From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ml01.01.org (Postfix) with ESMTPS id B731D203BEC1E for ; Mon, 27 Mar 2017 22:01:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=intel.com; i=@intel.com; q=dns/txt; s=intel; t=1490677284; x=1522213284; h=from:to:subject:date:message-id:references:in-reply-to: content-transfer-encoding:mime-version; bh=Zvg887HGWXDteWBF1Zd6YmvcVMcV1VfZ8AbC2zahWnk=; b=DGbnGobt3DxNrdIIugx9frYFTzWgp4lYzgp0tDCRWBYAutIjg/6hw3Qr fQB2houG6yGyPBEqC064UOOlaq5DFw==; Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 27 Mar 2017 22:01:24 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.36,235,1486454400"; d="scan'208";a="81319392" Received: from fmsmsx107.amr.corp.intel.com ([10.18.124.205]) by fmsmga005.fm.intel.com with ESMTP; 27 Mar 2017 22:01:24 -0700 Received: from fmsmsx101.amr.corp.intel.com (10.18.124.199) by fmsmsx107.amr.corp.intel.com (10.18.124.205) with Microsoft SMTP Server (TLS) id 14.3.319.2; Mon, 27 Mar 2017 22:01:23 -0700 Received: from shsmsx152.ccr.corp.intel.com (10.239.6.52) by fmsmsx101.amr.corp.intel.com (10.18.124.199) with Microsoft SMTP Server (TLS) id 14.3.319.2; Mon, 27 Mar 2017 22:01:23 -0700 Received: from shsmsx102.ccr.corp.intel.com ([169.254.2.212]) by SHSMSX152.ccr.corp.intel.com ([169.254.6.46]) with mapi id 14.03.0248.002; Tue, 28 Mar 2017 13:01:21 +0800 From: "Gao, Liming" To: "Kinney, Michael D" , Felix Poludov , "edk2-devel@lists.01.org" Thread-Topic: [RFC] GLOBAL_REMOVE_IF_UNREFERENCED, multiply defined symbols, and MSFT/GCC tool chains. Thread-Index: AdKkmm2mcThMLZckRnawazzXsHkPjwCDpsPAABg95DAAATdlkAAApmqAAACEyBAAAErC0AABt9zgABZ5ngA= Date: Tue, 28 Mar 2017 05:01:21 +0000 Message-ID: <4A89E2EF3DFEDB4C8BFDE51014F606A14D704414@shsmsx102.ccr.corp.intel.com> References: <9333E191E0D52B4999CE63A99BA663A002DEEEDA95@atlms1.us.megatrends.com> <4A89E2EF3DFEDB4C8BFDE51014F606A14D702B8A@shsmsx102.ccr.corp.intel.com> <9333E191E0D52B4999CE63A99BA663A002DEEF126B@atlms1.us.megatrends.com> <9333E191E0D52B4999CE63A99BA663A002DEEF1308@atlms1.us.megatrends.com> <9333E191E0D52B4999CE63A99BA663A002DEEF136D@atlms1.us.megatrends.com> In-Reply-To: Accept-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.239.127.40] MIME-Version: 1.0 Subject: Re: [RFC] GLOBAL_REMOVE_IF_UNREFERENCED, multiply defined symbols, and MSFT/GCC tool chains. X-BeenThere: edk2-devel@lists.01.org X-Mailman-Version: 2.1.22 Precedence: list List-Id: EDK II Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 28 Mar 2017 05:01:24 -0000 Content-Language: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable If platform decides not to fix them in platform code, they can redefine /D = GLOBAL_REMOVE_IF_UNREFERENCED =3D_declspec(selectany) in [BuildOptions] sec= tion of Platform.dsc.=20 Thanks Liming > -----Original Message----- > From: Kinney, Michael D > Sent: Tuesday, March 28, 2017 1:07 AM > To: Felix Poludov ; Gao, Liming ; e= dk2-devel@lists.01.org; Kinney, Michael D > > Subject: RE: [RFC] GLOBAL_REMOVE_IF_UNREFERENCED, multiply defined symbol= s, and MSFT/GCC tool chains. >=20 > Felix, >=20 > We need to find all instances of that usage and fix them. >=20 > We can make sure this issue is fixed for all open source packages > and open source platforms before this change is committed to master. >=20 > 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. >=20 > Perhaps give 1-2 weeks for verification so the package and platform > owners can resolve any issues found. >=20 > Other opinions? >=20 > Thanks, >=20 > Mike >=20 >=20 > > -----Original Message----- > > From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of = Felix Poludov > > Sent: Monday, March 27, 2017 9:17 AM > > To: Kinney, Michael D ; Gao, Liming > > ; edk2-devel@lists.01.org > > Subject: Re: [edk2] [RFC] GLOBAL_REMOVE_IF_UNREFERENCED, multiply defin= ed symbols, and > > MSFT/GCC tool chains. > > > > Mike, > > > > I completely agree. > > As far as code that breaks, the most typical problem I've seen is varia= ble 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.kinney@intel.com] > > Sent: Monday, March 27, 2017 12:07 PM > > To: Felix Poludov; Gao, Liming; edk2-devel@lists.01.org; Kinney, Michae= l D > > Subject: RE: [RFC] GLOBAL_REMOVE_IF_UNREFERENCED, multiply defined symb= ols, 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:Felixp@ami.com] > > > Sent: Monday, March 27, 2017 8:59 AM > > > To: Kinney, Michael D ; Gao, Liming > > > ; 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 o= f > > > breaking the build if multiple defined symbols are detected when MSFT= tool chain is > > used. > > > > > > -----Original Message----- > > > From: Kinney, Michael D [mailto:michael.d.kinney@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 bee= n 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-bounces@lists.01.org] On Behalf > > > > Of Felix Poludov > > > > Sent: Monday, March 27, 2017 7:59 AM > > > > To: Gao, Liming ; 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.gao@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 buil= d. > > > > 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 whe= n > > > > 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) #endi= f > > > > > > > > Thanks > > > > Liming > > > > >-----Original Message----- > > > > >From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behal= f > > > > >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_UNREF= ERENCED. > > > > >For a while usage of the macro was the only option to enable globa= l > > > > >variable optimization. > > > > >Starting from VS2013 compiler supports /Gw flag that enables globa= l > > > > >variable optimization without a special declarator. > > > > > > > > > >I propose to make the following modifications: > > > > > > > > > >1. Change GLOBAL_REMOVE_IF_UNREFERENCED definition to an empt= y > > > > >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 =3D_declspec(selectany) > > > > > > > > > > > > > > >The advantages of these modifications are: > > > > > > > > > >- Better detection of on potential errors by breaking the b= uild when > > > > >symbol is defined more than once. > > > > > > > > > >- Improved consistency between MSFT and GCC tool chains > > > > > > > > > >- Improved link time optimization with VS2013 and newer MSF= T 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 i= s > > > > >a good idea. > > > > >For example, see Ard's arguments in this commit comment > > > > >https://github.com/tianocore/edk2/commit/214a3b79417f64bf2faae74af= 4 > > > > >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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