Liming, I agree that would work, but I would recommend the issue be fixed in the sources to avoid use of multiple defined symbols.
Mike > -----Original Message----- > From: Gao, Liming > Sent: Monday, March 27, 2017 10:01 PM > To: Kinney, Michael D <michael.d.kin...@intel.com>; Felix Poludov > <fel...@ami.com>; > edk2-devel@lists.01.org > Subject: RE: [RFC] GLOBAL_REMOVE_IF_UNREFERENCED, multiply defined symbols, > and > MSFT/GCC tool chains. > > If platform decides not to fix them in platform code, they can redefine /D > GLOBAL_REMOVE_IF_UNREFERENCED =_declspec(selectany) in [BuildOptions] section > of > Platform.dsc. > > Thanks > Liming > > -----Original Message----- > > From: Kinney, Michael D > > Sent: Tuesday, March 28, 2017 1:07 AM > > To: Felix Poludov <fel...@ami.com>; Gao, Liming <liming....@intel.com>; > > edk2- > de...@lists.01.org; Kinney, Michael D > > <michael.d.kin...@intel.com> > > Subject: RE: [RFC] GLOBAL_REMOVE_IF_UNREFERENCED, multiply defined symbols, > > and > MSFT/GCC tool chains. > > > > Felix, > > > > We need to find all instances of that usage and fix them. > > > > We can make sure this issue is fixed for all open source packages > > and open source platforms before this change is committed to master. > > > > I recommend you generate a new version of the patch based on feedback > > from this thread and ask all package and platform owners to verify that > > their packages and platforms build with that change. > > > > Perhaps give 1-2 weeks for verification so the package and platform > > owners can resolve any issues found. > > > > Other opinions? > > > > Thanks, > > > > Mike > > > > > > > -----Original Message----- > > > From: edk2-devel [mailto:edk2-devel-boun...@lists.01.org] On Behalf Of > > > Felix > Poludov > > > Sent: Monday, March 27, 2017 9:17 AM > > > To: Kinney, Michael D <michael.d.kin...@intel.com>; Gao, Liming > > > <liming....@intel.com>; edk2-devel@lists.01.org > > > Subject: Re: [edk2] [RFC] GLOBAL_REMOVE_IF_UNREFERENCED, multiply defined > > > symbols, > and > > > MSFT/GCC tool chains. > > > > > > Mike, > > > > > > I completely agree. > > > As far as code that breaks, the most typical problem I've seen is > > > variable or > constant > > > defined in a header file included by more than one C file. > > > > > > Are you going to make these modifications or do you want me to submit a > > > patch? > > > > > > -----Original Message----- > > > From: Kinney, Michael D [mailto:michael.d.kin...@intel.com] > > > Sent: Monday, March 27, 2017 12:07 PM > > > To: Felix Poludov; Gao, Liming; edk2-devel@lists.01.org; Kinney, Michael D > > > Subject: RE: [RFC] GLOBAL_REMOVE_IF_UNREFERENCED, multiply defined > > > symbols, and > > > MSFT/GCC tool chains. > > > > > > Felix, > > > > > > What is the condition that will fail if /Gw is set and > GLOBAL_REMOVE_IF_UNREFERENCED > > > is defined to nothing? > > > > > > If these are real bugs, then I think we should identify those bugs and > > > fix them > and > > > then apply this strong policy for newer VS compilers. > > > > > > Mike > > > > > > > -----Original Message----- > > > > From: Felix Poludov [mailto:fel...@ami.com] > > > > Sent: Monday, March 27, 2017 8:59 AM > > > > To: Kinney, Michael D <michael.d.kin...@intel.com>; Gao, Liming > > > > <liming....