Emit error when calling/declaring functions with unavailable vectors.

On some architectures, vector types may have a different ABI when
relevant target features are enabled.

As discussed in rust-lang/lang-team#235, this
turns out to very easily lead to unsound code.

This commit makes it an error 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.

Cargo.lock

@@ -4138,6 +4138,7 @@ dependencies = [
 name = "rustc_monomorphize"
 version = "0.0.0"
 dependencies = [
+ "rustc_abi",
  "rustc_data_structures",
  "rustc_errors",
  "rustc_fluent_macro",

compiler/rustc_monomorphize/Cargo.toml

@@ -5,6 +5,7 @@ edition = "2021"
 
 [dependencies]
 # tidy-alphabetical-start
+rustc_abi = { path = "../rustc_abi" }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_errors = { path = "../rustc_errors" }
 rustc_fluent_macro = { path = "../rustc_fluent_macro" }

compiler/rustc_monomorphize/messages.ftl

@@ -1,3 +1,10 @@
+monomorphize_abi_error_disabled_vector_type_call =
+  ABI error: this function call uses a {$required_feature} vector type, which is not enabled in the caller
+  .help = consider enabling it globally (-C target-feature=+{$required_feature}) or locally (#[target_feature(enable="{$required_feature}")])
+monomorphize_abi_error_disabled_vector_type_def =
+  ABI error: this function definition uses a {$required_feature} vector type, which is not enabled
+  .help = consider enabling it globally (-C target-feature=+{$required_feature}) or locally (#[target_feature(enable="{$required_feature}")])
+
 monomorphize_couldnt_dump_mono_stats =
     unexpected error occurred while dumping monomorphization stats: {$error}
 

compiler/rustc_monomorphize/src/collector.rs

@@ -205,6 +205,7 @@
 //! this is not implemented however: a mono item will be produced
 //! regardless of whether it is actually needed or not.
 
+mod abi_check;
 mod move_check;
 
 use std::path::PathBuf;
@@ -766,6 +767,7 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirUsedCollector<'a, 'tcx> {
                 self.used_mentioned_items.insert(MentionedItem::Fn(callee_ty));
                 let callee_ty = self.monomorphize(callee_ty);
                 self.check_fn_args_move_size(callee_ty, args, *fn_span, location);
+                abi_check::check_call_site_abi(tcx, callee_ty, *fn_span, self.body.source.instance);
                 visit_fn_use(self.tcx, callee_ty, true, source, &mut self.used_items)
             }
             mir::TerminatorKind::Drop { ref place, .. } => {
@@ -1207,6 +1209,7 @@ fn collect_items_of_instance<'tcx>(
     mentioned_items: &mut MonoItems<'tcx>,
     mode: CollectionMode,
 ) {
+    abi_check::check_instance_abi(tcx, instance);
     let body = tcx.instance_mir(instance.def);
     // Naively, in "used" collection mode, all functions get added to *both* `used_items` and
     // `mentioned_items`. Mentioned items processing will then notice that they have already been

