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Emit warning when calling/declaring functions with unavailable vectors.
On some architectures, vector types may have a different ABI depending on whether the relevant target features are enabled. (The ABI when the feature is disabled is often not specified, but LLVM implements some de-facto ABI.) As discussed in rust-lang/lang-team#235, this turns out to very easily lead to unsound code. This commit makes it a post-monomorphization future-incompat warning to declare or call functions using those vector types in a context in which the corresponding target features are disabled, if using an ABI for which the difference is relevant. This ensures that these functions are always called with a consistent ABI. See the [nomination comment](rust-lang#127731 (comment)) for more discussion. Part of rust-lang#116558
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,160 @@ | ||
| //! This module ensures that if a function's ABI requires a particular target feature, | ||
| //! that target feature is enabled both on the callee and all callers. | ||
| use rustc_hir::CRATE_HIR_ID; | ||
| use rustc_hir::def::DefKind; | ||
| use rustc_middle::query::Providers; | ||
| use rustc_middle::ty::inherent::*; | ||
| use rustc_middle::ty::{self, Instance, InstanceKind, ParamEnv, Ty, TyCtxt}; | ||
| use rustc_session::lint::builtin::ABI_UNSUPPORTED_VECTOR_TYPES; | ||
| use rustc_span::def_id::DefId; | ||
| use rustc_span::{DUMMY_SP, Span, Symbol}; | ||
| use rustc_target::abi::call::{FnAbi, PassMode}; | ||
| use rustc_target::abi::{BackendRepr, RegKind}; | ||
|
|
||
| use crate::errors::{AbiErrorDisabledVectorTypeCall, AbiErrorDisabledVectorTypeDef}; | ||
|
|
||
| fn uses_vector_registers(mode: &PassMode, repr: &BackendRepr) -> bool { | ||
| match mode { | ||
| PassMode::Ignore | PassMode::Indirect { .. } => false, | ||
| PassMode::Cast { pad_i32: _, cast } => { | ||
| cast.prefix.iter().any(|r| r.is_some_and(|x| x.kind == RegKind::Vector)) | ||
| || cast.rest.unit.kind == RegKind::Vector | ||
| } | ||
| PassMode::Direct(..) | PassMode::Pair(..) => matches!(repr, BackendRepr::Vector { .. }), | ||
| } | ||
| } | ||
|
|
||
| fn do_check_abi<'tcx>( | ||
| tcx: TyCtxt<'tcx>, | ||
| abi: &FnAbi<'tcx, Ty<'tcx>>, | ||
| target_feature_def: DefId, | ||
| mut emit_err: impl FnMut(&'static str), | ||
| ) { | ||
| let Some(feature_def) = tcx.sess.target.features_for_correct_vector_abi() else { | ||
| return; | ||
| }; | ||
| let codegen_attrs = tcx.codegen_fn_attrs(target_feature_def); | ||
| for arg_abi in abi.args.iter().chain(std::iter::once(&abi.ret)) { | ||
| let size = arg_abi.layout.size; | ||
| if uses_vector_registers(&arg_abi.mode, &arg_abi.layout.backend_repr) { | ||
| // Find the first feature that provides at least this vector size. | ||
| let feature = match feature_def.iter().find(|(bits, _)| size.bits() <= *bits) { | ||
| Some((_, feature)) => feature, | ||
| None => { | ||
| emit_err("<no available feature for this size>"); | ||
| continue; | ||
| } | ||
| }; | ||
| let feature_sym = Symbol::intern(feature); | ||
| if !tcx.sess.unstable_target_features.contains(&feature_sym) | ||
| && !codegen_attrs.target_features.iter().any(|x| x.name == feature_sym) | ||
| { | ||
| emit_err(feature); | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| /// Checks that the ABI of a given instance of a function does not contain vector-passed arguments | ||
| /// or return values for which the corresponding target feature is not enabled. | ||
| fn check_instance_abi<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) { | ||
| let param_env = ParamEnv::reveal_all(); | ||
| let Ok(abi) = tcx.fn_abi_of_instance(param_env.and((instance, ty::List::empty()))) else { | ||
| // An error will be reported during codegen if we cannot determine the ABI of this | ||