@intel.com>; edk2-devel@lists.01.org > > > > Subject: RE: [RFC] GLOBAL_REMOVE_IF_UNREFERENCED, multiply defined > > > > symbols, and MSFT/GCC tool chains. > > > > > > > > Mike, > > > > > > > > What do you think about defining GLOBAL_REMOVE_IF_UNREFERENCED in the > > > > tool chain definition file as an empty macro for a newer VS compilers? > > > > If this is done, as Liming pointed out, some code that compiles today > > > > may break. > > > > If this is not done, variables declared with > > > > GLOBAL_REMOVE_IF_UNREFERENCED are not subject to the default policy of > > > > breaking the build if multiple defined symbols are detected when MSFT > > > > tool chain > is > > > used. > > > > > > > > -----Original Message----- > > > > From: Kinney, Michael D [mailto:michael.d.kin...@intel.com] > > > > Sent: Monday, March 27, 2017 11:35 AM > > > > To: Felix Poludov; Gao, Liming; edk2-devel@lists.01.org; Kinney, > > > > Michael D > > > > Subject: RE: [RFC] GLOBAL_REMOVE_IF_UNREFERENCED, multiply defined > > > > symbols, and MSFT/GCC tool chains. > > > > > > > > Felix, > > > > > > > > I prefer the default policy to break the build if multiple defined > > > > symbols are detected. > > > > > > > > Exceptions should only be allowed to support a specific compiler or a > > > > specific level of compiler optimizations. > > > > > > > > I do like the addition of the /Gw switch to the newer VS compilers. > > > > Adding the current GLOBAL_REMOVE_IF_UNREFERENCED macro to global > > > > variable declarations is a manual process that usually requires > > > > inspection of PE/COFF images to notice that data that should have been > > > > optimized > > > away is still present. > > > > > > > > Adding the #ifndef also looks like a good way to adopt the /Gw switch > > > > in newer VS Compilers and preserve backwards compatibility with older VS > compilers. > > > > > > > > Thanks, > > > > > > > > Mike > > > > > > > > > > > > > -----Original Message----- > > > > > From: edk2-devel [mailto:edk2-devel-boun...@lists.01.org] On Behalf > > > > > Of Felix Poludov > > > > > Sent: Monday, March 27, 2017 7:59 AM > > > > > To: Gao, Liming <liming....@intel.com>; edk2-devel@lists.01.org > > > > > Subject: Re: [edk2] [RFC] GLOBAL_REMOVE_IF_UNREFERENCED, multiply > > > > > defined symbols, and MSFT/GCC tool chains. > > > > > > > > > > Liming, > > > > > > > > > > Yes surrounding GLOBAL_REMOVE_IF_UNREFERENCED with #ifndef would be an > > > improvement. > > > > > Can you make this change? > > > > > > > > > > On the other note, don't you think that EDKII should have a generic > > > > > policy regarding multiply defined symbols (whether they are allowed > > > > > or not)? > > > > > Today, they may or may not work depending on the compiler used. > > > > > > > > > > -----Original Message----- > > > > > From: Gao, Liming [mailto:liming....@intel.com] > > > > > Sent: Monday, March 27, 2017 12:49 AM > > > > > To: Felix Poludov; edk2-devel@lists.01.org > > > > > Cc: Gao, Liming > > > > > Subject: RE: [RFC] GLOBAL_REMOVE_IF_UNREFERENCED, multiply defined > > > > > symbols, and MSFT/GCC tool chains. > > > > > > > > > > Felix: > > > > > This changes the default MSFT build behavior. It will impact all > > > > > platforms even if this platform has no requirement to pass GCC build. > > > > > I suggest to update platform DSC to enable it in MSFT tool chain if > > > > > this platform > > > > needs to support MSFT and GCC both. > > > > > > > > > > In Base.h: I agree to define GLOBAL_REMOVE_IF_UNREFERENCED only when > > > > > it is not defined. Then, Platform.dsc can append compiler option /D > > > > > GLOBAL_REMOVE_IF_UNREFERE to the different value in [BuildOptions] > > > > > section. > > > > > > > > > > #ifndef GLOBAL_REMOVE_IF_UNREFERENCED > > > > > #define GLOBAL_REMOVE_IF_UNREFERENCED __declspec(selectany) #endif > > > > > > > > > > Thanks > > > > > Liming > > > > > >-----Original Message----- > > > > > >From: edk2-devel [mailto:edk2-devel-boun...