compiler/rustc_monomorphize/src/collector/abi_check.rs

@@ -0,0 +1,97 @@
+use rustc_abi::Abi;
+use rustc_middle::ty::{self, Instance, InstanceKind, ParamEnv, Ty, TyCtxt};
+use rustc_span::def_id::DefId;
+use rustc_span::{Span, Symbol};
+use rustc_target::abi::call::{FnAbi, PassMode};
+
+use crate::errors::{AbiErrorDisabledVectorTypeCall, AbiErrorDisabledVectorTypeDef};
+
+// Represents the least-constraining feature that is required for vector types up to a certain size
+// to have their "proper" ABI.
+const X86_VECTOR_FEATURES: &'static [(u64, &'static str)] =
+    &[(128, "sse"), (256, "avx"), (512, "avx512f")];
+
+fn do_check_abi<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    abi: &FnAbi<'tcx, Ty<'tcx>>,
+    target_feature_def: DefId,
+    emit_err: impl Fn(&'static str),
+) {
+    let feature_def = if tcx.sess.target.arch == "x86" || tcx.sess.target.arch == "x86_64" {
+        X86_VECTOR_FEATURES
+    } else if tcx.sess.target.arch == "aarch64" {
+        // ABI on aarch64 does not depend on target features.
+        return;
+    } else {
+        // FIXME: add support for non-tier1 architectures
+        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 matches!(arg_abi.layout.abi, Abi::Vector { .. })
+            && !matches!(arg_abi.mode, PassMode::Indirect { .. })
+        {
+            let feature = match feature_def.iter().find(|(bits, _)| size.bits() <= *bits) {
+                Some((_, feature)) => feature,
+                None => panic!("Unknown vector size: {}; arg = {:?}", size.bits(), arg_abi),
+            };
+            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.
+pub 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| {
+        tcx.dcx().emit_err(AbiErrorDisabledVectorTypeDef {
+            span: tcx.def_span(instance.def_id()),
+            required_feature,
+        });
+    })
+}
+
+/// 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 fn check_call_site_abi<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    ty: Ty<'tcx>,
+    span: Span,
+    caller: InstanceKind<'tcx>,
+) {
+    let param_env = ParamEnv::reveal_all();
+    let callee_abi = match *ty.kind() {
+        ty::FnPtr(..) => tcx.fn_abi_of_fn_ptr(param_env.and((ty.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;
+            }
+            let instance = ty::Instance::expect_resolve(tcx, param_env, def_id, args, span);
+            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;
+    };
+    do_check_abi(tcx, callee_abi, caller.def_id(), |required_feature| {
+        tcx.dcx().emit_err(AbiErrorDisabledVectorTypeCall { span, required_feature });
+    })
+}

compiler/rustc_monomorphize/src/errors.rs

@@ -92,3 +92,21 @@ pub(crate) struct StartNotFound;
 pub(crate) struct UnknownCguCollectionMode<'a> {
     pub mode: &'a str,
 }
+
+#[derive(Diagnostic)]
+#[diag(monomorphize_abi_error_disabled_vector_type_def)]
+#[help]
+pub struct AbiErrorDisabledVectorTypeDef<'a> {
+    #[primary_span]
+    pub span: Span,
+    pub required_feature: &'a str,
+}
+
+#[derive(Diagnostic)]
+#[diag(monomorphize_abi_error_disabled_vector_type_call)]
+#[help]
+pub struct AbiErrorDisabledVectorTypeCall<'a> {
+    #[primary_span]
+    pub span: Span,
+    pub required_feature: &'a str,
+}

library/core/src/primitive_docs.rs

@@ -1752,8 +1752,7 @@ mod prim_ref {}
 ///
 /// For two signatures to be considered *ABI-compatible*, they must use a compatible ABI string,
 /// must take the same number of arguments, the individual argument types and the return types must
-/// be ABI-compatible, and the target feature requirements must be met (see the subsection below for
-/// the last point). The ABI string is declared via `extern "ABI" fn(...) -> ...`; note that
+/// be ABI-compatible. The ABI string is declared via `extern "ABI" fn(...) -> ...`; note that
 /// `fn name(...) -> ...` implicitly uses the `"Rust"` ABI string and `extern fn name(...) -> ...`
 /// implicitly uses the `"C"` ABI string.
 ///
@@ -1821,24 +1820,6 @@ mod prim_ref {}
 /// Behavior since transmuting `None::<NonZero<i32>>` to `NonZero<i32>` violates the non-zero
 /// requirement.
 ///
-/// #### Requirements concerning target features
-///
-/// Under some conditions, the signature used by the caller and the callee can be ABI-incompatible
-/// even if the exact same ABI string and types are being used. As an example, the
-/// `std::arch::x86_64::__m256` type has a different `extern "C"` ABI when the `avx` feature is
-/// enabled vs when it is not enabled.
-///
-/// Therefore, to ensure ABI compatibility when code using different target features is combined
-/// (such as via `#[target_feature]`), we further require that one of the following conditions is
-/// met:
-///
-/// - The function uses the `"Rust"` ABI string (which is the default without `extern`).
-/// - Caller and callee are using the exact same set of target features. For the callee we consider
-///   the features enabled (via `#[target_feature]` and `-C target-feature`/`-C target-cpu`) at the
-///   declaration site; for the caller we consider the features enabled at the call site.
-/// - Neither any argument nor the return value involves a SIMD type (`#[repr(simd)]`) that is not
-///   behind a pointer indirection (i.e., `*mut __m256` is fine, but `(i32, __m256)` is not).
-///
 /// ### Trait implementations
 ///
 /// In this documentation the shorthand `fn(T₁, T₂, …, Tₙ)` is used to represent non-variadic

