crate: expose `cfg` for general 64-bit `time_t` functionality by dybucc · Pull Request #5411 · rust-lang/libc

dybucc · 2026-08-14T14:00:37Z

Description

This patch adds support for a new cfg for easily toggling support for
64-bit time_t in supported platforms. This really only sets up the any
one of linux_time_bits64, gnu_time_bits64 or uclibc_time64.

The name of the cfg is time64.

Note support for the equivalent flag in musl has not been included
because we already have set-up automatic detection and toggling of the
corresponding cfg under supported targets ¹.

Checklist

Relevant tests in libc-test/semver have been updated
Commit messages permalink to headers for added or changed API
Placeholder or unstable values like *LAST or *MAX have the
standard doc comment
Tested locally (cargo test -p libc-test --target mytarget);
especially relevant for platforms that may not be checked in CI

@rustbot label +stable-nominated

https://github.com/rust-lang/libc/blob/1a8e71f33b1d6ea1e072210e7fc994417bbb2e34/build.rs#L181-L190 ↩

tgross35

Could you also update CI to use this cfg rather than the current glibc/musl cfg? Since this is what we're most likely to ship, we should make sure it works.

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rustbot · 2026-08-25T08:31:11Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

dybucc · 2026-08-29T10:00:07Z

I think it's done now. While checking through the CI workflow file, I
noticed that we even though we set the "updated but deprecated"
RUST_LIBC_UNSTABLE_MUSL_V1_2 environment variable for certain targets
¹, we still check for RUSTC_LIBC_UNSTABLE_MUSL_V1_2_3 in build.rs
².

I was wondering what's our stance on that change for stable releases,
and whether we should even set the deprecated environment variable in
CI. It seems wrong.

@rustbot ready

tgross35

Two small things then LGTM

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dybucc · 2026-09-01T14:57:17Z

Wondering if you saw ¹, @tgross35?

@rustbot ready

https://github.com/rust-lang/libc/pull/5411#issuecomment-5461679894 ↩

tgross35 · 2026-09-04T09:31:42Z

I think it's done now. While checking through the CI workflow file, I noticed that we even though we set the "updated but deprecated" RUST_LIBC_UNSTABLE_MUSL_V1_2 environment variable for certain targets 1, we still check for RUSTC_LIBC_UNSTABLE_MUSL_V1_2_3 in build.rs 2.

I was wondering what's our stance on that change for stable releases, and whether we should even set the deprecated environment variable in CI. It seems wrong.

Oh, I did mean to update main.yaml here. Could you do that?

I'm not sure I follow the rest, why do you consider RUST_LIBC_UNSTABLE_MUSL_V1_2 "updated but deprecated"? And what do we need to take a stance on regarding stable releases?

tgross35 · 2026-09-07T08:19:26Z

Could you rebase this once #5508 lands? let musl_v1_2 = ..., let uclibc_time64 = ..., and let gnu32_time64.

tgross35 · 2026-09-07T08:20:00Z

Also please update the commit summary and PR title to mention the name of the config, it doesn't actually show up anywhere except the env form :)

tgross35 · 2026-09-20T22:01:53Z

Cherry picked the AIX skip as #5541 to unblock other things

Add `cfg` enabling `time64` functionality across all supported targets. This ensures users have a simple entry point to the crate functionality gated behind one of `linux_time_bits64`, `uclibc_time64` and `gnu_time_bits64`. The new `cfg` goes by the name `libc_unstable_time64`.

Switch as many uses of other target-specific `cfg`s with the `time64` `cfg` introduced in the prior patch.

- Change indentation of two YAML arrays to consistently appear as nested within the key that corresponds with the array. - Change one inconsistent use of single quotes with double quotes for YAML strings.

Replace use of `RUST_LIBC_UNSTABLE_MUSL_V1_2` with `TEST_MUSL_V1_2` in the PowerPC CI runs. The former is deprecated; The latter is used in CI scripts to set the right unstable `cfg` for functionality gated behind musl's v1.2.

rustbot · 2026-09-21T07:19:13Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

tgross35

Sorry for the conflict but I think that should resolve the uclibc issue. LGTM assuming CI passes

View changes since this review

Add `cfg` enabling `time64` functionality across all supported targets. This ensures users have a simple entry point to the crate functionality gated behind one of `linux_time_bits64`, `uclibc_time64` and `gnu_time_bits64`. The new `cfg` goes by the name `libc_unstable_time64`. (backport <rust-lang#5411>) (cherry picked from commit 9a1b7f8)

Switch as many uses of other target-specific `cfg`s with the `time64` `cfg` introduced in the prior patch. (backport <rust-lang#5411>) (cherry picked from commit 39f6b9b)

- Change indentation of two YAML arrays to consistently appear as nested within the key that corresponds with the array. - Change one inconsistent use of single quotes with double quotes for YAML strings. (backport <rust-lang#5411>) (cherry picked from commit 76f110d)

Replace use of `RUST_LIBC_UNSTABLE_MUSL_V1_2` with `TEST_MUSL_V1_2` in the PowerPC CI runs. The former is deprecated; The latter is used in CI scripts to set the right unstable `cfg` for functionality gated behind musl's v1.2. (backport <rust-lang#5411>) (cherry picked from commit dde449d)

Add `cfg` enabling `time64` functionality across all supported targets. This ensures users have a simple entry point to the crate functionality gated behind one of `linux_time_bits64`, `uclibc_time64` and `gnu_time_bits64`. The new `cfg` goes by the name `libc_unstable_time64`. (backport <rust-lang#5411>) (cherry picked from commit 9a1b7f8)

Switch as many uses of other target-specific `cfg`s with the `time64` `cfg` introduced in the prior patch. (backport <rust-lang#5411>) (cherry picked from commit 39f6b9b)

- Change indentation of two YAML arrays to consistently appear as nested within the key that corresponds with the array. - Change one inconsistent use of single quotes with double quotes for YAML strings. (backport <rust-lang#5411>) (cherry picked from commit 76f110d)

Replace use of `RUST_LIBC_UNSTABLE_MUSL_V1_2` with `TEST_MUSL_V1_2` in the PowerPC CI runs. The former is deprecated; The latter is used in CI scripts to set the right unstable `cfg` for functionality gated behind musl's v1.2. (backport <rust-lang#5411>) (cherry picked from commit dde449d)

rustbot added S-waiting-on-review stable-nominated This PR should be considered for cherry-pick to libc's stable release branch labels Aug 14, 2026

tgross35 requested changes Aug 25, 2026

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Comment thread build.rs Outdated

rustbot added S-waiting-on-author and removed S-waiting-on-review labels Aug 25, 2026

dybucc force-pushed the time64-global-cfg branch from 98e48b9 to 1ab4287 Compare August 29, 2026 06:37