Auto merge of #115699 - RalfJung:interpret-abi-compat, r=oli-obk

interpret: change ABI-compat test to be type-based

This makes the test consistent across targets. Otherwise the chances are very high that ABI mismatches get accepted on x86_64 but still fail on many other targets with more complicated ABIs.

This implements (most of) the rules described in rust-lang/rust#115476.

Author: bors

src/diagnostics.rs

@@ -199,6 +199,7 @@ pub fn report_error<'tcx, 'mir>(
     e: InterpErrorInfo<'tcx>,
 ) -> Option<(i64, bool)> {
     use InterpError::*;
+    use UndefinedBehaviorInfo::*;
 
     let mut msg = vec![];
 
@@ -271,7 +272,7 @@ pub fn report_error<'tcx, 'mir>(
         (title, helps)
     } else {
         let title = match e.kind() {
-            UndefinedBehavior(UndefinedBehaviorInfo::ValidationError(validation_err))
+            UndefinedBehavior(ValidationError(validation_err))
                 if matches!(
                     validation_err.kind,
                     ValidationErrorKind::PointerAsInt { .. } | ValidationErrorKind::PartialPointer
@@ -299,7 +300,7 @@ pub fn report_error<'tcx, 'mir>(
         let helps = match e.kind() {
             Unsupported(_) =>
                 vec![(None, format!("this is likely not a bug in the program; it indicates that the program performed an operation that the interpreter does not support"))],
-            UndefinedBehavior(UndefinedBehaviorInfo::AlignmentCheckFailed { .. })
+            UndefinedBehavior(AlignmentCheckFailed { .. })
                 if ecx.machine.check_alignment == AlignmentCheck::Symbolic
             =>
                 vec![
@@ -311,13 +312,20 @@ pub fn report_error<'tcx, 'mir>(
                     (None, format!("this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior")),
                     (None, format!("see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information")),
                 ];
-                if let UndefinedBehaviorInfo::PointerUseAfterFree(alloc_id, _) | UndefinedBehaviorInfo::PointerOutOfBounds { alloc_id, .. } = info {
-                    if let Some(span) = ecx.machine.allocated_span(*alloc_id) {
-                        helps.push((Some(span), format!("{:?} was allocated here:", alloc_id)));
+                match info {
+                    PointerUseAfterFree(alloc_id, _) | PointerOutOfBounds { alloc_id, .. } => {
+                        if let Some(span) = ecx.machine.allocated_span(*alloc_id) {
+                            helps.push((Some(span), format!("{:?} was allocated here:", alloc_id)));
+                        }
+                        if let Some(span) = ecx.machine.deallocated_span(*alloc_id) {
+                            helps.push((Some(span), format!("{:?} was deallocated here:", alloc_id)));
+                        }
                     }
-                    if let Some(span) = ecx.machine.deallocated_span(*alloc_id) {
-                        helps.push((Some(span), format!("{:?} was deallocated here:", alloc_id)));
+                    AbiMismatchArgument { .. } | AbiMismatchReturn { .. } => {
+                        helps.push((None, format!("this means these two types are not *guaranteed* to be ABI-compatible across all targets")));
+                        helps.push((None, format!("if you think this code should be accepted anyway, please report an issue")));
                     }
+                    _ => {},
                 }
                 helps
             }
@@ -339,7 +347,7 @@ pub fn report_error<'tcx, 'mir>(
     // We want to dump the allocation if this is `InvalidUninitBytes`. Since `format_error` consumes `e`, we compute the outut early.
     let mut extra = String::new();
     match e.kind() {
-        UndefinedBehavior(UndefinedBehaviorInfo::InvalidUninitBytes(Some((alloc_id, access)))) => {
+        UndefinedBehavior(InvalidUninitBytes(Some((alloc_id, access)))) => {
             writeln!(
                 extra,
                 "Uninitialized memory occurred at {alloc_id:?}{range:?}, in this allocation:",

tests/fail/function_pointers/abi_mismatch_array_vs_struct.stderr

@@ -6,6 +6,8 @@ LL |     g(Default::default())
    |
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
+   = help: this means these two types are not *guaranteed* to be ABI-compatible across all targets
+   = help: if you think this code should be accepted anyway, please report an issue
    = note: BACKTRACE:
    = note: inside `main` at $DIR/abi_mismatch_array_vs_struct.rs:LL:CC
 

tests/fail/function_pointers/abi_mismatch_int_vs_float.stderr

@@ -6,6 +6,8 @@ LL |     g(42)
    |
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
+   = help: this means these two types are not *guaranteed* to be ABI-compatible across all targets
+   = help: if you think this code should be accepted anyway, please report an issue
    = note: BACKTRACE:
    = note: inside `main` at $DIR/abi_mismatch_int_vs_float.rs:LL:CC
 

tests/fail/function_pointers/abi_mismatch_raw_pointer.stderr

@@ -6,6 +6,8 @@ LL |     g(&42 as *const i32)
    |
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
+   = help: this means these two types are not *guaranteed* to be ABI-compatible across all targets
+   = help: if you think this code should be accepted anyway, please report an issue
    = note: BACKTRACE:
    = note: inside `main` at $DIR/abi_mismatch_raw_pointer.rs:LL:CC
 

tests/fail/function_pointers/abi_mismatch_return_type.stderr

@@ -6,6 +6,8 @@ LL |     g()
    |
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
+   = help: this means these two types are not *guaranteed* to be ABI-compatible across all targets
+   = help: if you think this code should be accepted anyway, please report an issue
    = note: BACKTRACE:
    = note: inside `main` at $DIR/abi_mismatch_return_type.rs:LL:CC
 

