[clang] [clang][X86] Only define __CET__ macro for X86 targets (PR #127616)

[Ming-Yi Lai via cfe-commits]

https://github.com/mylai-mtk created https://github.com/llvm/llvm-project/pull/127616

The `-fcf-protection` flag is now also used to enable CFI features for the RISC-V target, so it's not suitable to define `__CET__` solely based on the flag anymore. This patch moves the definition of the `__CET__` macro into X86 target hook, so only X86 targets with the `-fcf-protection` flag would enable the `__CET__` macro.

>From 348e70f60f29e7fbc0f16b0f0125853cdd832b03 Mon Sep 17 00:00:00 2001
From: Ming-Yi Lai <ming-yi.lai at mediatek.com>
Date: Tue, 18 Feb 2025 18:30:35 +0800
Subject: [PATCH] [clang][X86] Only define __CET__ macro for X86 targets

The `-fcf-protection` flag is now also used to enable CFI features for the
RISC-V target, so it's not suitable to define `__CET__` solely based on the
flag anymore. This patch moves the definition of the `__CET__` macro into X86
target hook, so only X86 targets with the `-fcf-protection` flag would enable
the `__CET__` macro.
---
 clang/lib/Basic/Targets/X86.cpp                      |  4 ++++
 clang/lib/Frontend/CompilerInvocation.cpp            | 11 -----------
 clang/test/Preprocessor/riscv-cf-protection-return.c |  2 ++
 3 files changed, 6 insertions(+), 11 deletions(-)

diff --git a/clang/lib/Basic/Targets/X86.cpp b/clang/lib/Basic/Targets/X86.cpp
index 84a05cec04e7f..e4d3ad04fe9de 100644
--- a/clang/lib/Basic/Targets/X86.cpp
+++ b/clang/lib/Basic/Targets/X86.cpp
@@ -1109,6 +1109,10 @@ void X86TargetInfo::getTargetDefines(const LangOptions &Opts,
 
   if (HasFloat128)
     Builder.defineMacro("__SIZEOF_FLOAT128__", "16");
+
+  if (Opts.CFProtectionReturn || Opts.CFProtectionBranch)
+    Builder.defineMacro("__CET__", Twine{(Opts.CFProtectionReturn << 1) |
+                                         Opts.CFProtectionBranch});
 }
 
 bool X86TargetInfo::isValidFeatureName(StringRef Name) const {
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index b9a5c0589ebc4..4eb743acf327f 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -4776,17 +4776,6 @@ static bool ParsePreprocessorArgs(PreprocessorOptions &Opts, ArgList &Args,
     }
   }
 
-  // Add the __CET__ macro if a CFProtection option is set.
-  if (const Arg *A = Args.getLastArg(OPT_fcf_protection_EQ)) {
-    StringRef Name = A->getValue();
-    if (Name == "branch")
-      Opts.addMacroDef("__CET__=1");
-    else if (Name == "return")
-      Opts.addMacroDef("__CET__=2");
-    else if (Name == "full")
-      Opts.addMacroDef("__CET__=3");
-  }
-
   // Add macros from the command line.
   for (const auto *A : Args.filtered(OPT_D, OPT_U)) {
     if (A->getOption().matches(OPT_D))
diff --git a/clang/test/Preprocessor/riscv-cf-protection-return.c b/clang/test/Preprocessor/riscv-cf-protection-return.c
index 3a93a88fa6839..a4cbaa1edf68c 100644
--- a/clang/test/Preprocessor/riscv-cf-protection-return.c
+++ b/clang/test/Preprocessor/riscv-cf-protection-return.c
@@ -40,5 +40,7 @@
 // RUN: -menable-experimental-extensions -fcf-protection=full -E -dM %s -o - \
 // RUN: | FileCheck --check-prefixes=SHSTK-MACRO %s
 
+// SHSTK-MACRO-NOT: __CET__
 // SHSTK-MACRO: __riscv_shadow_stack 1{{$}}
+// SHSTK-MACRO-NOT: __CET__
 // NO-MACRO-NOT: __riscv_shadow_stack