Rollup merge of #69839 - RalfJung:miri-error-cleanup, r=oli-obk

Miri error reform

Some time ago we started moving Miri errors into a few distinct categories, but we never classified all the old errors. That's what this PR does.

~~This is on top of https://github.com/rust-lang/rust/pull/69762; [relative diff](https://github.com/RalfJung/rust/compare/validity-errors...RalfJung:miri-error-cleanup).~~

r? @oli-obk

Fixes https://github.com/rust-lang/const-eval/issues/4

9 files changed, 203 insertions, 171 deletions

diff --git a/src/librustc_mir/interpret/eval_context.rs b/src/librustc_mir/interpret/eval_context.rs
index 450e6b2e2d6..481719bfa8e 100644
--- a/src/librustc_mir/interpret/eval_context.rs
+++ b/src/librustc_mir/interpret/eval_context.rs
@@ -138,7 +138,7 @@ pub enum LocalValue<Tag = (), Id = AllocId> {
 impl<'tcx, Tag: Copy + 'static> LocalState<'tcx, Tag> {
     pub fn access(&self) -> InterpResult<'tcx, Operand<Tag>> {
         match self.value {
-            LocalValue::Dead => throw_unsup!(DeadLocal),
+            LocalValue::Dead => throw_ub!(DeadLocal),
             LocalValue::Uninitialized => {
                 bug!("The type checker should prevent reading from a never-written local")
             }
@@ -152,7 +152,7 @@ impl<'tcx, Tag: Copy + 'static> LocalState<'tcx, Tag> {
         &mut self,
     ) -> InterpResult<'tcx, Result<&mut LocalValue<Tag>, MemPlace<Tag>>> {
         match self.value {
-            LocalValue::Dead => throw_unsup!(DeadLocal),
+            LocalValue::Dead => throw_ub!(DeadLocal),
             LocalValue::Live(Operand::Indirect(mplace)) => Ok(Err(mplace)),
             ref mut local @ LocalValue::Live(Operand::Immediate(_))
             | ref mut local @ LocalValue::Uninitialized => Ok(Ok(local)),
@@ -326,7 +326,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 if self.tcx.is_mir_available(did) {
                     Ok(self.tcx.optimized_mir(did).unwrap_read_only())
                 } else {
-                    throw_unsup!(NoMirFor(self.tcx.def_path_str(def_id)))
+                    throw_unsup!(NoMirFor(def_id))
                 }
             }
             _ => Ok(self.tcx.instance_mir(instance)),
diff --git a/src/librustc_mir/interpret/intern.rs b/src/librustc_mir/interpret/intern.rs
index 9b13db2289e..90b8a493299 100644
--- a/src/librustc_mir/interpret/intern.rs
+++ b/src/librustc_mir/interpret/intern.rs
@@ -327,7 +327,7 @@ pub fn intern_const_alloc_recursive<M: CompileTimeMachine<'mir, 'tcx>>(
         if let Err(error) = interned {
             // This can happen when e.g. the tag of an enum is not a valid discriminant. We do have
             // to read enum discriminants in order to find references in enum variant fields.
-            if let err_unsup!(ValidationFailure(_)) = error.kind {
+            if let err_ub!(ValidationFailure(_)) = error.kind {
                 let err = crate::const_eval::error_to_const_error(&ecx, error);
                 match err.struct_error(
                     ecx.tcx,
@@ -390,7 +390,7 @@ pub fn intern_const_alloc_recursive<M: CompileTimeMachine<'mir, 'tcx>>(
             }
         } else if ecx.memory.dead_alloc_map.contains_key(&alloc_id) {
             // dangling pointer
-            throw_unsup!(ValidationFailure("encountered dangling pointer in final constant".into()))
+            throw_ub_format!("encountered dangling pointer in final constant")
         } else if ecx.tcx.alloc_map.lock().get(alloc_id).is_none() {
             // We have hit an `AllocId` that is neither in local or global memory and isn't marked
             // as dangling by local memory.
diff --git a/src/librustc_mir/interpret/intrinsics.rs b/src/librustc_mir/interpret/intrinsics.rs
index 37a60bcc836..03aedad0d98 100644
--- a/src/librustc_mir/interpret/intrinsics.rs
+++ b/src/librustc_mir/interpret/intrinsics.rs
@@ -135,7 +135,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 let bits = self.force_bits(val, layout_of.size)?;
                 let kind = match layout_of.abi {
                     ty::layout::Abi::Scalar(ref scalar) => scalar.value,
-                    _ => throw_unsup!(TypeNotPrimitive(ty)),
+                    _ => bug!("{} called on invalid type {:?}", intrinsic_name, ty),
                 };
                 let (nonzero, intrinsic_name) = match intrinsic_name {
                     sym::cttz_nonzero => (true, sym::cttz),
@@ -246,9 +246,9 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                     let layout = self.layout_of(substs.type_at(0))?;
                     let r_val = self.force_bits(r.to_scalar()?, layout.size)?;
                     if let sym::unchecked_shl | sym::unchecked_shr = intrinsic_name {
-                        throw_ub_format!("Overflowing shift by {} in `{}`", r_val, intrinsic_name);
+                        throw_ub_format!("overflowing shift by {} in `{}`", r_val, intrinsic_name);
                     } else {
-                        throw_ub_format!("Overflow executing `{}`", intrinsic_name);
+                        throw_ub_format!("overflow executing `{}`", intrinsic_name);
                     }
                 }
                 self.write_scalar(val, dest)?;
diff --git a/src/librustc_mir/interpret/machine.rs b/src/librustc_mir/interpret/machine.rs
index 0e70e54ad85..c9d32f62400 100644
--- a/src/librustc_mir/interpret/machine.rs
+++ b/src/librustc_mir/interpret/machine.rs
@@ -286,8 +286,10 @@ pub trait Machine<'mir, 'tcx>: Sized {
         int: u64,
     ) -> InterpResult<'tcx, Pointer<Self::PointerTag>> {
         Err((if int == 0 {
-            err_unsup!(InvalidNullPointerUsage)
+            // This is UB, seriously.
+            err_ub!(InvalidIntPointerUsage(0))
         } else {
+            // This is just something we cannot support during const-eval.
             err_unsup!(ReadBytesAsPointer)
         })
         .into())
diff --git a/src/librustc_mir/interpret/memory.rs b/src/librustc_mir/interpret/memory.rs
index 82a467c7ba9..5b2cd89a122 100644
--- a/src/librustc_mir/interpret/memory.rs
+++ b/src/librustc_mir/interpret/memory.rs
@@ -215,7 +215,10 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
         kind: MemoryKind<M::MemoryKinds>,
     ) -> InterpResult<'tcx, Pointer<M::PointerTag>> {
         if ptr.offset.bytes() != 0 {
-            throw_unsup!(ReallocateNonBasePtr)
+            throw_ub_format!(
+                "reallocating {:?} which does not point to the beginning of an object",
+                ptr
+            );
         }
 
