[Buildroot] Binutils 2.41 cannot compile old Linux kernels

[Buildroot] Binutils 2.41 cannot compile old Linux kernels

[Edgar Bonet]

Hello Buildroot people!

Early this morning, the autobuilder wrote:
> Detail of defconfig failures for master [71 failures follow]

Trying to understand why there are so many failures. I examined three of
them:

 * acmesystems_aria_g25_256mb[0]
 * acmesystems_arietta_g25_256mb
 * atmel_sama5d3xek

and they all failed for the same reason: an incompatibility between old
Linux kernels and binutils 2.41. The failures were presumably triggered
by this patch from 2024-03-03:

    e88225ed88 package/binutils: make 2.41 the default version

Specifically, the assembly syntax

    .section ".proc.info.init", #alloc

which on old kernels is used by multiple files in arch/arm, is supported
by binutils 2.40 for all ELF targets “for compatibility with the Solaris
assembler”.[1] However, binutils 2.41 only supports this syntax for
Sparc ELF targets.[2]

The syntax was fixed on Linux by this commit

    790756c7e022 ARM: 8933/1: replace Sun/Solaris style flag on section directive

released on Linux mainline v5.5-rc1. This patch was then backported to
several stable branches (in v4.14.329, v4.19.298 and v5.4.203).

Now I wonder, what would be the proper way of fixing this issue within
buildroot? A straightforward solution is to add

    BR2_BINUTILS_VERSION_2_40_X=y

to those defconfigs, but this doesn't look like a long-term solution, as
buildroot will eventually drop support for this version of binutils.
Another option would be to bump the kernel version, but I assume this
should be done (and tested) by the maintainers of the affected
defconfigs. A third option would be to add Linux commit 790756c7e022 as
a patch, like:

    BR2_LINUX_KERNEL_PATCH=.../0001-ARM-8933-1-replace-Sun-Solaris-style-flag-on-section.patch

Any opinions?

Best regards,

Edgar Bonet.

[0] https://gitlab.com/buildroot.org/buildroot/-/jobs/6544500975
[1] https://sourceware.org/binutils/docs-2.40/as/Section.html
[2] https://sourceware.org/binutils/docs-2.41/as/Section.html
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Re: [Buildroot] Binutils 2.41 cannot compile old Linux kernels

[Thomas Petazzoni via buildroot]

Hello Edgar,

Thanks for having looked into this issue. See below some feedback.

On Sat, 6 Apr 2024 21:32:46 +0200
Edgar Bonet <bonet@grenoble.cnrs.fr> wrote:

> Another option would be to bump the kernel version, but I assume this
> should be done (and tested) by the maintainers of the affected
> defconfigs.

This is definitely the right thing. If those maintainers are no longer
available, it means those defconfigs are unmaintained and should be
dropped.

In my opinion, this is actually a good side effect of those toolchain
changes: they allow from time to time to detect that some defconfigs
are bitrotting, without being maintained, and encourages us to revisit
the relevance of such defconfigs in Buildroot.

Best regards,

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com
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