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.
