Hi. 2018-07-06 19:41 GMT+09:00 Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>: > On Fri, Jul 06, 2018 at 03:37:58PM +0900, Masahiro Yamada wrote: >> >> > > Also see https://bugzilla.kernel.org/show_bug.cgi?id=200385 , >> >> > > >> >> > > 0a1756bd2897951c03c1cb671bdfd40729ac2177 is acting up >> >> > > too with the same symptoms >> >> > >> >> > I tracked it down to -flto in LDFLAGS. I'll look more into this. >> >> >> >> -flto in LDFLAGS screws up this part of paging_prepare(): >> > >> > +Masahiro, Michal. >> > >> > I've got it wrong. *Any* LDFLAGS option passed to make this way: >> > >> > make LDFLAGS="..." >> > >> > would cause a issue. Even empty. >> > >> > It overrides all assignments to the variable in the makefile. >> > As result the image is built without -pie and linker doesn't generate >> > position independed code. >> > >> > Looks like the patch below helps, but my make-fu is poor. >> > I don't see many override directives in kernel makefiles. >> > It makes me think that there's a better way to fix this. >> > >> > Hm? >> >> >> LDFLAGS is for internal-use. >> Please do not override it from the command line. > > Can we generate a build error if a user try to override LDFLAGS, CFLAGS or > other critical internal-use-only variables? Yes, Make can check where variables came from. > This breakage was rather hard to debug. We need to have some kind of > fail-safe for the future. > >> You want to pass your own linker flags >> for building vmlinux and modules, >> but do not want to pass them to >> the decompressor (arch/x86/boot/compressed). >> >> Correct? > > I personally don't think that changing compiler/linker options for kernel > build is good idea in general. > >> Kbuild provides a way for users >> to pass additional linker flags to modules. >> (LDFLAGS_MODULE) >> >> >> But, there is no way to do that for vmlinux. >> >> It is easy to support it, though. >> >> https://patchwork.kernel.org/patch/10510833/ >> >> If this is the one you want, I can merge this. >> >> >> make LDFLAGS_KERNEL=... LDFLAGS_MODULE=... >> will allow you to append linker flags. > > Okay. It makes me wounder if we should taint kernel in such cases? > Custom compiler/linker flags are risky and can lead to weird bugs. OK. So, what problem are we discussing? > I've got it wrong. *Any* LDFLAGS option passed to make this way: > > make LDFLAGS="..." In your previous mail, I thought you were asking me how to pass custom linker flags. If not, we do not need to think about that case. Just say "Do not do that". -- Best Regards Masahiro Yamada -- To unsubscribe from this list: send the line "unsubscribe linux-x86_64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
