Stream: general

Topic: ✔ Did anyone manage to run a wasm32-wasi-threads module?

Cheng Shao (Feb 08 2023 at 14:08):

Given wasmtime recently landed support, I tried to run a pthread hello world program, and encountered two issues:

• I had to patch wasmtime to change thread_spawn to thread-spawn to match what wasi-libc uses
• I had to pass -Wl,--import-memory,--shared-memory to satisfy the requirement of importing a shared linear memory, but I couldn't find a way to tell the linker to also export the memory

Did anyone else manage to compile and run a wasm32-wasi-threads module?

Andrew Brown (Feb 08 2023 at 19:06):

Yes, I hope to publish a blog post explaining all the details soon but there are a few remaining issues to work through.

Andrew Brown (Feb 08 2023 at 19:08):

One of the reasons that I'm working on https://github.com/WebAssembly/wasi-sdk/pull/293 is that LLVM 16 provides the --export-memory and --import-memory flags in a way that allows the "import, then export" paradigm currently necessary in Wasmtime. Once I have that working I plan to publish a pre-release of wasi-sdk that has all the right tools to make things work.

Cheng Shao (Feb 08 2023 at 19:25):

Ah, --export-memory, that was new in wasm-ld and i was looking at the old manpage. I just got an example to run, the behavior is a bit odd but that's kinda expected in the early days. Thanks for your work.

Notification Bot (Feb 08 2023 at 19:25):

Cheng Shao has marked this topic as resolved.

Andrew Brown (Feb 08 2023 at 20:19):

Yeah, the "import, then export" idea is odd (if that's what you're referring to). @YAMAMOTO Takashi opened up https://github.com/WebAssembly/WASI/issues/502 to discuss this topic generally; feel free to comment there if you have a strong opinion one way or another.

Cheng Shao (Feb 08 2023 at 20:23):

No, I mean the runtime result is incorrect. Though I'm not sure if it's a wasi-libc issue or wasmtime issue, so don't know where to report it..

Andrew Brown (Feb 08 2023 at 20:40):

Oh, that's interesting! If you can diagnose which side it is on, please open a bug. The whole idea of this experimental wasi-sdk release is to bring to light these kinds of issues. Can you say more about the project and what you see?

Cheng Shao (Feb 08 2023 at 21:12):

The bug report is at https://gist.github.com/TerrorJack/a3128331031377a38d50912b0eab609c

Andrew Brown (Feb 08 2023 at 23:15):

Thanks, I'll take a look!

YAMAMOTO Takashi (Feb 09 2023 at 03:01):

Cheng Shao said:

The bug report is at https://gist.github.com/TerrorJack/a3128331031377a38d50912b0eab609c

you should use large enough --max-memory.
eg.

spacetanuki% /opt/wasi-sdk-19.5g0236e959edbc/bin/clang -Wall --target=wasm32-wasi-threads -pthread thread.c -o thread.wasm -Wl,--import-memory,--max-memory=655360
spacetanuki% ~/git/toywasm/b.thread/toywasm --wasi thread.wasm
Thread - 2
Thread - 1
spacetanuki%

Andrew Brown (Feb 10 2023 at 18:27):

Yeah, that's it... wow, that was unintuitive. I just was taking a look at @Cheng Shao's report today and I can confirm that adding --max-memory=655360 to the linker flags makes everything start working again.

Andrew Brown (Feb 10 2023 at 18:32):

I guess non-PoC code would have error-checking like the following:

int ret = pthread_create(&thread1, NULL, &thread, (void *) thr);
if (ret) {
    printf("failed to spawn: %s\n", strerror(ret));
}

Which prints the following for me:

failed to spawn: Resource temporarily unavailable

Last updated: Dec 23 2024 at 12:05 UTC