Auto merge of #133950 - matthiaskrgr:rollup-b7g5p73, r=matthiaskrgr

Rollup of 5 pull requests

Successful merges:

 - #130777 (rust_for_linux: -Zreg-struct-return commandline flag for X86 (#116973))
 - #133211 (Extend Miri to correctly pass mutable pointers through FFI)
 - #133790 (Improve documentation for Vec::extend_from_within)
 - #133930 (rustbook: update to use new mdbook-trpl package from The Book)
 - #133931 (Only allow PassMode::Direct for aggregates on wasm when using the C ABI)

r? `@ghost`
`@rustbot` modify labels: rollup

compiler/rustc_codegen_gcc/src/context.rs

@@ -544,7 +544,10 @@ impl<'gcc, 'tcx> HasWasmCAbiOpt for CodegenCx<'gcc, 'tcx> {
 
 impl<'gcc, 'tcx> HasX86AbiOpt for CodegenCx<'gcc, 'tcx> {
     fn x86_abi_opt(&self) -> X86Abi {
-        X86Abi { regparm: self.tcx.sess.opts.unstable_opts.regparm }
+        X86Abi {
+            regparm: self.tcx.sess.opts.unstable_opts.regparm,
+            reg_struct_return: self.tcx.sess.opts.unstable_opts.reg_struct_return,
+        }
     }
 }
 

compiler/rustc_const_eval/src/const_eval/dummy_machine.rs

@@ -168,9 +168,9 @@ impl<'tcx> interpret::Machine<'tcx> for DummyMachine {
         })
     }
 
-    fn expose_ptr(
+    fn expose_provenance(
-        _ecx: &mut InterpCx<'tcx, Self>,
+        _ecx: &InterpCx<'tcx, Self>,
-        _ptr: interpret::Pointer<Self::Provenance>,
+        _provenance: Self::Provenance,
     ) -> interpret::InterpResult<'tcx> {
         unimplemented!()
     }

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -21,9 +21,8 @@ use crate::errors::{LongRunning, LongRunningWarn};
 use crate::fluent_generated as fluent;
 use crate::interpret::{
     self, AllocId, AllocRange, ConstAllocation, CtfeProvenance, FnArg, Frame, GlobalAlloc, ImmTy,
-    InterpCx, InterpResult, MPlaceTy, OpTy, Pointer, RangeSet, Scalar, compile_time_machine,
+    InterpCx, InterpResult, MPlaceTy, OpTy, RangeSet, Scalar, compile_time_machine, interp_ok,
-    interp_ok, throw_exhaust, throw_inval, throw_ub, throw_ub_custom, throw_unsup,
+    throw_exhaust, throw_inval, throw_ub, throw_ub_custom, throw_unsup, throw_unsup_format,
-    throw_unsup_format,
 };
 
 /// When hitting this many interpreted terminators we emit a deny by default lint
@@ -586,7 +585,10 @@ impl<'tcx> interpret::Machine<'tcx> for CompileTimeMachine<'tcx> {
     }
 
     #[inline(always)]
-    fn expose_ptr(_ecx: &mut InterpCx<'tcx, Self>, _ptr: Pointer) -> InterpResult<'tcx> {
+    fn expose_provenance(
+        _ecx: &InterpCx<'tcx, Self>,
+        _provenance: Self::Provenance,
+    ) -> InterpResult<'tcx> {
         // This is only reachable with -Zunleash-the-miri-inside-of-you.
         throw_unsup_format!("exposing pointers is not possible at compile-time")
     }

compiler/rustc_const_eval/src/interpret/cast.rs

@@ -238,7 +238,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         let scalar = src.to_scalar();
         let ptr = scalar.to_pointer(self)?;
         match ptr.into_pointer_or_addr() {
-            Ok(ptr) => M::expose_ptr(self, ptr)?,
+            Ok(ptr) => M::expose_provenance(self, ptr.provenance)?,
             Err(_) => {} // Do nothing, exposing an invalid pointer (`None` provenance) is a NOP.
         };
         interp_ok(ImmTy::from_scalar(

compiler/rustc_const_eval/src/interpret/machine.rs

@@ -327,11 +327,11 @@ pub trait Machine<'tcx>: Sized {
         addr: u64,
     ) -> InterpResult<'tcx, Pointer<Option<Self::Provenance>>>;
 
-    /// Marks a pointer as exposed, allowing it's provenance
+    /// Marks a pointer as exposed, allowing its provenance
     /// to be recovered. "Pointer-to-int cast"
-    fn expose_ptr(
+    fn expose_provenance(
-        ecx: &mut InterpCx<'tcx, Self>,
+        ecx: &InterpCx<'tcx, Self>,
-        ptr: Pointer<Self::Provenance>,
+        provenance: Self::Provenance,
     ) -> InterpResult<'tcx>;
 
     /// Convert a pointer with provenance into an allocation-offset pair and extra provenance info.

compiler/rustc_const_eval/src/interpret/memory.rs

@@ -944,6 +944,52 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         interp_ok(())
     }
 
+    /// Handle the effect an FFI call might have on the state of allocations.
+    /// This overapproximates the modifications which external code might make to memory:
+    /// We set all reachable allocations as initialized, mark all provenances as exposed
+    /// and overwrite them with `Provenance::WILDCARD`.
+    pub fn prepare_for_native_call(
+        &mut self,
+        id: AllocId,
+        initial_prov: M::Provenance,
+    ) -> InterpResult<'tcx> {
+        // Expose provenance of the root allocation.
+        M::expose_provenance(self, initial_prov)?;
+
+        let mut done = FxHashSet::default();
+        let mut todo = vec![id];
+        while let Some(id) = todo.pop() {
+            if !done.insert(id) {
+                // We already saw this allocation before, don't process it again.
+                continue;
+            }
+            let info = self.get_alloc_info(id);
+
+            // If there is no data behind this pointer, skip this.
+            if !matches!(info.kind, AllocKind::LiveData) {
+                continue;
+            }
+
+            // Expose all provenances in this allocation, and add them to `todo`.
+            let alloc = self.get_alloc_raw(id)?;
+            for prov in alloc.provenance().provenances() {
+                M::expose_provenance(self, prov)?;
+                if let Some(id) = prov.get_alloc_id() {
+                    todo.push(id);
+                }
+            }
+
+            // Prepare for possible write from native code if mutable.
+            if info.mutbl.is_mut() {
+                self.get_alloc_raw_mut(id)?
+                    .0
+                    .prepare_for_native_write()
+                    .map_err(|e| e.to_interp_error(id))?;
+            }
+        }
+        interp_ok(())
+    }
+
     /// Create a lazy debug printer that prints the given allocation and all allocations it points
     /// to, recursively.
     #[must_use]

compiler/rustc_interface/src/tests.rs

@@ -832,6 +832,7 @@ fn test_unstable_options_tracking_hash() {
     tracked!(precise_enum_drop_elaboration, false);
     tracked!(profile_sample_use, Some(PathBuf::from("abc")));
     tracked!(profiler_runtime, "abc".to_string());
+    tracked!(reg_struct_return, true);
     tracked!(regparm, Some(3));
     tracked!(relax_elf_relocations, Some(true));
     tracked!(remap_cwd_prefix, Some(PathBuf::from("abc")));

compiler/rustc_middle/src/mir/interpret/allocation.rs

@@ -643,6 +643,28 @@ impl<Prov: Provenance, Extra, Bytes: AllocBytes> Allocation<Prov, Extra, Bytes>
         Ok(())
     }
 
