Issue about errno when using WASI

[lhespress]

I am testing the WASI by thread example, and find an issue about errno, my steps are following:

wasi-sdk-14.0/bin/clang -O3 -mbulk-memory -matomics -ftls-model=local-exec -pthread -z stack-size=8192 -Wl,--initial-memory=65536 -Wl,--shared-memory -Wl,--no-entry -Wl,--allow-undefined -Wl,--strip-all -Wl,--export=main -o thread.wasm thread.c

The result is relocation R_WASM_MEMORY_ADDR_TLS_SLEB cannot be used against errno in non-TLS section: .bss.

My thread code is following:

#include <stdio.h>
#include <errno.h>

int main(void)
{
    errno = 21;
    printf("thread exit %d\n", errno);

    return 0;
}

[sbc100]

This is most likely because non of the wasi-sdk core libraries such as libc and libc++ and compiler-rt are compiled with threading support.

In order to experiment with threading you would need to rebuild the whole SDK with -pthread in the cflags.

Also, you don't need -mbulk-memory -matomics since those should be implied by -pthread. I'm pretty sure the same is true for -ftls-model=local-exec. Just -pthread should be sufficient.

[lhespress]

@sbc100 when i remove -mbulk-memory -matomics -ftls-model=local-exec, it shows the error only -ftls-model=local-exec is supported for now on non-Emscripten OSes: variable errno, so it should include -ftls-model=local-exec and have the same error as i first opened.

[sbc100]

Ok, so -ftls-model=local-exec is needed for now that, but the other two should are not.

[sbc100]

I guess this is really a duplicate of WebAssembly/WASI#296 and can probably be closes as such?

[sunfishcode]

Yes, this is being pursued in https://reviews.llvm.org/D130053 and WebAssembly/wasi-libc#307.

[vapier]

In order to experiment with threading you would need to rebuild the whole SDK with -pthread in the cflags.

this still seems to be the case with wasi-sdk-24. if that flag is required for correct behavior when using the new wasi threads target, shouldn't it be implied automatically?

[yamt]

In order to experiment with threading you would need to rebuild the whole SDK with -pthread in the cflags.

this still seems to be the case with wasi-sdk-24. if that flag is required for correct behavior when using the new wasi threads target, shouldn't it be implied automatically?

you don't need to "rebuild the whole SDK" as the recent wasi-sdk ships wasi-threads build of the libraries.

[vapier]

sorry, meant to emphasize the consistent usage of the flag, not rebuilding the sdk. if you use the threads target but not the pthreads flag, things will link, but you end up with multiple errno storage as described in this report. so if the pthreads flag is required, why isn't it implied when using the threads target?