On 2015-12-04 08:43:29, Ard Biesheuvel wrote: > On 4 December 2015 at 17:27, Laszlo Ersek <[email protected]> wrote: > > On 12/04/15 17:23, Paolo Bonzini wrote: > >> > >> > >> On 04/12/2015 11:39, Laszlo Ersek wrote: > >>> (4) Linking those two files into a complete program is a violation of > >>> "6.7 External definitions": > >>> > >>> [...] If an identifier declared with external linkage is used in an > >>> expression (other than as part of the operand of a *sizeof* > >>> operator), somewhere in the entire program there shall be exactly > >>> one external definition for the identifier [...] > >>> > >>> Again, how does the argument go? > >>> > >>> - In each file we have exactly one tentative definition, and no > >>> declaration that would be, in its own right, an external definition. > >>> Based on (2), the files must behave exactly as-if there was one > >>> external *definition* for "x" in each. > >>> > >>> - Argument (3) explains why "x" has external *linkage*. > >>> > >>> - Argument (4) applies to "x" because "x" has external linkage, and is > >>> used in a non-sizeof expression. And the requirement set forth in (4) > >>> is broken by the program because the program is required to behave > >>> exactly as if "x" had two external definitions. > >>> > >>> In practical terms: > >>> > >>> - If you compile the first version of the program (without any special > >>> options), it links together successfully: > >>> > >>> $ gcc -std=c89 -pedantic -Wall -Wextra -o f f1.c f2.c > >>> > >>> - If you compile the second (equivalent) version of the program, > >>> linkage fails: > >>> > >>> $ gcc -std=c89 -pedantic -Wall -Wextra -o f-b f1-b.c f2-b.c > >>> > >>> /tmp/cc8Isbn8.o:(.bss+0x0): multiple definition of `x' > >>> /tmp/cciQUlDz.o:(.bss+0x0): first defined here > >>> collect2: error: ld returned 1 exit status > >>> > >>> - The gcc bug is that linking the first version *too* should fail, > >>> without any particular options. > >> > >> That's true, but it would break existing code that declares variables in > >> headers without "extern". > > > > I agree. After I posted the email I pondered what it would take to fix > > this in gcc. It would be impossible. :) > > > >> That's why Visual Studio does the same. > > > > Looks plausible. > > > > Thanks! > > Laszlo > > > > Indeed. Liming is looking into that. I spotted very few issues with > -fno-common, only two in CryptoPkg, so I think we should disallow > common allocations going forward if we can, especially since the > modularity of EDK2 makes it almost impossible to guarantee that it > never leads to problems. > > Qin has already acked a fix for one of those issues, I will ping him > for the other one. In the mean time, perhaps GCC users could double > check whether there is any breakage? Laszlo, could you check your OVMF > builds, please?
I'm seeing a build error with MdeModulePkg and OvmfPkg. This is with gcc 5.2 using the GCC49 toolchain. Both cases seem to be unitialized global variables declared in a single .c file. I'm not sure what needs to be changed to fix this. MdeModulePkg: "ld" -o Build/MdeModule/DEBUG_GCC49/X64/MdeModulePkg/Application/MemoryProfileInfo/MemoryProfileInfo/DEBUG/MemoryProfileInfo.dll -nostdlib -n -q --gc-sections -z common-page-size=0x40 --entry _ModuleEntryPoint -u _ModuleEntryPoint -Map Build/MdeModule/DEBUG_GCC49/X64/MdeModulePkg/Application/MemoryProfileInfo/MemoryProfileInfo/DEBUG/MemoryProfileInfo.map -melf_x86_64 --oformat=elf64-x86-64 --start-group @Build/MdeModule/DEBUG_GCC49/X64/MdeModulePkg/Application/MemoryProfileInfo/MemoryProfileInfo/OUTPUT/static_library_files.lst --end-group --defsym=PECOFF_HEADER_SIZE=0x228 --script=BaseTools/Scripts/GccBase.lds `mNameString' referenced in section `.text.GetDriverNameString' of Build/MdeModule/DEBUG_GCC49/X64/MdeModulePkg/Application/MemoryProfileInfo/MemoryProfileInfo/OUTPUT/MemoryProfileInfo.lib(MemoryProfileInfo.obj): defined in discarded section `COMMON' of Build/MdeModule/DEBUG_GCC49/X64/MdeModulePkg/Application/MemoryProfileInfo/MemoryProfileInfo/OUTPUT/MemoryProfileInfo.lib(MemoryProfileInfo.obj) `mNameString' referenced in section `.text.GetDriverNameString' of Build/MdeModule/DEBUG_GCC49/X64/MdeModulePkg/Application/MemoryProfileInfo/MemoryProfileInfo/OUTPUT/MemoryProfileInfo.lib(MemoryProfileInfo.obj): defined in discarded section `COMMON' of Build/MdeModule/DEBUG_GCC49/X64/MdeModulePkg/Application/MemoryProfileInfo/MemoryProfileInfo/OUTPUT/MemoryProfileInfo.lib(MemoryProfileInfo.obj) `mNameString' referenced in section `.text.GetDriverNameString' of Build/MdeModule/DEBUG_GCC49/X64/MdeModulePkg/Application/MemoryProfileInfo/MemoryProfileInfo/OUTPUT/MemoryProfileInfo.lib(MemoryProfileInfo.obj): defined in discarded section `COMMON' of Build/MdeModule/DEBUG_GCC49/X64/MdeModulePkg/Application/MemoryProfileInfo/MemoryProfileInfo/OUTPUT/MemoryProfileInfo.lib(MemoryProfileInfo.obj) `mNameString' referenced in section `.text.GetDriverNameString' of Build/MdeModule/DEBUG_GCC49/X64/MdeModulePkg/Application/MemoryProfileInfo/MemoryProfileInfo/OUTPUT/MemoryProfileInfo.lib(MemoryProfileInfo.obj): defined in discarded section `COMMON' of Build/MdeModule/DEBUG_GCC49/X64/MdeModulePkg/Application/MemoryProfileInfo/MemoryProfileInfo/OUTPUT/MemoryProfileInfo.lib(MemoryProfileInfo.obj) `mNameString' referenced in section `.text.DumpMemoryProfileDriverInfo' of Build/MdeModule/DEBUG_GCC49/X64/MdeModulePkg/Application/MemoryProfileInfo/MemoryProfileInfo/OUTPUT/MemoryProfileInfo.lib(MemoryProfileInfo.obj): defined in discarded section `COMMON' of Build/MdeModule/DEBUG_GCC49/X64/MdeModulePkg/Application/MemoryProfileInfo/MemoryProfileInfo/OUTPUT/MemoryProfileInfo.lib(MemoryProfileInfo.obj) make: *** [Build/MdeModule/DEBUG_GCC49/X64/MdeModulePkg/Application/MemoryProfileInfo/MemoryProfileInfo/DEBUG/MemoryProfileInfo.dll] Error 1 OvmfPkg: "ld" -o Build/OvmfX64/DEBUG_GCC49/X64/IntelFrameworkModulePkg/Universal/StatusCode/Pei/StatusCodePei/DEBUG/StatusCodePei.dll -nostdlib -n -q --gc-sections -z common-page-size=0x40 --entry _ModuleEntryPoint -u _ModuleEntryPoint -Map Build/OvmfX64/DEBUG_GCC49/X64/IntelFrameworkModulePkg/Universal/StatusCode/Pei/StatusCodePei/DEBUG/StatusCodePei.map -melf_x86_64 --oformat=elf64-x86-64 --start-group @Build/OvmfX64/DEBUG_GCC49/X64/IntelFrameworkModulePkg/Universal/StatusCode/Pei/StatusCodePei/OUTPUT/static_library_files.lst --end-group --defsym=PECOFF_HEADER_SIZE=0x228 --script=BaseTools/Scripts/GccBase.lds `gNullVaList' referenced in section `.text.AsciiBSPrint' of Build/OvmfX64/DEBUG_GCC49/X64/MdePkg/Library/BasePrintLib/BasePrintLib/OUTPUT/BasePrintLib.lib(PrintLib.obj): defined in discarded section `COMMON' of Build/OvmfX64/DEBUG_GCC49/X64/MdePkg/Library/BasePrintLib/BasePrintLib/OUTPUT/BasePrintLib.lib(PrintLib.obj) GNUmakefile:406: recipe for target 'Build/OvmfX64/DEBUG_GCC49/X64/IntelFrameworkModulePkg/Universal/StatusCode/Pei/StatusCodePei/DEBUG/StatusCodePei.dll' failed make: *** [Build/OvmfX64/DEBUG_GCC49/X64/IntelFrameworkModulePkg/Universal/StatusCode/Pei/StatusCodePei/DEBUG/StatusCodePei.dll] Error 1 -Jordan _______________________________________________ edk2-devel mailing list [email protected] https://lists.01.org/mailman/listinfo/edk2-devel