@lists.01.org] On Behalf > > > > > >Of Felix Poludov > > > > > >Sent: Friday, March 24, 2017 8:53 PM > > > > > >To: edk2-devel@lists.01.org > > > > > >Subject: [edk2] [RFC] GLOBAL_REMOVE_IF_UNREFERENCED, multiply > > > > > >defined symbols, and MSFT/GCC tool chains. > > > > > > > > > > > >Trying to add GCC support to projects based on MSFT tool chain, I'm > > > > > >keep stumbling into multiply defined symbol errors reported by GCC > > > > > >linker. > > > > > >An attempt to understand why the errors are not reported by the > > > > > >Microsoft linker lead me to GLOBAL_REMOVE_IF_UNREFERENCED macro. > > > > > >The purpose of the macro is to enable link time optimization of > > > > > >global variables. > > > > > >However, the way it's defined for MSFT tool chain > > > > > >(__declspec(selectany) ) has a side effect of explicitly allowing > > > > > >multiple instances of a symbol defined with > > > > > >GLOBAL_REMOVE_IF_UNREFERENCED. > > > > > >For a while usage of the macro was the only option to enable global > > > > > >variable optimization. > > > > > >Starting from VS2013 compiler supports /Gw flag that enables global > > > > > >variable optimization without a special declarator. > > > > > > > > > > > >I propose to make the following modifications: > > > > > > > > > > > >1. Change GLOBAL_REMOVE_IF_UNREFERENCED definition to an empty > > > > > >macro. > > > > > > > > > > > >Or more specifically, update macro definition in Base.h as follows: > > > > > > > > > > > >#ifndef GLOBAL_REMOVE_IF_UNREFERENCED > > > > > > > > > > > >#define GLOBAL_REMOVE_IF_UNREFERENCED > > > > > > > > > > > >#endif > > > > > > > > > > > >2. Update VS2013 and VS2015 compiler flags to add /Gw option > > > > > > > > > > > >3. Update compiler flags for older MSFT tool chains to define > > > > > >GLOBAL_REMOVE_IF_UNREFERENCED in a backward compatible manner for > > > > > >targets that enable optimization. > > > > > > > > > > > >/D GLOBAL_REMOVE_IF_UNREFERENCED =_declspec(selectany) > > > > > > > > > > > > > > > > > >The advantages of these modifications are: > > > > > > > > > > > >- Better detection of on potential errors by breaking the > > > > > >build when > > > > > >symbol is defined more than once. > > > > > > > > > > > >- Improved consistency between MSFT and GCC tool chains > > > > > > > > > > > >- Improved link time optimization with VS2013 and newer MSFT > > > > > >tool > chains. > > > > > > > > > > > >For example, mGaugeData in > > > > > >MdeModulePkg/Library/DxeCorePerformanceLib/DxeCorePerformanceLib.c > > > > > >is not declared as GLOBAL_REMOVE_IF_UNREFERENCED, so > > > > > > > > > > > >today performance library is linked with DXE Core even when > > > > > >performance measurements are disabled. > > > > > > > > > > > >The alternative option is to enable support of multiply defined > > > > > >symbols on GCC tool chain. > > > > > >One way to do it is by defining the macro as #define > > > > > >GLOBAL_REMOVE_IF_UNREFERENCED __attribute__((weak)) > > > > > > > > > > > >However, I'm not sure that embracing multiple symbol definitions is > > > > > >a good idea. > > > > > >For example, see Ard's arguments in this commit comment > > > > > >https://github.com/tianocore/edk2/commit/214a3b79417f64bf2faae74af4 > > > > > >2c > > > > > >1 > > > > > >b9d23f50dc8 > > > > > > > > > > > >Thanks > > > > > >Felix > > > > > > > > > > > >Please consider the environment before printing this email. > > > > > > > > > > > >The information contained in this message may be confidential and > > > > > >proprietary to American Megatrends, Inc. 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