Add support for control-flow protection

This change adds a flag for configuring control-flow protection in the
LLVM backend. In Clang, this flag is exposed as `-fcf-protection` with
options `none|branch|return|full`. This convention is followed for
`rustc`, though as a codegen option: `rustc -Z
cf-protection=<none|branch|return|full>`.

Co-authored-by: BlackHoleFox <blackholefoxdev@gmail.com>

1 files changed, 20 insertions, 1 deletions

diff --git a/compiler/rustc_codegen_llvm/src/context.rs b/compiler/rustc_codegen_llvm/src/context.rs
index 8672459b5da..373ae21d192 100644
--- a/compiler/rustc_codegen_llvm/src/context.rs
+++ b/compiler/rustc_codegen_llvm/src/context.rs
@@ -21,7 +21,8 @@ use rustc_middle::ty::layout::{
 };
 use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
 use rustc_middle::{bug, span_bug};
-use rustc_session::config::{BranchProtection, CFGuard, CrateType, DebugInfo, PAuthKey, PacRet};
+use rustc_session::config::{BranchProtection, CFGuard, CFProtection};
+use rustc_session::config::{CrateType, DebugInfo, PAuthKey, PacRet};
 use rustc_session::Session;
 use rustc_span::source_map::Span;
 use rustc_span::symbol::Symbol;
@@ -287,6 +288,24 @@ pub unsafe fn create_module<'ll>(
         );
     }
 
+    // Pass on the control-flow protection flags to LLVM (equivalent to `-fcf-protection` in Clang).
+    if let CFProtection::Branch | CFProtection::Full = sess.opts.debugging_opts.cf_protection {
+        llvm::LLVMRustAddModuleFlag(
+            llmod,
+            llvm::LLVMModFlagBehavior::Override,
+            "cf-protection-branch\0".as_ptr().cast(),
+            1,
+        )
+    }
+    if let CFProtection::Return | CFProtection::Full = sess.opts.debugging_opts.cf_protection {
+        llvm::LLVMRustAddModuleFlag(
+            llmod,
+            llvm::LLVMModFlagBehavior::Override,
+            "cf-protection-return\0".as_ptr().cast(),
+            1,
+        )
+    }
+
     llmod
 }