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    Subject[PATCH 4.4 101/160] powerpc/boot: Ensure _zimage_start is a weak symbol
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Joel Stanley <joel@jms.id.au>

    [ Upstream commit ee9d21b3b3583712029a0db65a4b7c081d08d3b3 ]

    When building with clang crt0's _zimage_start is not marked weak, which
    breaks the build when linking the kernel image:

    $ objdump -t arch/powerpc/boot/crt0.o |grep _zimage_start$
    0000000000000058 g .text 0000000000000000 _zimage_start

    ld: arch/powerpc/boot/wrapper.a(crt0.o): in function '_zimage_start':
    (.text+0x58): multiple definition of '_zimage_start';
    arch/powerpc/boot/pseries-head.o:(.text+0x0): first defined here

    Clang requires the .weak directive to appear after the symbol is
    declared. The binutils manual says:

    This directive sets the weak attribute on the comma separated list of
    symbol names. If the symbols do not already exist, they will be
    created.

    So it appears this is different with clang. The only reference I could
    see for this was an OpenBSD mailing list post[1].

    Changing it to be after the declaration fixes building with Clang, and
    still works with GCC.

    $ objdump -t arch/powerpc/boot/crt0.o |grep _zimage_start$
    0000000000000058 w .text 0000000000000000 _zimage_start

    Reported to clang as https://bugs.llvm.org/show_bug.cgi?id=38921

    [1] https://groups.google.com/forum/#!topic/fa.openbsd.tech/PAgKKen2YCY

    Signed-off-by: Joel Stanley <joel@jms.id.au>
    Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/powerpc/boot/crt0.S | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    --- a/arch/powerpc/boot/crt0.S
    +++ b/arch/powerpc/boot/crt0.S
    @@ -47,8 +47,10 @@ p_end: .long _end
    p_pstack: .long _platform_stack_top
    #endif

    - .weak _zimage_start
    .globl _zimage_start
    + /* Clang appears to require the .weak directive to be after the symbol
    + * is defined. See https://bugs.llvm.org/show_bug.cgi?id=38921 */
    + .weak _zimage_start
    _zimage_start:
    .globl _zimage_start_lib
    _zimage_start_lib:

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