         // For simplicities' sake, we implement reallocate as "alloc, copy, dealloc".
@@ -251,7 +254,10 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
         trace!("deallocating: {}", ptr.alloc_id);
 
         if ptr.offset.bytes() != 0 {
-            throw_unsup!(DeallocateNonBasePtr)
+            throw_ub_format!(
+                "deallocating {:?} which does not point to the beginning of an object",
+                ptr
+            );
         }
 
         let (alloc_kind, mut alloc) = match self.alloc_map.remove(&ptr.alloc_id) {
@@ -259,29 +265,32 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
             None => {
                 // Deallocating static memory -- always an error
                 return Err(match self.tcx.alloc_map.lock().get(ptr.alloc_id) {
-                    Some(GlobalAlloc::Function(..)) => err_unsup!(DeallocatedWrongMemoryKind(
-                        "function".to_string(),
-                        format!("{:?}", kind),
-                    )),
-                    Some(GlobalAlloc::Static(..)) | Some(GlobalAlloc::Memory(..)) => err_unsup!(
-                        DeallocatedWrongMemoryKind("static".to_string(), format!("{:?}", kind))
-                    ),
-                    None => err_unsup!(DoubleFree),
+                    Some(GlobalAlloc::Function(..)) => err_ub_format!("deallocating a function"),
+                    Some(GlobalAlloc::Static(..)) | Some(GlobalAlloc::Memory(..)) => {
+                        err_ub_format!("deallocating static memory")
+                    }
+                    None => err_ub!(PointerUseAfterFree(ptr.alloc_id)),
                 }
                 .into());
             }
         };
 
