Re: [Buildroot] [PATCH] package/busybox: disable stack optimization for i386 target

From: Thomas Petazzoni via buildroot <buildroot@buildroot.org>
To: Romain Naour <romain.naour@gmail.com>
Cc: buildroot@buildroot.org
Subject: Re: [Buildroot] [PATCH] package/busybox: disable stack optimization for i386 target
Date: Sat, 11 Feb 2023 10:49:34 +0100	[thread overview]
Message-ID: <20230211104934.4c34267c@windsurf> (raw)
In-Reply-To: <20230210233658.3763549-1-romain.naour@gmail.com>

On Sat, 11 Feb 2023 00:36:58 +0100
Romain Naour <romain.naour@gmail.com> wrote:

> The toolchain-builder project reported an issue with Qemu 7.2.0 for
> x86-core2--glibc--bleeding-edge toolchain [1]:
> 
>   Run /sbin/init as init process
>   random: fast init done
>   EXT4-fs (vda): warning: mounting unchecked fs, running e2fsck is recommended
>   EXT4-fs (vda): re-mounted. Opts: (null). Quota mode: disabled.
>   Starting syslogd: OK
>   traps: syslogd[52] general protection fault ip:b7e21465 sp:bfe59e6c error:0 in libc.so.6[b7d9b000+123000]
>   Starting klogd: OK
>   traps: klogd[56] general protection fault ip:b7e94465 sp:bf8f069c error:0 in libc.so.6[b7e0e000+123000]
>   Running sysctl: traps: logger[62] general protection fault ip:b7e48b6c sp:bfd7d194 error:0 in libc.so.6[b7e05000+123000]
>   Segmentation fault
>   traps: logger[64] general protection fault ip:b7dd3b6c sp:bf9b8604 error:0 in libc.so.6[b7d90000+123000]
>   Segmentation fault
> 
>   (Followed by a kernel panic.)
> 
> Testing with the pevious Qemu release (7.1.0) allows to boot the system without any problem.
> 
> Building qemu sources between 7.1.0 and 7.2.0 allows to identify the first "bad" commit [2] and
> report to the Qemu project [3].
> 
> Thanks to Qemu maintainers review, several issues was noticed:
> 
>   "The default i386 busybox build config does not respect glibc's requirements around stack alignment
>   (see [4] for previous discussions and a workaround)."
> 
> Disabling CONFIG_STACK_OPTIMIZATION_386 option (as suggested in the Gentoo bug report) fixed the issue!
> 
> This option has been added and enabled by default in buxybox 1_29_0, so it was used since then the for
> Buildroot's qemu defconfig.
> 
> Note: The x86-i686--glibc--bleeding-edge (generic x86) doesn't trigger the issue with
> CONFIG_STACK_OPTIMIZATION_386 enabled.
> 
> Fixes:
> https://gitlab.com/buildroot.org/toolchains-builder/-/jobs/3731683337
> 
> [1] https://gitlab.com/buildroot.org/toolchains-builder/-/jobs/3731683337
> [2] https://gitlab.com/qemu-project/qemu/-/commit/958e1dd1300f37f18b2161dfb4eb806fc8c19b44
> [3] https://gitlab.com/qemu-project/qemu/-/issues/1478
> [4] https://bugs.gentoo.org/725674

Thanks a lo for the great investigation. Do we understand precisely
what is happening? The link at [4] does not really have an explanation,
it only has experimental observations that lead to the conclusion that
disabling CONFIG_STACK_OPTIMIZATION_386 is a work-around, but it does
not really explain what is happening.

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