Getting SIGSEGV with Rust 1.47.0 on macos

[sagacity]

I'm getting intermittent SIGSEGV: invalid memory reference crashes when compiling projects. This has started happening when upgrading from 1.46.0 (stable) to 1.47.0 (stable) on MacOS.

For instance, compiling the master branch of https://github.com/gfx-rs/wgpu-rs:
cargo run --example cube

error: could not compile syn.

Caused by: process didn't exit successfully: rustc --crate-name syn --edition=2018 /Users/rjacobs/.cargo/registry/src/github.tiyicn.workers.dev-1ecc6299db9ec823/syn-1.0.31/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi --crate-type lib --emit=dep-info,metadata,link -C embed-bitcode=no -C debuginfo=2 --cfg 'feature="clone-impls"' --cfg 'feature="default"' --cfg 'feature="derive"' --cfg 'feature="extra-traits"' --cfg 'feature="full"' --cfg 'feature="parsing"' --cfg 'feature="printing"' --cfg 'feature="proc-macro"' --cfg 'feature="quote"' --cfg 'feature="visit"' -C metadata=3015984c4aad08eb -C extra-filename=-3015984c4aad08eb --out-dir /Users/rjacobs/sandbox/wgpu-rs/target/debug/deps -L dependency=/Users/rjacobs/sandbox/wgpu-rs/target/debug/deps --extern proc_macro2=/Users/rjacobs/sandbox/wgpu-rs/target/debug/deps/libproc_macro2-ca449e9a62227554.rmeta --extern quote=/Users/rjacobs/sandbox/wgpu-rs/target/debug/deps/libquote-4e89379d9f53f035.rmeta --extern unicode_xid=/Users/rjacobs/sandbox/wgpu-rs/target/debug/deps/libunicode_xid-4f1ac68564fd7c97.rmeta --cap-lints allow --cfg syn_disable_nightly_tests (signal: 11, SIGSEGV: invalid memory reference)`

If I simply start the build again with cargo run --example cube eventually it will compile and run correctly. Also, in the above example it's syn that fails, but other crates may also cause the crash randomly.

Sometimes I'm also getting panics in rustc instead of SIGSEGV. I assume this is related to miscompilation in an earlier stage. I can't really add too many other details since I'm no debugging expert on MacOS but I'm happy to run some debugging commands to help.

rustc --version --verbose:
rustc 1.47.0 (18bf6b4 2020-10-07)
binary: rustc
commit-hash: 18bf6b4
commit-date: 2020-10-07
host: x86_64-apple-darwin
release: 1.47.0
LLVM version: 11.0

[jyn514]

SEGV sounds like it might be running out of memory - do you know how much memory it takes up when compiling this project? free -h will tell you, or command time -v cargo build.

[sagacity]

@jyn514 max memory reported by zsh time is approx 680MiB for the wgpu build, which doesn't indicate out of memory.

After rebooting my laptop I'm not seeing these crashes anymore, though. Perhaps it was running out of memory before the reboot, but there was nothing in the system indicating a lack of resources.

I'll see if I can artificially reduce available memory and see if I can reproduce.

[sagacity]

Even with significant memory pressure (via the memory_pressure tool) I can't reproduce the issue anymore.

This could mean two things imo:

• I just had some rogue kernel extension on my machine stomping on memory somehow
• The crashes are somehow related to where in memory the compilation process is running

Neither seem very likely, but I guess that's all I can do for now. Feel free to close this ticket if you agree, otherwise I'm happy to do some more experiments.

[apiraino]

@RoyJacobs feel free to report back if you can reproduce the issue again. Also, you might want to subscribe to linked issue #77869