-Zretpoline and -Zretpoline-external-thunk flags (target modifiers) to enable retpoline-related target features

6 files changed, 107 insertions, 0 deletions

diff --git a/compiler/rustc_session/messages.ftl b/compiler/rustc_session/messages.ftl
index 528c52eace7..61953614c77 100644
--- a/compiler/rustc_session/messages.ftl
+++ b/compiler/rustc_session/messages.ftl
@@ -40,6 +40,11 @@ session_file_is_not_writeable = output file {$file} is not writeable -- check it
 
 session_file_write_fail = failed to write `{$path}` due to error `{$err}`
 
+session_forbidden_ctarget_feature =
+    target feature `{$feature}` cannot be {$enabled} with `-Ctarget-feature`: {$reason}
+    .note = this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+session_forbidden_ctarget_feature_issue = for more information, see issue #116344 <https://github.com/rust-lang/rust/issues/116344>
+
 session_function_return_requires_x86_or_x86_64 = `-Zfunction-return` (except `keep`) is only supported on x86 and x86_64
 
 session_function_return_thunk_extern_requires_non_large_code_model = `-Zfunction-return=thunk-extern` is only supported on non-large code models
@@ -132,6 +137,9 @@ session_target_stack_protector_not_supported = `-Z stack-protector={$stack_prote
 session_unleashed_feature_help_named = skipping check for `{$gate}` feature
 session_unleashed_feature_help_unnamed = skipping check that does not even have a feature gate
 
+session_unstable_ctarget_feature =
+    unstable feature specified for `-Ctarget-feature`: `{$feature}`
+    .note = this feature is not stably supported; its behavior can change in the future
 session_unstable_virtual_function_elimination = `-Zvirtual-function-elimination` requires `-Clto`
 
 session_unsupported_crate_type_for_target =
diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index 60e1b465ba9..8984634e5ec 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -2649,6 +2649,15 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
 
     let prints = collect_print_requests(early_dcx, &mut cg, &unstable_opts, matches);
 
+    // -Zretpoline-external-thunk also requires -Zretpoline
+    if unstable_opts.retpoline_external_thunk {
+        unstable_opts.retpoline = true;
+        target_modifiers.insert(
+            OptionsTargetModifiers::UnstableOptions(UnstableOptionsTargetModifiers::retpoline),
+            "true".to_string(),
+        );
+    }
+
     let cg = cg;
 
