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Re: [PATCH] gcc/config/nios2/nios2.c: Let custom_builtin_name[*] always be zero terminated string
- From: Chen Gang <gang dot chen dot 5i5j at gmail dot com>
- To: Chung-Lin Tang <cltang at codesourcery dot com>, Chung-Lin Tang <chunglin_tang at mentor dot com>, Jeff Law <law at redhat dot com>, sandra at codesourcery dot com
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Sat, 26 Jul 2014 18:42:57 +0800
- Subject: Re: [PATCH] gcc/config/nios2/nios2.c: Let custom_builtin_name[*] always be zero terminated string
- Authentication-results: sourceware.org; auth=none
- References: <53D3205B dot 9050907 at gmail dot com> <53D34B8F dot 4080301 at mentor dot com> <53D359AE dot 9080707 at gmail dot com> <53D36FD7 dot 1070505 at codesourcery 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
>>>> 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.
> '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)'
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
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).
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