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The field wasn't defined previously. And the enum wasn't defined as `[repr(C)]`. This missing field could result in memory corruption if a Rust-allocated `PyStatus` was passed to a Python API, which could perform an out-of-bounds write. In my code, the out-of-bounds write corrupted a variable on the stack, leading to a segfault due to illegal memory access. However, this crash only occurred on Rust 1.54! So I initially mis-attribted it as a compiler bug / regression. It appears that a low-level Rust change in 1.54.0 changed the LLVM IR in such a way to cause LLVM optimization passes to produce sufficiently different assembly code, tickling the crash. See rust-lang/rust#87947 if you want to see the wild goose chase I went on in Rust / LLVM land to potentially pin this on a compiler bug. Lessen learned: Rust crashes are almost certainly due to use of `unsafe`.
davidhewitt
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Aug 14, 2021
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Yikes, sorry about that.
We've started merging breaking changes for 0.15, so I wasn't planning to do a release any time soon. However this looks pretty bad, so I might merge this and a few of your other FFI fixes into a 0.14.3.
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The field wasn't defined previously. And the enum wasn't defined as
[repr(C)].This missing field could result in memory corruption if a Rust-allocated
PyStatuswas passed to a Python API, which could perform anout-of-bounds write. In my code, the out-of-bounds write corrupted a
variable on the stack, leading to a segfault due to illegal memory
access. However, this crash only occurred on Rust 1.54! So I initially
mis-attribted it as a compiler bug / regression. It appears that a
low-level Rust change in 1.54.0 changed the LLVM IR in such a way to
cause LLVM optimization passes to produce sufficiently different
assembly code, tickling the crash. See
rust-lang/rust#87947 if you want to see
the wild goose chase I went on in Rust / LLVM land to potentially
pin this on a compiler bug.
Lessen learned: Rust crashes are almost certainly due to use of
unsafe.