tests/fail/function_pointers/abi_mismatch_simple.stderr

@@ -6,6 +6,8 @@ LL |     g(42)
    |
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
+   = help: this means these two types are not *guaranteed* to be ABI-compatible across all targets
+   = help: if you think this code should be accepted anyway, please report an issue
    = note: BACKTRACE:
    = note: inside `main` at $DIR/abi_mismatch_simple.rs:LL:CC
 

tests/fail/function_pointers/abi_mismatch_vector.stderr

@@ -6,6 +6,8 @@ LL |     g(Default::default())
    |
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
+   = help: this means these two types are not *guaranteed* to be ABI-compatible across all targets
+   = help: if you think this code should be accepted anyway, please report an issue
    = note: BACKTRACE:
    = note: inside `main` at $DIR/abi_mismatch_vector.rs:LL:CC
 

tests/pass/function_calls/abi_compat.rs

@@ -1,10 +1,17 @@
 use std::mem;
 use std::num;
+use std::ptr;
 
 #[derive(Copy, Clone, Default)]
 struct Zst;
 
-fn test_abi_compat<T: Copy, U: Copy>(t: T, u: U) {
+#[repr(transparent)]
+#[derive(Copy, Clone)]
+struct Wrapper<T>(T);
+
+fn id<T>(x: T) -> T { x }
+
+fn test_abi_compat<T: Clone, U: Clone>(t: T, u: U) {
     fn id<T>(x: T) -> T {
         x
     }
@@ -16,10 +23,10 @@ fn test_abi_compat<T: Copy, U: Copy>(t: T, u: U) {
     // in both directions.
     let f: fn(T) -> T = id;
     let f: fn(U) -> U = unsafe { std::mem::transmute(f) };
-    let _val = f(u);
+    let _val = f(u.clone());
     let f: fn(U) -> U = id;
     let f: fn(T) -> T = unsafe { std::mem::transmute(f) };
-    let _val = f(t);
+    let _val = f(t.clone());
 
     // And then we do the same for `extern "C"`.
     let f: extern "C" fn(T) -> T = id_c;
@@ -32,9 +39,6 @@ fn test_abi_compat<T: Copy, U: Copy>(t: T, u: U) {
 
 /// Ensure that `T` is compatible with various repr(transparent) wrappers around `T`.
 fn test_abi_newtype<T: Copy + Default>() {
-    #[repr(transparent)]
-    #[derive(Copy, Clone)]
-    struct Wrapper1<T>(T);
     #[repr(transparent)]
     #[derive(Copy, Clone)]
     struct Wrapper2<T>(T, ());
@@ -46,31 +50,38 @@ fn test_abi_newtype<T: Copy + Default>() {
     struct Wrapper3<T>(Zst, T, [u8; 0]);
 
     let t = T::default();
-    test_abi_compat(t, Wrapper1(t));
+    test_abi_compat(t, Wrapper(t));
     test_abi_compat(t, Wrapper2(t, ()));
     test_abi_compat(t, Wrapper2a((), t));
     test_abi_compat(t, Wrapper3(Zst, t, []));
     test_abi_compat(t, mem::MaybeUninit::new(t)); // MaybeUninit is `repr(transparent)`
 }
 
 fn main() {
-    // Here we check:
-    // - u32 vs char is allowed
-    // - u32 vs NonZeroU32/Option<NonZeroU32> is allowed
-    // - reference vs raw pointer is allowed
-    // - references to things of the same size and alignment are allowed
-    // These are very basic tests that should work on all ABIs. However it is not clear that any of
-    // these would be stably guaranteed. Code that relies on this is equivalent to code that relies
-    // on the layout of `repr(Rust)` types. They are also fragile: the same mismatches in the fields
-    // of a struct (even with `repr(C)`) will not always be accepted by Miri.
-    // Note that `bool` and `u8` are *not* compatible, at least on x86-64!
-    // One of them has `arg_ext: Zext`, the other does not.
-    // Similarly, `i32` and `u32` are not compatible on s390x due to different `arg_ext`.
-    test_abi_compat(0u32, 'x');
+    // Here we check some of the guaranteed ABI compatibilities.
+    // Different integer types of the same size and sign.
+    if cfg!(target_pointer_width = "32") {
+        test_abi_compat(0usize, 0u32);
+        test_abi_compat(0isize, 0i32);
+    } else {
+        test_abi_compat(0usize, 0u64);
+        test_abi_compat(0isize, 0i64);
+    }
     test_abi_compat(42u32, num::NonZeroU32::new(1).unwrap());
-    test_abi_compat(0u32, Some(num::NonZeroU32::new(1).unwrap()));
+    // Reference/pointer types with the same pointee.
     test_abi_compat(&0u32, &0u32 as *const u32);
+    test_abi_compat(&mut 0u32 as *mut u32, Box::new(0u32));
+    test_abi_compat(&(), ptr::NonNull::<()>::dangling());
+    // Reference/pointer types with different but sized pointees.
     test_abi_compat(&0u32, &([true; 4], [0u32; 0]));
+    // `fn` types
+    test_abi_compat(main as fn(), id::<i32> as fn(i32) -> i32);
+    // Guaranteed null-pointer-optimizations.
+    test_abi_compat(&0u32 as *const u32, Some(&0u32));
+    test_abi_compat(main as fn(), Some(main as fn()));
+    test_abi_compat(0u32, Some(num::NonZeroU32::new(1).unwrap()));
+    test_abi_compat(&0u32 as *const u32, Some(Wrapper(&0u32)));
+    test_abi_compat(0u32, Some(Wrapper(num::NonZeroU32::new(1).unwrap())));
 
     // These must work for *any* type, since we guarantee that `repr(transparent)` is ABI-compatible
     // with the wrapped field.