linux-kernel - Re: [PATCH RFC bpf-next 3/4] bpf/selftests: add tests to validate proper arguments alignment on ARM64

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Message-Id: <D9J11FERN5K4.1OUFGN6L9LM9E@bootlin.com>
Date: Tue, 29 Apr 2025 11:49:08 +0200
From: Alexis Lothoré <alexis.lothore@...tlin.com>
To: Alexis Lothoré <alexis.lothore@...tlin.com>, "Eduard
 Zingerman" <eddyz87@...il.com>
Cc: "Alexei Starovoitov" <ast@...nel.org>, "Daniel Borkmann"
 <daniel@...earbox.net>, "John Fastabend" <john.fastabend@...il.com>,
 "Andrii Nakryiko" <andrii@...nel.org>, "Martin KaFai Lau"
 <martin.lau@...ux.dev>, "Song Liu" <song@...nel.org>, "Yonghong Song"
 <yonghong.song@...ux.dev>, "KP Singh" <kpsingh@...nel.org>, "Stanislav
 Fomichev" <sdf@...ichev.me>, "Hao Luo" <haoluo@...gle.com>, "Jiri Olsa"
 <jolsa@...nel.org>, "Puranjay Mohan" <puranjay@...nel.org>, "Xu Kuohai"
 <xukuohai@...weicloud.com>, "Catalin Marinas" <catalin.marinas@....com>,
 "Will Deacon" <will@...nel.org>, "Mykola Lysenko" <mykolal@...com>, "Shuah
 Khan" <shuah@...nel.org>, "Maxime Coquelin" <mcoquelin.stm32@...il.com>,
 "Alexandre Torgue" <alexandre.torgue@...s.st.com>, "Florent Revest"
 <revest@...omium.org>, "Bastien Curutchet" <bastien.curutchet@...tlin.com>,
 <ebpf@...uxfoundation.org>, "Thomas Petazzoni"
 <thomas.petazzoni@...tlin.com>, <bpf@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
 <linux-kselftest@...r.kernel.org>,
 <linux-stm32@...md-mailman.stormreply.com>
Subject: Re: [PATCH RFC bpf-next 3/4] bpf/selftests: add tests to validate
 proper arguments alignment on ARM64

On Mon Apr 28, 2025 at 10:41 PM CEST, Alexis Lothoré wrote:
> On Mon Apr 28, 2025 at 6:52 PM CEST, Eduard Zingerman wrote:
>> Alexis Lothoré <alexis.lothore@...tlin.com> writes:

> If things really behaved correctly, f would not have the correct value but
> would still be handled as a 16 bytes value, so the test would not fail with
> "actual 35 != 43", but something like "actual
> 27254487904906932132179118915584 != 43" (43 << 64 | 35) I guess. I still
> need to sort this out.

And so indeed, the broken value is a big one:

(gdb) p skel->bss->t11_f
$4 = 793209995169510719523
(gdb) p/x skel->bss->t11_f
$5 = 0x2b0000000000000023
(gdb)

But we see the 35 (0x23) value in the error log because the formatters used in
ASSERT_EQ truncate the actual value.

Alexis

-- 
Alexis Lothoré, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com