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make enabling the neon target feature a FCW

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This commit is contained in:
Ralf Jung
2025-05-01 11:34:52 +02:00
parent 30c87defe6
commit 3c020e59a2
7 changed files with 120 additions and 13 deletions
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2
compiler/rustc_codegen_ssa/messages.ftl
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@@ -1,5 +1,7 @@
codegen_ssa_L4Bender_exporting_symbols_unimplemented = exporting symbols not implemented yet for L4Bender
codegen_ssa_aarch64_softfloat_neon = enabling the `neon` target feature on the current target is unsound due to ABI issues
codegen_ssa_add_native_library = failed to add native library {$library_path}: {$error}
codegen_ssa_aix_strip_not_used = using host's `strip` binary to cross-compile to AIX which is not guaranteed to work

1
compiler/rustc_codegen_ssa/src/codegen_attrs.rs
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@@ -299,6 +299,7 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
}
from_target_feature_attr(
tcx,
did,
attr,
rust_target_features,
&mut codegen_fn_attrs.target_features,

4
compiler/rustc_codegen_ssa/src/errors.rs
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@@ -1316,3 +1316,7 @@ pub(crate) struct XcrunSdkPathWarning {
pub sdk_name: &'static str,
pub stderr: String,
}
#[derive(LintDiagnostic)]
#[diag(codegen_ssa_aarch64_softfloat_neon)]
pub(crate) struct Aarch64SoftfloatNeon;

23
compiler/rustc_codegen_ssa/src/target_features.rs
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@@ -8,6 +8,7 @@ use rustc_hir::def_id::{DefId, LOCAL_CRATE, LocalDefId};
use rustc_middle::middle::codegen_fn_attrs::TargetFeature;
use rustc_middle::query::Providers;
use rustc_middle::ty::TyCtxt;
use rustc_session::lint::builtin::AARCH64_SOFTFLOAT_NEON;
use rustc_session::parse::feature_err;
use rustc_span::{Span, Symbol, sym};
use rustc_target::target_features::{self, Stability};
@@ -18,6 +19,7 @@ use crate::errors;
/// Enabled target features are added to `target_features`.
pub(crate) fn from_target_feature_attr(
tcx: TyCtxt<'_>,
did: LocalDefId,
attr: &hir::Attribute,
rust_target_features: &UnordMap<String, target_features::Stability>,
target_features: &mut Vec<TargetFeature>,
@@ -92,11 +94,22 @@ pub(crate) fn from_target_feature_attr(
// generating code so "it's fine".
if !tcx.sess.opts.actually_rustdoc {
if abi_feature_constraints.incompatible.contains(&name.as_str()) {
tcx.dcx().emit_err(errors::ForbiddenTargetFeatureAttr {
span: item.span(),
feature: name.as_str(),
reason: "this feature is incompatible with the target ABI",
});
// For "neon" specifically, we emit an FCW instead of a hard error.
// See <https://github.com/rust-lang/rust/issues/134375>.
if tcx.sess.target.arch == "aarch64" && name.as_str() == "neon" {
tcx.emit_node_span_lint(
AARCH64_SOFTFLOAT_NEON,
tcx.local_def_id_to_hir_id(did),
item.span(),
errors::Aarch64SoftfloatNeon,
);
} else {
tcx.dcx().emit_err(errors::ForbiddenTargetFeatureAttr {
span: item.span(),
feature: name.as_str(),
reason: "this feature is incompatible with the target ABI",
});
}
}
}
target_features.push(TargetFeature { name, implied: name != feature_sym })