tests/assembly/simd-bitmask.rs

@@ -1,3 +1,4 @@
+//@ ignore-test
 //@ revisions: x86 x86-avx2 x86-avx512 aarch64
 //@ [x86] compile-flags: --target=x86_64-unknown-linux-gnu -C llvm-args=-x86-asm-syntax=intel
 //@ [x86] needs-llvm-components: x86

tests/assembly/simd-intrinsic-gather.rs

@@ -1,3 +1,4 @@
+//@ ignore-test
 //@ revisions: x86-avx512
 //@ [x86-avx512] compile-flags: --target=x86_64-unknown-linux-gnu -C llvm-args=-x86-asm-syntax=intel
 //@ [x86-avx512] compile-flags: -C target-feature=+avx512f,+avx512vl,+avx512bw,+avx512dq

tests/assembly/simd-intrinsic-mask-load.rs

@@ -1,3 +1,4 @@
+//@ ignore-test
 //@ revisions: x86-avx2 x86-avx512
 //@ [x86-avx2] compile-flags: --target=x86_64-unknown-linux-gnu -C llvm-args=-x86-asm-syntax=intel
 //@ [x86-avx2] compile-flags: -C target-feature=+avx2

tests/assembly/simd-intrinsic-mask-reduce.rs

@@ -1,3 +1,4 @@
+//@ ignore-test
 // verify that simd mask reductions do not introduce additional bit shift operations
 //@ revisions: x86 aarch64
 //@ [x86] compile-flags: --target=x86_64-unknown-linux-gnu -C llvm-args=-x86-asm-syntax=intel

tests/assembly/simd-intrinsic-mask-store.rs

@@ -1,3 +1,4 @@
+//@ ignore-test
 //@ revisions: x86-avx2 x86-avx512
 //@ [x86-avx2] compile-flags: --target=x86_64-unknown-linux-gnu -C llvm-args=-x86-asm-syntax=intel
 //@ [x86-avx2] compile-flags: -C target-feature=+avx2

tests/assembly/simd-intrinsic-scatter.rs

@@ -1,3 +1,4 @@
+//@ ignore-test
 //@ revisions: x86-avx512
 //@ [x86-avx512] compile-flags: --target=x86_64-unknown-linux-gnu -C llvm-args=-x86-asm-syntax=intel
 //@ [x86-avx512] compile-flags: -C target-feature=+avx512f,+avx512vl,+avx512bw,+avx512dq

tests/assembly/simd-intrinsic-select.rs

@@ -1,3 +1,4 @@
+//@ ignore-test
 //@ revisions: x86-avx2 x86-avx512 aarch64
 //@ [x86-avx2] compile-flags: --target=x86_64-unknown-linux-gnu -C llvm-args=-x86-asm-syntax=intel
 //@ [x86-avx2] compile-flags: -C target-feature=+avx2

tests/ui/simd-abi-checks.rs

@@ -0,0 +1,69 @@
+//@ only-x86_64
+//@ build-fail
+
+#![feature(avx512_target_feature)]
+#![feature(portable_simd)]
+#![allow(improper_ctypes_definitions)]
+
+use std::arch::x86_64::*;
+
+#[repr(transparent)]
+struct Wrapper(__m256);
+
+unsafe extern "C" fn w(_: Wrapper) {
+    //~^ ABI error: this function definition uses a avx vector type, which is not enabled
+    todo!()
+}
+
+unsafe extern "C" fn f(_: __m256) {
+    //~^ ABI error: this function definition uses a avx vector type, which is not enabled
+    todo!()
+}
+
+unsafe extern "C" fn g() -> __m256 {
+    //~^ ABI error: this function definition uses a avx vector type, which is not enabled
+    todo!()
+}
+
+#[target_feature(enable = "avx2")]
+unsafe extern "C" fn favx(_: __m256) {
+    todo!()
+}
+
+#[target_feature(enable = "avx")]
+unsafe extern "C" fn gavx() -> __m256 {
+    todo!()
+}
+
+fn as_f64x8(d: __m512d) -> std::simd::f64x8 {
+    unsafe { std::mem::transmute(d) }
+}
+
+unsafe fn test() {
+    let arg = std::mem::transmute([0.0f64; 8]);
+    as_f64x8(arg);
+}
+
+fn main() {
+    unsafe {
+        f(g());
+        //~^ ERROR ABI error: this function call uses a avx vector type, which is not enabled in the caller
+        //~| ERROR ABI error: this function call uses a avx vector type, which is not enabled in the caller
+    }
+
+    unsafe {
+        favx(gavx());
+        //~^ ERROR ABI error: this function call uses a avx vector type, which is not enabled in the caller
+        //~| ERROR ABI error: this function call uses a avx vector type, which is not enabled in the caller
+    }
+
+    unsafe {
+        test();
+    }
+
+    unsafe {
+        w(Wrapper(g()));
+        //~^ ERROR ABI error: this function call uses a avx vector type, which is not enabled in the caller
+        //~| ERROR ABI error: this function call uses a avx vector type, which is not enabled in the caller
+    }
+}

