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unsized_fn_params allows some unsized locals #111175
Labels
A-MIR
Area: Mid-level IR (MIR) - https://blog.rust-lang.org/2016/04/19/MIR.html
F-unsized_fn_params
`#![feature(unsized_fn_params)]`
requires-nightly
This issue requires a nightly compiler in some way.
Comments
I forgot how exactly #78152 works, but for some reason it lets this pass. Either the analysis should reject this, or MIR building needs to not create an unsized local here. |
jyn514
added
A-MIR
Area: Mid-level IR (MIR) - https://blog.rust-lang.org/2016/04/19/MIR.html
I-unsound
Issue: A soundness hole (worst kind of bug), see: https://en.wikipedia.org/wiki/Soundness
requires-nightly
This issue requires a nightly compiler in some way.
F-unsized_fn_params
`#![feature(unsized_fn_params)]`
labels
May 4, 2023
The bad MIR builing is here:
Any unsized function call operand other than a |
rustbot
removed
the
I-unsound
Issue: A soundness hole (worst kind of bug), see: https://en.wikipedia.org/wiki/Soundness
label
May 23, 2023
RalfJung
changed the title
unsized_fn_params allows some unsized locals, hitting unsound alloca codegen path
unsized_fn_params allows some unsized locals
Aug 6, 2023
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Labels
A-MIR
Area: Mid-level IR (MIR) - https://blog.rust-lang.org/2016/04/19/MIR.html
F-unsized_fn_params
`#![feature(unsized_fn_params)]`
requires-nightly
This issue requires a nightly compiler in some way.
Found in rust-lang/miri#2872: this code
with
-Zmir-opt-level=0
generates this LLVM IRNotice the
alloca
. This is bad! Our alloca code path is unsound (it does not properly account for alignment); the point of theunsized_fn_params
feature gate (separate fromunsized_locals
) was to avoid hitting that code path.I repeat my stance that we should remove the unsound alloca code path (effectively de-imlementing unsized locals) to ensure this can never happen.
We don't have a MIR building ping group AFAIK, so Cc @rust-lang/wg-mir-opt I guess.
Here's a Miri testcase:
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