         if alloc_kind != kind {
-            throw_unsup!(DeallocatedWrongMemoryKind(
-                format!("{:?}", alloc_kind),
-                format!("{:?}", kind),
-            ))
+            throw_ub_format!(
+                "deallocating `{:?}` memory using `{:?}` deallocation operation",
+                alloc_kind,
+                kind
+            );
         }
         if let Some((size, align)) = old_size_and_align {
             if size != alloc.size || align != alloc.align {
-                let bytes = alloc.size;
-                throw_unsup!(IncorrectAllocationInformation(size, bytes, align, alloc.align))
+                throw_ub_format!(
+                    "incorrect layout on deallocation: allocation has size {} and alignment {}, but gave size {} and alignment {}",
+                    alloc.size.bytes(),
+                    alloc.align.bytes(),
+                    size.bytes(),
+                    align.bytes(),
+                )
             }
         }
 
@@ -338,7 +347,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
             } else {
                 // The biggest power of two through which `offset` is divisible.
                 let offset_pow2 = 1 << offset.trailing_zeros();
-                throw_unsup!(AlignmentCheckFailed {
+                throw_ub!(AlignmentCheckFailed {
                     has: Align::from_bytes(offset_pow2).unwrap(),
                     required: align,
                 })
@@ -360,7 +369,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
                 assert!(size.bytes() == 0);
                 // Must be non-NULL.
                 if bits == 0 {
-                    throw_unsup!(InvalidNullPointerUsage)
+                    throw_ub!(InvalidIntPointerUsage(0))
                 }
                 // Must be aligned.
                 if let Some(align) = align {
@@ -375,7 +384,10 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
                 // It is sufficient to check this for the end pointer. The addition
                 // checks for overflow.
                 let end_ptr = ptr.offset(size, self)?;
-                end_ptr.check_inbounds_alloc(allocation_size, msg)?;
+                if end_ptr.offset > allocation_size {
+                    // equal is okay!
+                    throw_ub!(PointerOutOfBounds { ptr: end_ptr.erase_tag(), msg, allocation_size })
+                }
                 // Test align. Check this last; if both bounds and alignment are violated
                 // we want the error to be about the bounds.
                 if let Some(align) = align {
@@ -385,7 +397,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
                         // got picked we might be aligned even if this check fails.
                         // We instead have to fall back to converting to an integer and checking
                         // the "real" alignment.
-                        throw_unsup!(AlignmentCheckFailed { has: alloc_align, required: align });
+                        throw_ub!(AlignmentCheckFailed { has: alloc_align, required: align });
                     }
                     check_offset_align(ptr.offset.bytes(), align)?;
                 }
@@ -402,7 +414,9 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
         let (size, _align) = self
             .get_size_and_align(ptr.alloc_id, AllocCheck::MaybeDead)
             .expect("alloc info with MaybeDead cannot fail");
-        ptr.check_inbounds_alloc(size, CheckInAllocMsg::NullPointerTest).is_err()
+        // If the pointer is out-of-bounds, it may be null.
+        // Note that one-past-the-end (offset == size) is still inbounds, and never null.
+        ptr.offset > size
     }
 }
 
