Re: [PATCH 2/2] MdeModulePkg/UdfDxe: suppress incorrect compiler warning in ReadFile()

[Laszlo Ersek <lersek@redhat.com>]

On 09/14/17 03:20, Zeng, Star wrote:
> Seemingly, VS has similar issue with GCC.
> 
> VS2010/VS2012 still have the building failures below after this patch. :(
> edk2\mdemodulepkg\universal\disk\udfdxe\filesystemoperations.c(1083) : error C2220: warning treated as error - no 'executable' file generated
> edk2\mdemodulepkg\universal\disk\udfdxe\filesystemoperations.c(1083) : warning C4701: potentially uninitialized local variable 'FilePosition' used
> edk2\mdemodulepkg\universal\disk\udfdxe\filesystemoperations.c(1078) : warning C4701: potentially uninitialized local variable 'FinishedSeeking' used
> edk2\mdemodulepkg\universal\disk\udfdxe\filesystemoperations.c(1167) : warning C4701: potentially uninitialized local variable 'Data' used
> edk2\mdemodulepkg\universal\disk\udfdxe\filesystemoperations.c(1167) : warning C4703: potentially uninitialized local pointer variable 'Data' used
> 
> 
> Liming, Dandan and Hao,
> Do you remember how we fix this kind of false alarm before?
> Just initialize the variable at the beginning of the function?

I think that all such warnings should be evaluated carefully.

Can you please file a TianoCore BZ about the above? Paulo might want to
take a look.

Thanks!
Laszlo


> -----Original Message-----
> From: Zeng, Star 
> Sent: Thursday, September 14, 2017 8:43 AM
> To: Ard Biesheuvel <ard.biesheuvel@linaro.org>; Laszlo Ersek <lersek@redhat.com>
> Cc: Ni, Ruiyu <ruiyu.ni@intel.com>; Dong, Eric <eric.dong@intel.com>; edk2-devel-01 <edk2-devel@lists.01.org>; Gao, Liming <liming.gao@intel.com>; Zeng, Star <star.zeng@intel.com>
> Subject: RE: [edk2] [PATCH 2/2] MdeModulePkg/UdfDxe: suppress incorrect compiler warning in ReadFile()
> 
> Comparing adding workaround in code with suppressing it in *OLD* version GCCs, I prefer the latter personally.
> 
> 
> Thanks,
> Star
> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Ard Biesheuvel
> Sent: Thursday, September 14, 2017 2:52 AM
> To: Laszlo Ersek <lersek@redhat.com>
> Cc: Ni, Ruiyu <ruiyu.ni@intel.com>; Dong, Eric <eric.dong@intel.com>; edk2-devel-01 <edk2-devel@lists.01.org>; Gao, Liming <liming.gao@intel.com>; Zeng, Star <star.zeng@intel.com>
> Subject: Re: [edk2] [PATCH 2/2] MdeModulePkg/UdfDxe: suppress incorrect compiler warning in ReadFile()
> 
> On 13 September 2017 at 11:49, Laszlo Ersek <lersek@redhat.com> wrote:
>> On 09/13/17 08:43, Zeng, Star wrote:
>>> Beyond the Rb (I do not want to block this patch series), I am curious about one question.
>>>
>>> There may be more this kind of workarounds to fix the build failure.
>>> Is it possible to disable the warning (like below example for VS) for specific version of GCC for this kind of false alarm?
>>>
>>>
>>> ProcessorBind.h:
>>> #if defined(_MSC_EXTENSIONS)
>>>
>>> ...
>>>
>>> #if _MSC_VER == 1800 || _MSC_VER == 1900
>>>
>>> //
>>> // Disable these warnings for VS2013.
>>> //
>>>
>>> //
>>> // This warning is for potentially uninitialized local variable, and 
>>> it may cause false // positive issues in VS2013 and VS2015 build // 
>>> #pragma warning ( disable : 4701 )
>>>
>>> //
>>> // This warning is for potentially uninitialized local pointer 
>>> variable, and it may cause // false positive issues in VS2013 and
>>> VS2015 build // #pragma warning ( disable : 4703 )
>>>
>>> #endif
>>>
>>> #endif
>>
>> I think starting with gcc-4.6, gcc supports the "diagnostics" pragma, 
>> which can be used to suppress warnings.
>>
>> Unfortunately, there's no pragma to suppress *only* the incorrect 
>> warnings :) So if we set the pragma, we could lose even those warnings 
>> that point out real bugs.
>>
> 
> That applies to the VS case as well. But I think doing this for older GCCs is fine, most EDK2 developers use a newer version anyway, so we will not lose any coverage by doing so.
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