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
> /* 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"
> @@ -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.
> +#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"
> + 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 :)
johannes