@@ -432,13 +446,13 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
         let alloc = tcx.alloc_map.lock().get(id);
         let alloc = match alloc {
             Some(GlobalAlloc::Memory(mem)) => Cow::Borrowed(mem),
-            Some(GlobalAlloc::Function(..)) => throw_unsup!(DerefFunctionPointer),
-            None => throw_unsup!(DanglingPointerDeref),
+            Some(GlobalAlloc::Function(..)) => throw_ub!(DerefFunctionPointer(id)),
+            None => throw_ub!(PointerUseAfterFree(id)),
             Some(GlobalAlloc::Static(def_id)) => {
                 // We got a "lazy" static that has not been computed yet.
                 if tcx.is_foreign_item(def_id) {
                     trace!("get_static_alloc: foreign item {:?}", def_id);
-                    throw_unsup!(ReadForeignStatic)
+                    throw_unsup!(ReadForeignStatic(def_id))
                 }
                 trace!("get_static_alloc: Need to compute {:?}", def_id);
                 let instance = Instance::mono(tcx.tcx, def_id);
@@ -524,7 +538,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
             // to give us a cheap reference.
             let alloc = Self::get_static_alloc(memory_extra, tcx, id)?;
             if alloc.mutability == Mutability::Not {
-                throw_unsup!(ModifiedConstantMemory)
+                throw_ub!(WriteToReadOnly(id))
             }
             match M::STATIC_KIND {
                 Some(kind) => Ok((MemoryKind::Machine(kind), alloc.into_owned())),
@@ -538,7 +552,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
             Ok(a) => {
                 let a = &mut a.1;
                 if a.mutability == Mutability::Not {
-                    throw_unsup!(ModifiedConstantMemory)
+                    throw_ub!(WriteToReadOnly(id))
                 }
                 Ok(a)
             }
@@ -568,7 +582,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
         if self.get_fn_alloc(id).is_some() {
             return if let AllocCheck::Dereferenceable = liveness {
                 // The caller requested no function pointers.
-                throw_unsup!(DerefFunctionPointer)
+                throw_ub!(DerefFunctionPointer(id))
             } else {
                 Ok((Size::ZERO, Align::from_bytes(1).unwrap()))
             };
@@ -596,12 +610,12 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
                 if let AllocCheck::MaybeDead = liveness {
                     // Deallocated pointers are allowed, we should be able to find
                     // them in the map.
-                    Ok(*self.dead_alloc_map.get(&id).expect(
-                        "deallocated pointers should all be recorded in \
-                            `dead_alloc_map`",
-                    ))
+                    Ok(*self
+                        .dead_alloc_map
+                        .get(&id)
+                        .expect("deallocated pointers should all be recorded in `dead_alloc_map`"))
                 } else {
-                    throw_unsup!(DanglingPointerDeref)
+                    throw_ub!(PointerUseAfterFree(id))
                 }
             }
         }
@@ -626,10 +640,10 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
     ) -> InterpResult<'tcx, FnVal<'tcx, M::ExtraFnVal>> {
         let ptr = self.force_ptr(ptr)?; // We definitely need a pointer value.
         if ptr.offset.bytes() != 0 {
-            throw_unsup!(InvalidFunctionPointer)
+            throw_ub!(InvalidFunctionPointer(ptr.erase_tag()))
         }
         let id = M::canonical_alloc_id(self, ptr.alloc_id);
-        self.get_fn_alloc(id).ok_or_else(|| err_unsup!(ExecuteMemory).into())
+        self.get_fn_alloc(id).ok_or_else(|| err_ub!(InvalidFunctionPointer(ptr.erase_tag())).into())
     }
 
     pub fn mark_immutable(&mut self, id: AllocId) -> InterpResult<'tcx> {
diff --git a/src/librustc_mir/interpret/operand.rs b/src/librustc_mir/interpret/operand.rs
index 75452b9395b..316cf2ee419 100644
--- a/src/librustc_mir/interpret/operand.rs
+++ b/src/librustc_mir/interpret/operand.rs
@@ -343,7 +343,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         let len = mplace.len(self)?;
         let bytes = self.memory.read_bytes(mplace.ptr, Size::from_bytes(len as u64))?;
         let str = ::std::str::from_utf8(bytes)
-            .map_err(|err| err_unsup!(ValidationFailure(err.to_string())))?;
+            .map_err(|err| err_ub_format!("this string is not valid UTF-8: {}", err))?;
         Ok(str)
     }
 