+    /// Initialize all previously uninitialized bytes in the entire allocation, and set
+    /// provenance of everything to `Wildcard`. Before calling this, make sure all
+    /// provenance in this allocation is exposed!
+    pub fn prepare_for_native_write(&mut self) -> AllocResult {
+        let full_range = AllocRange { start: Size::ZERO, size: Size::from_bytes(self.len()) };
+        // Overwrite uninitialized bytes with 0, to ensure we don't leak whatever their value happens to be.
+        for chunk in self.init_mask.range_as_init_chunks(full_range) {
+            if !chunk.is_init() {
+                let uninit_bytes = &mut self.bytes
+                    [chunk.range().start.bytes_usize()..chunk.range().end.bytes_usize()];
+                uninit_bytes.fill(0);
+            }
+        }
+        // Mark everything as initialized now.
+        self.mark_init(full_range, true);
+
+        // Set provenance of all bytes to wildcard.
+        self.provenance.write_wildcards(self.len());
+
+        Ok(())
+    }
+
     /// Remove all provenance in the given memory range.
     pub fn clear_provenance(&mut self, cx: &impl HasDataLayout, range: AllocRange) -> AllocResult {
         self.provenance.clear(range, cx)?;

compiler/rustc_middle/src/mir/interpret/allocation/provenance_map.rs

@@ -195,6 +195,25 @@ impl<Prov: Provenance> ProvenanceMap<Prov> {
 
         Ok(())
     }
+
+    /// Overwrites all provenance in the allocation with wildcard provenance.
+    ///
+    /// Provided for usage in Miri and panics otherwise.
+    pub fn write_wildcards(&mut self, alloc_size: usize) {
+        assert!(
+            Prov::OFFSET_IS_ADDR,
+            "writing wildcard provenance is not supported when `OFFSET_IS_ADDR` is false"
+        );
+        let wildcard = Prov::WILDCARD.unwrap();
+
+        // Remove all pointer provenances, then write wildcards into the whole byte range.
+        self.ptrs.clear();
+        let last = Size::from_bytes(alloc_size);
+        let bytes = self.bytes.get_or_insert_with(Box::default);
+        for offset in Size::ZERO..last {
+            bytes.insert(offset, wildcard);
+        }
+    }
 }
 
 /// A partial, owned list of provenance to transfer into another allocation.

compiler/rustc_middle/src/mir/interpret/pointer.rs

@@ -66,6 +66,9 @@ pub trait Provenance: Copy + fmt::Debug + 'static {
     ///   pointer, and implement ptr-to-int transmutation by stripping provenance.
     const OFFSET_IS_ADDR: bool;
 
+    /// If wildcard provenance is implemented, contains the unique, general wildcard provenance variant.
+    const WILDCARD: Option<Self>;
+
     /// Determines how a pointer should be printed.
     fn fmt(ptr: &Pointer<Self>, f: &mut fmt::Formatter<'_>) -> fmt::Result;
 
@@ -168,6 +171,9 @@ impl Provenance for CtfeProvenance {
     // so ptr-to-int casts are not possible (since we do not know the global physical offset).
     const OFFSET_IS_ADDR: bool = false;
 
+    // `CtfeProvenance` does not implement wildcard provenance.
+    const WILDCARD: Option<Self> = None;
+
     fn fmt(ptr: &Pointer<Self>, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         // Print AllocId.
         fmt::Debug::fmt(&ptr.provenance.alloc_id(), f)?; // propagates `alternate` flag
@@ -197,6 +203,9 @@ impl Provenance for AllocId {
     // so ptr-to-int casts are not possible (since we do not know the global physical offset).
     const OFFSET_IS_ADDR: bool = false;
 
+    // `AllocId` does not implement wildcard provenance.
+    const WILDCARD: Option<Self> = None;
+
     fn fmt(ptr: &Pointer<Self>, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         // Forward `alternate` flag to `alloc_id` printing.
         if f.alternate() {

compiler/rustc_middle/src/ty/layout.rs

@@ -552,7 +552,10 @@ impl<'tcx> HasWasmCAbiOpt for TyCtxt<'tcx> {
 
 impl<'tcx> HasX86AbiOpt for TyCtxt<'tcx> {
     fn x86_abi_opt(&self) -> X86Abi {
-        X86Abi { regparm: self.sess.opts.unstable_opts.regparm }
+        X86Abi {
+            regparm: self.sess.opts.unstable_opts.regparm,
+            reg_struct_return: self.sess.opts.unstable_opts.reg_struct_return,
+        }
     }
 }
 

compiler/rustc_session/messages.ftl

@@ -135,5 +135,6 @@ session_unsupported_crate_type_for_target =
 
 session_unsupported_dwarf_version = requested DWARF version {$dwarf_version} is greater than 5
 
+session_unsupported_reg_struct_return_arch = `-Zreg-struct-return` is only supported on x86
 session_unsupported_regparm = `-Zregparm={$regparm}` is unsupported (valid values 0-3)
 session_unsupported_regparm_arch = `-Zregparm=N` is only supported on x86

compiler/rustc_session/src/errors.rs

@@ -489,6 +489,10 @@ pub(crate) struct UnsupportedRegparm {
 #[diag(session_unsupported_regparm_arch)]
 pub(crate) struct UnsupportedRegparmArch;
 
+#[derive(Diagnostic)]
+#[diag(session_unsupported_reg_struct_return_arch)]
+pub(crate) struct UnsupportedRegStructReturnArch;
+
 #[derive(Diagnostic)]
 #[diag(session_failed_to_create_profiler)]
 pub(crate) struct FailedToCreateProfiler {

compiler/rustc_session/src/options.rs

@@ -1988,6 +1988,9 @@ options! {
         "enable queries of the dependency graph for regression testing (default: no)"),
     randomize_layout: bool = (false, parse_bool, [TRACKED],
         "randomize the layout of types (default: no)"),
+    reg_struct_return: bool = (false, parse_bool, [TRACKED],
+        "On x86-32 targets, it overrides the default ABI to return small structs in registers.
+        It is UNSOUND to link together crates that use different values for this flag!"),
     regparm: Option<u32> = (None, parse_opt_number, [TRACKED],
         "On x86-32 targets, setting this to N causes the compiler to pass N arguments \
         in registers EAX, EDX, and ECX instead of on the stack for\

compiler/rustc_session/src/session.rs

@@ -1305,6 +1305,11 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
             sess.dcx().emit_err(errors::UnsupportedRegparmArch);
         }
     }
+    if sess.opts.unstable_opts.reg_struct_return {
+        if sess.target.arch != "x86" {
+            sess.dcx().emit_err(errors::UnsupportedRegStructReturnArch);
+        }
+    }
 
