zfs 2.1.0 needlessly links in libatomic

[hvdijk]

System information

Type	Version/Name
Distribution Name
Distribution Version
Linux Kernel	5.13.1
Architecture	x86_64 (x32)
ZFS Version	2.1.0
SPL Version

Describe the problem you're observing

zpool fails to start unless libatomic.so is present.

Describe how to reproduce the problem

Install zfs 2.1.0.

Include any warning/errors/backtraces from the system logs

N/A

https://github.com/openzfs/zfs/blob/master/config/user-libatomic.m4#L14 claims:

dnl # Technically, we could check if the platform *actually* needs -latomic,
dnl # or if it has native support for all the intrinsics we use,
dnl # but it /really/ doesn't matter, and C11 recommends to always link it.

It really does matter. When using zfs for the root partition, zfs needs to be installed on initramfs. initramfs should be small; it seems silly to force a shared library to be included there that is completely unused.

Workaround: build zfs in a chroot where libatomic.so is not available.

P.S.: The "C11 recommends to always link it" cannot be right, C11 does not acknowledge the existence of any libatomic library. I imagine it is intended to say something else, but I do not quite know what. It would be useful if this could be reworded.

[behlendorf]

Thanks for filing this, it does seem like we could be a bit smarter about this. cc: @nabijaczleweli

[nabijaczleweli]

I mean, it's 31k, but I can see how that's an annoyance in absence of LTO; see #12359

[hvdijk]

Thanks, tested on top of 2.1.0 and can confirm it correctly detects that -latomic is not needed on my system, the resulting binaries are the same as when vanilla 2.1.0 is built in a chroot without libatomic.