     let sysroot_opt = matches.opt_str("sysroot").map(|m| PathBuf::from(&m));
diff --git a/compiler/rustc_session/src/errors.rs b/compiler/rustc_session/src/errors.rs
index bf95014843d..9c591dcf619 100644
--- a/compiler/rustc_session/src/errors.rs
+++ b/compiler/rustc_session/src/errors.rs
@@ -501,3 +501,20 @@ pub(crate) struct SoftFloatIgnored;
 #[note]
 #[note(session_soft_float_deprecated_issue)]
 pub(crate) struct SoftFloatDeprecated;
+
+#[derive(Diagnostic)]
+#[diag(session_forbidden_ctarget_feature)]
+#[note]
+#[note(session_forbidden_ctarget_feature_issue)]
+pub(crate) struct ForbiddenCTargetFeature<'a> {
+    pub feature: &'a str,
+    pub enabled: &'a str,
+    pub reason: &'a str,
+}
+
+#[derive(Diagnostic)]
+#[diag(session_unstable_ctarget_feature)]
+#[note]
+pub(crate) struct UnstableCTargetFeature<'a> {
+    pub feature: &'a str,
+}
diff --git a/compiler/rustc_session/src/features.rs b/compiler/rustc_session/src/features.rs
new file mode 100644
index 00000000000..70a088a236f
--- /dev/null
+++ b/compiler/rustc_session/src/features.rs
@@ -0,0 +1,59 @@
+use rustc_target::target_features::Stability;
+
+use crate::Session;
+use crate::errors::{ForbiddenCTargetFeature, UnstableCTargetFeature};
+
+pub trait StabilityExt {
+    /// Returns whether the feature may be toggled via `#[target_feature]` or `-Ctarget-feature`.
+    /// Otherwise, some features also may only be enabled by flag (target modifier).
+    /// (It might still be nightly-only even if this returns `true`, so make sure to also check
+    /// `requires_nightly`.)
+    fn is_toggle_permitted(&self, sess: &Session) -> Result<(), &'static str>;
+
+    /// Check that feature is correctly enabled/disabled by command line flag (emits warnings)
+    fn verify_feature_enabled_by_flag(&self, sess: &Session, enable: bool, feature: &str);
+}
+
+impl StabilityExt for Stability {
+    fn is_toggle_permitted(&self, sess: &Session) -> Result<(), &'static str> {
+        match self {
+            Stability::Forbidden { reason } => Err(reason),
+            Stability::TargetModifierOnly { reason, flag } => {
+                if !sess.opts.target_feature_flag_enabled(*flag) { Err(reason) } else { Ok(()) }
+            }
+            _ => Ok(()),
+        }
+    }
+    fn verify_feature_enabled_by_flag(&self, sess: &Session, enable: bool, feature: &str) {
+        if let Err(reason) = self.is_toggle_permitted(sess) {
+            sess.dcx().emit_warn(ForbiddenCTargetFeature {
+                feature,
+                enabled: if enable { "enabled" } else { "disabled" },
+                reason,
+            });
+        } else if self.requires_nightly().is_some() {
+            // An unstable feature. Warn about using it. It makes little sense
+            // to hard-error here since we just warn about fully unknown
+            // features above.
+            sess.dcx().emit_warn(UnstableCTargetFeature { feature });
+        }
+    }
+}
+
+pub fn retpoline_features_by_flags(sess: &Session, features: &mut Vec<&str>) {
+    // -Zretpoline without -Zretpoline-external-thunk enables
+    // retpoline-indirect-branches and retpoline-indirect-calls target features
+    let unstable_opts = &sess.opts.unstable_opts;
+    if unstable_opts.retpoline && !unstable_opts.retpoline_external_thunk {
+        features.push("+retpoline-indirect-branches");
+        features.push("+retpoline-indirect-calls");
+    }
+    // -Zretpoline-external-thunk (maybe, with -Zretpoline too) enables
+    // retpoline-external-thunk, retpoline-indirect-branches and
+    // retpoline-indirect-calls target features
+    if unstable_opts.retpoline_external_thunk {
+        features.push("+retpoline-external-thunk");
+        features.push("+retpoline-indirect-branches");
+        features.push("+retpoline-indirect-calls");
+    }
+}
diff --git a/compiler/rustc_session/src/lib.rs b/compiler/rustc_session/src/lib.rs
index 5e5872ee068..4added19e56 100644
--- a/compiler/rustc_session/src/lib.rs
+++ b/compiler/rustc_session/src/lib.rs
@@ -29,6 +29,7 @@ pub use session::*;
 pub mod output;
 
 pub use getopts;
+pub mod features;
 
 rustc_fluent_macro::fluent_messages! { "../messages.ftl" }
 
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 12fa05118ca..7da48830b6a 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -290,6 +290,14 @@ macro_rules! top_level_options {
                 mods.sort_by(|a, b| a.opt.cmp(&b.opt));
                 mods
             }
+
+            pub fn target_feature_flag_enabled(&self, flag: &str) -> bool {
+                match flag {
+                    "retpoline" => self.unstable_opts.retpoline,
+                    "retpoline-external-thunk" => self.unstable_opts.retpoline_external_thunk,
+                    _ => false,
+                }
+            }
         }
     );
 }
@@ -2446,6 +2454,11 @@ options! {
     remark_dir: Option<PathBuf> = (None, parse_opt_pathbuf, [UNTRACKED],
         "directory into which to write optimization remarks (if not specified, they will be \
 written to standard error output)"),
+    retpoline: bool = (false, parse_bool, [TRACKED TARGET_MODIFIER],
+        "enables retpoline-indirect-branches and retpoline-indirect-calls target features (default: no)"),
+    retpoline_external_thunk: bool = (false, parse_bool, [TRACKED TARGET_MODIFIER],
+        "enables retpoline-external-thunk, retpoline-indirect-branches and retpoline-indirect-calls \
+        target features (default: no)"),
     sanitizer: SanitizerSet = (SanitizerSet::empty(), parse_sanitizers, [TRACKED],
         "use a sanitizer"),
     sanitizer_cfi_canonical_jump_tables: Option<bool> = (Some(true), parse_opt_bool, [TRACKED],