Mike: Yes. /Gw option is added since VS2013. The older VS version can't use this option. I suggest we always define GLOBAL_REMOVE_IF_UNREFERENCED as empty, and drop this size optimization for the older version MS compiler. I collect its size of OvmfIa32X64 DEBUG tip with VS2015 tool chain on. After define it as empty, DXE Raw size increases ~55K, but PEI raw size and the compressed size doesn't increase big.
1. Define GLOBAL_REMOVE_IF_UNREFERENCED as __declspec(selectany). FV Space Information SECFV [10%Full] 212992 total, 22816 used, 190176 free FVMAIN_COMPACT [62%Full] 1753088 total, 1099872 used, 653216 free DXEFV [39%Full] 10485760 total, 4099344 used, 6386416 free PEIFV [18%Full] 917504 total, 172072 used, 745432 free 2. Define GLOBAL_REMOVE_IF_UNREFERENCED as empty. FV Space Information SECFV [10%Full] 212992 total, 22912 used, 190080 free FVMAIN_COMPACT [63%Full] 1753088 total, 1105992 used, 647096 free DXEFV [39%Full] 10485760 total, 4154480 used, 6331280 free PEIFV [18%Full] 917504 total, 173448 used, 744056 free FVMAIN_COMPACT +6120 DXEFV + 55136 PEIFV + 1376 3. Define GLOBAL_REMOVE_IF_UNREFERENCED as empty and append /Gw option. FV Space Information. SECFV [10%Full] 212992 total, 22816 used, 190176 free FVMAIN_COMPACT [62%Full] 1753088 total, 1099552 used, 653536 free DXEFV [39%Full] 10485760 total, 4097456 used, 6388304 free PEIFV [18%Full] 917504 total, 171944 used, 745560 free FVMAIN_COMPACT -320 DXEFV -1888 PEIFV -128 Thanks Liming >-----Original Message----- >From: Kinney, Michael D >Sent: Friday, May 26, 2017 2:20 PM >To: Gao, Liming <liming....@intel.com>; af...@apple.com; Laszlo Ersek ><ler...@redhat.com>; Kinney, Michael D <michael.d.kin...@intel.com> >Cc: Wu, Hao A <hao.a...@intel.com>; edk2-devel@lists.01.org; Fan, Jeff ><jeff....@intel.com>; Felix Poludov <fel...@ami.com>; Ard Biesheuvel ><ard.biesheu...@linaro.org> >Subject: RE: [edk2] [Patch] SourceLevelDebugPkg/SecPeiDebugAgentLib: Fix >duplicate symbol > >Liming, > >I agree with /Gw. That works for newer versions of VS. We will >need to adjust the behavior of GLOBAL_REMOVE_IF_UNREFERENCED based >on VS version as well. > >We can not define GLOBAL_REMOVE_IF_UNREFERENCED to static. We also >use this macro for globals that are required to be exported from >a library. So static should be added to the globals that are not >exported. > >The challenge is that older versions of VS require >GLOBAL_REMOVE_IF_UNREFERENCED to be mapped to __declspec(selectany) >and static can not be combined with __declspec(selectany). > >Mike > >> -----Original Message----- >> From: Gao, Liming >> Sent: Thursday, May 25, 2017 10:21 PM >> To: Kinney, Michael D <michael.d.kin...@intel.com>; af...@apple.com; >Laszlo Ersek >> <ler...@redhat.com>; Kinney, Michael D <michael.d.kin...@intel.com> >> Cc: Wu, Hao A <hao.a...@intel.com>; edk2-devel@lists.01.org; Fan, Jeff >> <jeff....@intel.com>; Felix Poludov <fel...@ami.com>; Ard Biesheuvel >> <ard.biesheu...@linaro.org> >> Subject: RE: [edk2] [Patch] SourceLevelDebugPkg/SecPeiDebugAgentLib: Fix >> duplicate symbol >> >> Mike: >> I remember community suggests to use VS /Gw option to remove the >global data, >> and then can define GLOBAL_REMOVE_IF_UNREFERENCED as empty or >static. >> >> Thanks >> Liming >> >-----Original Message----- >> >From: edk2-devel [mailto:edk2-devel-boun...@lists.01.org] On Behalf Of >> >Kinney, Michael D >> >Sent: Friday, May 26, 2017 6:42 AM >> >To: af...@apple.com; Laszlo Ersek <ler...@redhat.com>; Kinney, Michael >D >> ><michael.d.kin...@intel.com> >> >Cc: Wu, Hao A <hao.a...@intel.com>; edk2-devel@lists.01.org; Fan, Jeff >> ><jeff....@intel.com>; Felix Poludov <fel...@ami.com>; Ard Biesheuvel >> ><ard.biesheu...@linaro.org> >> >Subject: Re: [edk2] [Patch] SourceLevelDebugPkg/SecPeiDebugAgentLib: >Fix >> >duplicate symbol >> > >> >Andrew, >> > >> >The VS compilers available when GLOBAL_REMOVE_IF_UNREFERENCED >was >> >added referred to __declspec( selectany ) as putting the symbol into its >own >> >comdat, so it was then available to be optimized away with the use of >OPT:REF. >> > >> >I think it is time to re-evaluate the VS optimizers to see if they can >> >optimize >> >away global variables without being decorated with__declspec( selectany ). >If >> >we can remove __declspec( selectany ), then we have a path to use >STATIC >> >properly to hide global variables that are not declared as extern in the >library >> >class. >> > >> >I will investigate some more. >> > >> >Mike >> > >> >From: af...@apple.com [mailto:af...@apple.com] >> >Sent: Thursday, May 25, 2017 2:26 PM >> >To: Laszlo Ersek <ler...@redhat.com> >> >Cc: Ard Biesheuvel <ard.biesheu...@linaro.org>; Wu, Hao A >> ><hao.a...@intel.com>; edk2-devel@lists.01.org; Felix Poludov >> ><fel...@ami.com>; Kinney, Michael D <michael.d.kin...@intel.com>; Fan, >> >Jeff <jeff....@intel.com> >> >Subject: Re: [edk2] [Patch] SourceLevelDebugPkg/SecPeiDebugAgentLib: >Fix >> >duplicate symbol >> > >> > >> >On May 25, 2017, at 2:02 PM, Laszlo Ersek >> ><ler...@redhat.com<mailto:ler...