     // The code model check applies to `thunk` and `thunk-extern`, but not `thunk-inline`, so it is
     // kept as a `match` to force a change if new ones are added, even if we currently only support

compiler/rustc_target/src/callconv/mod.rs

@@ -661,7 +661,9 @@ impl<'a, Ty> FnAbi<'a, Ty> {
                     }
                     _ => (x86::Flavor::General, None),
                 };
-                x86::compute_abi_info(cx, self, x86::X86Options { flavor, regparm });
+                let reg_struct_return = cx.x86_abi_opt().reg_struct_return;
+                let opts = x86::X86Options { flavor, regparm, reg_struct_return };
+                x86::compute_abi_info(cx, self, opts);
             }
             "x86_64" => match abi {
                 spec::abi::Abi::SysV64 { .. } => x86_64::compute_abi_info(cx, self),

compiler/rustc_target/src/callconv/x86.rs

@@ -14,6 +14,7 @@ pub(crate) enum Flavor {
 pub(crate) struct X86Options {
     pub flavor: Flavor,
     pub regparm: Option<u32>,
+    pub reg_struct_return: bool,
 }
 
 pub(crate) fn compute_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>, opts: X86Options)
@@ -31,7 +32,7 @@ where
             // https://www.angelcode.com/dev/callconv/callconv.html
             // Clang's ABI handling is in lib/CodeGen/TargetInfo.cpp
             let t = cx.target_spec();
-            if t.abi_return_struct_as_int {
+            if t.abi_return_struct_as_int || opts.reg_struct_return {
                 // According to Clang, everyone but MSVC returns single-element
                 // float aggregates directly in a floating-point register.
                 if !t.is_like_msvc && fn_abi.ret.layout.is_single_fp_element(cx) {

compiler/rustc_target/src/spec/mod.rs

@@ -2117,6 +2117,8 @@ pub struct X86Abi {
     /// On x86-32 targets, the regparm N causes the compiler to pass arguments
     /// in registers EAX, EDX, and ECX instead of on the stack.
     pub regparm: Option<u32>,
+    /// Override the default ABI to return small structs in registers
+    pub reg_struct_return: bool,
 }
 
 pub trait HasX86AbiOpt {

compiler/rustc_ty_utils/src/abi.rs

@@ -473,20 +473,30 @@ fn fn_abi_sanity_check<'tcx>(
                         // This really shouldn't happen even for sized aggregates, since
                         // `immediate_llvm_type` will use `layout.fields` to turn this Rust type into an
                         // LLVM type. This means all sorts of Rust type details leak into the ABI.
-                        // However wasm sadly *does* currently use this mode so we have to allow it --
+                        // However wasm sadly *does* currently use this mode for it's "C" ABI so we
-                        // but we absolutely shouldn't let any more targets do that.
+                        // have to allow it -- but we absolutely shouldn't let any more targets do
-                        // (Also see <https://github.com/rust-lang/rust/issues/115666>.)
+                        // that. (Also see <https://github.com/rust-lang/rust/issues/115666>.)
                         //
                         // The unstable abi `PtxKernel` also uses Direct for now.
                         // It needs to switch to something else before stabilization can happen.
                         // (See issue: https://github.com/rust-lang/rust/issues/117271)
-                        assert!(
+                        //
-                            matches!(&*tcx.sess.target.arch, "wasm32" | "wasm64")
+                        // And finally the unadjusted ABI is ill specified and uses Direct for all
-                                || matches!(spec_abi, ExternAbi::PtxKernel | ExternAbi::Unadjusted),
+                        // args, but unfortunately we need it for calling certain LLVM intrinsics.
-                            "`PassMode::Direct` for aggregates only allowed for \"unadjusted\" and \"ptx-kernel\" functions and on wasm\n\
+
-                          Problematic type: {:#?}",
+                        match spec_abi {
-                            arg.layout,
+                            ExternAbi::Unadjusted => {}
-                        );
+                            ExternAbi::PtxKernel => {}
+                            ExternAbi::C { unwind: _ }
+                                if matches!(&*tcx.sess.target.arch, "wasm32" | "wasm64") => {}
+                            _ => {
+                                panic!(
+                                    "`PassMode::Direct` for aggregates only allowed for \"unadjusted\" and \"ptx-kernel\" functions and on wasm\n\
+                                      Problematic type: {:#?}",
+                                    arg.layout,
+                                );
+                            }
+                        }
                     }
                 }
             }

library/alloc/src/vec/mod.rs

@@ -3025,26 +3025,29 @@ impl<T: Clone, A: Allocator> Vec<T, A> {
         self.spec_extend(other.iter())
     }
 
-    /// Copies elements from `src` range to the end of the vector.
+    /// Given a range `src`, clones a slice of elements in that range and appends it to the end.
+    ///
+    /// `src` must be a range that can form a valid subslice of the `Vec`.
     ///
     /// # Panics
     ///
-    /// Panics if the starting point is greater than the end point or if
+    /// Panics if starting index is greater than the end index
-    /// the end point is greater than the length of the vector.
+    /// or if the index is greater than the length of the vector.
     ///
     /// # Examples
     ///
     /// ```
-    /// let mut vec = vec![0, 1, 2, 3, 4];
+    /// let mut characters = vec!['a', 'b', 'c', 'd', 'e'];
+    /// characters.extend_from_within(2..);
+    /// assert_eq!(characters, ['a', 'b', 'c', 'd', 'e', 'c', 'd', 'e']);
     ///
-    /// vec.extend_from_within(2..);
+    /// let mut numbers = vec![0, 1, 2, 3, 4];
-    /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4]);
+    /// numbers.extend_from_within(..2);
+    /// assert_eq!(numbers, [0, 1, 2, 3, 4, 0, 1]);
     ///
-    /// vec.extend_from_within(..2);
+    /// let mut strings = vec![String::from("hello"), String::from("world"), String::from("!")];
-    /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1]);
+    /// strings.extend_from_within(1..=2);
-    ///
+    /// assert_eq!(strings, ["hello", "world", "!", "world", "!"]);
-    /// vec.extend_from_within(4..8);
-    /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1, 4, 2, 3, 4]);
     /// ```
     #[cfg(not(no_global_oom_handling))]
     #[stable(feature = "vec_extend_from_within", since = "1.53.0")]

src/doc/book

@@ -1 +1 @@
-Subproject commit 614c19cb4025636eb2ba68ebb3d44e3bd3a5e6e4
+Subproject commit 9900d976bbfecf4e8124da54351a9ad85ee3c7f3