| // function. | ||
| return; | ||
| }; | ||
| do_check_abi(tcx, abi, instance.def_id(), |required_feature| { | ||
| let span = tcx.def_span(instance.def_id()); | ||
| tcx.emit_node_span_lint( | ||
| ABI_UNSUPPORTED_VECTOR_TYPES, | ||
| CRATE_HIR_ID, | ||
| span, | ||
| AbiErrorDisabledVectorTypeDef { span, required_feature }, | ||
| ); | ||
| }) | ||
| } | ||
|
|
||
| fn call_site_abi_missing_features<'tcx>( | ||
| tcx: TyCtxt<'tcx>, | ||
| (callee, caller): (Ty<'tcx>, DefId), | ||
| ) -> Vec<String> { | ||
| let mut answer = vec![]; | ||
| let param_env = ParamEnv::reveal_all(); | ||
| let callee_abi = match *callee.kind() { | ||
| ty::FnPtr(..) => { | ||
| tcx.fn_abi_of_fn_ptr(param_env.and((callee.fn_sig(tcx), ty::List::empty()))) | ||
| } | ||
| ty::FnDef(def_id, args) => { | ||
| // Intrinsics are handled separately by the compiler. | ||
| if tcx.intrinsic(def_id).is_some() { | ||
| return vec![]; | ||
| } | ||
| let instance = ty::Instance::expect_resolve(tcx, param_env, def_id, args, DUMMY_SP); | ||
| tcx.fn_abi_of_instance(param_env.and((instance, ty::List::empty()))) | ||
| } | ||
| _ => { | ||
| panic!("Invalid function call"); | ||
| } | ||
| }; | ||
|
|
||
| let Ok(callee_abi) = callee_abi else { | ||
| // ABI failed to compute; this will not get through codegen. | ||
| return vec![]; | ||
| }; | ||
| do_check_abi(tcx, callee_abi, caller, |required_feature| { | ||
| answer.push(required_feature.to_string()); | ||
| }); | ||
| answer | ||
| } | ||
|
|
||
| /// Checks that a call expression does not try to pass a vector-passed argument which requires a | ||
| /// target feature that the caller does not have, as doing so causes UB because of ABI mismatch. | ||
| pub(super) fn check_call_site_abi<'tcx>( | ||
| tcx: TyCtxt<'tcx>, | ||
| callee: Ty<'tcx>, | ||
| span: Span, | ||
| caller: InstanceKind<'tcx>, | ||
| ) { | ||
| if callee.fn_sig(tcx).abi().is_rust() { | ||
| // "Rust" ABI never passes arguments in vector registers. | ||
| return; | ||
| } | ||
| for required_feature in tcx.call_site_abi_missing_features((callee, caller.def_id())) { | ||
| tcx.emit_node_span_lint( | ||
| ABI_UNSUPPORTED_VECTOR_TYPES, | ||
| CRATE_HIR_ID, | ||
| span, | ||
| AbiErrorDisabledVectorTypeCall { span, required_feature }, | ||
| ); | ||
| } | ||
| } | ||
|
|
||
| pub(super) fn provide(providers: &mut Providers) { | ||
| *providers = Providers { check_instance_abi, call_site_abi_missing_features, ..*providers } | ||
| } | ||
|
|
||
| pub(super) fn should_check_instance_abi<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) -> bool { | ||
| // We do not need to check the instance for feature-dependent ABI if we can determine that the | ||
| // function has "Rust" ABI, which is known not to be feature-dependent. | ||
| // Note that the check is still correct on Rust ABI functions, but somewhat expensive. Hence, | ||
| // checking for "Rust" ABI is just an optimization. | ||
| // We also avoid to try to determine the type of the instance, as doing so involves running a | ||
| // query that does not usually run for unchanged functions in incremental builds. | ||
| if let InstanceKind::Item(def) | InstanceKind::ReifyShim(def, ..) = instance.def { | ||
| // fn_sig ICEs on defs that are not functions. | ||
| if matches!(tcx.def_kind(def), DefKind::Fn | DefKind::AssocFn) { | ||
| !tcx.fn_sig(def).skip_binder().abi().is_rust() | ||
| } else if matches!(tcx.def_kind(def), DefKind::Ctor(..)) { | ||
| // Struct constructors are certainly always fine. | ||
| false | ||
| } else { | ||
| true | ||
| } | ||
| } else if matches!(instance.def, InstanceKind::DropGlue(..) | InstanceKind::CloneShim(..)) { | ||
| // Drop glue and clone shims are always fine. | ||
| false | ||
| } else { | ||
| true | ||
| } | ||
| } |
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