From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: Re: [PATCH] mm: Outline copy_overflow()
Date: Tue, 8 Feb 2022 19:04:36 +0000 [thread overview]
Message-ID: <71382581-ffcb-dc1b-8719-ddbd7738fb4a@csgroup.eu> (raw)
In-Reply-To: <20220207124002.edd04bf6d2abac8a01e35144@linux-foundation.org>
Le 07/02/2022 à 21:40, Andrew Morton a écrit :
> On Mon, 7 Feb 2022 11:55:18 +0100 Christophe Leroy <christophe.leroy@csgroup.eu> wrote:
>
>> While building a small config with CONFIG_CC_OPTIMISE_FOR_SIZE,
>> I ended up with more than 50 times the following function in vmlinux:
>>
>> c00243bc <copy_overflow>:
>> c00243bc: 94 21 ff f0 stwu r1,-16(r1)
>> c00243c0: 7c 85 23 78 mr r5,r4
>> c00243c4: 7c 64 1b 78 mr r4,r3
>> c00243c8: 3c 60 c0 62 lis r3,-16286
>> c00243cc: 7c 08 02 a6 mflr r0
>> c00243d0: 38 63 5e e5 addi r3,r3,24293
>> c00243d4: 90 01 00 14 stw r0,20(r1)
>> c00243d8: 4b ff 82 45 bl c001c61c <__warn_printk>
>> c00243dc: 0f e0 00 00 twui r0,0
>> c00243e0: 80 01 00 14 lwz r0,20(r1)
>> c00243e4: 38 21 00 10 addi r1,r1,16
>> c00243e8: 7c 08 03 a6 mtlr r0
>> c00243ec: 4e 80 00 20 blr
>>
>> That function being a non conditional warning on an error path,
>> it is not worth inlining.
>>
>> Outline it.
>
> "uninline" is the conventional term for this.
>
>> This reduces the size of vmlinux by almost 4kbytes.
>
> Did you consider uninlining check_copy_size() instead?
>
If you uninline check_copy_size() you loose the benefit of constant
folding and build time overflow detection for constant sizes, and I'm
not sure __builtin_object_size() works at all if uninlined.
Christophe
prev parent reply other threads:[~2022-02-08 19:04 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-07 10:55 [PATCH] mm: Outline copy_overflow() Christophe Leroy
2022-02-07 13:46 ` kernel test robot
2022-02-07 20:40 ` Andrew Morton
2022-02-08 19:04 ` Christophe Leroy [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=71382581-ffcb-dc1b-8719-ddbd7738fb4a@csgroup.eu \
--to=christophe.leroy@csgroup.eu \
--cc=akpm@linux-foundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).