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

[Jan Kiszka <jan.kiszka@web.de>]

Jan Kiszka wrote:
> Laurent Desnogues wrote:
>> 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 :-)
> 
> Yeah, preprocessed and Lindent'ed, this looks really buggy.
> 
>> 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".
> 
> Obviously, detecting uninitialized variables with gcc still leaves room
> for improvement. Version 4.3 actually seem to have regressed in this case.
> 
>>>> 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
> 
> OK, that makes sense, partially. My feeling is that there are some more
> typos/thinkos in this code. First, the macro for 8/16/32 bit checks for
> a shift width of -8/-16/-32, but the 64-bit version uses -63?! And then
> we have this (for signed rshl):
> 
>  dest = src >> (width - 1);
>  dest++;
>  dest >>= 1;
> 
> Looks like nothing else than dest = 0, no? Paul?

One more:
    [NEON_FN for rshl_s8/16/32]
    ...
    } else if (tmp == -sizeof(src1) * 8) { \
        dest = src1 >> (tmp - 1); \
ie.
    if (tmp == -8/-16/-32) {
        dest = src1 >> (-9/-17/-33);

Jan