diff options
| -rw-r--r-- | library/std/src/io/error.rs | 7 | ||||
| -rw-r--r-- | library/std/src/io/error/repr_bitpacked.rs | 18 |
2 files changed, 20 insertions, 5 deletions
diff --git a/library/std/src/io/error.rs b/library/std/src/io/error.rs index 449771c6761..8f82778e90b 100644 --- a/library/std/src/io/error.rs +++ b/library/std/src/io/error.rs @@ -83,6 +83,10 @@ enum ErrorData<C> { Custom(C), } +// `#[repr(align(4))]` is probably redundant, it should have that value or +// higher already. We include it just because repr_bitpacked.rs's encoding +// requires an alignment >= 4 (note that `#[repr(align)]` will not reduce the +// alignment required by the struct, only increase it). #[repr(align(4))] #[doc(hidden)] pub(crate) struct SimpleMessage { @@ -106,6 +110,9 @@ pub(crate) macro const_io_error($kind:expr, $message:expr $(,)?) { }) } +// As with `SimpleMessage`: `#[repr(align(4))]` here is just because +// repr_bitpacked's encoding requires it. In practice it almost certainly be +// already be this high or higher. #[derive(Debug)] #[repr(align(4))] struct Custom { diff --git a/library/std/src/io/error/repr_bitpacked.rs b/library/std/src/io/error/repr_bitpacked.rs index 8ff0bcc7cb5..281cbdc23e4 100644 --- a/library/std/src/io/error/repr_bitpacked.rs +++ b/library/std/src/io/error/repr_bitpacked.rs @@ -56,7 +56,7 @@ //! //! Conceptually you might think of this more like: //! -//! ```ignore +//! ```ignore (exposition-only) //! union Repr { //! // holds integer (Simple/Os) variants, and //! // provides access to the tag bits. @@ -159,7 +159,7 @@ impl Repr { #[inline] pub(super) const fn new_simple_message(m: &'static SimpleMessage) -> Self { - // Safety: We're a Repr, decode_repr is fine. + // Safety: References are never null. Self(unsafe { NonNull::new_unchecked(m as *const _ as *mut ()) }) } @@ -213,7 +213,7 @@ where TAG_SIMPLE => { let kind_bits = (bits >> 32) as u32; let kind = kind_from_prim(kind_bits).unwrap_or_else(|| { - debug_assert!(false, "Invalid io::error::Repr bits: `Repr({:#016x})`", bits); + debug_assert!(false, "Invalid io::error::Repr bits: `Repr({:#018x})`", bits); // This means the `ptr` passed in was not valid, which voilates // the unsafe contract of `decode_repr`. // @@ -299,8 +299,11 @@ fn kind_from_prim(ek: u32) -> Option<ErrorKind> { } // Some static checking to alert us if a change breaks any of the assumptions -// that our encoding relies on. If any of these are hit on a platform that -// libstd supports, we should just make sure `repr_unpacked.rs` is used. +// that our encoding relies on for correctness and soundness. (Some of these are +// a bit overly thorough/cautious, admittedly) +// +// If any of these are hit on a platform that libstd supports, we should just +// make sure `repr_unpacked.rs` is used instead. macro_rules! static_assert { ($condition:expr) => { const _: [(); 0] = [(); (!$condition) as usize]; @@ -332,6 +335,11 @@ static_assert!(TAG_SIMPLE != 0); static_assert!(TAG_SIMPLE_MESSAGE == 0); // Check that the point of all of this still holds. +// +// We'd check against `io::Error`, but *technically* it's allowed to vary, +// as it's not `#[repr(transparent)]`/`#[repr(C)]`. We could add that, but +// the `#[repr()]` would show up in rustdoc, which might be seen as a stable +// commitment. static_assert!(size_of::<Repr>() == 8); static_assert!(size_of::<Option<Repr>>() == 8); static_assert!(size_of::<Result<(), Repr>>() == 8); |