Why does MIPS/Linux always reserve 32 bytes in the top of each process's kernel stack space

[zhan rongkai <zhanrk@gmail.com>]

Hi, everyone:

Why does MIPS/Linux always reserve 32 bytes in the top of each
process's kernel stack space.

See arch/mips/kernel/process.c:

int copy_thread(int nr, unsigned long clone_flags, unsigned long usp,
        unsigned long unused, struct task_struct *p, struct pt_regs *regs)
{
        struct thread_info *ti = p->thread_info;
        struct pt_regs *childregs;
        long childksp;

        childksp = (unsigned long)ti + THREAD_SIZE - 32;
        ......
}

-- 
Rongkai Zhan