• Alistair Strachan's avatar
    x86: vdso: Use $LD instead of $CC to link · 379d98dd
    Alistair Strachan authored
    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.
    
    Clang is a retargetable compiler, and each invocation of it must provide
    --target=<something> --gcc-toolchain=<something> to allow it to find the
    correct binutils for cross compilation. These flags had been added to
    KBUILD_CFLAGS, but the vdso code uses CC and not KBUILD_CFLAGS (for various
    reasons) which breaks clang's ability to find the correct linker when cross
    compiling.
    
    Most of the time this goes unnoticed because the host linker is new enough
    to work anyway, or is incompatible and skipped, but this cannot be reliably
    assumed.
    
    This change alters the vdso makefile to just use LD directly, which
    bypasses clang and thus the searching problem. The makefile will just use
    ${CROSS_COMPILE}ld instead, which is always what we want. This matches the
    method used to link vmlinux.
    
    This drops references to DISABLE_LTO; this option doesn't seem to be set
    anywhere, and not knowing what its possible values are, it's not clear how
    to convert it from CC to LD flag.
    Signed-off-by: default avatarAlistair Strachan <astrachan@google.com>
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Acked-by: default avatarAndy Lutomirski <luto@kernel.org>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: kernel-team@android.com
    Cc: joel@joelfernandes.org
    Cc: Andi Kleen <andi.kleen@intel.com>
    Link: https://lkml.kernel.org/r/20180803173931.117515-1-astrachan@google.com
    379d98dd
Makefile 5.92 KB