58
compiler/rustc_lint_defs/src/builtin.rs
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@@ -16,6 +16,7 @@ declare_lint_pass! {
/// that are used by other parts of the compiler.
HardwiredLints => [
// tidy-alphabetical-start
AARCH64_SOFTFLOAT_NEON,
ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE,
AMBIGUOUS_ASSOCIATED_ITEMS,
AMBIGUOUS_GLOB_IMPORTS,
@@ -5043,14 +5044,14 @@ declare_lint! {
///
/// ```text
/// error: this function function definition is affected by the wasm ABI transition: it passes an argument of non-scalar type `MyType`
/// --> $DIR/wasm_c_abi_transition.rs:17:1
/// |
/// | pub extern "C" fn my_fun(_x: MyType) {}
/// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/// |
/// = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
/// = note: for more information, see issue #138762 <https://github.com/rust-lang/rust/issues/138762>
/// = help: the "C" ABI Rust uses on wasm32-unknown-unknown will change to align with the standard "C" ABI for this target
/// --> $DIR/wasm_c_abi_transition.rs:17:1
/// |
/// | pub extern "C" fn my_fun(_x: MyType) {}
/// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/// |
/// = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
/// = note: for more information, see issue #138762 <https://github.com/rust-lang/rust/issues/138762>
/// = help: the "C" ABI Rust uses on wasm32-unknown-unknown will change to align with the standard "C" ABI for this target
/// ```
///
/// ### Explanation
@@ -5067,3 +5068,44 @@ declare_lint! {
reference: "issue #138762 <https://github.com/rust-lang/rust/issues/138762>",
};
}
declare_lint! {
/// The `aarch64_softfloat_neon` lint detects usage of `#[target_feature(enable = "neon")]` on
/// softfloat aarch64 targets. Enabling this target feature causes LLVM to alter the ABI of
/// function calls, making this attribute unsound to use.
///
/// ### Example
///
/// ```rust,ignore (needs aarch64-unknown-none-softfloat)
/// #[target_feature(enable = "neon")]
/// fn with_neon() {}
/// ```
///
/// This will produce:
///
/// ```text
/// error: enabling the `neon` target feature on the current target is unsound due to ABI issues
/// --> $DIR/abi-incompatible-target-feature-attribute-fcw.rs:11:18
/// |
/// | #[target_feature(enable = "neon")]
/// | ^^^^^^^^^^^^^^^
/// |
/// = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
/// = note: for more information, see issue #134375 <https://github.com/rust-lang/rust/issues/134375>
/// ```
///
/// ### Explanation
///
/// If a function like `with_neon` above ends up containing calls to LLVM builtins, those will
/// not use the correct ABI. This is caused by a lack of support in LLVM for mixing code with
/// and without the `neon` target feature. The target feature should never have been stabilized
/// on this target due to this issue, but the problem was not known at the time of
/// stabilization.
pub AARCH64_SOFTFLOAT_NEON,
Warn,
"detects code that could be affected by ABI issues on aarch64 softfloat targets",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorReportInDeps,
reference: "issue #134375 <https://github.com/rust-lang/rust/issues/134375>",
};
}

14
tests/ui/target-feature/abi-incompatible-target-feature-attribute-fcw.rs Normal file
View File

@@ -0,0 +1,14 @@
//@ compile-flags: --crate-type=lib
//@ compile-flags: --target=aarch64-unknown-none-softfloat
//@ needs-llvm-components: aarch64
#![feature(no_core, lang_items)]
#![no_core]
#![deny(aarch64_softfloat_neon)]
#[lang = "sized"]
pub trait Sized {}
#[target_feature(enable = "neon")]
//~^ERROR: enabling the `neon` target feature on the current target is unsound
//~|WARN: previously accepted
pub unsafe fn my_fun() {}

31
tests/ui/target-feature/abi-incompatible-target-feature-attribute-fcw.stderr Normal file
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@@ -0,0 +1,31 @@
error: enabling the `neon` target feature on the current target is unsound due to ABI issues
--> $DIR/abi-incompatible-target-feature-attribute-fcw.rs:11:18
|
LL | #[target_feature(enable = "neon")]
| ^^^^^^^^^^^^^^^
|
= warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
= note: for more information, see issue #134375 <https://github.com/rust-lang/rust/issues/134375>
note: the lint level is defined here
--> $DIR/abi-incompatible-target-feature-attribute-fcw.rs:6:9
|
LL | #![deny(aarch64_softfloat_neon)]
| ^^^^^^^^^^^^^^^^^^^^^^
error: aborting due to 1 previous error
Future incompatibility report: Future breakage diagnostic:
error: enabling the `neon` target feature on the current target is unsound due to ABI issues
--> $DIR/abi-incompatible-target-feature-attribute-fcw.rs:11:18
|
LL | #[target_feature(enable = "neon")]
| ^^^^^^^^^^^^^^^
|
= warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
= note: for more information, see issue #134375 <https://github.com/rust-lang/rust/issues/134375>
note: the lint level is defined here
--> $DIR/abi-incompatible-target-feature-attribute-fcw.rs:6:9
|
LL | #![deny(aarch64_softfloat_neon)]
| ^^^^^^^^^^^^^^^^^^^^^^