BuildKit fails to start container process under Rosetta emulation

[natevw]

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• I've read the contributing guidelines and wholeheartedly agree. I've also read the issue reporting guide.

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• I have found a bug that the documentation does not mention anything about my problem
• I have found a bug that there are no open or closed issues that are related to my problem
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Description of bug

Bug description

BuildKit fails to RUN commands when running under amd64 emulation through Rosetta, logging a "signal: trace/breakpoint trap" / "failed to open elf at -exec-root=/var/run/docker" error.

Reproduction

I am running containers under Apple's container runtime, but need them to be running as essentially --platform=linux/amd64 and supporting "Docker in Docker" usage. I am able to run images within the nested Docker daemon, but building them fails:

# start dind daemon
container run -d --rm --arch amd64 --cap-add ALL --read-only-path NONE -v .:/repro --name rosetta-repro docker.io/docker:29.7.2

# attempt a build
cat <<EOF > Dockerfile
FROM debian
RUN uname -a
EOF
container exec -w /repro rosetta-repro docker build .

That build command always crashes with an error like:

#‌5 [2/2] RUN uname -a
#‌5 0.182 runc run failed: unable to start container process: error during container init: error running prestart hook #0: signal: trace/breakpoint trap, stdout: , stderr: rosetta error: failed to open elf at -exec-root=/var/run/docker
#‌5 0.182
#‌5 ERROR: process "/bin/sh -c uname -a" did not complete successfully: exit code: 1

Workaround / alternative

If I instead use Docker's legacy build system with same as above, setting DOCKER_BUILDKIT=0:

container exec -w /repro -e DOCKER_BUILDKIT=0 rosetta-repro docker build .

the build completes successfully, with its RUN uname -a step logging something like:

Linux 129cc24a0c02 6.18.5 #1 SMP Wed Jan 28 20:00:41 UTC 2026 x86_64 GNU/Linux

Version information

The host of all this is running container CLI version 1.3.0 (build: release, commit: d6de569) under macOS 26.6.2 (25G83). My understanding is that the overall setup ends up being:

• Apple Silicon (arm64) host
• running a lightweight Linux VM per container (still arm64/aarch64)
• the processes of the container itself are launched as amd64/x84_64
  • presumedly via the usual binfmt mechanism but with Apple's own Rosetta helper (rather than e.g. Qemu) as the handler, see https://developer.apple.com/documentation/virtualization/running-intel-binaries-in-linux-vms
• thus the whole container namespace is running emulated, which seems to generally work except for something inside BuildKit

[weaversam8]

I can confirm this is an issue, and it doesn't just affect Apple's container runtime. Colima (a Docker Desktop alternative) provides a --vz-rosetta flag that mounts the Rosetta binary into the VM it runs the docker daemon in, and registers it with binfmt_misc to emulate the x86_64 architecture.

I think this is due to buildkit's archutil binary executing within a chroot that is missing /proc/self/exe. It appears Rosetta depends on this to look up its own executable path, and if it isn't there, Rosetta fails with an error:

rosetta error: Unable to open /proc/self/exe: 2

To replicate this on an arm64 Mac if you have a running Colima VM with --vz-rosetta:

# ensure your VM is running with rosetta support:
colima start --vz-rosetta

# in the buildkit repo, build the amd64 archutil binary:
docker buildx build -f hack/dockerfiles/archutil.Dockerfile --target exits -o type=local,dest=/tmp/archutil-bins .

# run the archutil binary under rosetta:
docker run -i --rm alpine sh -c 'cat > /archutil-amd64 && chmod +x /archutil-amd64; mkdir /chroot && cp /archutil-amd64 /chroot/ && chroot /chroot /archutil-amd64; echo "exit code=$?"' < /tmp/archutil-bins/amd64

This produces the following output for me if my Colima VM has Rosetta enabled:

WARNING: The requested image's platform (linux/amd64) does not match the detected host platform (linux/arm64/v8) and no specific platform was requested
rosetta error: Unable to open /proc/self/exe: 2
 Trace/breakpoint trap (core dumped)
exit code=133

and this output if I turn off Rosetta and rely on Colima using its own bundled QEMU as the binfmt_utils executable:

WARNING: The requested image's platform (linux/amd64) does not match the detected host platform (linux/arm64/v8) and no specific platform was requested
exit code=66

(in this case, exit code 66 is expected, and 133 is unexpected).