出现一个莫明奇妙的编译错误：
../../kernel/fork.c
At end of source: : internal error: Uncaught exception Assertion failed raised
at ../../../bril/optimiser/dominators.c:910 (in pass
cleanup_scalar_stores_nonopt during compilation of _copy_process).
Please submit a bug report with this message, the command line used,
type of machine and the output of the compiler when you add -ED -v
to the command line. Please also send us the pre-processed file that
is generated by the -ED option (the file generated is named
<original_filename>.i)
1 catastrophic error detected in the compilation of "../../kernel/fork.c".
Compilation aborted.
cc3089: fatal error: Compilation failed
Tool failed with exit/exception code: 1.
Build was unsuccessful.
注释掉所有代码，一步步往上添加，问题出在copy_process函数，进一步查找终于发现问题在于这个函数中的这个语句：
if (unlikely(!cpu_isset(task_cpu(p), p->cpus_allowed) ||
!cpu_online(task_cpu(p))))
set_task_cpu(p, smp_processor_id());
当不加这行时没有错误。当加上这个语句时，出现上述错误。
回顾一下unlikely的定义：
#define unlikely(x) expected_false(!!(x))
确实是做优化用的，既然此处编译不过，就去了它，改为：
if (/*unlikely(*/!cpu_isset(task_cpu(p), p->cpus_allowed) ||
!cpu_online(task_cpu(p))/*)*/)
set_task_cpu(p, smp_processor_id());