[Python-Dev] Fix strncpy warning with gcc 8 (#5840)

[Eric V. Smith]

On 3/6/2018 6:52 AM, Serhiy Storchaka wrote:
> 06.03.18 12:34, Xiang Zhang пише:
>> https://github.com/python/cpython/commit/efd2bac1564f8141a4eab1bf8779b412974b8d69 
>>
>> commit: efd2bac1564f8141a4eab1bf8779b412974b8d69
>> branch: master
>> author: Siddhesh Poyarekar <siddhesh.poyarekar at gmail.com>
>> committer: Xiang Zhang <angwerzx at 126.com>
>> date: 2018-03-06T18:34:35+08:00
>> summary:
>>
>> Fix strncpy warning with gcc 8 (#5840)
>>
>> The length in strncpy is one char too short and as a result it leads
>> to a build warning with gcc 8.  Comment out the strncpy since the
>> interpreter aborts immediately after anyway.
>>
>> files:
>> M Python/pystrtod.c
>>
>> diff --git a/Python/pystrtod.c b/Python/pystrtod.c
>> index 9bf936386210..601f7c691edf 100644
>> --- a/Python/pystrtod.c
>> +++ b/Python/pystrtod.c
>> @@ -1060,8 +1060,8 @@ format_float_short(double d, char format_code,
>>           else {
>>               /* shouldn't get here: Gay's code should always return
>>                  something starting with a digit, an 'I',  or 'N' */
>> -            strncpy(p, "ERR", 3);
>> -            /* p += 3; */
>> +            /* strncpy(p, "ERR", 3);
>> +               p += 3; */
>>               Py_UNREACHABLE();
>>           }
>>           goto exit;
>>
> 
> I think this code was added for purpose. In the case of programming 
> error we could get meaningful value in post-mortal debugging. But after 
> replacing assert(0) with Py_UNREACHABLE this perhaps lost a sense.
> 
> If this code is no longer needed it is better to remove it than keeping 
> an obscure comment.
> 
> What are your thoughts @warsaw and @ericvsmith?
> 
> Py_UNREACHABLE was added in issue31338 by Barry. The original code was 
> added in issue1580 by Eric Smith (maybe it was copied from other place).

Mark Dickinson and/or I wrote that. I agree that leaving the two 
commented out lines is confusing. I suggest deleting them, and of course 
leave the comment about Gay's code.

Eric