@@ -457,7 +457,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         layout: Option<TyLayout<'tcx>>,
     ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
         let base_op = match place.local {
-            mir::RETURN_PLACE => throw_unsup!(ReadFromReturnPointer),
+            mir::RETURN_PLACE => throw_ub!(ReadFromReturnPlace),
             local => {
                 // Do not use the layout passed in as argument if the base we are looking at
                 // here is not the entire place.
diff --git a/src/librustc_mir/interpret/place.rs b/src/librustc_mir/interpret/place.rs
index a4815b9696e..107cfee5ace 100644
--- a/src/librustc_mir/interpret/place.rs
+++ b/src/librustc_mir/interpret/place.rs
@@ -926,7 +926,7 @@ where
             // most likey we *are* running `typeck` right now. Investigate whether we can bail out
             // on `typeck_tables().has_errors` at all const eval entry points.
             debug!("Size mismatch when transmuting!\nsrc: {:#?}\ndest: {:#?}", src, dest);
-            throw_unsup!(TransmuteSizeDiff(src.layout.ty, dest.layout.ty));
+            throw_inval!(TransmuteSizeDiff(src.layout.ty, dest.layout.ty));
         }
         // Unsized copies rely on interpreting `src.meta` with `dest.layout`, we want
         // to avoid that here.
diff --git a/src/librustc_mir/interpret/terminator.rs b/src/librustc_mir/interpret/terminator.rs
index 473ed9d13ec..22a081a9c8e 100644
--- a/src/librustc_mir/interpret/terminator.rs
+++ b/src/librustc_mir/interpret/terminator.rs
@@ -172,13 +172,19 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             trace!("Skipping callee ZST");
             return Ok(());
         }
-        let caller_arg = caller_arg.next().ok_or_else(|| err_unsup!(FunctionArgCountMismatch))?;
+        let caller_arg = caller_arg.next().ok_or_else(|| {
+            err_ub_format!("calling a function with fewer arguments than it requires")
+        })?;
         if rust_abi {
             assert!(!caller_arg.layout.is_zst(), "ZSTs must have been already filtered out");
         }
         // Now, check
         if !Self::check_argument_compat(rust_abi, caller_arg.layout, callee_arg.layout) {
-            throw_unsup!(FunctionArgMismatch(caller_arg.layout.ty, callee_arg.layout.ty))
+            throw_ub_format!(
+                "calling a function with argument of type {:?} passing data of type {:?}",
+                callee_arg.layout.ty,
+                caller_arg.layout.ty
+            )
         }
         // We allow some transmutes here
         self.copy_op_transmute(caller_arg, callee_arg)
@@ -223,7 +229,11 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 abi => abi,
             };
             if normalize_abi(caller_abi) != normalize_abi(callee_abi) {
-                throw_unsup!(FunctionAbiMismatch(caller_abi, callee_abi))
+                throw_ub_format!(
+                    "calling a function with ABI {:?} using caller ABI {:?}",
+                    callee_abi,
+                    caller_abi
+                )
             }
         }
 
@@ -253,110 +263,108 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                     StackPopCleanup::Goto { ret: ret.map(|p| p.1), unwind },
                 )?;
 
