properly catch invalid-drop-fn errors

src/librustc_middle/mir/interpret/error.rs

@@ -3,8 +3,7 @@ use super::{AllocId, Pointer, RawConst, ScalarMaybeUndef};
 use crate::mir::interpret::ConstValue;
 use crate::ty::layout::LayoutError;
 use crate::ty::query::TyCtxtAt;
-use crate::ty::tls;
-use crate::ty::{self, layout, Ty};
+use crate::ty::{self, layout, tls, FnSig, Ty};
 
 use rustc_data_structures::sync::Lock;
 use rustc_errors::{struct_span_err, DiagnosticBuilder, ErrorReported};
@@ -329,7 +328,7 @@ impl fmt::Display for CheckInAllocMsg {
 }
 
 /// Error information for when the program caused Undefined Behavior.
-pub enum UndefinedBehaviorInfo {
+pub enum UndefinedBehaviorInfo<'tcx> {
     /// Free-form case. Only for errors that are never caught!
     Ub(String),
     /// Unreachable code was executed.
@@ -347,6 +346,8 @@ pub enum UndefinedBehaviorInfo {
     PointerArithOverflow,
     /// Invalid metadata in a wide pointer (using `str` to avoid allocations).
     InvalidMeta(&'static str),
+    /// Invalid drop function in vtable.
+    InvalidDropFn(FnSig<'tcx>),
     /// Reading a C string that does not end within its allocation.
     UnterminatedCString(Pointer),
     /// Dereferencing a dangling pointer after it got freed.
@@ -393,7 +394,7 @@ pub enum UndefinedBehaviorInfo {
     },
 }
 
-impl fmt::Display for UndefinedBehaviorInfo {
+impl fmt::Display for UndefinedBehaviorInfo<'_> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         use UndefinedBehaviorInfo::*;
         match self {
@@ -406,6 +407,11 @@ impl fmt::Display for UndefinedBehaviorInfo {
             RemainderByZero => write!(f, "calculating the remainder with a divisor of zero"),
             PointerArithOverflow => write!(f, "overflowing in-bounds pointer arithmetic"),
             InvalidMeta(msg) => write!(f, "invalid metadata in wide pointer: {}", msg),
+            InvalidDropFn(sig) => write!(
+                f,
+                "invalid drop function signature: got {}, expected exactly one argument which must be a pointer type",
+                sig
+            ),
             UnterminatedCString(p) => write!(
                 f,
                 "reading a null-terminated string starting at {} with no null found before end of allocation",
@@ -448,9 +454,7 @@ impl fmt::Display for UndefinedBehaviorInfo {
             InvalidFunctionPointer(p) => {
                 write!(f, "using {} as function pointer but it does not point to a function", p)
             }
-            InvalidStr(err) => {
-                write!(f, "this string is not valid UTF-8: {}", err)
-            }
+            InvalidStr(err) => write!(f, "this string is not valid UTF-8: {}", err),
             InvalidUndefBytes(Some(p)) => write!(
                 f,
                 "reading uninitialized memory at {}, but this operation requires initialized memory",
@@ -554,7 +558,7 @@ impl dyn MachineStopType {
 
 pub enum InterpError<'tcx> {
     /// The program caused undefined behavior.
-    UndefinedBehavior(UndefinedBehaviorInfo),
+    UndefinedBehavior(UndefinedBehaviorInfo<'tcx>),
     /// The program did something the interpreter does not support (some of these *might* be UB
     /// but the interpreter is not sure).
     Unsupported(UnsupportedOpInfo),

src/librustc_mir/interpret/operand.rs

@@ -327,8 +327,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     pub fn read_str(&self, mplace: MPlaceTy<'tcx, M::PointerTag>) -> InterpResult<'tcx, &str> {
         let len = mplace.len(self)?;
         let bytes = self.memory.read_bytes(mplace.ptr, Size::from_bytes(len))?;
-        let str = ::std::str::from_utf8(bytes)
-            .map_err(|err| err_ub!(InvalidStr(err)))?;
+        let str = ::std::str::from_utf8(bytes).map_err(|err| err_ub!(InvalidStr(err)))?;
         Ok(str)
     }
 

src/librustc_mir/interpret/traits.rs

@@ -147,13 +147,11 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         // The drop function takes `*mut T` where `T` is the type being dropped, so get that.
         let args = fn_sig.inputs();
         if args.len() != 1 {
-            throw_ub_format!("drop fn should have 1 argument, but signature is {:?}", fn_sig);
+            throw_ub!(InvalidDropFn(fn_sig));
         }
         let ty = args[0]
             .builtin_deref(true)
-            .ok_or_else(|| {
-                err_ub_format!("drop fn argument type {} is not a pointer type", args[0])
-            })?
+            .ok_or_else(|| err_ub!(InvalidDropFn(fn_sig)))?
             .ty;
         Ok((drop_instance, ty))
     }

src/librustc_mir/interpret/validity.rs

@@ -313,6 +313,7 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
                 try_validation!(
                     self.ecx.read_drop_type_from_vtable(vtable),
                     self.path,
+                    err_ub!(InvalidDropFn(..)) |
                     err_ub!(DanglingIntPointer(..)) |
                     err_ub!(InvalidFunctionPointer(..)) |
                     err_unsup!(ReadBytesAsPointer) =>