Auto merge of #68180 - ajpaverd:cfguard-rust, r=nagisa

Add support for Control Flow Guard on Windows.

LLVM now supports Windows Control Flow Guard (CFG): https://github.com/llvm/llvm-project/commit/d157a9bc8ba1085cc4808c6941412322a7fd884e
This patch adds support for rustc to emit the required LLVM module flags to enable CFG metadata (cfguard=1) or metadata and checks (cfguard=2). The LLVM module flags are ignored on unsupported targets and operating systems.

1 files changed, 11 insertions, 1 deletions

diff --git a/src/librustc_codegen_llvm/context.rs b/src/librustc_codegen_llvm/context.rs
index 50a35fe3dcf..6b31f14410d 100644
--- a/src/librustc_codegen_llvm/context.rs
+++ b/src/librustc_codegen_llvm/context.rs
@@ -12,7 +12,7 @@ use rustc_codegen_ssa::traits::*;
 use crate::callee::get_fn;
 use rustc::bug;
 use rustc::mir::mono::CodegenUnit;
-use rustc::session::config::{self, DebugInfo};
+use rustc::session::config::{self, CFGuard, DebugInfo};
 use rustc::session::Session;
 use rustc::ty::layout::{
     FnAbiExt, HasParamEnv, LayoutError, LayoutOf, PointeeInfo, Size, TyLayout, VariantIdx,
@@ -227,6 +227,16 @@ pub unsafe fn create_module(
         llvm::LLVMRustAddModuleFlag(llmod, avoid_plt, 1);
     }
 
+    // Set module flags to enable Windows Control Flow Guard (/guard:cf) metadata
+    // only (`cfguard=1`) or metadata and checks (`cfguard=2`).
+    match sess.opts.debugging_opts.control_flow_guard {
+        CFGuard::Disabled => {}
+        CFGuard::NoChecks => {
+            llvm::LLVMRustAddModuleFlag(llmod, "cfguard\0".as_ptr() as *const _, 1)
+        }
+        CFGuard::Checks => llvm::LLVMRustAddModuleFlag(llmod, "cfguard\0".as_ptr() as *const _, 2),
+    }
+
     llmod
 }