• Herton Ronaldo Krzesinski's avatar
    mtd: nandsim: don't open code a do_div helper · 596fd462
    Herton Ronaldo Krzesinski authored
    We don't need to open code the divide function, just use div_u64 that
    already exists and do the same job. While this is a straightforward
    clean up, there is more to that, the real motivation for this.
    
    While building on a cross compiling environment in armel, using gcc
    4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5), I was getting the following build
    error:
    
    ERROR: "__aeabi_uldivmod" [drivers/mtd/nand/nandsim.ko] undefined!
    
    After investigating with objdump and hand built assembly version
    generated with the compiler, I narrowed __aeabi_uldivmod as being
    generated from the divide function. When nandsim.c is built with
    -fno-inline-functions-called-once, that happens when
    CONFIG_DEBUG_SECTION_MISMATCH is enabled, the do_div optimization in
    arch/arm/include/asm/div64.h doesn't work as expected with the open
    coded divide function: even if the do_div we are using doesn't have a
    constant divisor, the compiler still includes the else parts of the
    optimized do_div macro, and translates the divisions there to use
    __aeabi_uldivmod, instead of only calling __do_div_asm -> __do_div64 and
    optimizing/removing everything else out.
    
    So to reproduce, gcc 4.6 plus CONFIG_DEBUG_SECTION_MISMATCH=y and
    CONFIG_MTD_NAND_NANDSIM=m should do it, building on armel.
    
    After this change, the compiler does the intended thing even with
    -fno-inline-functions-called-once, and optimizes out as expected the
    constant handling in the optimized do_div on arm. As this also avoids a
    build issue, I'm marking for Stable, as I think is applicable for this
    case.
    Signed-off-by: default avatarHerton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
    Cc: stable@vger.kernel.org
    Acked-by: default avatarNicolas Pitre <nico@linaro.org>
    Signed-off-by: default avatarArtem Bityutskiy <artem.bityutskiy@linux.intel.com>
    Signed-off-by: default avatarDavid Woodhouse <David.Woodhouse@intel.com>
    596fd462
nandsim.c 66.8 KB