On Wed, 2009-10-21 at 23:21 +0800, Wu Zhangjin wrote:
> > +unsigned long ftrace_get_parent_addr(unsigned long self_addr,
> > + unsigned long parent,
> > + unsigned long parent_addr,
> > + unsigned long fp)
> > +{
> > + unsigned long sp, ip, ra;
> > + unsigned int code;
> > +
> > + /* move to the instruction "move ra, at" */
> > + ip = self_addr - 8;
> > +
> > + /* search the text until finding the "move s8, sp" instruction or
> > + * "s{d,w} ra, offset(sp)" instruction */
> > + do {
> > + ip -= 4;
> > + /* read the text we want to match */
> > + if (probe_kernel_read(&code, (void *)ip, 4)) {
> > + WARN_ON(1);
> > + panic("read the text failure\n");
> > + }
> > +
> > + /* if the first instruction above "move at, ra" is "move
> > + * s8(fp), sp", means the function is a leaf */
> > + if ((code & MOV_FP_SP) == MOV_FP_SP)
> > + return parent_addr;
> > + } while (((code & S_RA) != S_RA));
> > +
> > + sp = fp + (code & STACK_OFFSET_MASK);
> > + ra = *(unsigned long *)sp;
> > +
>
> Seems missed the fault protection here? is there a need? never met fault
> in this place and also the following two places, so, are we safe to
> remove all of the fault protection?
Is that "sp" basically already been check by the above
probe_kernel_read? If so, then it should be fine not to do the check
again.
-- Steve
>
> Regards
> Wu Zhangjin
>
> > + if (ra == parent)
> > + return sp;
> > + else
> > + panic
> > + ("failed on getting stack address of ra\n: addr: 0x%lx, code: 0x%x\n",
> > + ip, code);
> > +}
> > +
