h"
 #include "clang/Basic/CodeGenOptions.h"
 #include "clang/Basic/LLVM.h"
 #include "clang/Basic/LangOptions.h"
@@ -1727,6 +1728,9 @@ class TargetInfo : public TransferrableTargetInfo,
   virtual bool
   checkCFProtectionBranchSupported(DiagnosticsEngine &Diags) const;
 
+  /// Get the target default CFBranchLabelScheme scheme
+  virtual CFBranchLabelSchemeKind getDefaultCFBranchLabelScheme() const;
+
   /// Check if the target supports CFProtection return.
   virtual bool
   checkCFProtectionReturnSupported(DiagnosticsEngine &Diags) const;

clang/include/clang/Driver/Options.td

@@ -2841,6 +2841,10 @@ def fcf_protection : Flag<["-"], "fcf-protection">, Group<f_Group>,
   Visibility<[ClangOption, CLOption, CC1Option]>,
   Alias<fcf_protection_EQ>, AliasArgs<["full"]>,
   HelpText<"Enable cf-protection in 'full' mode">;
+def mcf_branch_label_scheme_EQ : Joined<["-"], "mcf-branch-label-scheme=">,
+  Visibility<[ClangOption, CC1Option]>, Group<m_Group>,
+  HelpText<"Select label scheme for branch control-flow architecture protection">,
+  Values<"unlabeled,func-sig">;
 def mfunction_return_EQ : Joined<["-"], "mfunction-return=">,
   Group<m_Group>, Visibility<[ClangOption, CLOption, CC1Option]>,
   HelpText<"Replace returns with jumps to ``__x86_return_thunk`` (x86 only, error otherwise)">,

clang/lib/Basic/TargetInfo.cpp

@@ -192,6 +192,11 @@ void TargetInfo::resetDataLayout(StringRef DL, const char *ULP) {
   UserLabelPrefix = ULP;
 }
 
+CFBranchLabelSchemeKind TargetInfo::getDefaultCFBranchLabelScheme() const {
+  // if this hook is called, the target should override it
+  llvm::report_fatal_error("not implemented");
+}
+
 bool
 TargetInfo::checkCFProtectionBranchSupported(DiagnosticsEngine &Diags) const {
   Diags.Report(diag::err_opt_not_valid_on_target) << "cf-protection=branch";

clang/lib/Basic/Targets/RISCV.h

@@ -138,6 +138,10 @@ class RISCVTargetInfo : public TargetInfo {
       return true;
     return TargetInfo::checkCFProtectionBranchSupported(Diags);
   }
+
+  CFBranchLabelSchemeKind getDefaultCFBranchLabelScheme() const override {
+    return CFBranchLabelSchemeKind::FuncSig;
+  };
 };
 class LLVM_LIBRARY_VISIBILITY RISCV32TargetInfo : public RISCVTargetInfo {
 public:

clang/lib/Basic/Targets/X86.h

@@ -273,6 +273,10 @@ class LLVM_LIBRARY_VISIBILITY X86TargetInfo : public TargetInfo {
     return TargetInfo::checkCFProtectionBranchSupported(Diags);
   };
 
+  CFBranchLabelSchemeKind getDefaultCFBranchLabelScheme() const override {
+    return CFBranchLabelSchemeKind::Unlabeled;
+  };
+
   virtual bool validateOperandSize(const llvm::StringMap<bool> &FeatureMap,
                                    StringRef Constraint, unsigned Size) const;