[asterisk-dev] [Code Review] 4530: clang compiler warning: -Wgnu-variable-sized-type-not-at-end

[Diederik de Groot]

> On March 27, 2015, 2:11 a.m., Matt Jordan wrote:
> > /branches/13/main/stdtime/localtime.c, lines 357-361
> > <https://reviewboard.asterisk.org/r/4530/diff/1/?file=72936#file72936line357>
> >
> >     Just curious, what was the compiler warning on this one?
> 
> Diederik de Groot wrote:
>     There can only be one variable size struct element and it has to be at the last position. Having them anywhere in the struct is a gcc extension.
> 
> rmudgett wrote:
>     This is not a valid fix!!  The buf.name field is supposed to be the extra space that the buf.iev.name field represents.
> 
> rmudgett wrote:
>     I'd suggest using ast_alloca() or alloca() to create space for buf instead.
> 
> Diederik de Groot wrote:
>     I did not interpret this correctly i guess. Doesn't this mean a union should have been used instead ?
>     Can you give me an example of how you would restructure this using alloca.
> 
> rmudgett wrote:
>     Unions have all members overlapping each other.  That is not what is needed here.  The struct inotify_event has a last member named name and the locally defined struct for buf is reserving space for buf.iev.name with the buf.name array.
>     
>     Since clang is complaining about this we need to change the definition of buf and the usage of it in the rest of the function.
>     
>     struct inotify_event *buf;
>     size_t real_sizeof_buf = sizeof(*buf) + FILENAME_MAX + 1;
>     
>     buf = ast_alloca(real_sizeof_buf);
>     
>     Where used:
>     sizeof(buf) becomes real_sizeof_buf
>     sizeof(buf.iev) becomes sizeof(*buf)
>     buf.iev.wd becomes buf->wd
>     
>     Since buf is not a good name because it is now misleading, renaming buf to iev would be better.

Thanks... Resolves the issue and even looks cleaner than the original :-)


- Diederik


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On March 26, 2015, 7:12 p.m., Diederik de Groot wrote:
> 
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> This is an automatically generated e-mail. To reply, visit:
> https://reviewboard.asterisk.org/r/4530/
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> 
> (Updated March 26, 2015, 7:12 p.m.)
> 
> 
> Review request for Asterisk Developers.
> 
> 
> Bugs: ASTERISK-24917
>     https://issues.asterisk.org/jira/browse/ASTERISK-24917
> 
> 
> Repository: Asterisk
> 
> 
> Description
> -------
> 
> clang's static analyzer will throw quite a number warnings / errors during compilation, some of which can be very helpfull in finding corner-case bugs\nclang compiler warning:-Wgnu-variable-sized-type-not-at-end
> 
> 
> Diffs
> -----
> 
>   /branches/13/main/stdtime/localtime.c 433444 
> 
> Diff: https://reviewboard.asterisk.org/r/4530/diff/
> 
> 
> Testing
> -------
> 
> 
> Thanks,
> 
> Diederik de Groot
> 
>

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