tests/ui/simd-abi-checks.stderr

@@ -0,0 +1,74 @@
+error: ABI error: this function call uses a avx vector type, which is not enabled in the caller
+  --> $DIR/simd-abi-checks.rs:49:11
+   |
+LL |         f(g());
+   |           ^^^
+   |
+   = help: consider enabling it globally (-C target-feature=+avx) or locally (#[target_feature(enable="avx")])
+
+error: ABI error: this function call uses a avx vector type, which is not enabled in the caller
+  --> $DIR/simd-abi-checks.rs:49:9
+   |
+LL |         f(g());
+   |         ^^^^^^
+   |
+   = help: consider enabling it globally (-C target-feature=+avx) or locally (#[target_feature(enable="avx")])
+
+error: ABI error: this function call uses a avx vector type, which is not enabled in the caller
+  --> $DIR/simd-abi-checks.rs:55:14
+   |
+LL |         favx(gavx());
+   |              ^^^^^^
+   |
+   = help: consider enabling it globally (-C target-feature=+avx) or locally (#[target_feature(enable="avx")])
+
+error: ABI error: this function call uses a avx vector type, which is not enabled in the caller
+  --> $DIR/simd-abi-checks.rs:55:9
+   |
+LL |         favx(gavx());
+   |         ^^^^^^^^^^^^
+   |
+   = help: consider enabling it globally (-C target-feature=+avx) or locally (#[target_feature(enable="avx")])
+
+error: ABI error: this function call uses a avx vector type, which is not enabled in the caller
+  --> $DIR/simd-abi-checks.rs:65:19
+   |
+LL |         w(Wrapper(g()));
+   |                   ^^^
+   |
+   = help: consider enabling it globally (-C target-feature=+avx) or locally (#[target_feature(enable="avx")])
+
+error: ABI error: this function call uses a avx vector type, which is not enabled in the caller
+  --> $DIR/simd-abi-checks.rs:65:9
+   |
+LL |         w(Wrapper(g()));
+   |         ^^^^^^^^^^^^^^^
+   |
+   = help: consider enabling it globally (-C target-feature=+avx) or locally (#[target_feature(enable="avx")])
+
+error: ABI error: this function definition uses a avx vector type, which is not enabled
+  --> $DIR/simd-abi-checks.rs:23:1
+   |
+LL | unsafe extern "C" fn g() -> __m256 {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: consider enabling it globally (-C target-feature=+avx) or locally (#[target_feature(enable="avx")])
+
+error: ABI error: this function definition uses a avx vector type, which is not enabled
+  --> $DIR/simd-abi-checks.rs:18:1
+   |
+LL | unsafe extern "C" fn f(_: __m256) {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: consider enabling it globally (-C target-feature=+avx) or locally (#[target_feature(enable="avx")])
+
+error: ABI error: this function definition uses a avx vector type, which is not enabled
+  --> $DIR/simd-abi-checks.rs:13:1
+   |
+LL | unsafe extern "C" fn w(_: Wrapper) {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: consider enabling it globally (-C target-feature=+avx) or locally (#[target_feature(enable="avx")])
+
+error: aborting due to 9 previous errors
+