rustc_monomorphize/mono_checks/
abi_check.rs

1//! This module ensures that if a function's ABI requires a particular target feature,
2//! that target feature is enabled both on the callee and all callers.
3use rustc_abi::{BackendRepr, CanonAbi, RegKind, X86Call};
4use rustc_hir::{CRATE_HIR_ID, HirId};
5use rustc_middle::mir::{self, Location, traversal};
6use rustc_middle::ty::{self, Instance, InstanceKind, Ty, TyCtxt};
7use rustc_span::def_id::DefId;
8use rustc_span::{DUMMY_SP, Span, Symbol, sym};
9use rustc_target::callconv::{FnAbi, PassMode};
10
11use crate::errors;
12
13/// Are vector registers used?
14enum UsesVectorRegisters {
15    /// e.g. `neon`
16    FixedVector,
17    /// e.g. `sve`
18    ScalableVector,
19    No,
20}
21
22/// Determines whether the combination of `mode` and `repr` will use fixed vector registers,
23/// scalable vector registers or no vector registers.
24fn passes_vectors_by_value(mode: &PassMode, repr: &BackendRepr) -> UsesVectorRegisters {
25    match mode {
26        PassMode::Ignore | PassMode::Indirect { .. } => UsesVectorRegisters::No,
27        PassMode::Cast { pad_i32: _, cast }
28            if cast.prefix.iter().any(|r| r.is_some_and(|x| x.kind == RegKind::Vector))
29                || cast.rest.unit.kind == RegKind::Vector =>
30        {
31            UsesVectorRegisters::FixedVector
32        }
33        PassMode::Direct(..) | PassMode::Pair(..)
34            if matches!(repr, BackendRepr::SimdVector { .. }) =>
35        {
36            UsesVectorRegisters::FixedVector
37        }
38        PassMode::Direct(..) | PassMode::Pair(..)
39            if matches!(repr, BackendRepr::ScalableVector { .. }) =>
40        {
41            UsesVectorRegisters::ScalableVector
42        }
43        _ => UsesVectorRegisters::No,
44    }
45}
46
47/// Checks whether a certain function ABI is compatible with the target features currently enabled
48/// for a certain function.
49/// `is_call` indicates whether this is a call-site check or a definition-site check;
50/// this is only relevant for the wording in the emitted error.
51fn do_check_simd_vector_abi<'tcx>(
52    tcx: TyCtxt<'tcx>,
53    abi: &FnAbi<'tcx, Ty<'tcx>>,
54    def_id: DefId,
55    is_call: bool,
56    loc: impl Fn() -> (Span, HirId),
57) {
58    let codegen_attrs = tcx.codegen_fn_attrs(def_id);
59    let have_feature = |feat: Symbol| {
60        let target_feats = tcx.sess.unstable_target_features.contains(&feat);
61        let fn_feats = codegen_attrs.target_features.iter().any(|x| x.name == feat);
62        target_feats || fn_feats
63    };
64    for arg_abi in abi.args.iter().chain(std::iter::once(&abi.ret)) {
65        let size = arg_abi.layout.size;
66        match passes_vectors_by_value(&arg_abi.mode, &arg_abi.layout.backend_repr) {
67            UsesVectorRegisters::FixedVector => {
68                let feature_def = tcx.sess.target.features_for_correct_fixed_length_vector_abi();
69                // Find the first feature that provides at least this vector size.
70                let feature = match feature_def.iter().find(|(bits, _)| size.bits() <= *bits) {
71                    Some((_, feature)) => feature,
72                    None => {
73                        let (span, _hir_id) = loc();
74                        tcx.dcx().emit_err(errors::AbiErrorUnsupportedVectorType {
75                            span,
76                            ty: arg_abi.layout.ty,
77                            is_call,
78                        });
79                        continue;
80                    }
81                };
82                if !feature.is_empty() && !have_feature(Symbol::intern(feature)) {
83                    let (span, _hir_id) = loc();
84                    tcx.dcx().emit_err(errors::AbiErrorDisabledVectorType {
85                        span,
86                        required_feature: feature,
87                        ty: arg_abi.layout.ty,
88                        is_call,
89                        is_scalable: false,
90                    });
91                }
92            }
93            UsesVectorRegisters::ScalableVector => {
94                let Some(required_feature) =
95                    tcx.sess.target.features_for_correct_scalable_vector_abi()
96                else {
97                    continue;
98                };
99                if !required_feature.is_empty() && !have_feature(Symbol::intern(required_feature)) {
100                    let (span, _) = loc();
101                    tcx.dcx().emit_err(errors::AbiErrorDisabledVectorType {
102                        span,
103                        required_feature,
104                        ty: arg_abi.layout.ty,
105                        is_call,
106                        is_scalable: true,
107                    });
108                }
109            }
110            UsesVectorRegisters::No => {
111                continue;
112            }
113        }
114    }
115    // The `vectorcall` ABI is special in that it requires SSE2 no matter which types are being passed.
116    if abi.conv == CanonAbi::X86(X86Call::Vectorcall) && !have_feature(sym::sse2) {
117        let (span, _hir_id) = loc();
118        tcx.dcx().emit_err(errors::AbiRequiredTargetFeature {
119            span,
120            required_feature: "sse2",
121            abi: "vectorcall",
122            is_call,
123        });
124    }
125}
126
127/// Emit an error when a non-rustic ABI has unsized parameters.
128/// Unsized types do not have a stable layout, so should not be used with stable ABIs.
129/// `is_call` indicates whether this is a call-site check or a definition-site check;
130/// this is only relevant for the wording in the emitted error.
