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"Invalid cast" with vec::iter(fail) #2151

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jruderman opened this issue Apr 7, 2012 · 0 comments
Closed

"Invalid cast" with vec::iter(fail) #2151

jruderman opened this issue Apr 7, 2012 · 0 comments
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A-codegen Area: Code generation

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@jruderman
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fn main() {
    vec::iter(fail) {|i|
        log (error, i * 2);
    };
}

Breaks rustc with:

Assertion failed: (S->getType()->isPointerTy() && "Invalid cast"), function getPointerCast, file /Users/jruderman/code/rust/src/llvm/lib/VMCore/Constants.cpp, line 1405.
@nikomatsakis nikomatsakis mentioned this issue Apr 7, 2012
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bors added a commit to rust-lang-ci/rust that referenced this issue Sep 22, 2022
@bors
Auto merge of rust-lang#2151 - RalfJung:numbers, r=oli-obk
5832dd1 
enable number validity checking and ptr::invalid checking by default

This removes the `-Zmiri-check-number-validity` flag, enabling its effects by default. (We don't error when the flag is passed, for backwards compatibility.) We also enable by default that transmuting an integer to a pointer now creates a pointer with `None` provenance, which is invalid to dereference (and, in the case of a function pointer, invalid to call). I did this together since it is all related to ptr2int/int2ptr transmutation.

Two new flags are added to optionally take back these stricter checks:
- `-Zmiri-allow-uninit-numbers` makes Miri accept uninit data in integers and floats
- `-Zmiri-allow-ptr-int-transmute` makes Miri accept pointers (provenance data) in integers and floats, *and* makes Miri treat int2ptr transmutes as equivalent to a cast.

The flag names make sense IMO, but they are somewhat inconsistent with our existing flags since we usually call things `-Zmiri-disable-$CHECK` rather than `-Zmiri-allow-$THING`. But `-Zmiri-disable-uninit-number-check` sounds silly?

(Whenever I say "transmute" this includes union and pointer based type punning.)
Cc `@saethlin` I hope this won't break everything?^^ I think the most risky part is the int2ptr transmute aspect, in particular around function pointers where no `as` casts are possible. The correct pattern is to first cast to a raw ptr and then transmute that to a fn ptr. We should probably document this better, in the `transmute` documentation and maybe in the documentation for the `fn()` type. I should run this PR against the std test suite before we land it.
r? `@oli-obk`

- [x] Ensure stdlib docs recommend "usize -> raw ptr -> fn ptr" for int-to-fnptr casts: rust-lang#97321
- [x] Run the stdlib test suite
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@nikomatsakis @jruderman