• Dave Martin's avatar
    ARM: 6781/1: Thumb-2: Work around buggy Thumb-2 short branch relocations in gas · 6f685c5c
    Dave Martin authored
    Various binutils versions can resolve Thumb-2 branches to
    locally-defined, preemptible global symbols as short-range "b.n"
    branch instructions.
    
    This is a problem, because there's no guarantee the final
    destination of the symbol, or any candidate locations for a
    trampoline, are within range of the branch.  For this reason, the
    kernel does not support fixing up the R_ARM_THM_JUMP11 (102)
    relocation in modules at all, and it makes little sense to add
    support.
    
    The symptom is that the kernel fails with an "unsupported
    relocation" error when loading some modules.
    
    Until fixed tools are available, passing
    -fno-optimize-sibling-calls to gcc should prevent gcc generating
    code which hits this problem, at the cost of a bit of extra runtime
    stack usage in some cases.
    
    The problem is described in more detail at:
        https://bugs.launchpad.net/binutils-linaro/+bug/725126
    
    Only Thumb-2 kernels are affected.
    
    This patch adds a new CONFIG_THUMB2_AVOID_R_ARM_THM_JUMP11 config
    option which adds -fno-optimize-sibling-calls to CFLAGS_MODULE
    when building a Thumb-2 kernel.
    Signed-off-by: default avatarDave Martin <dave.martin@linaro.org>
    Acked-by: default avatarNicolas Pitre <nicolas.pitre@linaro.org>
    Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
    6f685c5c
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