Compilation errors on Ubuntu 8.10 Intrepid Ibex

[Igor Sysoev]

On Tue, Nov 11, 2008 at 12:35:40AM +0300, Maxim Dounin wrote:

> Hello!
> 
> On Mon, Nov 10, 2008 at 11:34:37PM +0300, Igor Sysoev wrote:
> 
> > On Mon, Nov 10, 2008 at 09:38:39AM -0800, Eric Benson wrote:
> > 
> > > Compiling either 0.6.32 or 0.7.20 on a new Ubuntu 8.10 installation with gcc 4.3.2 causes errors due to a new compiler warning (when combined with the use of -Werror in CFLAGS). There is now a compiler warning when the return value of write() is ignored. This causes errors in a number of placees in nginx. I have included a log showing the compiler output as well as a patch file showing the changes I made to avoid these errors.
> > 
> > Thank you.
> > However, there is more elegant way to suppress this warning without
> > stub variables:
> > 
> >       (void) write_fd(...)
> > 
> > Could you test the attached patch ?
> 
> No, warn_unused_result warning can't be avoided by casting to 
> void: 
> 
> $ cat unused.c
> int foo() __attribute__((warn_unused_result));
> 
> int
> foo()
> {
>         return 1;
> }
> 
> int
> main()
> {
>         (void) foo();
> 
>         return 0;
> }
> $ gcc unused.c
> unused.c: In function 'main':
> unused.c:12: warning: ignoring return value of 'foo', declared with attribute warn_unused_result
> 
> More details here:
> 
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25509
> 
> However I don't think it's a good idea to use stub variables.  
> Probably something like
> 
>     if (ngx_write_fd(...) == NGX_FILE_ERROR) {
>         /* void */
>     }
> 
> would be better.
> 
> Maxim Dounin
> 
> p.s. Actually I think that it's glibc's bug.  But we probably have 
> to live with it, at least for some time.

I believe this is gcc bug because I explictly says that I do not need
the function result using (void) case.

Dummy result checking as well as stub variable are security/reliabilty
profanation.  The (void) cast should be compact way to do the same.


-- 
Igor Sysoev
http://sysoev.ru/en/