@redhat.com>> wrote: >> > >> >On 05/25/17 22:37, Andrew Fish wrote: >> > >> > >> > >> >On May 25, 2017, at 1:28 PM, Laszlo Ersek >> ><ler...@redhat.com<mailto:ler...@redhat.com>> wrote: >> > >> >On 05/25/17 22:11, Ard Biesheuvel wrote: >> > >> >On 25 May 2017 at 13:06, Kinney, Michael D >> ><michael.d.kin...@intel.com<mailto:michael.d.kin...@intel.com>> >wrote: >> > >> >Laszlo and Andrew, >> > >> >With the information that has been collected on this thread, I >> >still think this patch in its original form is a good change >> >to resolve the this one specific duplicate symbol issue for all >> >tool chains. 'static' can not be mixed with >> >GLOBAL_REMOVE_IF_UNREFERENCED for MSFT tool chains, so renaming >> >the global variable is the easiest way to remove the duplicate. >> > >> >GLOBAL_REMOVE_IF_UNREFERENCED itself is problematic imo. I think it >> >was Felix who reported on this recently? >> > >> >STATIC is really the only sensible way to deal with this for symbols >> >that are only referenced by a single compilation unit. >> > >> > >> >I will continue to work on ways to detect duplicate symbols for >> >all tool chains and will enter a Bugzilla issue to for that >> >feature. >> > >> >In addition, the idea of detecting if a library is exporting more >> >than the library class defines is another good feature to consider >> >and I will enter a Bugzilla issue for that one as well. >> > >> >If we can find ways to both restrict the symbols exported by a >> >library and strip all symbols that are unused, then we can have >> >additional Bugzilla issues to perform that clean up on each >> >library instance that is exporting more than the library class. >> > >> >A static library is nothing more than an archive containing a >> >collection of object files. Sadly, that implies that we cannot >> >distinguish between symbols that may only be referenced by other >> >objects in the same static library and symbols that are exported to >> >the library client. >> > >> >Do we know for a fact that, with /OPT:REF, VS does not strip unused >> >*static* variables and functions? >> > >> >I mean, is it certain that *replacing* GLOBAL_REMOVE_IF_UNREFERENCED >> >with STATIC in this case would lead to a size increase? >> > >> >If that's the case, then I'm fine if we go ahead with this patch, I'd >> >just like to request that Mike please file some of those BZs, and please >> >reference them from the commit message (as the longer term solution), >> >before committing the patch. >> > >> >Clang will warn if you have unused static variables when warnings are >cranked >> >up. >> > >> >~/work/Compiler>cat static.c >> >static unsigned char gTest[] = { 42 }; >> > >> >static int test () >> >{ >> > return 1; >> >} >> > >> >int main () >> >{ >> > return 0; >> >} >> >~/work/Compiler>clang -Os static.c -Wall >> >static.c:1:22: warning: unused variable 'gTest' [-Wunused-variable] >> >static unsigned char gTest[] = { 42 }; >> > ^ >> >static.c:3:12: warning: unused function 'test' [-Wunused-function] >> >static int test () >> > ^ >> >2 warnings generated. >> > >> >Sorry, my question was imprecise. >> > >> >Assume there is a public library function ("external linkage") that >> >calls a static function in the same library instance and uses a static >> >variable in the same library instance. Then this library instance is >> >linked into a driver, but the driver never actually calls the extern >> >function -- so the static variable and the static function too become >> >useless. >> > >> >In this case, will /OPT:REF remove the static variable and the static >> >function too? >> > >> >It seems counter-intuitive to me that an internal-only function or an >> >internal-only variable has to be declared extern (via >> >GLOBAL_REMOVE_IF_UNREFERENCED) just so it can be eliminated at link >> >time, if it is never referenced (transitively). >> > >> > >> >Laszlo, >> > >> >I agree. The LLVM LTO does not have an issue "doing the right thing". >Seems >> >like static is also more of a compile time concept vs a link time (global >> >optimization) kind of thing? >> > >> >Given on VC++ GLOBAL_REMOVE_IF_UNREFERENCED maps to >> >__declspec( selectany ) I would guess maybe it has more to due with >> >supporting old non standard header files that can't change without >breaking >> >compatibility. >> > >> >MSDN on __declspec( selectany ) : >> >A global data item can normally be initialized only once in an EXE or DLL >> project. >> >selectany can be used in initializing global data defined by headers, when >the >> >same header appears in more than one source file. selectany is available in >> >both the C and C++ compilers. >> > >> >Thanks, >> > >> >Andrew Fish >> > >> > >> > >> >Thanks >> >Laszlo >> >_______________________________________________ >> >edk2-devel mailing list >> >edk2-devel@lists.01.org<mailto:edk2-devel@lists.01.org> >> >https://lists.01.org/mailman/listinfo/edk2-devel >> > >> >_______________________________________________ >> >edk2-devel mailing list >> >edk2-devel@lists.01.org >> >https://lists.01.org/mailman/listinfo/edk2-devel _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel
