Description
Code
Can't provide a minimal example for obvious reasons :)
$ git clone https://github.com/bytecodealliance/wasmtime/
$ cd wasmtime
$ git checkout 87817f38a128caa76eaa6a3c3c8ceac81a329a3e
$ cd cranelift/codegen
$ RUST_MIN_STACK=1048576 cargo +1.80.0 build
On my Linux x86_64 system this deterministically crashes in the rustc parser due to call stack exhaustion (i.e. a call stack overflow). The full output is here. (Note I haven't built a Rust compiler with symbols, because I have enough information to establish the cause without needing symbols.)
The file that's failing to parse is this one. It is an autogenerated file called isle_opt.rs, and is generated by the cranelift-codegen build script.
This also reproduces with rustc 1.82.0-nightly (f8060d282 2024-07-30).
What's the RUST_MIN_STACK doing, you might ask? Well, long story behind this, but I got here by first diagnosing the issue on illumos, which crashed in the same spot with the same crate (illumos stack trace), without requiring RUST_MIN_STACK to be set.
- In fact, on illumos, the issue occurs whether
RUST_MIN_STACKis set to 1MiB, 2MiB (default) or 4MiB. This is consistent with the description below.
What's happening is:
- This file in
cranelift-codegenis triggering the crash by requiring more than 1MiB of stack space.- The
rustcparser running againstcranelift-codegenneeds more than 1MiB of stack space, but less than 2MiB.
- The
- Had this bug occurred on other platforms like Linux, this issue would have been a showstopper. However, it wasn't visible on those platforms because:
- Threads created by Rust use a 2MiB stack by default.
rustcrequests a 1MiB stack segment with a 100KiB red zone.- On other platforms like Linux,
stackercan see that well over 100KiB of stack space is left, and so it does not allocate a new segment. - On illumos, this logic doesn't exist.
stackercannot see how much stack was left, and so it unconditionally allocates a new 1MiB segment. - This 1MiB stack is simply not enough to parse
isle_opt.rs.
With RUST_MIN_STACK used to set a stack size <= 1MiB, we would expect that:
rustccallsstackeras before.- There are two possibilities: either
stackerdecides there is enough stack space and doesn't create a new segment, or it decides there isn't enough and does create a new 1MiB segment. - In either case, 1MiB is simply not enough to parse
cranelift-codegen, and the program crashes.
To the best of my understanding, this is a bug in rustc's use of stacker. The fact that 1MiB just isn't enough to parse that file was being masked by the default stack size of 2MiB.
I think the fix is that rustc should be calling stacker more often in its recursive sections -- if it did, then stacker would allocate a new segment as soon as less than 100KiB of stack space was available.
(A secondary issue is that stacker should be able to detect stack sizes on illumos -- I'll try sending a PR for that separately.)
Meta
Reproes with both:
rustc --version --verbose:
rustc 1.80.0 (051478957 2024-07-21)
binary: rustc
commit-hash: 051478957371ee0084a7c0913941d2a8c4757bb9
commit-date: 2024-07-21
host: x86_64-unknown-linux-gnu
release: 1.80.0
LLVM version: 18.1.7
and
rustc 1.82.0-nightly (f8060d282 2024-07-30)
binary: rustc
commit-hash: f8060d282d42770fadd73905e3eefb85660d3278
commit-date: 2024-07-30
host: x86_64-unknown-linux-gnu
release: 1.82.0-nightly
LLVM version: 18.1.7
Error output
https://gist.github.com/sunshowers/3ac000e5a5022acd3f07886a16a39520