131fn do_check_unsized_params<'tcx>(
132    tcx: TyCtxt<'tcx>,
133    fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
134    is_call: bool,
135    loc: impl Fn() -> (Span, HirId),
136) {
137    // Unsized parameters are allowed with the (unstable) "Rust" (and similar) ABIs.
138    if fn_abi.conv.is_rustic_abi() {
139        return;
140    }
141
142    for arg_abi in fn_abi.args.iter() {
143        if !arg_abi.layout.layout.is_sized() {
144            let (span, _hir_id) = loc();
145            tcx.dcx().emit_err(errors::AbiErrorUnsupportedUnsizedParameter {
146                span,
147                ty: arg_abi.layout.ty,
148                is_call,
149            });
150        }
151    }
152}
153
154/// Checks the ABI of an Instance, emitting an error when:
155///
156/// - a non-rustic ABI uses unsized parameters
157/// - the signature requires target features that are not enabled
158fn check_instance_abi<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) {
159    let typing_env = ty::TypingEnv::fully_monomorphized();
160    let Ok(abi) = tcx.fn_abi_of_instance(typing_env.as_query_input((instance, ty::List::empty())))
161    else {
162        // An error will be reported during codegen if we cannot determine the ABI of this
163        // function.
164        tcx.dcx().delayed_bug("ABI computation failure should lead to compilation failure");
165        return;
166    };
167    // Unlike the call-site check, we do also check "Rust" ABI functions here.
168    // This should never trigger, *except* if we start making use of vector registers
169    // for the "Rust" ABI and the user disables those vector registers (which should trigger a
170    // warning as that's clearly disabling a "required" target feature for this target).
171    // Using such a function is where disabling the vector register actually can start leading
172    // to soundness issues, so erroring here seems good.
173    let loc = || {
174        let def_id = instance.def_id();
175        (
176            tcx.def_span(def_id),
177            def_id.as_local().map(|did| tcx.local_def_id_to_hir_id(did)).unwrap_or(CRATE_HIR_ID),
178        )
179    };
180    do_check_unsized_params(tcx, abi, /*is_call*/ false, loc);
181    do_check_simd_vector_abi(tcx, abi, instance.def_id(), /*is_call*/ false, loc);
182}
183
184/// Check the ABI at a call site, emitting an error when:
185///
186/// - a non-rustic ABI uses unsized parameters
187/// - the signature requires target features that are not enabled
188fn check_call_site_abi<'tcx>(
189    tcx: TyCtxt<'tcx>,
190    callee: Ty<'tcx>,
191    caller: InstanceKind<'tcx>,
192    loc: impl Fn() -> (Span, HirId) + Copy,
193) {
194    if callee.fn_sig(tcx).abi().is_rustic_abi() {
195        // We directly handle the soundness of Rust ABIs -- so let's skip the majority of
196        // call sites to avoid a perf regression.
197        return;
198    }
199    let typing_env = ty::TypingEnv::fully_monomorphized();
200    let callee_abi = match *callee.kind() {
201        ty::FnPtr(..) => {
202            tcx.fn_abi_of_fn_ptr(typing_env.as_query_input((callee.fn_sig(tcx), ty::List::empty())))
203        }
204        ty::FnDef(def_id, args) => {
205            // Intrinsics are handled separately by the compiler.
206            if tcx.intrinsic(def_id).is_some() {
207                return;
208            }
209            let instance = ty::Instance::expect_resolve(tcx, typing_env, def_id, args, DUMMY_SP);
210            tcx.fn_abi_of_instance(typing_env.as_query_input((instance, ty::List::empty())))
211        }
212        _ => {
213            panic!("Invalid function call");
214        }
215    };
216
217    let Ok(callee_abi) = callee_abi else {
218        // ABI failed to compute; this will not get through codegen.
219        return;
220    };
221    do_check_unsized_params(tcx, callee_abi, /*is_call*/ true, loc);
222    do_check_simd_vector_abi(tcx, callee_abi, caller.def_id(), /*is_call*/ true, loc);
223}
224
225fn check_callees_abi<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>, body: &mir::Body<'tcx>) {
226    // Check all function call terminators.
227    for (bb, _data) in traversal::mono_reachable(body, tcx, instance) {
228        let terminator = body.basic_blocks[bb].terminator();
229        match terminator.kind {
230            mir::TerminatorKind::Call { ref func, ref fn_span, .. }
231            | mir::TerminatorKind::TailCall { ref func, ref fn_span, .. } => {
232                let callee_ty = func.ty(body, tcx);
233                let callee_ty = instance.instantiate_mir_and_normalize_erasing_regions(
234                    tcx,
235                    ty::TypingEnv::fully_monomorphized(),
236                    ty::EarlyBinder::bind(callee_ty),
237                );
238                check_call_site_abi(tcx, callee_ty, body.source.instance, || {
239                    let loc = Location {
240                        block: bb,
241                        statement_index: body.basic_blocks[bb].statements.len(),
242                    };
243                    (
244                        *fn_span,
245                        body.source_info(loc)
246                            .scope
247                            .lint_root(&body.source_scopes)
248                            .unwrap_or(CRATE_HIR_ID),
249                    )
250                });
251            }
252            _ => {}
253        }
254    }
255}
256
257pub(crate) fn check_feature_dependent_abi<'tcx>(
258    tcx: TyCtxt<'tcx>,
259    instance: Instance<'tcx>,
260    body: &'tcx mir::Body<'tcx>,
261) {
262    check_instance_abi(tcx, instance);
263    check_callees_abi(tcx, instance, body);
264}
rustc_monomorphize/mono_checks/abi_check.rs

rustc_monomorphize/mono_checks/
abi_check.rs