src/doc/unstable-book/src/compiler-flags/reg-struct-return.md

@@ -0,0 +1,15 @@
+# `reg-struct-return`
+
+The tracking issue for this feature is: https://github.com/rust-lang/rust/issues/116973.
+
+------------------------
+
+Option -Zreg-struct-return causes the compiler to return small structs in registers
+instead of on the stack for extern "C"-like functions.
+It is UNSOUND to link together crates that use different values for this flag.
+It is only supported on `x86`.
+
+It is equivalent to [Clang]'s and [GCC]'s `-freg-struct-return`.
+
+[Clang]: https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-freg-struct-return
+[GCC]: https://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html#index-freg-struct-return

src/tools/miri/src/alloc_addresses/mod.rs

@@ -286,9 +286,9 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
 
 impl<'tcx> EvalContextExt<'tcx> for crate::MiriInterpCx<'tcx> {}
 pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
-    fn expose_ptr(&mut self, alloc_id: AllocId, tag: BorTag) -> InterpResult<'tcx> {
+    fn expose_ptr(&self, alloc_id: AllocId, tag: BorTag) -> InterpResult<'tcx> {
-        let this = self.eval_context_mut();
+        let this = self.eval_context_ref();
-        let global_state = this.machine.alloc_addresses.get_mut();
+        let mut global_state = this.machine.alloc_addresses.borrow_mut();
         // In strict mode, we don't need this, so we can save some cycles by not tracking it.
         if global_state.provenance_mode == ProvenanceMode::Strict {
             return interp_ok(());
@@ -299,8 +299,10 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             return interp_ok(());
         }
         trace!("Exposing allocation id {alloc_id:?}");
-        let global_state = this.machine.alloc_addresses.get_mut();
         global_state.exposed.insert(alloc_id);
+        // Release the global state before we call `expose_tag`, which may call `get_alloc_info_extra`,
+        // which may need access to the global state.
+        drop(global_state);
         if this.machine.borrow_tracker.is_some() {
             this.expose_tag(alloc_id, tag)?;
         }

src/tools/miri/src/borrow_tracker/mod.rs

@@ -302,8 +302,8 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         }
     }
 
-    fn expose_tag(&mut self, alloc_id: AllocId, tag: BorTag) -> InterpResult<'tcx> {
+    fn expose_tag(&self, alloc_id: AllocId, tag: BorTag) -> InterpResult<'tcx> {
-        let this = self.eval_context_mut();
+        let this = self.eval_context_ref();
         let method = this.machine.borrow_tracker.as_ref().unwrap().borrow().borrow_tracker_method;
         match method {
             BorrowTrackerMethod::StackedBorrows => this.sb_expose_tag(alloc_id, tag),

src/tools/miri/src/borrow_tracker/stacked_borrows/mod.rs

@@ -1011,8 +1011,8 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
     }
 
     /// Mark the given tag as exposed. It was found on a pointer with the given AllocId.
-    fn sb_expose_tag(&mut self, alloc_id: AllocId, tag: BorTag) -> InterpResult<'tcx> {
+    fn sb_expose_tag(&self, alloc_id: AllocId, tag: BorTag) -> InterpResult<'tcx> {
-        let this = self.eval_context_mut();
+        let this = self.eval_context_ref();
 
         // Function pointers and dead objects don't have an alloc_extra so we ignore them.
         // This is okay because accessing them is UB anyway, no need for any Stacked Borrows checks.

src/tools/miri/src/borrow_tracker/tree_borrows/mod.rs

@@ -532,8 +532,8 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
     }
 
     /// Mark the given tag as exposed. It was found on a pointer with the given AllocId.
-    fn tb_expose_tag(&mut self, alloc_id: AllocId, tag: BorTag) -> InterpResult<'tcx> {
+    fn tb_expose_tag(&self, alloc_id: AllocId, tag: BorTag) -> InterpResult<'tcx> {
-        let this = self.eval_context_mut();
+        let this = self.eval_context_ref();
 
         // Function pointers and dead objects don't have an alloc_extra so we ignore them.
         // This is okay because accessing them is UB anyway, no need for any Tree Borrows checks.

src/tools/miri/src/machine.rs

@@ -270,6 +270,9 @@ impl interpret::Provenance for Provenance {
     /// We use absolute addresses in the `offset` of a `StrictPointer`.
     const OFFSET_IS_ADDR: bool = true;
 
+    /// Miri implements wildcard provenance.
+    const WILDCARD: Option<Self> = Some(Provenance::Wildcard);
+
     fn get_alloc_id(self) -> Option<AllocId> {
         match self {
             Provenance::Concrete { alloc_id, .. } => Some(alloc_id),
@@ -1242,8 +1245,8 @@ impl<'tcx> Machine<'tcx> for MiriMachine<'tcx> {
     /// Called on `ptr as usize` casts.
     /// (Actually computing the resulting `usize` doesn't need machine help,
     /// that's just `Scalar::try_to_int`.)
-    fn expose_ptr(ecx: &mut InterpCx<'tcx, Self>, ptr: StrictPointer) -> InterpResult<'tcx> {
+    fn expose_provenance(ecx: &InterpCx<'tcx, Self>, provenance: Self::Provenance) -> InterpResult<'tcx> {
-        match ptr.provenance {
+        match provenance {
             Provenance::Concrete { alloc_id, tag } => ecx.expose_ptr(alloc_id, tag),
             Provenance::Wildcard => {
                 // No need to do anything for wildcard pointers as

src/tools/miri/src/shims/native_lib.rs

@@ -3,8 +3,11 @@ use std::ops::Deref;
 
 use libffi::high::call as ffi;
 use libffi::low::CodePtr;
-use rustc_abi::{BackendRepr, HasDataLayout};
+use rustc_abi::{BackendRepr, HasDataLayout, Size};
-use rustc_middle::ty::{self as ty, IntTy, UintTy};
+use rustc_middle::{
+    mir::interpret::Pointer,
+    ty::{self as ty, IntTy, UintTy},
+};
 use rustc_span::Symbol;
 
 use crate::*;
@@ -75,6 +78,11 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 unsafe { ffi::call::<()>(ptr, libffi_args.as_slice()) };
                 return interp_ok(ImmTy::uninit(dest.layout));
             }
+            ty::RawPtr(..) => {
+                let x = unsafe { ffi::call::<*const ()>(ptr, libffi_args.as_slice()) };
+                let ptr = Pointer::new(Provenance::Wildcard, Size::from_bytes(x.addr()));
+                Scalar::from_pointer(ptr, this)
+            }
             _ => throw_unsup_format!("unsupported return type for native call: {:?}", link_name),
         };
         interp_ok(ImmTy::from_scalar(scalar, dest.layout))
@@ -152,8 +160,26 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             if !matches!(arg.layout.backend_repr, BackendRepr::Scalar(_)) {
                 throw_unsup_format!("only scalar argument types are support for native calls")
             }
-            libffi_args.push(imm_to_carg(this.read_immediate(arg)?, this)?);
+            let imm = this.read_immediate(arg)?;
+            libffi_args.push(imm_to_carg(&imm, this)?);
+            // If we are passing a pointer, prepare the memory it points to.
+            if matches!(arg.layout.ty.kind(), ty::RawPtr(..)) {
+                let ptr = imm.to_scalar().to_pointer(this)?;
+                let Some(prov) = ptr.provenance else {
+                    // Pointer without provenance may not access any memory.
+                    continue;
+                };
+                // We use `get_alloc_id` for its best-effort behaviour with Wildcard provenance.
+                let Some(alloc_id) = prov.get_alloc_id() else {
+                    // Wildcard pointer, whatever it points to must be already exposed.
+                    continue;
+                };
+                this.prepare_for_native_call(alloc_id, prov)?;
+            }
         }
+        
+        // FIXME: In the future, we should also call `prepare_for_native_call` on all previously
+        // exposed allocations, since C may access any of them.
 
