netdev - Re: [PATCH 1/2] kernel/bpf: change "char *" string form to "char []"

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Date:   Fri, 13 May 2022 10:04:30 +0800
From:   liqiong <liqiong@...china.com>
To:     Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>
Cc:     Yonghong Song <yhs@...com>, Andrii Nakryiko <andrii@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        hukun@...china.com, qixu@...china.com, yuzhe@...china.com,
        renyu@...china.com
Subject: Re: [PATCH 1/2] kernel/bpf: change "char *" string form to "char []"



在 2022年05月13日 04:59, Daniel Borkmann 写道:
> 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 ?

Hi daniel,

I have fixed all the string form in kernel tree, summited  two patches. 
Have searched the kernel tree by "grep  -nHre char.*\*.*=.*\"",  and checked all the "char *foo = "bar" "
string form,  only five  instances are needed to fix in bpf direcotry (2 files) and trace directory (2 files).
In most cases, need a char pointer anyway, just like this:

[const] char *foo = "bar";
if (xxx)
    foo = "blash";

In this situation, can't  change  "char *foo"  to  "char foo[]".

This work was published in "KernelJanitors/Todo".  So, I fixed.

Thanks.

>
> Thanks,
> Daniel