diff options
author | Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com> | 2012-05-16 16:21:52 -0300 |
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committer | David Woodhouse <David.Woodhouse@intel.com> | 2012-07-06 16:59:33 +0100 |
commit | 596fd46268634082314b3af1ded4612e1b7f3f03 (patch) | |
tree | eaec1116cfc24d25b54912dcd71f34f761f74491 /Documentation | |
parent | 021796b892dcad45743f3196e3eef7222870dd55 (diff) |
mtd: nandsim: don't open code a do_div helper
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: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
Cc: stable@vger.kernel.org
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Diffstat (limited to 'Documentation')
0 files changed, 0 insertions, 0 deletions