         // Convert them to `libffi::high::Arg` type.
         let libffi_args = libffi_args
@@ -220,7 +246,7 @@ impl<'a> CArg {
 
 /// Extract the scalar value from the result of reading a scalar from the machine,
 /// and convert it to a `CArg`.
-fn imm_to_carg<'tcx>(v: ImmTy<'tcx>, cx: &impl HasDataLayout) -> InterpResult<'tcx, CArg> {
+fn imm_to_carg<'tcx>(v: &ImmTy<'tcx>, cx: &impl HasDataLayout) -> InterpResult<'tcx, CArg> {
     interp_ok(match v.layout.ty.kind() {
         // If the primitive provided can be converted to a type matching the type pattern
         // then create a `CArg` of this primitive value with the corresponding `CArg` constructor.
@@ -238,18 +264,10 @@ fn imm_to_carg<'tcx>(v: ImmTy<'tcx>, cx: &impl HasDataLayout) -> InterpResult<'t
         ty::Uint(UintTy::U64) => CArg::UInt64(v.to_scalar().to_u64()?),
         ty::Uint(UintTy::Usize) =>
             CArg::USize(v.to_scalar().to_target_usize(cx)?.try_into().unwrap()),
-        ty::RawPtr(_, mutability) => {
+        ty::RawPtr(..) => {
-            // Arbitrary mutable pointer accesses are not currently supported in Miri.
+            let s = v.to_scalar().to_pointer(cx)?.addr();
-            if mutability.is_mut() {
+            // This relies on the `expose_provenance` in `addr_from_alloc_id`.
-                throw_unsup_format!(
+            CArg::RawPtr(std::ptr::with_exposed_provenance_mut(s.bytes_usize()))
-                    "unsupported mutable pointer type for native call: {}",
-                    v.layout.ty
-                );
-            } else {
-                let s = v.to_scalar().to_pointer(cx)?.addr();
-                // This relies on the `expose_provenance` in `addr_from_alloc_id`.
-                CArg::RawPtr(std::ptr::with_exposed_provenance_mut(s.bytes_usize()))
-            }
         }
         _ => throw_unsup_format!("unsupported argument type for native call: {}", v.layout.ty),
     })

src/tools/miri/tests/native-lib/pass/ptr_read_access.rs

@@ -3,17 +3,14 @@
 //@only-on-host
 
 fn main() {
-    test_pointer();
+    test_access_pointer();
-
+    test_access_simple();
-    test_simple();
+    test_access_nested();
-
+    test_access_static();
-    test_nested();
-
-    test_static();
 }
 
-// Test void function that dereferences a pointer and prints its contents from C.
+/// Test function that dereferences an int pointer and prints its contents from C.
-fn test_pointer() {
+fn test_access_pointer() {
     extern "C" {
         fn print_pointer(ptr: *const i32);
     }
@@ -23,8 +20,8 @@ fn test_pointer() {
     unsafe { print_pointer(&x) };
 }
 
-// Test function that dereferences a simple struct pointer and accesses a field.
+/// Test function that dereferences a simple struct pointer and accesses a field.
-fn test_simple() {
+fn test_access_simple() {
     #[repr(C)]
     struct Simple {
         field: i32,
@@ -39,8 +36,8 @@ fn test_simple() {
     assert_eq!(unsafe { access_simple(&simple) }, -42);
 }
 
-// Test function that dereferences nested struct pointers and accesses fields.
+/// Test function that dereferences nested struct pointers and accesses fields.
-fn test_nested() {
+fn test_access_nested() {
     use std::ptr::NonNull;
 
     #[derive(Debug, PartialEq, Eq)]
@@ -61,8 +58,8 @@ fn test_nested() {
     assert_eq!(unsafe { access_nested(&nested_2) }, 97);
 }
 
-// Test function that dereferences static struct pointers and accesses fields.
+/// Test function that dereferences a static struct pointer and accesses fields.
-fn test_static() {
+fn test_access_static() {
     #[repr(C)]
     struct Static {
         value: i32,

