undefined reference to `__umoddi3'解决办法

主机配置：ubuntu 11.10下利用交叉编译工具arm-linux-gcc编译内核；

目标板：AT91SAM9260

内核版本：linux-2.6.24

在编译内核linux-2.6.24的过程中遇到错误：

kernel/built-in.o: In function `getnstimeofday':
utsname_sysctl.c:(.text+0x23c64): undefined reference to `__umoddi3'
kernel/built-in.o: In function `do_gettimeofday':
utsname_sysctl.c:(.text+0x23d18): undefined reference to `__udivdi3'
utsname_sysctl.c:(.text+0x23d34): undefined reference to `__umoddi3'
kernel/built-in.o: In function `timekeeping_resume':
utsname_sysctl.c:(.text+0x23ec0): undefined reference to `__udivdi3'
utsname_sysctl.c:(.text+0x23ee0): undefined reference to `__umoddi3'
kernel/built-in.o: In function `update_wall_time':
utsname_sysctl.c:(.text+0x24640): undefined reference to `__udivdi3'
utsname_sysctl.c:(.text+0x24660): undefined reference to `__umoddi3'
utsname_sysctl.c:(.text+0x246f4): undefined reference to `__udivdi3'
utsname_sysctl.c:(.text+0x24714): undefined reference to `__umoddi3'
make: *** [.tmp_vmlinux1] Error 1

网上查阅了，说是include/linux/time.h文件中函数timespec_add_ns()的loop循环在编译过程中被优化掉了。

static inline void timespec_add_ns(struct timespec *a, u64 ns)
{
	ns += a->tv_nsec;
	while(unlikely(ns >= NSEC_PER_SEC)) {
		ns -= NSEC_PER_SEC;
		a->tv_sec++;
	}
	a->tv_nsec = ns;
}

利用https://lkml.org/lkml/2008/2/22/464的patch，可以解决这个问题。打上patch之后的函数是：

static inline void timespec_add_ns(struct timespec *a, u64 ns)
{
	ns += a->tv_nsec;
	while(unlikely(ns >= NSEC_PER_SEC)) {
		/* The following asm() prevents the compiler from
		 * optimising this loop into a modulo operation.  */
		asm("" : "+r"(ns));

		ns -= NSEC_PER_SEC;
		a->tv_sec++;
	}
	a->tv_nsec = ns;
}

更改之后编译顺利通过。