From: David Laight <David.Laight@ACULAB.COM>
To: 'Daniel Borkmann' <daniel@iogearbox.net>,
liqiong <liqiong@nfschina.com>, Yonghong Song <yhs@fb.com>,
Andrii Nakryiko <andrii@kernel.org>,
"Martin KaFai Lau" <kafai@fb.com>,
Song Liu <songliubraving@fb.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"bpf@vger.kernel.org" <bpf@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"hukun@nfschina.com" <hukun@nfschina.com>,
"qixu@nfschina.com" <qixu@nfschina.com>,
"yuzhe@nfschina.com" <yuzhe@nfschina.com>,
"renyu@nfschina.com" <renyu@nfschina.com>
Subject: RE: [PATCH 1/2] kernel/bpf: change "char *" string form to "char []"
Date: Fri, 13 May 2022 11:14:34 +0000 [thread overview]
Message-ID: <017900c07229451085f82ae1e71cd825@AcuMS.aculab.com> (raw)
In-Reply-To: <92cc4844-5815-c3b0-63be-2e54dc36e1d9@iogearbox.net>
From: Daniel Borkmann
> Sent: 12 May 2022 22:00
>
> On 5/12/22 7:08 PM, liqiong wrote:
> > 在 2022年05月12日 23:16, Yonghong Song 写道:
> >>
> >> On 5/12/22 7:28 AM, liqiong wrote:
> >>> The string form of "char []" declares a single variable. It is better
> >>> than "char *" which creates two variables.
> >>
> >> Could you explain in details about why it is better in generated codes?
> >> It is not clear to me why your patch is better than the original code.
> >
> > The string form of "char *" creates two variables in the final assembly output,
> > a static string, and a char pointer to the static string. Use "objdump -S -D *.o",
> > can find out the static string occurring at "Contents of section .rodata".
>
> There are ~360 instances of this type in the tree from a quick grep, do you
> plan to convert all them ?
There are also all the places with const char *names[] = ...;
where the actual names are all similar length so replacing with
const char names[][n] saves space.
Although that transformation has a bigger effect on shared libs.
David
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Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
prev parent reply other threads:[~2022-05-13 11:14 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-12 14:28 [PATCH 1/2] kernel/bpf: change "char *" string form to "char []" liqiong
2022-05-12 15:16 ` Yonghong Song
2022-05-12 17:08 ` liqiong
2022-05-12 20:59 ` Daniel Borkmann
2022-05-13 2:04 ` liqiong
2022-05-13 11:14 ` David Laight [this message]
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