src/tools/miri/tests/native-lib/pass/ptr_write_access.rs

@@ -0,0 +1,208 @@
+// Only works on Unix targets
+//@ignore-target: windows wasm
+//@only-on-host
+//@compile-flags: -Zmiri-permissive-provenance
+
+
+#![feature(box_as_ptr)]
+
+use std::mem::MaybeUninit;
+use std::ptr::null;
+
+fn main() {
+    test_increment_int();
+    test_init_int();
+    test_init_array();
+    test_init_static_inner();
+    test_exposed();
+    test_swap_ptr();
+    test_swap_ptr_tuple();
+    test_overwrite_dangling();
+    test_pass_dangling();
+    test_swap_ptr_triple_dangling();
+    test_return_ptr();
+}
+
+/// Test function that modifies an int.
+fn test_increment_int() {
+    extern "C" {
+        fn increment_int(ptr: *mut i32);
+    }
+
+    let mut x = 11;
+
+    unsafe { increment_int(&mut x) };
+    assert_eq!(x, 12);
+}
+
+/// Test function that initializes an int.
+fn test_init_int() {
+    extern "C" {
+        fn init_int(ptr: *mut i32, val: i32);
+    }
+
+    let mut x = MaybeUninit::<i32>::uninit();
+    let val = 21;
+
+    let x = unsafe {
+        init_int(x.as_mut_ptr(), val);
+        x.assume_init()
+    };
+    assert_eq!(x, val);
+}
+
+/// Test function that initializes an array.
+fn test_init_array() {
+    extern "C" {
+        fn init_array(ptr: *mut i32, len: usize, val: i32);
+    }
+
+    const LEN: usize = 3;
+    let mut array = MaybeUninit::<[i32; LEN]>::uninit();
+    let val = 31;
+    
+    let array = unsafe {
+        init_array(array.as_mut_ptr().cast::<i32>(), LEN, val);
+        array.assume_init()
+    };
+    assert_eq!(array, [val; LEN]);
+}
+
+/// Test function that initializes an int pointed to by an immutable static.
+fn test_init_static_inner() {
+    #[repr(C)]
+    struct SyncPtr {
+        ptr: *mut i32
+    }
+    unsafe impl Sync for SyncPtr {}
+
+    extern "C" {
+        fn init_static_inner(s_ptr: *const SyncPtr, val: i32);
+    }
+
+    static mut INNER: MaybeUninit<i32> = MaybeUninit::uninit();
+    #[allow(static_mut_refs)]
+    static STATIC: SyncPtr = SyncPtr { ptr: unsafe { INNER.as_mut_ptr() } };
+    let val = 41;
+
+    let inner = unsafe {
+        init_static_inner(&STATIC, val);
+        INNER.assume_init()
+    };
+    assert_eq!(inner, val);
+}
+
+// Test function that marks an allocation as exposed.
+fn test_exposed() {
+    extern "C" {
+        fn ignore_ptr(ptr: *const i32);
+    }
+
+    let x = 51;
+    let ptr = &raw const x;
+    let p = ptr.addr();
+
+    unsafe { ignore_ptr(ptr) };
+    assert_eq!(unsafe { *(p as *const i32) }, x);
+}
+
+/// Test function that swaps two pointers and exposes the alloc of an int.
+fn test_swap_ptr() {
+    extern "C" {
+        fn swap_ptr(pptr0: *mut *const i32, pptr1: *mut *const i32);
+    }
+
+    let x = 61;
+    let (mut ptr0, mut ptr1) = (&raw const x, null());
+
+    unsafe { swap_ptr(&mut ptr0, &mut ptr1) };
+    assert_eq!(unsafe { *ptr1 }, x);
+}
+
+/// Test function that swaps two pointers in a struct and exposes the alloc of an int.
+fn test_swap_ptr_tuple() {
+    #[repr(C)]
+    struct Tuple {
+        ptr0: *const i32,
+        ptr1: *const i32,
+    }
+
+    extern "C" {
+        fn swap_ptr_tuple(t_ptr: *mut Tuple);
+    }
+
+    let x = 71;
+    let mut tuple = Tuple { ptr0: &raw const x, ptr1: null() };
+
+    unsafe { swap_ptr_tuple(&mut tuple) }
+    assert_eq!(unsafe { *tuple.ptr1 }, x);
+}
+
+/// Test function that interacts with a dangling pointer.
+fn test_overwrite_dangling() {
+    extern "C" {
+        fn overwrite_ptr(pptr: *mut *const i32);
+    }
+
+    let b = Box::new(81);
+    let mut ptr = Box::as_ptr(&b);
+    drop(b);
+
+    unsafe { overwrite_ptr(&mut ptr) };
+    assert_eq!(ptr, null());
+}
+
+/// Test function that passes a dangling pointer.
+fn test_pass_dangling() {
+    extern "C" {
+        fn ignore_ptr(ptr: *const i32);
+    }
+
+    let b = Box::new(91);
+    let ptr = Box::as_ptr(&b);
+    drop(b);
+
+    unsafe { ignore_ptr(ptr) };
+}
+
+/// Test function that interacts with a struct storing a dangling pointer.
+fn test_swap_ptr_triple_dangling() {
+    #[repr(C)]
+    struct Triple {
+        ptr0: *const i32,
+        ptr1: *const i32,
+        ptr2: *const i32,
+    }
+
+    extern "C" {
+        fn swap_ptr_triple_dangling(t_ptr: *const Triple);
+    }
+
+    let x = 101;
+    let b = Box::new(111);
+    let ptr = Box::as_ptr(&b);
+    drop(b);
+    let z = 121;
+    let triple = Triple {
+        ptr0: &raw const x,
+        ptr1: ptr,
+        ptr2: &raw const z
+    };
+
+    unsafe { swap_ptr_triple_dangling(&triple) }
+    assert_eq!(unsafe { *triple.ptr2 }, x);
+}
+
+
+/// Test function that directly returns its pointer argument.
+fn test_return_ptr() {
+    extern "C" {
+        fn return_ptr(ptr: *const i32) -> *const i32;
+    }
+
+    let x = 131;
+    let ptr = &raw const x;
+
+    let ptr = unsafe { return_ptr(ptr) };
+    assert_eq!(unsafe { *ptr }, x);
+}

src/tools/miri/tests/native-lib/ptr_read_access.c

@@ -3,13 +3,13 @@
 // See comments in build_native_lib()
 #define EXPORT __attribute__((visibility("default")))
 
-/* Test: test_pointer */
+/* Test: test_access_pointer */
 
 EXPORT void print_pointer(const int *ptr) {
   printf("printing pointer dereference from C: %d\n", *ptr);
 }
 
-/* Test: test_simple */
+/* Test: test_access_simple */
 
 typedef struct Simple {
   int field;
@@ -19,7 +19,7 @@ EXPORT int access_simple(const Simple *s_ptr) {
   return s_ptr->field;
 }
 
-/* Test: test_nested */
+/* Test: test_access_nested */
 
 typedef struct Nested {
   int value;
@@ -38,7 +38,7 @@ EXPORT int access_nested(const Nested *n_ptr) {
   return n_ptr->value;
 }
 
-/* Test: test_static */
+/* Test: test_access_static */
 
 typedef struct Static {
     int value;

src/tools/miri/tests/native-lib/ptr_write_access.c

@@ -0,0 +1,90 @@
+#include <stddef.h>
+
+// See comments in build_native_lib()
+#define EXPORT __attribute__((visibility("default")))
+
+/* Test: test_increment_int */
+
+EXPORT void increment_int(int *ptr) {
+  *ptr += 1;
+}
+
+/* Test: test_init_int */
+
+EXPORT void init_int(int *ptr, int val) {
+  *ptr = val;
+}
+
+/* Test: test_init_array */
+
+EXPORT void init_array(int *array, size_t len, int val) {
+  for (size_t i = 0; i < len; i++) {
+    array[i] = val;
+  }
+}
+
+/* Test: test_init_static_inner */
+
+typedef struct SyncPtr {
+    int *ptr;
+} SyncPtr;
+
+EXPORT void init_static_inner(const SyncPtr *s_ptr, int val) {
+  *(s_ptr->ptr) = val;
+}
+
+/* Tests: test_exposed, test_pass_dangling */
+
+EXPORT void ignore_ptr(__attribute__((unused)) const int *ptr) {
+  return;
+}
+
+/* Test: test_expose_int */
+EXPORT void expose_int(const int *int_ptr, const int **pptr) {
+  *pptr = int_ptr;
+}
+
+/* Test: test_swap_ptr */
+
+EXPORT void swap_ptr(const int **pptr0, const int **pptr1) {
+  const int *tmp = *pptr0;
+  *pptr0 = *pptr1;
+  *pptr1 = tmp;
+}
+
+/* Test: test_swap_ptr_tuple */
+
+typedef struct Tuple {
+    int *ptr0;
+    int *ptr1;
+} Tuple;
+
+EXPORT void swap_ptr_tuple(Tuple *t_ptr) {
+  int *tmp = t_ptr->ptr0;
+  t_ptr->ptr0 = t_ptr->ptr1;
+  t_ptr->ptr1 = tmp;
+}
+
+/* Test: test_overwrite_dangling */
+
+EXPORT void overwrite_ptr(const int **pptr) {
+  *pptr = NULL;
+}
+
+/* Test: test_swap_ptr_triple_dangling */
+
+typedef struct Triple {
+    int *ptr0;
+    int *ptr1;
+    int *ptr2;
+} Triple;
+
+EXPORT void swap_ptr_triple_dangling(Triple *t_ptr) {
+  int *tmp = t_ptr->ptr0;
+  t_ptr->ptr0 = t_ptr->ptr2;
+  t_ptr->ptr2 = tmp;
+}
+
+EXPORT const int *return_ptr(const int *ptr) {
+  return ptr;
+}

