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    powerpc: Fix COFF zImage booting on old powermacs · c7c77cdf
    Paul Mackerras authored
    [ Upstream commit 5564597d51c8ff5b88d95c76255e18b13b760879 ]
    
    Commit 6975a783 ("powerpc/boot: Allow building the zImage wrapper
    as a relocatable ET_DYN", 2011-04-12) changed the procedure descriptor
    at the start of crt0.S to have a hard-coded start address of 0x500000
    rather than a reference to _zimage_start, presumably because having
    a reference to a symbol introduced a relocation which is awkward to
    handle in a position-independent executable.  Unfortunately, what is
    at 0x500000 in the COFF image is not the first instruction, but the
    procedure descriptor itself, that is, a word containing 0x500000,
    which is not a valid instruction.  Hence, booting a COFF zImage
    results in a "DEFAULT CATCH!, code=FFF00700" message from Open
    Firmware.
    
    This fixes the problem by (a) putting the procedure descriptor in the
    data section and (b) adding a branch to _zimage_start as the first
    instruction in the program.
    
    Fixes: 6975a783
    
     ("powerpc/boot: Allow building the zImage wrapper as a relocatable ET_DYN")
    Signed-off-by: default avatarPaul Mackerras <paulus@ozlabs.org>
    Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
    Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
    c7c77cdf