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.

2 files changed, 26 insertions, 1 deletions

diff --git a/src/librustc_codegen_ssa/back/link.rs b/src/librustc_codegen_ssa/back/link.rs
index f56a4170c0a..bc0322ffe1d 100644
--- a/src/librustc_codegen_ssa/back/link.rs
+++ b/src/librustc_codegen_ssa/back/link.rs
@@ -1,7 +1,7 @@
 use rustc::middle::cstore::{EncodedMetadata, LibSource, NativeLibrary, NativeLibraryKind};
 use rustc::middle::dependency_format::Linkage;
 use rustc::session::config::{
-    self, DebugInfo, OutputFilenames, OutputType, PrintRequest, Sanitizer,
+    self, CFGuard, DebugInfo, OutputFilenames, OutputType, PrintRequest, Sanitizer,
 };
 use rustc::session::search_paths::PathKind;
 /// For all the linkers we support, and information they might
@@ -1294,6 +1294,10 @@ fn link_args<'a, B: ArchiveBuilder<'a>>(
         cmd.pgo_gen();
     }
 
+    if sess.opts.debugging_opts.control_flow_guard != CFGuard::Disabled {
+        cmd.control_flow_guard();
+    }
+
     // FIXME (#2397): At some point we want to rpath our guesses as to
     // where extern libraries might live, based on the
     // addl_lib_search_paths
diff --git a/src/librustc_codegen_ssa/back/linker.rs b/src/librustc_codegen_ssa/back/linker.rs
index 695f171dfb4..5aafb8a12d7 100644
--- a/src/librustc_codegen_ssa/back/linker.rs
+++ b/src/librustc_codegen_ssa/back/linker.rs
@@ -106,6 +106,7 @@ pub trait Linker {
     fn no_relro(&mut self);
     fn optimize(&mut self);
     fn pgo_gen(&mut self);
+    fn control_flow_guard(&mut self);
     fn debuginfo(&mut self);
     fn no_default_libraries(&mut self);
     fn build_dylib(&mut self, out_filename: &Path);
@@ -360,6 +361,10 @@ impl<'a> Linker for GccLinker<'a> {
         self.cmd.arg("__llvm_profile_runtime");
     }
 
+    fn control_flow_guard(&mut self) {
+        self.sess.warn("Windows Control Flow Guard is not supported by this linker.");
+    }
+
     fn debuginfo(&mut self) {
         if let DebugInfo::None = self.sess.opts.debuginfo {
             // If we are building without debuginfo enabled and we were called with
@@ -660,6 +665,10 @@ impl<'a> Linker for MsvcLinker<'a> {
         // Nothing needed here.
     }
 
+    fn control_flow_guard(&mut self) {
+        self.cmd.arg("/guard:cf");
+    }
+
     fn debuginfo(&mut self) {
         // This will cause the Microsoft linker to generate a PDB file
         // from the CodeView line tables in the object files.
@@ -862,6 +871,10 @@ impl<'a> Linker for EmLinker<'a> {
         // noop, but maybe we need something like the gnu linker?
     }
 
+    fn control_flow_guard(&mut self) {
+        self.sess.warn("Windows Control Flow Guard is not supported by this linker.");
+    }
+
     fn debuginfo(&mut self) {
         // Preserve names or generate source maps depending on debug info
         self.cmd.arg(match self.sess.opts.debuginfo {
@@ -1058,6 +1071,10 @@ impl<'a> Linker for WasmLd<'a> {
 
     fn debuginfo(&mut self) {}
 
+    fn control_flow_guard(&mut self) {
+        self.sess.warn("Windows Control Flow Guard is not supported by this linker.");
+    }
+
     fn no_default_libraries(&mut self) {}
 
     fn build_dylib(&mut self, _out_filename: &Path) {
@@ -1233,6 +1250,10 @@ impl<'a> Linker for PtxLinker<'a> {
 
     fn no_default_libraries(&mut self) {}
 
+    fn control_flow_guard(&mut self) {
+        self.sess.warn("Windows Control Flow Guard is not supported by this linker.");
+    }
+
     fn build_dylib(&mut self, _out_filename: &Path) {}
 
     fn export_symbols(&mut self, _tmpdir: &Path, _crate_type: CrateType) {}