From: Mark Rutland <mark.rutland@arm.com>
To: Mark Brown <broonie@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>, Shuah Khan <shuah@kernel.org>,
Marc Zyngier <maz@kernel.org>, Oliver Upton <oupton@kernel.org>,
Fuad Tabba <fuad.tabba@linux.dev>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-kselftest@vger.kernel.org
Subject: Re: [PATCH 03/11] kselftest/arm64: Move exit calls out of fp-stress loads
Date: Wed, 30 Sep 2026 09:51:15 +0100 [thread overview]
Message-ID: <arzNg0jxDmbEMrJm@J2N7QTR9R3.cambridge.arm.com> (raw)
In-Reply-To: <arvm8O6kL1I9Plrw@J2N7QTR9R3.cambridge.arm.com>
On Tue, Sep 29, 2026 at 05:27:28PM +0100, Mark Rutland wrote:
> On Tue, Sep 01, 2026 at 06:06:43PM +0100, Mark Brown wrote:
> > When they detect corruption the fp-stress test loads print load specific
> > diagnostics and exits with a failure status. In preparation for
> > building versions intended to run as KVM guests factor the exits into
> > asm-utils-linux.S.
> >
> > No functional change.
>
> This is a good cleanup, but I do think it'd be worth noting that some of
> the existing asm was wrong and worked by coincidence.
>
> I did mention that in the patches I linked you to a while back:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/commit/?id=922d15ef46cb486a79f168949e103f6df26f4fba
Sorry, that was the wrong link; I meant to share:
https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/commit/?id=2db277185f5c252decdf49b25cd461782e890cd1
... which was another patch from that cleanup series:
https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=arm64/selftests/cleanup
The description of the problem from the commit message was:
| The barf functions in the fp-stress sub-tests erroneously place the
| status value into x1 (rather than x0) when invoking the exit syscall,
| potentially returning a different status than expected.
|
| By coincidence, the low 8 bits of x0 happen to be non-zero for all of
| these cases, and the exit will be treated as a failure by the fp-stress
| harness, which is the desired behaviour. Hence this doesn't lead to
| failing tests being reported as passing.
|
| In all cases x0 contains either:
|
| * The result of the prior write syscall made by the puts macro, which is
| a write of the two character string "]\n".
|
| * The result of the prior write syscall made by the putdecn() function,
| which is a write of the single-character '\n'.
|
| In either case, the return value of that write syscall may be a non-zero
| number of bytes written, or a negative error code. As the relevant
| strings are fewer than 256 characters, and all (positive) error codes
| are less than 256, the value in the low 8 bits of x0 will not be zero.
Mark.
next prev parent reply other threads:[~2026-09-30 8:51 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-01 17:06 [PATCH 00/11] kselftest/arm64: Add coverage of interactions with KVM to fp-stress Mark Brown
2026-09-01 17:06 ` [PATCH 01/11] kselftest/arm64: Factor Linux syscalls out of asm-utils.S Mark Brown
2026-09-29 16:01 ` Lorenzo Stoakes (ARM)
2026-09-01 17:06 ` [PATCH 02/11] kselftest/arm64: Factor shared signal handlers out of fp-stress loads Mark Brown
2026-09-29 16:07 ` Lorenzo Stoakes (ARM)
2026-09-01 17:06 ` [PATCH 03/11] kselftest/arm64: Move exit calls " Mark Brown
2026-09-29 16:22 ` Lorenzo Stoakes (ARM)
2026-09-29 21:56 ` Mark Brown
2026-09-30 8:41 ` Lorenzo Stoakes (ARM)
2026-09-29 16:27 ` Mark Rutland
2026-09-29 22:03 ` Mark Brown
2026-09-30 8:51 ` Mark Rutland [this message]
2026-09-01 17:06 ` [PATCH 04/11] kselftest/arm64: Use exit_error() rather than SIGABRT in fp-stress Mark Brown
2026-09-29 16:28 ` Mark Rutland
2026-09-29 16:31 ` Lorenzo Stoakes (ARM)
2026-09-01 17:06 ` [PATCH 05/11] kselftest/arm64: Exit with an error code on data mismatches " Mark Brown
2026-09-29 16:37 ` Lorenzo Stoakes (ARM)
2026-09-01 17:06 ` [PATCH 06/11] kselftest/arm64: Factor startup code out of fp-stress load programs Mark Brown
2026-09-30 12:39 ` Lorenzo Stoakes (ARM)
2026-09-01 17:06 ` [PATCH 07/11] kselftest/arm64: Remove the sched_yield()s from the fp-stress loads Mark Brown
2026-09-30 14:17 ` Lorenzo Stoakes (ARM)
2026-09-01 17:06 ` [PATCH 08/11] kselftest/arm64: Add a very simple VMM for use in fp-stress Mark Brown
2026-09-01 17:06 ` [PATCH 09/11] kselftest/arm64: Build KVM guest versions of the fp-stress loads Mark Brown
2026-09-01 17:06 ` [PATCH 10/11] kselftest/arm64: Use execv() to start fp-stress test loads Mark Brown
2026-09-01 17:06 ` [PATCH 11/11] kselftest/arm64: Run KVM guests from fp-stress Mark Brown
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