Re: [PATCH] gcc/config/nios2/nios2.c: Let custom_builtin_name[*] always be zero terminated string

[Chen Gang <gang dot chen dot 5i5j at gmail dot com>]

On 07/26/2014 05:07 PM, Chung-Lin Tang wrote:
> On 2014/7/26 03:33 PM, Chen Gang wrote:
>> On 07/26/2014 02:32 PM, Chung-Lin Tang wrote:
>>> On 14/7/26 11:28 AM, Chen Gang wrote:
>>>> The related strncpy() for custom_builtin_name[*] may set 5 none-zero
>>>> characters, which may cause custom_builtin_name[*] is none-zero
>>>> terminated.
>>>>
>>>> So add additional '\0' byte for custom_builtin_name[*].
>>>
>>> Where did you see this? Supposedly the snprintf of the custom function
>>> type string should at most be of 'xnxx' format; 4 characters at most,
>>
>> I guess, your 'xnxx' means "%cn%c%c", not "%sn%s%s" (which is current
>> implementation), also at present, "32 - n" is 17, not 4 for snprintf()
>> length limitation.
> 
> The use of %sn%s%s is intentional. That allows me to print "" directly
> using snprintf.
> 

OK, thanks.

> '32 - n' is to represent the rest of the 32-byte buffer, harmless
> really, as it is at most 4 chars.
> 
> Also, if I were to restrict it in the snprintf argument, it would be 5
> (including the null char) not 4.
> 

OK, thanks. And for me, I'd like to use 'sizeof(custom_builtin_name[0])'
instead of "32 - n" for snprintf().


>> If we are always sure it must be no more than 4 characters (at present,
>> it is, but in the future, I don't know). We can use strcpy() instead of
>> strncpy() for it -- that will let other readers no doubt.
>>
>> If we need let custom_builtin_name[*] not only zero terminated, but also
>> zero pad, we need pass '4' to strncpy() instead of '5', that also will
>> clear all doubts.
> 
> I don't understand what point you're trying to make here, really. As
> Andreas has noted in the other mail, strncpy does zero-termination
> automatically.
> 

strncpy will zero pad, but not be sure of the dest string will be zero
terminated, please "man strncpy" to get more details.

So for me, I'd like to use '4' instead of '5' for strncpy(), that will
clear all doubts (although, at present, it is not a bug, so this patch
can be skipped, if we are only focus on bug fix).


Thanks.
-- 
Chen Gang

Open, share, and attitude like air, water, and life which God blessed