Re: [PATCH] include/builddefs.in: ignore unused-result warning

[Zorro Lang <zlang@xxxxxxxxxx>]

On Mon, Jan 06, 2025 at 05:59:06PM +0800, Shiyang Ruan wrote:
> When build xfstests, a lot of "unused result" warning are reported:
> 
>     [CC] write_log.lo
> write_log.c: In function 'wlog_record_write':
> write_log.c:205:13: warning: ignoring return value of 'write' declared with attribute 'warn_unused_result' [-Wunused-result]
>   205 |             write(wfile->w_afd, wbuf, reclen);
>       |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> write_log.c:209:13: warning: ignoring return value of 'write' declared with attribute 'warn_unused_result' [-Wunused-result]
>   209 |             write(wfile->w_rfd, wbuf, reclen);
>       |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>     [CC] random.lo

Hi,

I never hit this build warning:

# make
...
Building lib
    [LTDEP]
    [CC] write_log.lo
    [LD]
Building ltp
    [CC]    doio
    [CC]    fsstress
...

Besides that ...

> 
> Mostly are calused by not using the return value of read()/write()/...
> Ignore this warning by adding `-Wno-unused-result` to CCFLAGS.  This
> won't cause other problem but make the log clean.
> 
> Signed-off-by: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
> ---
>  include/builddefs.in | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/builddefs.in b/include/builddefs.in
> index 7274cde8d..edf87ff00 100644
> --- a/include/builddefs.in
> +++ b/include/builddefs.in
> @@ -75,7 +75,7 @@ HAVE_RLIMIT_NOFILE = @have_rlimit_nofile@
>  NEED_INTERNAL_XFS_IOC_EXCHANGE_RANGE = @need_internal_xfs_ioc_exchange_range@
>  HAVE_FICLONE = @have_ficlone@
>  
> -GCCFLAGS = -funsigned-char -fno-strict-aliasing -Wall
> +GCCFLAGS = -funsigned-char -fno-strict-aliasing -Wall -Wno-unused-result

I'm not an expert of gcc. From the manual of gcc, it says:

       -Wno-unused-result
           Do not warn if a caller of a function marked with attribute "warn_unused_result" does not use its return value. The default is -Wunused-result.

Looks like the "-Wno-unused-result" works for "a function marked with
attribute warn_unused_result", e.g.

    int __attribute__((warn_unused_result)) foo(void)

I think fstests doesn't use that attribute.

Thanks,
Zorro


>  
>  ifeq ($(PKG_PLATFORM),linux)
>  PCFLAGS = -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 $(GCCFLAGS)
> -- 
> 2.43.0
> 
>