Re: [Qemu-devel] Re: [PATCH 0/7] clean build - eliminate warnings

[Laurent Desnogues <laurent.desnogues@gmail.com>]

On Sat, Feb 21, 2009 at 9:09 PM, Jan Kiszka <jan.kiszka@web.de> wrote:
> Laurent Desnogues wrote:
>> On Sat, Feb 21, 2009 at 8:00 PM, Jan Kiszka <jan.kiszka@web.de> wrote:
>>> When working on larger or intrusive changes like the monitor rework, the
>>> number of warnings a normal build generates (here: x86-64 host, gcc 4.3)
>>> is still too high. And sometimes these warnings are not just of cosmetic
>>> nature, see (reposted) patch 3.
>>>
>>> This series reduces the number of warnings significantly, still not to
>>> zero (someone would have to look into the NetWinder stuff), but almost:
>>>
>>> Warning summary for 2009-02-21 (changes since 2009-02-21-base)
>>>  generic          0    (-1)
>>>  softmmu          0   (-39)
>>>    x86            0     (0)
>>>    arm            0   (-10)
>>
>> This means that after applying your patch there should be no more
>> warning for the ARM target?
>
> At least for softmmu, at least with my compiler (depending on the
> precise version / distro patches, you may have different warnings
> enabled by default): yes.

I built softmmu and my Makefile has no other warning than the
default.

>>
>> On my machine (x86_64, gcc 4.1.2), I still get these:
>>
>>   CC    arm-softmmu/neon_helper.o
>> /home/ldesnogu/work/Emu/qemu/svn-ref/target-arm/neon_helper.c: In
>> function ‘helper_neon_rshl_s8’:
>> /home/ldesnogu/work/Emu/qemu/svn-ref/target-arm/neon_helper.c:469:
>> warning: ‘vdest.v1’ is used uninitialized in this function
>> /home/ldesnogu/work/Emu/qemu/svn-ref/target-arm/neon_helper.c:469:
>> warning: ‘vdest.v2’ is used uninitialized in this function
>> /home/ldesnogu/work/Emu/qemu/svn-ref/target-arm/neon_helper.c:469:
>> warning: ‘vdest.v3’ is used uninitialized in this function
>> /home/ldesnogu/work/Emu/qemu/svn-ref/target-arm/neon_helper.c:469:
>> warning: ‘vdest.v4’ is used uninitialized in this function
>> /home/ldesnogu/work/Emu/qemu/svn-ref/target-arm/neon_helper.c: In
>> function ‘helper_neon_rshl_s16’:
>> /home/ldesnogu/work/Emu/qemu/svn-ref/target-arm/neon_helper.c:470:
>> warning: ‘vdest.v1’ is used uninitialized in this function
>> /home/ldesnogu/work/Emu/qemu/svn-ref/target-arm/neon_helper.c:470:
>> warning: ‘vdest.v2’ is used uninitialized in this function
>> /home/ldesnogu/work/Emu/qemu/svn-ref/target-arm/neon_helper.c: In
>> function ‘helper_neon_rshl_s32’:
>> /home/ldesnogu/work/Emu/qemu/svn-ref/target-arm/neon_helper.c:471:
>> warning: ‘vdest.v1’ is used uninitialized in this function
>
> Has this been identified as a real issue or just compiler blindness (my
> series contains one "fix" for such blindness, see cris patch)? I'm
> currently a bit lost in those macros...

Yes, it's a real bug:  dest has not been given a value.  You can
look at preprocessed code :-) BTW, can gcc really say a value
is used uninitialized?  I have seen it pretending "may be used
uninitialized" though it is, but it was always right when it says
"is used uninitialized".

>>
>> Note a patch has been proposed in the past (by Aurélien IIRC).
>
> Do you have a reference at hand?

Try this:

http://article.gmane.org/gmane.comp.emulators.qemu/31206

HTH,

Laurent