src/tools/miri/tests/ui.rs

@@ -64,6 +64,7 @@ fn build_native_lib() -> PathBuf {
             // FIXME: Automate gathering of all relevant C source files in the directory.
             "tests/native-lib/scalar_arguments.c",
             "tests/native-lib/ptr_read_access.c",
+            "tests/native-lib/ptr_write_access.c",
             // Ensure we notice serious problems in the C code.
             "-Wall",
             "-Wextra",

src/tools/rustbook/Cargo.lock

@@ -709,30 +709,20 @@ dependencies = [
 ]
 
 [[package]]
-name = "mdbook-trpl-listing"
+name = "mdbook-trpl"
 version = "0.1.0"
 dependencies = [
+ "anyhow",
  "clap",
  "html_parser",
  "mdbook",
- "pulldown-cmark 0.10.3",
+ "pulldown-cmark 0.12.2",
- "pulldown-cmark-to-cmark 13.0.0",
+ "pulldown-cmark-to-cmark 19.0.0",
  "serde_json",
  "thiserror",
  "toml 0.8.19",
 ]
 
-[[package]]
-name = "mdbook-trpl-note"
-version = "1.0.0"
-dependencies = [
- "clap",
- "mdbook",
- "pulldown-cmark 0.10.3",
- "pulldown-cmark-to-cmark 13.0.0",
- "serde_json",
-]
-
 [[package]]
 name = "memchr"
 version = "2.7.4"
@@ -1010,7 +1000,6 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "76979bea66e7875e7509c4ec5300112b316af87fa7a252ca91c448b32dfe3993"
 dependencies = [
  "bitflags 2.6.0",
- "getopts",
  "memchr",
  "pulldown-cmark-escape 0.10.1",
  "unicase",
@@ -1028,6 +1017,19 @@ dependencies = [
  "unicase",
 ]
 
+[[package]]
+name = "pulldown-cmark"
+version = "0.12.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f86ba2052aebccc42cbbb3ed234b8b13ce76f75c3551a303cb2bcffcff12bb14"
+dependencies = [
+ "bitflags 2.6.0",
+ "getopts",
+ "memchr",
+ "pulldown-cmark-escape 0.11.0",
+ "unicase",
+]
+
 [[package]]
 name = "pulldown-cmark-escape"
 version = "0.10.1"
@@ -1040,15 +1042,6 @@ version = "0.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "007d8adb5ddab6f8e3f491ac63566a7d5002cc7ed73901f72057943fa71ae1ae"
 
-[[package]]
-name = "pulldown-cmark-to-cmark"
-version = "13.0.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f609795c8d835f79dcfcf768415b9fb57ef1b74891e99f86e73f43a7a257163b"
-dependencies = [
- "pulldown-cmark 0.10.3",
-]
-
 [[package]]
 name = "pulldown-cmark-to-cmark"
 version = "15.0.1"
@@ -1058,6 +1051,15 @@ dependencies = [
  "pulldown-cmark 0.11.3",
 ]
 
+[[package]]
+name = "pulldown-cmark-to-cmark"
+version = "19.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7d742adcc7b655dba3e9ebab47954ca229fc0fa1df01fdc94349b6f3a2e6d257"
+dependencies = [
+ "pulldown-cmark 0.12.2",
+]
+
 [[package]]
 name = "quote"
 version = "1.0.37"
@@ -1144,8 +1146,7 @@ dependencies = [
  "mdbook",
  "mdbook-i18n-helpers",
  "mdbook-spec",
- "mdbook-trpl-listing",
+ "mdbook-trpl",
- "mdbook-trpl-note",
 ]
 
 [[package]]

src/tools/rustbook/Cargo.toml

@@ -9,8 +9,7 @@ edition = "2021"
 [dependencies]
 clap = "4.0.32"
 env_logger = "0.11"
-mdbook-trpl-listing = { path = "../../doc/book/packages/mdbook-trpl-listing" }
+mdbook-trpl = { path = "../../doc/book/packages/mdbook-trpl" }
-mdbook-trpl-note = { path = "../../doc/book/packages/mdbook-trpl-note" }
 mdbook-i18n-helpers = "0.3.3"
 mdbook-spec = { path = "../../doc/reference/mdbook-spec" }
 

src/tools/rustbook/src/main.rs

@@ -6,8 +6,7 @@ use mdbook::MDBook;
 use mdbook::errors::Result as Result3;
 use mdbook_i18n_helpers::preprocessors::Gettext;
 use mdbook_spec::Spec;
-use mdbook_trpl_listing::TrplListing;
+use mdbook_trpl::{Figure, Listing, Note};
-use mdbook_trpl_note::TrplNote;
 
 fn main() {
     let crate_version = concat!("v", crate_version!());
@@ -109,11 +108,15 @@ pub fn build(args: &ArgMatches) -> Result3<()> {
     // preprocessor, or this should modify the config and use
     // MDBook::load_with_config.
     if book.config.get_preprocessor("trpl-note").is_some() {
-        book.with_preprocessor(TrplNote);
+        book.with_preprocessor(Note);
     }
 
     if book.config.get_preprocessor("trpl-listing").is_some() {
-        book.with_preprocessor(TrplListing);
+        book.with_preprocessor(Listing);
+    }
+
+    if book.config.get_preprocessor("trpl-figure").is_some() {
+        book.with_preprocessor(Figure);
     }
 
