[clang] [RISCV][clang] Use fcf-protection flag in Multilib Selection (PR #205202)

[Sam Elliott via cfe-commits]

https://github.com/lenary created https://github.com/llvm/llvm-project/pull/205202

This ensures that we can separate out multilibs that are or are not built with control flow protection enabled.

The initial version of the patch claims all values of these flags are incompatible. It might be the case that we could make this logic more complex if some versions do become compatible.

>From af9e7108c19f4580c009125a420e644be9ffe01d Mon Sep 17 00:00:00 2001
From: Sam Elliott <aelliott at qti.qualcomm.com>
Date: Mon, 22 Jun 2026 14:45:24 -0700
Subject: [PATCH] [RISCV][clang] Use fcf-protection flag in Multilib Selection

This ensures that we can separate out multilibs that are or are not
built with control flow protection enabled.

The initial version of the patch claims all values of these flags are
incompatible. It might be the case that we could make this logic more
complex if some versions do become compatible.
---
 clang/lib/Driver/ToolChain.cpp                  | 12 ++++++++++++
 clang/test/Driver/print-multi-selection-flags.c | 13 +++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/clang/lib/Driver/ToolChain.cpp b/clang/lib/Driver/ToolChain.cpp
index 7d93e7f65daf5..328f4f8c8f420 100644
--- a/clang/lib/Driver/ToolChain.cpp
+++ b/clang/lib/Driver/ToolChain.cpp
@@ -445,6 +445,18 @@ static void getRISCVMultilibFlags(const Driver &D, const llvm::Triple &Triple,
     Result.push_back("-fsanitize=shadow-call-stack");
   else
     Result.push_back("-fno-sanitize=shadow-call-stack");
+
+  const Arg *CFProtectionArg =
+      Args.getLastArgNoClaim(options::OPT_fcf_protection_EQ);
+  StringRef CFProtectionVal =
+      CFProtectionArg ? CFProtectionArg->getValue() : "none";
+  Result.push_back(("-fcf-protection=" + CFProtectionVal).str());
+
+  if (CFProtectionVal == "branch" || CFProtectionVal == "full") {
+    if (const Arg *SchemeArg =
+            Args.getLastArgNoClaim(options::OPT_mcf_branch_label_scheme_EQ))
+      Result.push_back(SchemeArg->getAsString(Args));
+  }
 }
 
 Multilib::flags_list
diff --git a/clang/test/Driver/print-multi-selection-flags.c b/clang/test/Driver/print-multi-selection-flags.c
index ba7b325892f9c..e5a116234c321 100644
--- a/clang/test/Driver/print-multi-selection-flags.c
+++ b/clang/test/Driver/print-multi-selection-flags.c
@@ -154,3 +154,16 @@
 // CHECK-OPT-OS: -Os
 // CHECK-OPT-NOT: -Oz
 // CHECK-OPT-NOT: -Os
+
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=riscv64-none-elf                                                         | FileCheck --check-prefix=CHECK-CF-PROTECTION-NONE --implicit-check-not="mcf-branch-label-scheme" %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=riscv64-none-elf -fcf-protection=none                                   | FileCheck --check-prefix=CHECK-CF-PROTECTION-NONE --implicit-check-not="mcf-branch-label-scheme" %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=riscv64-none-elf -fcf-protection=return                                 | FileCheck --check-prefix=CHECK-CF-PROTECTION-RETURN --implicit-check-not="mcf-branch-label-scheme" %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=riscv64-none-elf -fcf-protection=branch -mcf-branch-label-scheme=unlabeled | FileCheck --check-prefix=CHECK-CF-PROTECTION-BRANCH %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=riscv64-none-elf -fcf-protection=full   -mcf-branch-label-scheme=unlabeled | FileCheck --check-prefix=CHECK-CF-PROTECTION-FULL   %s
+// RUN: %clang -multi-lib-config=%S/Inputs/multilib/empty.yaml -print-multi-flags-experimental --target=riscv64-none-elf -fcf-protection        -mcf-branch-label-scheme=unlabeled | FileCheck --check-prefix=CHECK-CF-PROTECTION-FULL   %s
+// CHECK-CF-PROTECTION-NONE: -fcf-protection=none
+// CHECK-CF-PROTECTION-RETURN: -fcf-protection=return
+// CHECK-CF-PROTECTION-BRANCH: -fcf-protection=branch
+// CHECK-CF-PROTECTION-BRANCH: -mcf-branch-label-scheme=unlabeled
+// CHECK-CF-PROTECTION-FULL: -fcf-protection=full
+// CHECK-CF-PROTECTION-FULL: -mcf-branch-label-scheme=unlabeled