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Rollup merge of rust-lang#113441 - RalfJung:assign-no-overlap, r=oli-obk
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miri: check that assignments do not self-overlap

r? ``@oli-obk``
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matthiaskrgr authored Jul 7, 2023
2 parents 1808063 + 7a83ef8 commit 016036a
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Showing 3 changed files with 49 additions and 1 deletion.
7 changes: 6 additions & 1 deletion compiler/rustc_const_eval/src/interpret/place.rs
Original file line number Diff line number Diff line change
Expand Up @@ -700,8 +700,13 @@ where
assert_eq!(src.layout.size, dest.layout.size);
}

// Setting `nonoverlapping` here only has an effect when we don't hit the fast-path above,
// but that should at least match what LLVM does where `memcpy` is also only used when the
// type does not have Scalar/ScalarPair layout.
// (Or as the `Assign` docs put it, assignments "not producing primitives" must be
// non-overlapping.)
self.mem_copy(
src.ptr, src.align, dest.ptr, dest.align, dest_size, /*nonoverlapping*/ false,
src.ptr, src.align, dest.ptr, dest.align, dest_size, /*nonoverlapping*/ true,
)
}

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23 changes: 23 additions & 0 deletions src/tools/miri/tests/fail/overlapping_assignment.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,23 @@
#![feature(core_intrinsics)]
#![feature(custom_mir)]

use std::intrinsics::mir::*;

// It's not that easy to fool the MIR validity check
// which wants to prevent overlapping assignments...
// So we use two separate pointer arguments, and then arrange for them to alias.
#[custom_mir(dialect = "runtime", phase = "optimized")]
pub fn self_copy(ptr1: *mut [i32; 4], ptr2: *mut [i32; 4]) {
mir! {
{
*ptr1 = *ptr2; //~ERROR: overlapping ranges
Return()
}
}
}

pub fn main() {
let mut x = [0; 4];
let ptr = std::ptr::addr_of_mut!(x);
self_copy(ptr, ptr);
}
20 changes: 20 additions & 0 deletions src/tools/miri/tests/fail/overlapping_assignment.stderr
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@@ -0,0 +1,20 @@
error: Undefined Behavior: `copy_nonoverlapping` called on overlapping ranges
--> $DIR/overlapping_assignment.rs:LL:CC
|
LL | *ptr1 = *ptr2;
| ^^^^^^^^^^^^^ `copy_nonoverlapping` called on overlapping ranges
|
= 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
= note: BACKTRACE:
= note: inside `self_copy` at $DIR/overlapping_assignment.rs:LL:CC
note: inside `main`
--> $DIR/overlapping_assignment.rs:LL:CC
|
LL | self_copy(ptr, ptr);
| ^^^^^^^^^^^^^^^^^^^

note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

error: aborting due to previous error

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