-                // We want to pop this frame again in case there was an error, to put
-                // the blame in the right location.  Until the 2018 edition is used in
-                // the compiler, we have to do this with an immediately invoked function.
-                let res =
-                    (|| {
-                        trace!(
-                            "caller ABI: {:?}, args: {:#?}",
-                            caller_abi,
-                            args.iter()
-                                .map(|arg| (arg.layout.ty, format!("{:?}", **arg)))
-                                .collect::<Vec<_>>()
-                        );
-                        trace!(
-                            "spread_arg: {:?}, locals: {:#?}",
-                            body.spread_arg,
-                            body.args_iter()
-                                .map(|local| (
-                                    local,
-                                    self.layout_of_local(self.frame(), local, None).unwrap().ty
-                                ))
-                                .collect::<Vec<_>>()
-                        );
-
-                        // Figure out how to pass which arguments.
-                        // The Rust ABI is special: ZST get skipped.
-                        let rust_abi = match caller_abi {
-                            Abi::Rust | Abi::RustCall => true,
-                            _ => false,
+                // If an error is raised here, pop the frame again to get an accurate backtrace.
+                // To this end, we wrap it all in a `try` block.
+                let res: InterpResult<'tcx> = try {
+                    trace!(
+                        "caller ABI: {:?}, args: {:#?}",
+                        caller_abi,
+                        args.iter()
+                            .map(|arg| (arg.layout.ty, format!("{:?}", **arg)))
+                            .collect::<Vec<_>>()
+                    );
+                    trace!(
+                        "spread_arg: {:?}, locals: {:#?}",
+                        body.spread_arg,
+                        body.args_iter()
+                            .map(|local| (
+                                local,
+                                self.layout_of_local(self.frame(), local, None).unwrap().ty
+                            ))
+                            .collect::<Vec<_>>()
+                    );
+
+                    // Figure out how to pass which arguments.
+                    // The Rust ABI is special: ZST get skipped.
+                    let rust_abi = match caller_abi {
+                        Abi::Rust | Abi::RustCall => true,
+                        _ => false,
+                    };
+                    // We have two iterators: Where the arguments come from,
+                    // and where they go to.
+
+                    // For where they come from: If the ABI is RustCall, we untuple the
+                    // last incoming argument.  These two iterators do not have the same type,
+                    // so to keep the code paths uniform we accept an allocation
+                    // (for RustCall ABI only).
+                    let caller_args: Cow<'_, [OpTy<'tcx, M::PointerTag>]> =
+                        if caller_abi == Abi::RustCall && !args.is_empty() {
+                            // Untuple
+                            let (&untuple_arg, args) = args.split_last().unwrap();
+                            trace!("eval_fn_call: Will pass last argument by untupling");
+                            Cow::from(
+                                args.iter()
+                                    .map(|&a| Ok(a))
+                                    .chain(
+                                        (0..untuple_arg.layout.fields.count())
+                                            .map(|i| self.operand_field(untuple_arg, i as u64)),
+                                    )
+                                    .collect::<InterpResult<'_, Vec<OpTy<'tcx, M::PointerTag>>>>(
+                                    )?,
+                            )
+                        } else {
+                            // Plain arg passing
+                            Cow::from(args)
                         };
-                        // We have two iterators: Where the arguments come from,
-                        // and where they go to.
-
-                        // For where they come from: If the ABI is RustCall, we untuple the
-                        // last incoming argument.  These two iterators do not have the same type,
-                        // so to keep the code paths uniform we accept an allocation
-                        // (for RustCall ABI only).
-                        let caller_args: Cow<'_, [OpTy<'tcx, M::PointerTag>]> =
-                            if caller_abi == Abi::RustCall && !args.is_empty() {
-                                // Untuple
-                                let (&untuple_arg, args) = args.split_last().unwrap();
-                                trace!("eval_fn_call: Will pass last argument by untupling");
-                                Cow::from(args.iter().map(|&a| Ok(a))
-                                .chain((0..untuple_arg.layout.fields.count())
-                                    .map(|i| self.operand_field(untuple_arg, i as u64))
-                                )
-                                .collect::<InterpResult<'_, Vec<OpTy<'tcx, M::PointerTag>>>>()?)
-                            } else {
-                                // Plain arg passing
-                                Cow::from(args)
-                            };
-                        // Skip ZSTs
-                        let mut caller_iter = caller_args
-                            .iter()
-                            .filter(|op| !rust_abi || !op.layout.is_zst())
-                            .copied();
-
-                        // Now we have to spread them out across the callee's locals,
-                        // taking into account the `spread_arg`.  If we could write
