linux-kernel - Re: [PATCH 4/6] x86/coredump: use core regs, rather that TIF

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Date:	Tue, 7 Jun 2016 00:43:36 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Dmitry Safonov <dsafonov@...tuozzo.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...hat.com,
	luto@...capital.net, tglx@...utronix.de, hpa@...or.com,
	x86@...nel.org, 0x7f454c46@...il.com, gorcunov@...nvz.org,
	xemul@...tuozzo.com, khorenko@...tuozzo.com,
	Andy Lutomirski <luto@...nel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 4/6] x86/coredump: use core regs, rather that TIF_IA32
	flag

On 06/06, Oleg Nesterov wrote:
>
> On 06/01, Dmitry Safonov wrote:
> >
> >  static int fill_thread_core_info(struct elf_thread_core_info *t,
> >  				 const struct user_regset_view *view,
> > -				 long signr, size_t *total)
> > +				 long signr, size_t *total,
> > +				 struct pt_regs *regs __maybe_unused)
> >  {
> >  	unsigned int i;
> >
> > @@ -1652,11 +1653,11 @@ static int fill_thread_core_info(struct elf_thread_core_info *t,
> >  	 */
> >  	fill_prstatus(&t->prstatus, t->task, signr);
> >  	(void) view->regsets[0].get(t->task, &view->regsets[0],
> > -				    0, PR_REG_SIZE(t->prstatus.pr_reg),
> > +				    0, PR_REG_SIZE(t->prstatus.pr_reg, regs),
>
> Hmm. I don't understand this... Note that this "regs" argument has nothing
> to do with t->task if the process is multithreaded,
>
> > @@ -1772,7 +1773,8 @@ static int fill_note_info(struct elfhdr *elf, int phdrs,
> >  	 * Now fill in each thread's information.
> >  	 */
> >  	for (t = info->thread; t != NULL; t = t->next)
> > -		if (!fill_thread_core_info(t, view, siginfo->si_signo, &info->size))
> > +		if (!fill_thread_core_info(t, view, siginfo->si_signo,
> > +					&info->size, regs))
>
> fill_note_info(..., args) is called with args = task_pt_regs(dumper_thread).

forgot to mention... yes, this matches the fact we use a single "view"
for all threads, and we get it via task_user_regset_view(dump_task).

But this change (imo) adds even more confusion, and without the next patch
the logic looks "obviously wrong", becauase PR_REG_SIZE/etc look at
dumper_thread->cs while task_user_regset_view() checks thread flags.

Anyway I fail to understand these macros... Say, PR_REG_SIZE(S). Can't we
kill it and use regsets[0].n * regsets[0].size instead ? These numbers
should match whatever we do, if we call ->get().

Oleg.