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Subject: Re: [PATCH] ext4: fix -Wstringop-truncation warnings
To:     "Theodore Y. Ts'o" <tytso@mit.edu>
Cc:     adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org,
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References: <20201112093324.8052-1-wenlin.kang@windriver.com>
 <X9mLAlWbjrU5iE+r@mit.edu>
From:   Wenlin Kang <wenlin.kang@windriver.com>
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Date:   Thu, 17 Dec 2020 15:00:29 +0800
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On 2020/12/16 下午12:20, Theodore Y. Ts'o wrote:
> [Please note this e-mail is from an EXTERNAL e-mail address]
>
> On Thu, Nov 12, 2020 at 05:33:24PM +0800, Kang Wenlin wrote:
>> From: Wenlin Kang <wenlin.kang@windriver.com>
>>
>> The strncpy() function may create a unterminated string,
>> use strscpy_pad() instead.
>>
>> This fixes the following warning:
>>
>> fs/ext4/super.c: In function '__save_error_info':
>> fs/ext4/super.c:349:2: warning: 'strncpy' specified bound 32 equals destination size [-Wstringop-truncation]
>>    strncpy(es->s_last_error_func, func, sizeof(es->s_last_error_func));
>>    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> fs/ext4/super.c:353:3: warning: 'strncpy' specified bound 32 equals destination size [-Wstringop-truncation]
>>     strncpy(es->s_first_error_func, func,
>>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>      sizeof(es->s_first_error_func));
>>      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> What compiler are you using?  s_last_error_func is defined to not
> necessarily be NUL terminated.  So strscpy_pad() is not a proper
> replacement for strncpy() in this use case.


My compiler is gcc 8.2.0,  this is found in v4.18, and I see mainline 
codes is
using the same code too,  so sent this patch. But according to your 
instructions,
I just re-check the code, with "__nonstring" attribute, it seems it has 
fixed.
Thank for your explain.


>
>  From Documentation/process/deprecated:
>
>     If a caller is using non-NUL-terminated strings, strncpy() can
>     still be used, but destinations should be marked with the `__nonstring
>     <https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html>`_
>     attribute to avoid future compiler warnings.
>
> s_{first,last}_error_func is properly annotated with __nonstring in
> fs/ext4/ext4.h.
>
>                                                  - Ted


-- 
Thanks,
Wenlin Kang