-                        // this is a single iterator (that handles `spread_arg`), then
-                        // `pass_argument` would be the loop body. It takes care to
-                        // not advance `caller_iter` for ZSTs
-                        for local in body.args_iter() {
-                            let dest = self.eval_place(&mir::Place::from(local))?;
-                            if Some(local) == body.spread_arg {
-                                // Must be a tuple
-                                for i in 0..dest.layout.fields.count() {
-                                    let dest = self.place_field(dest, i as u64)?;
-                                    self.pass_argument(rust_abi, &mut caller_iter, dest)?;
-                                }
-                            } else {
-                                // Normal argument
+                    // Skip ZSTs
+                    let mut caller_iter =
+                        caller_args.iter().filter(|op| !rust_abi || !op.layout.is_zst()).copied();
+
+                    // Now we have to spread them out across the callee's locals,
+                    // taking into account the `spread_arg`.  If we could write
+                    // this is a single iterator (that handles `spread_arg`), then
+                    // `pass_argument` would be the loop body. It takes care to
+                    // not advance `caller_iter` for ZSTs.
+                    for local in body.args_iter() {
+                        let dest = self.eval_place(&mir::Place::from(local))?;
+                        if Some(local) == body.spread_arg {
+                            // Must be a tuple
+                            for i in 0..dest.layout.fields.count() {
+                                let dest = self.place_field(dest, i as u64)?;
                                 self.pass_argument(rust_abi, &mut caller_iter, dest)?;
                             }
+                        } else {
+                            // Normal argument
+                            self.pass_argument(rust_abi, &mut caller_iter, dest)?;
                         }
-                        // Now we should have no more caller args
-                        if caller_iter.next().is_some() {
-                            trace!("Caller has passed too many args");
-                            throw_unsup!(FunctionArgCountMismatch)
+                    }
+                    // Now we should have no more caller args
+                    if caller_iter.next().is_some() {
+                        throw_ub_format!("calling a function with more arguments than it expected")
+                    }
+                    // Don't forget to check the return type!
+                    if let Some((caller_ret, _)) = ret {
+                        let callee_ret = self.eval_place(&mir::Place::return_place())?;
+                        if !Self::check_argument_compat(
+                            rust_abi,
+                            caller_ret.layout,
+                            callee_ret.layout,
+                        ) {
+                            throw_ub_format!(
+                                "calling a function with return type {:?} passing \
+                                     return place of type {:?}",
+                                callee_ret.layout.ty,
+                                caller_ret.layout.ty
+                            )
                         }
-                        // Don't forget to check the return type!
-                        if let Some((caller_ret, _)) = ret {
-                            let callee_ret = self.eval_place(&mir::Place::return_place())?;
-                            if !Self::check_argument_compat(
-                                rust_abi,
-                                caller_ret.layout,
-                                callee_ret.layout,
-                            ) {
-                                throw_unsup!(FunctionRetMismatch(
-                                    caller_ret.layout.ty,
-                                    callee_ret.layout.ty
-                                ))
-                            }
-                        } else {
-                            let local = mir::RETURN_PLACE;
-                            let callee_layout = self.layout_of_local(self.frame(), local, None)?;
-                            if !callee_layout.abi.is_uninhabited() {
-                                throw_unsup!(FunctionRetMismatch(
-                                    self.tcx.types.never,
-                                    callee_layout.ty
-                                ))
-                            }
+                    } else {
+                        let local = mir::RETURN_PLACE;
+                        let callee_layout = self.layout_of_local(self.frame(), local, None)?;
+                        if !callee_layout.abi.is_uninhabited() {
+                            throw_ub_format!("calling a returning function without a return place")
                         }
-                        Ok(())
-                    })();
+                    }
+                };
                 match res {
                     Err(err) => {
                         self.stack.pop();
diff --git a/src/librustc_mir/interpret/validity.rs b/src/librustc_mir/interpret/validity.rs
index 05bb010959b..d93b78a5bd5 100644
--- a/src/librustc_mir/interpret/validity.rs
+++ b/src/librustc_mir/interpret/validity.rs
@@ -29,7 +29,7 @@ macro_rules! throw_validation_failure {
             write_path(&mut msg, where_);
         }
         write!(&mut msg, ", but expected {}", $details).unwrap();
-        throw_unsup!(ValidationFailure(msg))
+        throw_ub!(ValidationFailure(msg))
     }};
     ($what:expr, $where:expr) => {{
         let mut msg = format!("encountered {}", $what);
@@ -38,7 +38,7 @@ macro_rules! throw_validation_failure {
             msg.push_str(" at ");
             write_path(&mut msg, where_);
         }
-        throw_unsup!(ValidationFailure(msg))
+        throw_ub!(ValidationFailure(msg))
     }};
 }
 
