Dockerfile apt dependency gcc-9-multilib does not exist for aarch64 host (Mac M1)

[mrlnc]

Building the Docker image fails on aarch64 Ubuntu (VM on M1 macbook). Seems at least one package is unavailable for aarch64:

#5 35.68 E: Unable to locate package gcc-9-multilib

I was able to build the image when explicitly requesting the amd64 base image (seems to use some integrated emulation then?).

diff --git a/Dockerfile b/Dockerfile
index 3e6a2d4..e9b4ded 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM ubuntu:20.04
+FROM amd64/ubuntu:20.04
 LABEL "about"="FirmWire base img"
 
 ARG DEBIAN_FRONTEND=noninteractive

Am I doing something wrong here, or is there an easy fix besides emulation? I'm not sure if the resulting image works 100%, but at least the firmware does seem to come up and do its thing :-)

$ uname -a 
Linux ubuntu-parallels 5.15.0-47-generic #51-Ubuntu SMP Fri Aug 12 08:18:32 UTC 2022 aarch64 aarch64 aarch64 GNU/Linux
$ docker run --rm -it -v $(pwd):/firmwire firmwire
WARNING: The requested image's platform (linux/amd64) does not match the detected host platform (linux/arm64/v8) and no specific platform was requested
root@3630e1d821d9:/firmwire# uname -a
Linux 3630e1d821d9 5.15.0-47-generic #51-Ubuntu SMP Fri Aug 12 08:18:32 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux

I thought I'd be best to share this in an issue in case others are trying the same.

[grant-h]

Thank you for opening an issue! I believe the gcc-9-multilib metapackage does not have an arm64 port as seen here even on 22.04 (jammy) https://packages.ubuntu.com/jammy/gcc-9-multilib. In general I was having a lot of trouble with the multilib packaging even when not on a native aarch64 machine. Most of the issues were stemming from this longstanding bug https://bugs.launchpad.net/ubuntu/+source/gcc-defaults/+bug/1300211 (for arm, but could also apply to mips)

For now I think emulation mode for amd64 will have to suffice but I am worried it could affect your performance (I'm not even sure how the emulation for docker containers works). If an alternate package for gcc-9-multilib could be found that would still allow for the cross-compiler to be installed, then I'd be happy to edit the docker file.