ZST pointers and pointer equality #453
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Here it is: rust-lang/rust#54254 |
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miri engine: keep around some information for dead allocations We use it to make sure a dangling ptr is aligned and non-NULL. This makes some code pass that should pass (writing a ZST to a properly aligned dangling pointer), and makes some code fail that should fail (writing a ZST to a pointer obtained via pointer arithmetic from a real location, but ouf-of-bounds -- that pointer could be NULL, so we cannot allow writing to it). CTFE does not allow these operations; tests are added to miri with rust-lang/miri#453.
RalfJung
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I added another commit that makes pointer equality more strict, and adds compile-fail tests for all cases I can think of right now that I think should fail. |
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miri engine: keep around some information for dead allocations We use it to test if a dangling ptr is aligned and non-NULL. This makes some code pass that should pass (writing a ZST to a properly aligned dangling pointer), and makes some code fail that should fail (writing a ZST to a pointer obtained via pointer arithmetic from a real location, but ouf-of-bounds -- that pointer could be NULL, so we cannot allow writing to it). CTFE does not allow these operations; tests are added to miri with rust-lang/miri#453.
…; and fix ptr equality to fail all of them. At least these are the cases I can think of right now.
eddyb
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Corresponding rustc PR to make these actually pass is upcoming.
This is mostly a whole bunch of new tests to make sure that we rule out loading a ZST from an out-of-bounds pointer (because it might be NULL). Also, pointer equality changes to be more conservative, so I think that with this change we only return a result for an equality test when we can be sure -- with the sole exception of a one-past-the-end pointer of one allocation being compared to the first pointer of another allocation; these two could be equal if the allocations are placed right next to each other.