setup-build-env: enable GCC 15 installation

[theihor]

GCC 15 is not available in Ubuntu 24.04 repositories, which is the distro used by both github and self-hosted BPF CI runners.

To enable GCC 15 installation, make setup-build-env scripts set up Ubuntu 25.10 (questing) repositories and then install the packages.

Also update cross-compilation setup with a apt config restrictions instead of manipulating the source lists.

[eddyz87]

GCC 15 is not available in Ubuntu 24.04 repositories, which is the distro used by both github and self-hosted BPF CI runners.

To enable GCC 15 installation, make setup-build-env scripts set up Ubuntu 25.10 (questing) repositories and then install the packages.

whoa... that's a risky move, let me google a bit.

[eddyz87]

Will the following PPA work?
https://launchpad.net/~ubuntu-toolchain-r/+archive/ubuntu/ppa

It is official from Ubuntu itself, has gcc-15 package, claims to:

This PPA currently publishes packages for Plucky, Jammy, Focal, Bionic, Xenial, Wily, Vivid, Utopic, Trusty, Saucy, Raring, Quantal, Precise, Natty, Maverick, and Lucid.

[theihor]

Will the following PPA work? https://launchpad.net/~ubuntu-toolchain-r/+archive/ubuntu/ppa

It is official from Ubuntu itself, has gcc-15 package, claims to:

This PPA currently publishes packages for Plucky, Jammy, Focal, Bionic, Xenial, Wily, Vivid, Utopic, Trusty, Saucy, Raring, Quantal, Precise, Natty, Maverick, and Lucid.

This was one of the things I tried. Unfortunately, it doesn't work.

Try this:

$ podman run --rm -it ubuntu:noble /bin/bash
$ apt update && apt install -y sudo software-properties-common
$ sudo add-apt-repository ppa:ubuntu-toolchain-r/ppa
$ sudo apt-get update -y
$ sudo apt-get install gcc-15
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
E: Unable to locate package gcc-15

To enable GCC 15 installation, make setup-build-env scripts set up Ubuntu 25.10 (questing) repositories and then install the packages.

whoa... that's a risky move, let me google a bit.

I understand the concern, but in the context of bpf/libbpf CI, I don't think it's more risky than what we had so far.

If the setup-build-env is successful, the system is in a state when we are able to run kernel/selftests builds or test runs. After the ci job is done, we don't care if system dependencies are broken (which I don't think is likely btw), because we are not going to install anything else.

Sure, changes in upstream ubuntu packages may break this setup, but that has always been the case, and we already had issues when ubuntu archives were down, or with cross-compilation toolchain due to dependencies on cross-arch libs.

A viable alternative is to build gcc from source, but that's a bit more work to set up (build takes time, so the artifacts need to be cached similar to gcc-bpf). The apt repo hack appears to be working, and is easy to implement, so I want to try it first.

[eddyz87]

Will the following PPA work? https://launchpad.net/~ubuntu-toolchain-r/+archive/ubuntu/ppa
It is official from Ubuntu itself, has gcc-15 package, claims to:

This PPA currently publishes packages for Plucky, Jammy, Focal, Bionic, Xenial, Wily, Vivid, Utopic, Trusty, Saucy, Raring, Quantal, Precise, Natty, Maverick, and Lucid.

This was one of the things I tried. Unfortunately, it doesn't work.

Try this:

$ podman run --rm -it ubuntu:noble /bin/bash
$ apt update && apt install -y sudo software-properties-common
$ sudo add-apt-repository ppa:ubuntu-toolchain-r/ppa
$ sudo apt-get update -y
$ sudo apt-get install gcc-15
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
E: Unable to locate package gcc-15

Wellp, that's unfortunate.

To enable GCC 15 installation, make setup-build-env scripts set up Ubuntu 25.10 (questing) repositories and then install the packages.

whoa... that's a risky move, let me google a bit.

I understand the concern, but in the context of bpf/libbpf CI, I don't think it's more risky than what we had so far.

If the setup-build-env is successful, the system is in a state when we are able to run kernel/selftests builds or test runs.

There is no guarantee for that, really. Dependencies of some binaries or libraries can be broken. I don't think ubuntu is tested in this half-dist-upgraded configuration.

After the ci job is done, we don't care if system dependencies are broken (which I don't think is likely btw), because we are not going to install anything else.

Sure, changes in upstream ubuntu packages may break this setup, but that has always been the case, and we already had issues when ubuntu archives were down, or with cross-compilation toolchain due to dependencies on cross-arch libs.

A viable alternative is to build gcc from source, but that's a bit more work to set up (build takes time, so the artifacts need to be cached similar to gcc-bpf). The apt repo hack appears to be working, and is easy to implement, so I want to try it first.

I see, 🤞 .

[theihor]

Will the following PPA work? https://launchpad.net/~ubuntu-toolchain-r/+archive/ubuntu/ppa

This was one of the things I tried. Unfortunately, it doesn't work.

Wellp, that's unfortunate.

@eddyz87 looks like gcc-15 in this ppa is not available on ubuntu 24 (but why???)

[theihor]

To sum up:

• If GCC >= 15, we add Ubuntu 25.04 (plucky) apt repositories and install packages from there
• Ubuntu 25.10 (questing) doesn't work for us yet, because llvm haven't published builds for it

This approach seems to be working fine:

• on BPF CI runners https://github.com/kernel-patches/vmtest/actions/runs/18662972814
• and on github hosted runners https://github.com/libbpf/ci/actions/runs/18664864776

We can remove this hack when one of the following happens:

• GCC 15 is published for Ubuntu 24.04 (noble)
• GCC 15 is published to https://launchpad.net/~ubuntu-toolchain-r/+archive/ubuntu/ppa for Ubuntu 24.04 (noble)
• Ubuntu 26.04 is released, and all the runners are migrated to it (I assume GCC 15/16? will be available there)

If the hack doesn't bite me for at least a month, I'll call it a win.