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Build images for the other architecture - #48

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The127 merged 27 commits into

mainfrom

Oct 11, 2026

Merged

Build images for the other architecture#48
The127 merged 27 commits into
mainfrom
cross-arch

The127 commented Oct 10, 2026 •

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miso build --arch now takes amd64 and arm64 on both hosts. miso plan and miso shell take --arch too.

How it works:

The builder VM runs on the host architecture with KVM.
Programs of the target architecture run through QEMU user mode. miso fetches Debian's static qemu-user package by digest and registers it with binfmt_misc in the builder VM.
A CHECK of an image for the other architecture boots on TCG.
Base images, layer keys and the EFI loader and stub follow the target architecture.
RUN and shell get TARGETARCH in their environment.
The deb and rpm packages recommend the qemu-system package of the other architecture.

Not tested on real hardware yet: RUN steps under QEMU user mode, and a TCG check of a full disk.

Docs: I checked them and updated cli.md, imagefile.md, base-images.md, checks.md and caching.md.

Closes #31

BEGIN_COMMIT_OVERRIDE
feat: build images for the other architecture
END_COMMIT_OVERRIDE

The127 and others added 27 commits

October 11, 2026 12:08


          feat: run a machine of another architecture on TCG

dc7427e

KVM runs only machines of the host's architecture, so the check of an
image built for another one boots on TCG and says why.

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          feat: run a machine that names no architecture as amd64

587589d

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          feat: key layers by the architecture they are built for

d634c88

A scratch stage has no base digest, so without the architecture in the
key an amd64 and an arm64 build would share its layers.

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          refactor: take the architecture of a build from its command

8a0f2a4

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          feat: ask for a disk of the architecture of the plan

489ebfd

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          feat: make a disk with the loader and stub of its architecture

4587a52

The image may be of another architecture than the builder VM the agent
runs on, so the request names it.

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          feat: tell a run the architecture it builds for

aeaee9d

TARGETARCH lets one Imagefile install the kernel of either architecture.

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          feat: tell a shell the architecture its build is for

211483f

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          feat: load binfmt_misc in the builder VM

51c7183

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          feat: take the emulator of an image's architecture out of a pinned qe…

e5ffbd6

…mu-user package

The builder VM runs the programs of an image of another architecture
through it.

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          feat: refuse an emulator miso has no QEMU for, naming the architecture

42da282

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          feat: carry the emulator of another architecture in the builder's ini…

1b28ed4

…tramfs

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          feat: give every builder initramfs a directory of emulators

7d041c3

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          feat: register the builder VM's emulators on binfmt_misc

d5b3a28

They are registered as Debian registers its qemu-user, through a name
that keeps a program's argv[0], and opened right away, so a run in its
own root has them too.

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          feat: refuse an emulator of an architecture without a binfmt_misc entry

9e5202f

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          feat: write the builder's boot files with the emulators of a build

aa6e581

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          feat: boot the builder with the emulator of the architecture it build…

4e75184

…s for

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          feat: build an image for the other architecture

dae53ee

The builder VM keeps running on the host's architecture, on KVM. The
steps of the image run through QEMU in user mode and its checks boot on
TCG.

Closes #31

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          feat: plan a build for the architecture --arch names

936b044

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          feat: open a shell on the layers of the architecture --arch names

448fadf

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          feat: name the architecture in the shell a failed step hints at

6617ebd

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          refactor: take the architecture only from --arch

d871c3b

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          build: recommend the qemu-system of the other architecture

f237b6f

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          fix: set TARGETARCH once when the build file sets it

c00a0b1

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          refactor: build the arch list in error messages from arches

8c60a81

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          refactor: read --arch once in withBuilder

422642b

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>


          refactor: return the program from the loop in emulator.ready

6acab10

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: karo <karolin.kostial@gmail.com>

The127 force-pushed the cross-arch branch from 9b92f7b to 6acab10 Compare

October 11, 2026 10:08

codecov Bot commented Oct 11, 2026

Codecov Report

❌ Patch coverage is 66.66667% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.10%. Comparing base (0f52bd5) to head (6acab10).

Files with missing lines	Patch %	Lines
internal/boot/emulators.go	44.00%	14 Missing ⚠️
internal/boot/boot.go	0.00%	3 Missing ⚠️
internal/emulator/ready.go	83.33%	3 Missing ⚠️
internal/agent/parts.go	33.33%	2 Missing ⚠️
internal/boot/root.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #48      +/-   ##
==========================================
+ Coverage   55.35%   56.10%   +0.74%     
==========================================
  Files         286      288       +2     
  Lines        4702     4761      +59     
==========================================
+ Hits         2603     2671      +68     
+ Misses       2099     2090       -9

Flag	Coverage Δ
unit	`56.10% <66.66%> (+0.74%)`	⬆️

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The127 merged commit 56ff891 into main

9 checks passed

The127 deleted the cross-arch branch

October 11, 2026 10:11

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