From: "Arnd Bergmann" <arnd@arndb.de>
To: "Daniel Borkmann" <daniel@iogearbox.net>,
"Anton Protopopov" <aspsk@isovalent.com>,
"Alexei Starovoitov" <ast@kernel.org>,
"Andrii Nakryiko" <andrii@kernel.org>,
"Jiri Olsa" <jolsa@kernel.org>,
"Martin KaFai Lau" <martin.lau@linux.dev>,
"Stanislav Fomichev" <sdf@google.com>,
bpf@vger.kernel.org
Cc: "Alexander Lobakin" <aleksander.lobakin@intel.com>,
"Naresh Kamboju" <naresh.kamboju@linaro.org>
Subject: Re: [PATCH bpf-next] bpf: pack struct bpf_fib_lookup
Date: Thu, 04 Apr 2024 00:31:38 +0200 [thread overview]
Message-ID: <1c3d3079-e1f7-4420-b542-c3c451038963@app.fastmail.com> (raw)
In-Reply-To: <728951fe-ccd5-49d2-1584-fc97e2c2266e@iogearbox.net>
On Wed, Apr 3, 2024, at 23:00, Daniel Borkmann wrote:
> On 4/3/24 10:09 PM, Arnd Bergmann wrote:
>> On Wed, Apr 3, 2024, at 14:33, Anton Protopopov wrote:
>>>
>>> Declare this inner union as __attribute__((packed, aligned(2))) such
>>> that it always is of size 2 and is aligned to 16 bits.
>>
>> I think you probably want 32-bit alignment for the structure,
>> to keep the ABI unchanged on all other architectures.
>
> Fwiw, on x86 nothing should change on this regard, see below pahole dump
> before/after. I think similar might be true for other archs as otherwise
> we should have seen a kbuild bot complaint on hitting the size assert.
It's not the structure layout that changes, just its alignment.
Of course this is unlikely to cause actual bugs, but if there there
is no real need to change it, I would leave the alignment the same
as before.
Arnd
next prev parent reply other threads:[~2024-04-03 22:32 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-03 12:33 [PATCH bpf-next] bpf: pack struct bpf_fib_lookup Anton Protopopov
2024-04-03 12:37 ` Alexander Lobakin
2024-04-03 13:14 ` Daniel Borkmann
2024-04-03 17:52 ` Andrii Nakryiko
2024-04-03 20:09 ` Arnd Bergmann
2024-04-03 21:00 ` Daniel Borkmann
2024-04-03 22:31 ` Arnd Bergmann [this message]
2024-04-04 7:56 ` Anton Protopopov
2024-04-04 9:04 ` Alexander Lobakin
2024-04-04 9:39 ` Arnd Bergmann
2024-04-04 23:00 ` patchwork-bot+netdevbpf
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