uclibc fix kernel constant tests + docker ci build fixes by skrap · Pull Request #5261 · rust-lang/libc

skrap · 2026-07-07T21:44:51Z

Description

Today's uClibc builds in CI cannot test many recently-added linux kernel features, as the prebuilt bootlin toolchains they rely on are built against kernel 5.15.

This changes the ci/install-uclibc.sh script to use a toolchain provided via an environment variable. This allows projects and developers who want to run the uclibc tests to build based on kernel 7.0 headers, and use that toolchain for running the libc build and test in CI.

Best way to test is via:

UCLIBC_TOOLCHAIN_URL=https://github.com/skrap/libc-downstream-ci/releases/download/v0.1-toolchain/arm-buildroot-linux-uclibcgnueabihf_sdk-buildroot.tar.gz  \
LIBC_CI_ZBUILD_STD=1 \
TEST_UCLIBC_TIME64=1 \
RUSTUP_TOOLCHAIN=nightly \
./ci/run-docker.sh armv7-unknown-linux-uclibceabihf

NOTE: the toolchain URL provided above is from my github account and shouldn't be directly included in the source, as I'm sure I would get dinged for bandwidth usage. It's my expectation that developers would build their own or ask nicely to use mine in a responsible way.

Abandoned task: building a toolchain

My first attempt at this PR included building a toolchain from source via buildroot, but that process takes longer than the github action timeout (which seems to be 20 minutes) so I abandoned that approach.

Results

With this change, it's now possible for me to build the libc in a fork of the libc-downstream-ci example posted by @tgross35. See here for example.

Sources

N/A

Checklist

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

skrap · 2026-07-31T01:23:31Z

@rustbot review

tgross35

What is involved in preparing the SDK that gets downloaded? I think the current setup is fine enough, but if it's not too bad then I feel like the docker container may as well just build it. Or build it as part of run-docker.sh and copy it into the container to make caching easier.

View changes since this review

tgross35 · 2026-08-02T21:22:10Z

    if [ -n "${TEST_UCLIBC_TIME64:-}" ]; then
        build_args+=("--build-arg=TEST_UCLIBC_TIME64=1")
-        export RUSTFLAGS="$RUSTFLAGS --cfg=libc_unstable_uclibc_time64"
+        export RUSTFLAGS="${RUSTFLAGS:-} --cfg=libc_unstable_uclibc_time64"


"uclibc: move to configurable external prebuilt toolchain": maybe just export RUSTFLAGS="${RUSTFLAGS:-}" at the top of run() so we only need that in one place

tgross35 · 2026-08-02T21:22:42Z

    CC_armv7_unknown_linux_uclibceabihf=arm-buildroot-linux-uclibcgnueabihf-gcc \
    CARGO_TARGET_ARMV7_UNKNOWN_LINUX_UCLIBCEABIHF_LINKER=arm-buildroot-linux-uclibcgnueabihf-gcc \
-    CARGO_TARGET_ARMV7_UNKNOWN_LINUX_UCLIBCEABIHF_RUNNER="qemu-arm -L /toolchain/arm-buildroot-linux-uclibcgnueabihf/sysroot/"
+    CARGO_TARGET_ARMV7_UNKNOWN_LINUX_UCLIBCEABIHF_RUNNER="qemu-arm -L /toolchain/arm-buildroot-linux-uclibcgnueabihf/sysroot/"


"uclibc: move to configurable external prebuilt toolchain": missing trailing \n

tgross35 · 2026-08-02T21:45:04Z

I also think it would be fine to link to your GH URL since libc's frequent CI won't be needing it. But for that, ideally the script should be checked into your repo somewhere (or build+release via GHA?) and the sha could be checked here so it's easy to reproduce.

tgross35 · 2026-08-03T01:26:07Z

Also no problem of course but just a heads up, looks like the email you used here isn't linked to your GH account (e.g. https://github.com/rust-lang/libc/commit/3156347e405a3dcb48f1b639ed420681ea897745.patch).

tgross35 · 2026-08-04T05:27:14Z

@rustbot author

rustbot · 2026-08-04T05:27:18Z

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

skrap · 2026-08-18T18:23:44Z

What is involved in preparing the SDK that gets downloaded? I think the current setup is fine enough, but if it's not too bad then I feel like the docker container may as well just build it. Or build it as part of run-docker.sh and copy it into the container to make caching easier.

Unfortunately it's impractical, as it takes longer than the maximum builder lifetime allowed by github. My first attempt at this patchset did exactly as you asked, and it failed to work for exactly that reason: it would time out while preparing the docker image. So, I moved to a prebuilt toolchain.

tgross35 · 2026-08-19T06:41:37Z

Well that's surprising, does it need to build the whole kernel? I feel like I've even done that within a half hour GHA run.

