Rollup merge of #68824 - ajpaverd:cfguard-rustbuild, r=Mark-Simulacrum

Enable Control Flow Guard in rustbuild

Now that Rust supports Control Flow Guard (#68180), add a config.toml option to build the standard library with CFG enabled.

r? @nagisa

src/bootstrap/builder.rs

@@ -1135,6 +1135,20 @@ impl<'a> Builder<'a> {
             );
         }
 
+        // If Control Flow Guard is enabled, pass the `control_flow_guard=checks` flag to rustc
+        // when compiling the standard library, since this might be linked into the final outputs
+        // produced by rustc. Since this mitigation is only available on Windows, only enable it
+        // for the standard library in case the compiler is run on a non-Windows platform.
+        // This is not needed for stage 0 artifacts because these will only be used for building
+        // the stage 1 compiler.
+        if cfg!(windows)
+            && mode == Mode::Std
+            && self.config.control_flow_guard
+            && compiler.stage >= 1
+        {
+            rustflags.arg("-Zcontrol_flow_guard=checks");
+        }
+
         // For `cargo doc` invocations, make rustdoc print the Rust version into the docs
         cargo.env("RUSTDOC_CRATE_VERSION", self.rust_version());
 

src/bootstrap/config.rs

@@ -116,6 +116,7 @@ pub struct Config {
     pub targets: Vec<Interned<String>>,
     pub local_rebuild: bool,
     pub jemalloc: bool,
+    pub control_flow_guard: bool,
 
     // dist misc
     pub dist_sign_folder: Option<PathBuf>,
@@ -333,6 +334,7 @@ struct Rust {
     jemalloc: Option<bool>,
     test_compare_mode: Option<bool>,
     llvm_libunwind: Option<bool>,
+    control_flow_guard: Option<bool>,
 }
 
 /// TOML representation of how each build target is configured.
@@ -580,6 +582,7 @@ impl Config {
             set(&mut config.rust_verify_llvm_ir, rust.verify_llvm_ir);
             config.rust_thin_lto_import_instr_limit = rust.thin_lto_import_instr_limit;
             set(&mut config.rust_remap_debuginfo, rust.remap_debuginfo);
+            set(&mut config.control_flow_guard, rust.control_flow_guard);
 
             if let Some(ref backends) = rust.codegen_backends {
                 config.rust_codegen_backends =

src/bootstrap/configure.py

@@ -60,6 +60,7 @@ o("lld", "rust.lld", "build lld")
 o("lldb", "rust.lldb", "build lldb")
 o("missing-tools", "dist.missing-tools", "allow failures when building tools")
 o("use-libcxx", "llvm.use-libcxx", "build LLVM with libc++")
+o("control-flow-guard", "rust.control-flow-guard", "Enable Control Flow Guard")
 
 o("cflags", "llvm.cflags", "build LLVM with these extra compiler flags")
 o("cxxflags", "llvm.cxxflags", "build LLVM with these extra compiler flags")