Auto merge of #98112 - saethlin:mir-alignment-checks, r=oli-obk

Insert alignment checks for pointer dereferences when debug assertions are enabled

Closes rust-lang/rust#54915

- [x] Jake tells me this sounds like a place to use `MirPatch`, but I can't figure out how to insert a new basic block with a new terminator in the middle of an existing basic block, using `MirPatch`. (if nobody else backs up this point I'm checking this as "not actually a good idea" because the code looks pretty clean to me after rearranging it a bit)
- [x] Using `CastKind::PointerExposeAddress` is definitely wrong, we don't want to expose. Calling a function to get the pointer address seems quite excessive. ~I'll see if I can add a new `CastKind`.~ `CastKind::Transmute` to the rescue!
- [x] Implement a more helpful panic message like slice bounds checking.

r? `@oli-obk`

Author: bors

src/shims/panic.rs

@@ -220,6 +220,34 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                     },
                 )?;
             }
+            MisalignedPointerDereference { required, found } => {
+                // Forward to `panic_misaligned_pointer_dereference` lang item.
+
+                // First arg: required.
+                let required = this.read_scalar(&this.eval_operand(required, None)?)?;
+                // Second arg: found.
+                let found = this.read_scalar(&this.eval_operand(found, None)?)?;
+
+                // Call the lang item.
+                let panic_misaligned_pointer_dereference =
+                    this.tcx.lang_items().panic_misaligned_pointer_dereference_fn().unwrap();
+                let panic_misaligned_pointer_dereference =
+                    ty::Instance::mono(this.tcx.tcx, panic_misaligned_pointer_dereference);
+                this.call_function(
+                    panic_misaligned_pointer_dereference,
+                    Abi::Rust,
+                    &[required.into(), found.into()],
+                    None,
+                    StackPopCleanup::Goto {
+                        ret: None,
+                        unwind: match unwind {
+                            Some(cleanup) => StackPopUnwind::Cleanup(cleanup),
+                            None => StackPopUnwind::Skip,
+                        },
+                    },
+                )?;
+            }
+
             _ => {
                 // Forward everything else to `panic` lang item.
                 this.start_panic(

tests/fail/unaligned_pointers/alignment.rs

@@ -1,4 +1,5 @@
 //@normalize-stderr-test: "\| +\^+" -> "| ^"
+//@compile-flags: -Cdebug-assertions=no
 
 fn main() {
     // No retry needed, this fails reliably.

tests/fail/unaligned_pointers/atomic_unaligned.rs

@@ -1,4 +1,4 @@
-//@compile-flags: -Zmiri-symbolic-alignment-check
+//@compile-flags: -Zmiri-symbolic-alignment-check -Cdebug-assertions=no
 #![feature(core_intrinsics)]
 
 fn main() {

tests/fail/unaligned_pointers/drop_in_place.rs

@@ -1,3 +1,5 @@
+//@compile-flags: -Cdebug-assertions=no
+
 #[repr(transparent)]
 struct HasDrop(u8);
 

tests/fail/unaligned_pointers/dyn_alignment.rs

@@ -1,5 +1,5 @@
 // should find the bug even without validation and stacked borrows, but gets masked by optimizations
-//@compile-flags: -Zmiri-disable-validation -Zmiri-disable-stacked-borrows -Zmir-opt-level=0
+//@compile-flags: -Zmiri-disable-validation -Zmiri-disable-stacked-borrows -Zmir-opt-level=0 -Cdebug-assertions=no
 
 #[repr(align(256))]
 #[derive(Debug)]

tests/fail/unaligned_pointers/intptrcast_alignment_check.rs

@@ -1,4 +1,4 @@
-//@compile-flags: -Zmiri-symbolic-alignment-check -Zmiri-permissive-provenance
+//@compile-flags: -Zmiri-symbolic-alignment-check -Zmiri-permissive-provenance -Cdebug-assertions=no
 // With the symbolic alignment check, even with intptrcast and without
 // validation, we want to be *sure* to catch bugs that arise from pointers being
 // insufficiently aligned. The only way to achieve that is not not let programs

tests/fail/unaligned_pointers/reference_to_packed.rs

@@ -1,5 +1,5 @@
 // This should fail even without validation/SB
-//@compile-flags: -Zmiri-disable-validation -Zmiri-disable-stacked-borrows
+//@compile-flags: -Zmiri-disable-validation -Zmiri-disable-stacked-borrows -Cdebug-assertions=no
 
