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问题代码

ktime_t calltime, delta, rettime; unsigned long long duration; calltime = ktime_get();/*获取当前时间*/rettime = ktime_get();/*计算时间差 ktime_sub(A,B) 计算A-B的时间差 返回纳秒*/delta = ktime_sub(rettime,calltime);/*转换成微秒*/duration = (unsigned long long) ktime_to_ns(delta) >> 10;printk("[%s] running %lld  usecs %d ms at %d\n",__FUNCTION__, duration,(unsigned int)(duration/1000),__LINE__);

编译出错

/rk3288_pad/kernel/drivers/input/sensors/sensor-dev.c:505: undefined reference to `__aeabi_uldivmod'/data/weiqifa/rk3288_pad/kernel/drivers/input/sensors/sensor-dev.c:529: undefined reference to `__aeabi_uldivmod'Makefile:997: recipe for target 'vmlinux' failedmake: *** [vmlinux] Error 1

原因

在大多数32位CPU上，必须使用慢库函数实现64位除法。为了防止编译器生成非常慢的代码，Linux不实现这些功能。

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