On Thu, Jul 12, 2018 at 4:20 PM Andy Lutomirski <[email protected]> wrote: > > > On Jul 12, 2018, at 3:06 PM, H. Peter Anvin <[email protected]> wrote: > > > >> On 07/12/18 13:37, Alistair Strachan wrote: > >>> On Thu, Jul 12, 2018 at 1:25 PM H. Peter Anvin <[email protected]> wrote: > >>>> On 07/12/18 13:10, Alistair Strachan wrote: > >>>> The vdso{32,64}.so can fail to link with CC=clang when clang tries to > >>>> find a suitable GCC toolchain to link these libraries with. > >>>> > >>>> /usr/bin/ld: arch/x86/entry/vdso/vclock_gettime.o: > >>>> access beyond end of merged section (782) > >>>> > >>>> This happens because the host environment leaked into the cross > >>>> compiler environment due to the way clang searches for suitable GCC > >>>> toolchains. > >>>> > >>> > >>> Is this another clang bug that you want a workaround for in the kernel? > >> > >> Clang is a retargetable compiler (specified with --target=<something>) > >> and so it has a mechanism for searching for suitable binutils (from > >> another "GCC toolchain") to perform assembly and linkage. This > >> mechanism relies on both --target and --gcc-toolchain when > >> cross-compiling, otherwise it will fall back to searching /usr. > >> > >> The --target and --gcc-toolchain flags are already specified correctly > >> in the top level Makefile, but the vdso Makefile rolls its own linker > >> flags and doesn't use KBUILD_CFLAGS. Therefore, these flags get > >> incorrectly dropped from the vdso $CC link command line, and an > >> inconsistency is created between the "GCC toolchain" used to generate > >> the objects for the vdso, and the linker used to link them. > >> > > > > It sounds like there needs to be a more fundamental symbol than > > KBUILD_CFLAGS to contain these kinds of things. > > How about $(CC)?
I'm guessing, but I think this wasn't done originally because CC is something the user might reasonably specify on the command line (the other bit comes from CROSS_COMPILE), so doing this via CC would require us to override the CC passed in on the command line. Not sure how to do that, since the vdso makefile is executed with a submake, so the usual "override CC := $(CC) something else" followed by "export CC" doesn't work.
