提交 80bb3ef1 编写于 作者: X Xiangyu Lu 提交者: Russell King

ARM: 8027/1: fix do_div() bug in big-endian systems

In big-endian systems, "%1" get the most significant part of the value, cause the instruction to get the wrong result.

When viewing ftrace record in big-endian ARM systems, we found that
the timestamp errors:

swapper-0   [001] 1325.970000:   0:120:R ==> [001]    16:120:R events/1
events/1-16 [001] 1325.970000:   16:120:S ==> [001]    0:120:R swapper
swapper-0   [000] 1325.1000000:  0:120:R   + [000]    15:120:R events/0
swapper-0   [000] 1325.1000000:  0:120:R ==> [000]    15:120:R events/0
swapper-0   [000] 1326.030000:   0:120:R   + [000]  1150:120:R sshd
swapper-0   [000] 1326.030000:   0:120:R ==> [000]  1150:120:R sshd

When viewed ftrace records, it will call the do_div(n, base) function, which achieved arch/arm/include/asm/div64.h in. When n = 10000000, base = 1000000, in do_div(n, base) will execute "umull %Q0, %R0, %1, %Q2".
Reviewed-by: NDave Martin <Dave.Martin@arm.com>
Reviewed-by: NNicolas Pitre <nico@linaro.org>
Cc: <stable@vger.kernel.org> # 2.6.20+
Signed-off-by: NAlex Wu <wuquanming@huawei.com>
Signed-off-by: NXiangyu Lu <luxiangyu@huawei.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>
上级 244b4783
......@@ -156,7 +156,7 @@
/* Select the best insn combination to perform the */ \
/* actual __m * __n / (__p << 64) operation. */ \
if (!__c) { \
asm ( "umull %Q0, %R0, %1, %Q2\n\t" \
asm ( "umull %Q0, %R0, %Q1, %Q2\n\t" \
"mov %Q0, #0" \
: "=&r" (__res) \
: "r" (__m), "r" (__n) \
......
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