musl: fix CPU_SETSIZE

[xbjfk]

Description

musl upstream has changed the size from 128 to 1024 in upstream commit
bc695a5, which is in versions 1.2.4+. I see this was fixed for loongarch in this repository, but this change applies to all architectures.

Sources

loongarch commit that changes this
upstream change
upstream permalink

Checklist

• Relevant tests in libc-test/semver have been updated
• No placeholder or unstable values like *LAST or *MAX are
  included (see rust-lang/libc#3131)
• Tested locally (cd libc-test && cargo test --target mytarget);
  especially relevant for platforms that may not be checked in CI

I'm not sure if this can be nominated for 0.2. I would appreciate if someone could confirm.

NOTE: review/merge after #4438 - it includes a commit from that PR.

[xbjfk]

Hmmm, looks like the CI uses a version of musl from 6 years ago (1.1.24). Maybe the version should be upgraded? It feels awkward essentially keeping musl bugs around longer than they need to be to appease the CI which tests against an ancient version. RLIM_NLIMITS has the same issue.

[xbjfk]

Since it seems the minimum supported musl version by rust has been 1.2.3 for 2 years already, I think it is safe to update the CI version. I will look into this soon, and combine this with #3068 and #4438, as well as fix the other issues I am having when running tests (such as RLIM_NLIMITS being 16 now)

[tgross35]

Musl indeed really needs to be updated, it needs some help to get over the line (thank you for offering!).

Unfortunately we can't easily change things all at once because there are some user-visible breaks. I think the best solution is probably to add the new interfaces bit-by-bit under a new cfg(musl_v1_2), which can be set via an unstable environment variable for experimentation before the final switch (which will probably be libc's 1.0).

This is similar to what is being done for glibc's time, #4433.

[xbjfk]

I agree that there should be a new config option - I think the priority would be to get tests fully working on 1.2.3, and focus on making those changes compatible with libc 0.2. There are a couple of constant changes that will be non-breaking

[xbjfk]

Closing in favor of #4443