     if book.config.get_preprocessor("spec").is_some() {

tests/codegen/reg-struct-return.rs

@@ -0,0 +1,206 @@
+// Checks how `reg-struct-return` flag works with different calling conventions:
+// Return struct with 8/16/32/64 bit size will be converted into i8/i16/i32/i64
+// (like abi_return_struct_as_int target spec).
+// x86 only.
+
+//@ revisions: ENABLED DISABLED
+//@ add-core-stubs
+//@ compile-flags: --target i686-unknown-linux-gnu -O -C no-prepopulate-passes
+//@ [ENABLED] compile-flags: -Zreg-struct-return
+//@ needs-llvm-components: x86
+
+#![crate_type = "lib"]
+#![no_std]
+#![no_core]
+#![feature(no_core, lang_items)]
+
+extern crate minicore;
+use minicore::*;
+
+#[repr(C)]
+pub struct Foo {
+    x: u32,
+    y: u32,
+}
+
+#[repr(C)]
+pub struct Foo1 {
+    x: u32,
+}
+
+#[repr(C)]
+pub struct Foo2 {
+    x: bool,
+    y: bool,
+    z: i16,
+}
+
+#[repr(C)]
+pub struct Foo3 {
+    x: i16,
+    y: bool,
+    z: bool,
+}
+
+#[repr(C)]
+pub struct Foo4 {
+    x: char,
+    y: bool,
+    z: u8,
+}
+
+#[repr(C)]
+pub struct Foo5 {
+    x: u32,
+    y: u16,
+    z: u8,
+    a: bool,
+}
+
+#[repr(C)]
+pub struct FooOversize1 {
+    x: u32,
+    y: u32,
+    z: u32,
+}
+
+#[repr(C)]
+pub struct FooOversize2 {
+    f0: u16,
+    f1: u16,
+    f2: u16,
+    f3: u16,
+    f4: u16,
+}
+
+#[repr(C)]
+pub struct FooFloat1 {
+    x: f32,
+    y: f32,
+}
+
+#[repr(C)]
+pub struct FooFloat2 {
+    x: f64,
+}
+
+#[repr(C)]
+pub struct FooFloat3 {
+    x: f32,
+}
+
+pub mod tests {
+    use {
+        Foo, Foo1, Foo2, Foo3, Foo4, Foo5, FooFloat1, FooFloat2, FooFloat3, FooOversize1,
+        FooOversize2,
+    };
+
+    // ENABLED: i64 @f1()
+    // DISABLED: void @f1(ptr {{.*}}sret
+    #[no_mangle]
+    pub extern "fastcall" fn f1() -> Foo {
+        Foo { x: 1, y: 2 }
+    }
+
+    // CHECK: { i32, i32 } @f2()
+    #[no_mangle]
+    pub extern "Rust" fn f2() -> Foo {
+        Foo { x: 1, y: 2 }
+    }
+
+    // ENABLED: i64 @f3()
+    // DISABLED: void @f3(ptr {{.*}}sret
+    #[no_mangle]
+    pub extern "C" fn f3() -> Foo {
+        Foo { x: 1, y: 2 }
+    }
+
+    // ENABLED: i64 @f4()
+    // DISABLED: void @f4(ptr {{.*}}sret
+    #[no_mangle]
+    pub extern "cdecl" fn f4() -> Foo {
+        Foo { x: 1, y: 2 }
+    }
+
+    // ENABLED: i64 @f5()
+    // DISABLED: void @f5(ptr {{.*}}sret
+    #[no_mangle]
+    pub extern "stdcall" fn f5() -> Foo {
+        Foo { x: 1, y: 2 }
+    }
+
+    // ENABLED: i64 @f6()
+    // DISABLED: void @f6(ptr {{.*}}sret
+    #[no_mangle]
+    pub extern "thiscall" fn f6() -> Foo {
+        Foo { x: 1, y: 2 }
+    }
+
+    // ENABLED: i32 @f7()
+    // DISABLED: void @f7(ptr {{.*}}sret
+    #[no_mangle]
+    pub extern "C" fn f7() -> Foo1 {
+        Foo1 { x: 1 }
+    }
+
+    // ENABLED: i32 @f8()
+    // DISABLED: void @f8(ptr {{.*}}sret
+    #[no_mangle]
+    pub extern "C" fn f8() -> Foo2 {
+        Foo2 { x: true, y: false, z: 5 }
+    }
+
+    // ENABLED: i32 @f9()
+    // DISABLED: void @f9(ptr {{.*}}sret
+    #[no_mangle]
+    pub extern "C" fn f9() -> Foo3 {
+        Foo3 { x: 5, y: false, z: true }
+    }
+
+    // ENABLED: i64 @f10()
+    // DISABLED: void @f10(ptr {{.*}}sret
+    #[no_mangle]
+    pub extern "C" fn f10() -> Foo4 {
+        Foo4 { x: 'x', y: true, z: 170 }
+    }
+
+    // ENABLED: i64 @f11()
+    // DISABLED: void @f11(ptr {{.*}}sret
+    #[no_mangle]
+    pub extern "C" fn f11() -> Foo5 {
+        Foo5 { x: 1, y: 2, z: 3, a: true }
+    }
+
+    // CHECK: void @f12(ptr {{.*}}sret
+    #[no_mangle]
+    pub extern "C" fn f12() -> FooOversize1 {
+        FooOversize1 { x: 1, y: 2, z: 3 }
+    }
+
+    // CHECK: void @f13(ptr {{.*}}sret
+    #[no_mangle]
+    pub extern "C" fn f13() -> FooOversize2 {
+        FooOversize2 { f0: 1, f1: 2, f2: 3, f3: 4, f4: 5 }
+    }
+
+    // ENABLED: i64 @f14()
+    // DISABLED: void @f14(ptr {{.*}}sret
+    #[no_mangle]
+    pub extern "C" fn f14() -> FooFloat1 {
+        FooFloat1 { x: 1.0, y: 1.0 }
+    }
+
+    // ENABLED: double @f15()
+    // DISABLED: void @f15(ptr {{.*}}sret
+    #[no_mangle]
+    pub extern "C" fn f15() -> FooFloat2 {
+        FooFloat2 { x: 1.0 }
+    }
+
+    // ENABLED: float @f16()
+    // DISABLED: void @f16(ptr {{.*}}sret
+    #[no_mangle]
+    pub extern "C" fn f16() -> FooFloat3 {
+        FooFloat3 { x: 1.0 }
+    }
+}

tests/ui/invalid-compile-flags/reg-struct-return/requires-x86.aarch64.stderr

@@ -0,0 +1,4 @@
+error: `-Zreg-struct-return` is only supported on x86
+
+error: aborting due to 1 previous error
+

tests/ui/invalid-compile-flags/reg-struct-return/requires-x86.rs

@@ -0,0 +1,21 @@
+//@ revisions: x86 x86_64 aarch64
+
+//@ compile-flags: -Zreg-struct-return
+
+//@[x86] check-pass
+//@[x86] needs-llvm-components: x86
+//@[x86] compile-flags: --target i686-unknown-linux-gnu
+
+//@[x86_64] check-fail
+//@[x86_64] needs-llvm-components: x86
+//@[x86_64] compile-flags: --target x86_64-unknown-linux-gnu
+//@[x86_64] error-pattern: `-Zreg-struct-return` is only supported on x86
+
+//@[aarch64] check-fail
+//@[aarch64] needs-llvm-components: aarch64
+//@[aarch64] compile-flags: --target aarch64-unknown-linux-gnu
+//@[aarch64] error-pattern: `-Zreg-struct-return` is only supported on x86
+
+#![feature(no_core)]
+#![no_core]
+#![no_main]

tests/ui/invalid-compile-flags/reg-struct-return/requires-x86.x86_64.stderr

@@ -0,0 +1,4 @@
+error: `-Zreg-struct-return` is only supported on x86
+
+error: aborting due to 1 previous error
+