@@ -353,31 +353,39 @@ impl<'rt, 'mir, 'tcx, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, 'tcx, M
                     place.ptr, size, align
                 );
                 match err.kind {
-                    err_unsup!(InvalidNullPointerUsage) => {
+                    err_ub!(InvalidIntPointerUsage(0)) => {
                         throw_validation_failure!(format_args!("a NULL {}", kind), self.path)
                     }
-                    err_unsup!(AlignmentCheckFailed { required, has }) => {
-                        throw_validation_failure!(
-                            format_args!(
-                                "an unaligned {} \
-                                    (required {} byte alignment but found {})",
-                                kind,
-                                required.bytes(),
-                                has.bytes()
-                            ),
-                            self.path
-                        )
-                    }
+                    err_ub!(InvalidIntPointerUsage(i)) => throw_validation_failure!(
+                        format_args!("a {} to unallocated address {}", kind, i),
+                        self.path
+                    ),
+                    err_ub!(AlignmentCheckFailed { required, has }) => throw_validation_failure!(
+                        format_args!(
+                            "an unaligned {} (required {} byte alignment but found {})",
+                            kind,
+                            required.bytes(),
+                            has.bytes()
+                        ),
+                        self.path
+                    ),
                     err_unsup!(ReadBytesAsPointer) => throw_validation_failure!(
                         format_args!("a dangling {} (created from integer)", kind),
                         self.path
                     ),
-                    err_unsup!(PointerOutOfBounds { .. }) | err_unsup!(DanglingPointerDeref) => {
-                        throw_validation_failure!(
-                            format_args!("a dangling {} (not entirely in bounds)", kind),
-                            self.path
-                        )
-                    }
+                    err_ub!(PointerOutOfBounds { .. }) => throw_validation_failure!(
+                        format_args!(
+                            "a dangling {} (going beyond the bounds of its allocation)",
+                            kind
+                        ),
+                        self.path
+                    ),
+                    // This cannot happen during const-eval (because interning already detects
+                    // dangling pointers), but it can happen in Miri.
+                    err_ub!(PointerUseAfterFree(_)) => throw_validation_failure!(
+                        format_args!("a dangling {} (use-after-free)", kind),
+                        self.path
+                    ),
                     _ => bug!("Unexpected error during ptr inbounds test: {}", err),
                 }
             }
@@ -765,11 +773,11 @@ impl<'rt, 'mir, 'tcx, M: Machine<'mir, 'tcx>> ValueVisitor<'mir, 'tcx, M>
                     Err(err) => {
                         // For some errors we might be able to provide extra information
                         match err.kind {
-                            err_unsup!(ReadUndefBytes(offset)) => {
+                            err_ub!(InvalidUndefBytes(Some(ptr))) => {
                                 // Some byte was undefined, determine which
                                 // element that byte belongs to so we can
                                 // provide an index.
-                                let i = (offset.bytes() / layout.size.bytes()) as usize;
+                                let i = (ptr.offset.bytes() / layout.size.bytes()) as usize;
                                 self.path.push(PathElem::ArrayElem(i));
 
                                 throw_validation_failure!("undefined bytes", self.path)
@@ -817,7 +825,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         // Run it.
         match visitor.visit_value(op) {
             Ok(()) => Ok(()),
-            Err(err) if matches!(err.kind, err_unsup!(ValidationFailure { .. })) => Err(err),
+            Err(err) if matches!(err.kind, err_ub!(ValidationFailure { .. })) => Err(err),
             Err(err) if cfg!(debug_assertions) => {
                 bug!("Unexpected error during validation: {}", err)
             }