 #![allow(dead_code, unused_variables)]
 

tests/fail/unaligned_pointers/unaligned_ptr1.rs

@@ -1,5 +1,5 @@
 // This should fail even without validation or Stacked Borrows.
-//@compile-flags: -Zmiri-disable-validation -Zmiri-disable-stacked-borrows
+//@compile-flags: -Zmiri-disable-validation -Zmiri-disable-stacked-borrows -Cdebug-assertions=no
 
 fn main() {
     // Try many times as this might work by chance.

tests/fail/unaligned_pointers/unaligned_ptr2.rs

@@ -1,5 +1,5 @@
 // This should fail even without validation or Stacked Borrows.
-//@compile-flags: -Zmiri-disable-validation -Zmiri-disable-stacked-borrows
+//@compile-flags: -Zmiri-disable-validation -Zmiri-disable-stacked-borrows -Cdebug-assertions=no
 
 fn main() {
     // No retry needed, this fails reliably.

tests/fail/unaligned_pointers/unaligned_ptr3.rs

@@ -1,5 +1,5 @@
 // This should fail even without validation or Stacked Borrows.
-//@compile-flags: -Zmiri-disable-validation -Zmiri-disable-stacked-borrows
+//@compile-flags: -Zmiri-disable-validation -Zmiri-disable-stacked-borrows -Cdebug-assertions=no
 
 fn main() {
     // Try many times as this might work by chance.

tests/fail/unaligned_pointers/unaligned_ptr4.rs

@@ -1,5 +1,5 @@
 // This should fail even without validation or Stacked Borrows.
-//@compile-flags: -Zmiri-disable-validation -Zmiri-disable-stacked-borrows
+//@compile-flags: -Zmiri-disable-validation -Zmiri-disable-stacked-borrows -Cdebug-assertions=no
 
 fn main() {
     // Make sure we notice when a u16 is loaded at offset 1 into a u8 allocation.

tests/fail/unaligned_pointers/unaligned_ptr_addr_of.rs

@@ -1,5 +1,5 @@
 // This should fail even without validation or Stacked Borrows.
-//@compile-flags: -Zmiri-disable-validation -Zmiri-disable-stacked-borrows
+//@compile-flags: -Zmiri-disable-validation -Zmiri-disable-stacked-borrows -Cdebug-assertions=no
 use std::ptr;
 
 fn main() {

tests/fail/unaligned_pointers/unaligned_ptr_zst.rs

@@ -1,6 +1,6 @@
 // This should fail even without validation
 // Some optimizations remove ZST accesses, thus masking this UB.
-//@compile-flags: -Zmir-opt-level=0 -Zmiri-disable-validation
+//@compile-flags: -Zmir-opt-level=0 -Zmiri-disable-validation -Cdebug-assertions=no
 
 fn main() {
     // Try many times as this might work by chance.

tests/panic/alignment-assertion.rs

@@ -0,0 +1,9 @@
+//@compile-flags: -Zmiri-disable-alignment-check -Cdebug-assertions=yes
+
+fn main() {
+    let mut x = [0u32; 2];
+    let ptr: *mut u8 = x.as_mut_ptr().cast::<u8>();
+    unsafe {
+        *(ptr.add(1).cast::<u32>()) = 42;
+    }
+}

tests/panic/alignment-assertion.stderr

@@ -0,0 +1,2 @@
+thread 'main' panicked at 'misaligned pointer dereference: address must be a multiple of 0x4 but is $HEX', $DIR/alignment-assertion.rs:LL:CC
+note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/pass/disable-alignment-check.rs

@@ -1,6 +1,6 @@
 //@revisions: stack tree
 //@[tree]compile-flags: -Zmiri-tree-borrows
-//@compile-flags: -Zmiri-disable-alignment-check
+//@compile-flags: -Zmiri-disable-alignment-check -Cdebug-assertions=no
 
 fn main() {
     let mut x = [0u8; 20];