On Fri, 25 Oct 2024 18:22:29 +0900,
Johannes Berg wrote:
>
> On Thu, 2024-10-24 at 21:09 +0900, Hajime Tazaki wrote:
> > Since ptrace facility isn't used under !MMU of UML, there is different
> > code path to invoke proceeses/threads; on an entry to the syscall
>
> typo: processes
thanks. (I thought checkpatch.pl detects them..)
> > /* Called magically, see new_thread_handler above */
> > static void fork_handler(void)
> > {
> > - schedule_tail(current->thread.prev_sched);
> > + if (current->thread.prev_sched != NULL)
>
> nit: no need for "!= NULL"
will fix it.
> > @@ -134,6 +138,21 @@ static void fork_handler(void)
> >
> > current->thread.prev_sched = NULL;
> >
> > +#ifndef CONFIG_MMU
> > + /*
> > + * This fork can only come from libc's vfork, which
> > + * does this:
> > + * popq %%rdx;
> > + * call *%0; // vsyscall
> > + * pushq %%rdx;
> > + * %rdx stores the return address which is stored
> > + * at pt_regs[HOST_IP] at the moment. We still
> > + * need to pop the pushed address by "call" though,
> > + * so this is what this next line does.
> > + */
> > + if (current->thread.regs.regs.gp[HOST_ORIG_AX] == __NR_vfork)
> > + current->thread.regs.regs.gp[REGS_SP_INDEX] += 8;
> > +#endif
>
> Kind of ugly ... but I guess not much choice.
(indeed)
> > +#ifndef CONFIG_MMU
> > + current_top_of_stack = task_top_of_stack(to);
> > + current_ptregs = (long)task_pt_regs(to);
> > +
> > + if ((to->thread.regs.regs.gp[FS_BASE / sizeof(unsigned long)] == 0)
> > + || (to->mm == NULL))
>
> Put || on the previous line, "!to->mm"
will fix it.
> > + return;
> > +
> > + // rkj: this changes the FS on every context switch
>
> Not sure we're allowing C99 comments yet, and there shouldn't be a "rkj"
> tag either :)
this is my mistake; forgot to remove those private tags.
will fix it.
-- Hajime
