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Rollup merge of #126927 - workingjubilee:vaargsafe-is-unsafe, r=joboet

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core: VaArgSafe is an unsafe trait

`T: VaArgSafe` is relied on for soundness. Safe impls promise nothing. Therefore this must be an unsafe trait. Slightly pedantic, as only core can impl this, but we *could* choose to unseal the trait. That would allow soundly (but unsafely) implementing this for e.g. a `#[repr(C)] struct` that should be passable by varargs.

Relates to https://github.com/rust-lang/rust/issues/44930
This commit is contained in:
Matthias Krüger 2024-06-25 21:33:43 +02:00 committed by GitHub
commit 3795c56bd1
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1 changed files with 5 additions and 4 deletions
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9
library/core/src/ffi/mod.rs
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@ -484,7 +484,7 @@ mod sealed_trait {
all supported platforms",
issue = "44930"
)]
pub trait VaArgSafe {}
pub unsafe trait VaArgSafe {}
}
macro_rules! impl_va_arg_safe {
@ -494,7 +494,7 @@ macro_rules! impl_va_arg_safe {
reason = "the `c_variadic` feature has not been properly tested on \
all supported platforms",
issue = "44930")]
impl sealed_trait::VaArgSafe for $t {}
unsafe impl sealed_trait::VaArgSafe for $t {}
)+
}
}
@ -509,14 +509,15 @@ impl_va_arg_safe! {f64}
all supported platforms",
issue = "44930"
)]
impl<T> sealed_trait::VaArgSafe for *mut T {}
unsafe impl<T> sealed_trait::VaArgSafe for *mut T {}
#[unstable(
feature = "c_variadic",
reason = "the `c_variadic` feature has not been properly tested on \
all supported platforms",
issue = "44930"
)]
impl<T> sealed_trait::VaArgSafe for *const T {}
unsafe impl<T> sealed_trait::VaArgSafe for *const T {}
#[unstable(
feature = "c_variadic",