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

["Gao, Liming" <liming.gao@intel.com>]

Right. Just initialize them. They are not reported in VS2013&VS2015, because VS2013 and VS2015 disables this warning in ProcessorBind.h. If they are all false warning messages, I think we can propose to disable this warning for all VS tool chain. 

For GCC, if this warning is also false, could we add compiler to disable it, like -Wno-unused-but-set-variable.

> -----Original Message-----
> From: Zeng, Star
> Sent: Thursday, September 14, 2017 9:21 AM
> To: Ard Biesheuvel <ard.biesheuvel@linaro.org>; Laszlo Ersek <lersek@redhat.com>; Gao, Liming <liming.gao@intel.com>; Bi, Dandan
> <dandan.bi@intel.com>; Wu, Hao A <hao.a.wu@intel.com>
> Cc: Ni, Ruiyu <ruiyu.ni@intel.com>; Dong, Eric <eric.dong@intel.com>; edk2-devel-01 <edk2-devel@lists.01.org>
> Subject: RE: [edk2] [PATCH 2/2] MdeModulePkg/UdfDxe: suppress incorrect compiler warning in ReadFile()
> 
> 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?
> 
> 
> 
> Thanks,
> Star
> -----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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