linux-kernel - Re: [PATCH] mm: change "char *bdi_unknown_name" to "char bdi_unknown

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Message-ID: <f4317b85-0a7b-913c-6d45-9f8b7c65e40b@nfschina.com>
Date:   Fri, 13 May 2022 01:10:36 +0800
From:   liqiong <liqiong@...china.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: change "char *bdi_unknown_name" to "char
 bdi_unknown_name[]"



在 2022年05月12日 23:29, Muchun Song 写道:
> On Thu, May 12, 2022 at 04:26:37PM +0800, liqiong wrote:
>> "char bdi_unknown_nam[]" string form declares a single variable.
>> It is better then "char *bdi_unknown_name" which creates two
>> variables.
>>
> Sorry, I do not understand what you are saying here.  Creating
> two variables means what?
>
> Thanks.

Hi there，

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".


>  
>> Signed-off-by: liqiong <liqiong@...china.com>
>> ---
>>  mm/backing-dev.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
>> index 7176af65b103..4982ccc63536 100644
>> --- a/mm/backing-dev.c
>> +++ b/mm/backing-dev.c
>> @@ -20,7 +20,7 @@ struct backing_dev_info noop_backing_dev_info;
>>  EXPORT_SYMBOL_GPL(noop_backing_dev_info);
>>  
>>  static struct class *bdi_class;
>> -static const char *bdi_unknown_name = "(unknown)";
>> +static const char bdi_unknown_name[] = "(unknown)";
>>  
>>  /*
>>   * bdi_lock protects bdi_tree and updates to bdi_list. bdi_list has RCU
>> -- 
>> 2.11.0
>>
>>

-- 
李力琼 <13524287433>
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