Anyway if you can add a build script or instructions to your repo for reproduction and add a checksum, I still think it would be fine directly link your repo.

skrap · 2026-08-19T15:33:45Z

Well that's surprising, does it need to build the whole kernel? I feel like I've even done that within a half hour GHA run.

Anyway if you can add a build script or instructions to your repo for reproduction and add a checksum, I still think it would be fine directly link your repo.

Nah, the kernel isn't so bad. The costly part is building the rest of the cross toolchain, which includes (IIRC) 3 copies of GCC - one initial bootstrap GCC, one for host, and one for target. GCC is a beast. (But building rust itself is 10x longer!)

@rustbot review

tgross35

Two small things then LGTM.

Nah, the kernel isn't so bad. The costly part is building the rest of the cross toolchain, which includes (IIRC) 3 copies of GCC - one initial bootstrap GCC, one for host, and one for target. GCC is a beast. (But building rust itself is 10x longer!)

Ah that is not a fun build... I guess the toolchain can't be built with Clang's cross compilation?

View changes since this review

tgross35 · 2026-08-20T11:55:50Z

-ARG TEST_UCLIBC_TIME64
+ARG UCLIBC_TOOLCHAIN_URL
 COPY install-uclibc.sh /
-RUN /install-uclibc.sh "$TEST_UCLIBC_TIME64"
+RUN /install-uclibc.sh "$UCLIBC_TOOLCHAIN_URL"


Can you document this so people know where to look for a toolchain? Just a link to this PR and/or your repo.

tgross35 · 2026-08-20T11:59:18Z

@@ -1,22 +1,23 @@
-FROM ubuntu:23.10
+FROM ubuntu:25.04


Is this just the latest supported? (For my knowledge, no need to change to 26.04 either way)

Ah, no I was just copying from other Dockerfiles, but I see that you've since updated the base image on many to be 26.04. I'll follow suit.

tgross35 · 2026-08-20T12:02:41Z

+                // TODO: once uclibc catches up with the kernel headers, remove.
+                // See https://github.com/rust-lang/libc/issues/1896
+                "IPPROTO_MAX" => return true,


It's a rust-lang convention that TODO is for comments to be resolved before merge, FIXME for comments to be merged (I know there are a few exceptions here)

skrap · 2026-08-20T13:45:55Z

Ah that is not a fun build... I guess the toolchain can't be built with Clang's cross compilation?

That's not possible out of the box, no, and I want to stick with stock buildroot here.

The previous CI script used a prebuilt toolchain from bootlin, but this was based on kernel 5.15, which did not contain many of the kernel constants being tested.

rustbot · 2026-08-20T13:58:04Z

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.

skrap · 2026-08-20T13:58:06Z

@rustbot review

rustbot added A-CI Area: CI-related items ctest Issues relating to the ctest crate labels Jul 7, 2026

skrap force-pushed the bugfix/uclibc-docker-ci-build-fixes branch 3 times, most recently from 47c0db9 to 5aa06a0 Compare July 7, 2026 22:24

skrap changed the title ~~Bugfix/uclibc docker ci build fixes~~ uclibc fix kernel constant tests + docker ci build fixes Jul 8, 2026

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rustbot added O-arm O-linux O-linux-like O-unix labels Jul 13, 2026

skrap force-pushed the bugfix/uclibc-docker-ci-build-fixes branch 3 times, most recently from 662559d to 2454ca6 Compare July 31, 2026 01:21

skrap marked this pull request as ready for review July 31, 2026 01:23

rustbot added the S-waiting-on-review label Jul 31, 2026

tgross35 reviewed Aug 2, 2026

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rustbot added S-waiting-on-author and removed S-waiting-on-review labels Aug 4, 2026

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skrap force-pushed the bugfix/uclibc-docker-ci-build-fixes branch from 2454ca6 to 4f47b89 Compare August 19, 2026 14:49

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rustbot added S-waiting-on-review and removed S-waiting-on-author labels Aug 19, 2026

tgross35 reviewed Aug 20, 2026

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skrap added 5 commits August 20, 2026 09:49

uclibc: move to configurable external prebuilt toolchain

1a76e43

The previous CI script used a prebuilt toolchain from bootlin, but this was based on kernel 5.15, which did not contain many of the kernel constants being tested.

uclibc: time64 support in shmid_ds

4eb9e49

uclibc: un-suppress tests for kernel constants from 5.16+

c6da8c3

uclibc: fix build failures accumulated via recent commits.

c78f8a8

uclibc: inhibit test of IPPROTO_MAX for now

828343d

skrap force-pushed the bugfix/uclibc-docker-ci-build-fixes branch from 4f47b89 to 828343d Compare August 20, 2026 13:57

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Description

Abandoned task: building a toolchain

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skrap commented Jul 31, 2026

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