On Mon, Jan 6, 2020 at 5:29 AM Matthias Klose <d...@ubuntu.com> wrote: > > On 06.01.20 13:30, Wilco Dijkstra wrote: > > On 06.01.20 11:03, Andrew Pinski wrote: > >> +GCC > >> > >> On Mon, Jan 6, 2020 at 1:52 AM Matthias Klose <d...@ubuntu.com> wrote: > >>> > >>> In an archive test rebuild with binutils and GCC trunk, I see a lot of > >>> build > >>> failures on both aarch64-linux-gnu and arm-linux-gnueabihf failing with > >>> "multiple definition of symbols" when linking executables, e.g. > >> > >> THIS IS NOT A BINUTILS OR GCC BUG. > >> GCC changed the default to -fno-common. > >> It seems like for some reason, your non-aarch64/arm builds had changed > >> the default back to being with -fcommon turned on. > > > >> what would that be? I'm not aware of any active change doing that. > >> Packages > >> build on x86, ppc64el and s390x at least. > > > > Well if you want to build old archived code using latest GCC then you may > > need to > > force -fcommon just like you need to add many warning disables. Maybe you > > were > > using an older GCC for the other targets? As Andrew notes, this isn't > > Arm-specific. > > found out about why. Started the test rebuild with trunk 20191219, then gave > back all build failures yesterday with trunk 20200104. And I saw most of the > armhf/arm64 ftbfs when I retriggered failing builds. To get consistent > results > I should finish that test rebuild with the -fno-common change reverted. > > However, this is an undocumented change in the current NEWS, and seeing > literally hundreds of package failures, I doubt that's the right thing to do, > at > least without any deprecation warning first. Could that be handled, > deprecating > in GCC 10 first, and the changing that for GCC 11?
It is hard to get a warning for things like this. Also the documentation for -fcommon was changed and made clear for 8.1.0[1] that the default might be changing because it is not required by ISO C. "This is the behavior specified by -fcommon, and is the default for GCC on most targets. On the other hand, this behavior is not required by ISO C, ..." -fno-common: "This inhibits the merging of tentative definitions by the linker so you get a multiple-definition error if the same variable is defined in more than one compilation unit. " So I think it was "deprecated" in GCC for the last 2 major releases. Though nobody reads the manual these days. Thanks, Andrew Pinski [1] https://gcc.gnu.org/onlinedocs/gcc-8.1.0/gcc/Code-Gen-Options.html#index-fno-common > > Matthias
