C binaries built with zig cc and `-Os` on macos and linux segfaults

[cryi]

Zig Version

zig-0.11.0-dev.3050+05ceac52c.tar.xz

Steps to Reproduce and Observed Behavior

1. git clone --recurse-submodules https://github.com/cryi/eli-zig-os
2. build build container podman build ./containers/build/ -t elibuild
3. run build podman run -w "/root/luabuild" -v $(pwd):"/root/luabuild" -v "$(pwd)/toolchains:/opt/cross" -e TOOLCHAINS='zig:x86_64-linux-musl' -it elibuild

It produces binary release/eli-linux-x86_64. It complains about some dependencies missing during the build but ignore that. This is stripped version just for this issue.

Run produced binary:
4. release/eli-linux-x86_64
5. paste in: hash.sha256sum("aa",true) and hit enter to trigger segfault

Everything worked as expected with 0.11.0-dev.1928+3169f0529. I am not sure when was issue introduced but yesterday build (0.11.0-dev.3045+526065723) was affected too.

Notes:

• if I remove -Os produced binary works as expected
• to change used compiler edit containers/build/Dockerfile
• to change compile flags edit CMakeLists.txt#11
• the code we use to trigger segfault is in lua-mbed-hash module

Expected Behavior

Binaries compiled with -Os and -Oz should not segfault.

[squeek502]

Out of curiosity, does the segfault go away if you pass -fno-sanitize=undefined? Zig by default enables the undefined behavior sanitizer so it's possible that's what you're hitting.

[cryi]

Hi @squeek502 , no it does not go away. I would assume it is something more subtle as it was introduced somewhere between 0.11.0-dev.1928+3169f0529 and 0.11.0-dev.3045+526065723

[cryi]

Ok I narrowed it down to 2401+348751462 which works and 2455+48f98494f which does not. Major change between these is switch from clang 15.0.7 to 16.0.1.

[cryi]

Nvm this was actually issue with our code which just blew out when using Oz/Os with clang 16