Build failed with --cfg=rustix_use_libc

[huajingyun01]

Hi everyone,
for context, I was trying to compile awww 0.12.1 on Alpine Linux (loongarch64) and encountered some errors related to rustix：

error[E0433]: failed to resolve: could not find `runtime` in `rustix`
   --> daemon/src/wallpaper.rs:315:48
    |
315 |                         match unsafe { rustix::runtime::kernel_fork() } {
    |                                                ^^^^^^^ could not find `runtime` in `rustix`
    |
note: found an item that was configured out
   --> /home/alpine/aports/community/awww/tmp/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/rustix-1.1.4/src/lib.rs:317:9
    |
314 | #[cfg(linux_raw)]
    |       --------- the item is gated here
...
317 | pub mod runtime;
    |         ^^^^^^^

After checking, I found that the linux_raw backend does not support loongarch64, so I tried using the libc backend by setting RUSTFLAGS="$RUSTFLAGS --cfg=rustix_use_libc", but I got the same error.

Interestingly, I also tried building awww on x86_64 with the same RUSTFLAGS="$RUSTFLAGS --cfg=rustix_use_libc" and encountered the same error.

Is this a known issue? Any suggestions for this issue?
Thanks!

[sunfishcode]

awww uses rustix's "runtime" feature. This is "undocumented and unstable and experimental and not intended for general-purpose use.".

[sunfishcode]

It's impossible to implement rustix::runtime::kernel_fork for the libc backend, on any architecture.

Moreover, it's impossible even just to call rustix::runtime::kernel_fork at all, in any process that has a libc loaded into it, unless it's libc itself making the call.

[sunfishcode]

The fix for this issue is to change awww to call libc::fork instead of using rustix for this operation. That is basically the only way to perform a fork without invoking instant undefined behavior, in any process where a libc is present.

[huajingyun01]

Hi @sunfishcode Thank you very much for your detailed explanation and the fix suggestions.

I noticed a pull request that, if supported by rustix, should provide more complete support for the loongarch64 architecture. Looking forward to any updates.

Thank you again for your help.