From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga07.intel.com (mga07.intel.com [134.134.136.100]) (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 4610821BC6ADB for ; Mon, 27 Mar 2017 09:06:45 -0700 (PDT) Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by orsmga105.jf.intel.com with ESMTP; 27 Mar 2017 09:06:44 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.36,232,1486454400"; d="scan'208";a="1127647874" Received: from orsmsx105.amr.corp.intel.com ([10.22.225.132]) by fmsmga001.fm.intel.com with ESMTP; 27 Mar 2017 09:06:44 -0700 Received: from orsmsx161.amr.corp.intel.com (10.22.240.84) by ORSMSX105.amr.corp.intel.com (10.22.225.132) with Microsoft SMTP Server (TLS) id 14.3.319.2; Mon, 27 Mar 2017 09:06:39 -0700 Received: from orsmsx113.amr.corp.intel.com ([169.254.9.59]) by ORSMSX161.amr.corp.intel.com ([169.254.4.33]) with mapi id 14.03.0319.002; Mon, 27 Mar 2017 09:06:39 -0700 From: "Kinney, Michael D" To: Felix Poludov , "Gao, Liming" , "edk2-devel@lists.01.org" , "Kinney, Michael D" Thread-Topic: [RFC] GLOBAL_REMOVE_IF_UNREFERENCED, multiply defined symbols, and MSFT/GCC tool chains. Thread-Index: AdKkmm2mcThMLZckRnawazzXsHkPjwCDpsPAABg95DAAATdlkAAApmqAAACEyBA= Date: Mon, 27 Mar 2017 16:06:38 +0000 Message-ID: References: <9333E191E0D52B4999CE63A99BA663A002DEEEDA95@atlms1.us.megatrends.com> <4A89E2EF3DFEDB4C8BFDE51014F606A14D702B8A@shsmsx102.ccr.corp.intel.com> <9333E191E0D52B4999CE63A99BA663A002DEEF126B@atlms1.us.megatrends.com> <9333E191E0D52B4999CE63A99BA663A002DEEF1308@atlms1.us.megatrends.com> In-Reply-To: <9333E191E0D52B4999CE63A99BA663A002DEEF1308@atlms1.us.megatrends.com> Accept-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ctpclassification: CTP_IC x-titus-metadata-40: eyJDYXRlZ29yeUxhYmVscyI6IiIsIk1ldGFkYXRhIjp7Im5zIjoiaHR0cDpcL1wvd3d3LnRpdHVzLmNvbVwvbnNcL0ludGVsMyIsImlkIjoiMzBlMWQ0MWEtMzBhOS00ODQwLWIxMjctNmM2ZTRiNTg2MmM1IiwicHJvcHMiOlt7Im4iOiJDVFBDbGFzc2lmaWNhdGlvbiIsInZhbHMiOlt7InZhbHVlIjoiQ1RQX0lDIn1dfV19LCJTdWJqZWN0TGFiZWxzIjpbXSwiVE1DVmVyc2lvbiI6IjE1LjkuNi42IiwiVHJ1c3RlZExhYmVsSGFzaCI6Ikl1OWt2aFwvUWROZXhUZVRDUGZzY1lyU3F1N0hHSkd5Vk5iUzBzUjhWbU1ZPSJ9 x-originating-ip: [10.22.254.139] 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: Mon, 27 Mar 2017 16:06:45 -0000 Content-Language: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Felix, What is the condition that will fail if /Gw is set and=20 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 symbol= s, and > MSFT/GCC tool chains. >=20 > Mike, >=20 > What do you think about defining GLOBAL_REMOVE_IF_UNREFERENCED in the too= l 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_UNREFERENCE= D are not > subject to the default policy of breaking the build if multiple defined s= ymbols are > detected when MSFT tool chain is used. >=20 > -----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 symbol= s, and > MSFT/GCC tool chains. >=20 > Felix, >=20 > I prefer the default policy to break the build if multiple defined symbol= s are > detected. >=20 > Exceptions should only be allowed to support a specific compiler or a spe= cific level > of compiler optimizations. >=20 > I do like the addition of the /Gw switch to the newer VS compilers. Addi= ng the > current GLOBAL_REMOVE_IF_UNREFERENCED macro to global variable declaratio= ns is a > manual process that usually requires inspection of PE/COFF images to noti= ce that data > that should have been optimized away is still present. >=20 > 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. >=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 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 build. > > I suggest to update platform DSC to enable it in MSFT tool chain if thi= s 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] sect= ion. > > > > #ifndef GLOBAL_REMOVE_IF_UNREFERENCED > > #define GLOBAL_REMOVE_IF_UNREFERENCED __declspec(selectany) #endif > > > > Thanks > > Liming > > >-----Original Message----- > > >From: edk2-devel [mailto:edk2-devel-bounces@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 lin= ker. > > >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_UNREFEREN= CED. > > >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 =3D_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 to= ol 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/214a3b79417f64bf2faae74af42c > > >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. This communication is > > >intended to be read only by the individual or entity to whom it is > > >addressed or by their designee. If the reader of this message is not > > >the intended recipient, you are on notice that any distribution of > > >this message, in any form, is strictly prohibited. Please promptly > > >notify the sender by reply e-mail or by telephone at 770-246-8600, and= then delete > or destroy all copies of the transmission. > > >_______________________________________________ > > >edk2-devel mailing list > > >edk2-devel@lists.01.org > > >https://lists.01.org/mailman/listinfo/edk2-devel > > > > Please consider the environment before printing this email. > > > > The information contained in this message may be confidential and > > proprietary to American Megatrends, Inc. This communication is > > intended to be read only by the individual or entity to whom it is > > addressed or by their designee. 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