Add `-Zindirect-branch-cs-prefix` option

This is intended to be used for Linux kernel RETPOLINE builds.

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

3 files changed, 11 insertions, 1 deletions

diff --git a/compiler/rustc_session/src/errors.rs b/compiler/rustc_session/src/errors.rs
index bf95014843d..9471807df01 100644
--- a/compiler/rustc_session/src/errors.rs
+++ b/compiler/rustc_session/src/errors.rs
@@ -472,6 +472,10 @@ pub(crate) struct FunctionReturnRequiresX86OrX8664;
 pub(crate) struct FunctionReturnThunkExternRequiresNonLargeCodeModel;
 
 #[derive(Diagnostic)]
+#[diag(session_indirect_branch_cs_prefix_requires_x86_or_x86_64)]
+pub(crate) struct IndirectBranchCsPrefixRequiresX86OrX8664;
+
+#[derive(Diagnostic)]
 #[diag(session_unsupported_regparm)]
 pub(crate) struct UnsupportedRegparm {
     pub(crate) regparm: u32,
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index fce4d18a1d8..6d5be2d92cd 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -2296,7 +2296,7 @@ options! {
         - hash collisions of query keys
         - hash collisions when creating dep-nodes"),
     indirect_branch_cs_prefix: bool = (false, parse_bool, [TRACKED TARGET_MODIFIER],
-        "add cs prefix to call and jmp to indirect thunk (default: no)"),
+        "add `cs` prefix to `call` and `jmp` to indirect thunks (default: no)"),
     inline_llvm: bool = (true, parse_bool, [TRACKED],
         "enable LLVM inlining (default: yes)"),
     inline_mir: Option<bool> = (None, parse_opt_bool, [TRACKED],
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index c6956cf5f23..c8f4b511a7e 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -1368,6 +1368,12 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
         }
     }
 
+    if sess.opts.unstable_opts.indirect_branch_cs_prefix {
+        if sess.target.arch != "x86" && sess.target.arch != "x86_64" {
+            sess.dcx().emit_err(errors::IndirectBranchCsPrefixRequiresX86OrX8664);
+        }
+    }
+
     if let Some(regparm) = sess.opts.unstable_opts.regparm {
         if regparm > 3 {
             sess.dcx().emit_err(errors::UnsupportedRegparm { regparm });