Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel os linux

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: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Nicolas Pitre <nico@linaro.org>
Cc: <stable@vger.kernel.org> # 2.6.20+
Signed-off-by: Alex Wu <wuquanming@huawei.com>
Signed-off-by: Xiangyu Lu <luxiangyu@huawei.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

authored by

Xiangyu Lu and committed by
Russell King
80bb3ef1 244b4783

+1 -1
+1 -1
arch/arm/include/asm/div64.h
··· 156 156 /* Select the best insn combination to perform the */ \ 157 157 /* actual __m * __n / (__p << 64) operation. */ \ 158 158 if (!__c) { \ 159 - asm ( "umull %Q0, %R0, %1, %Q2\n\t" \ 159 + asm ( "umull %Q0, %R0, %Q1, %Q2\n\t" \ 160 160 "mov %Q0, #0" \ 161 161 : "=&r" (__res) \ 162 162 : "r" (__m), "r" (__n) \