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

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Message-ID: <42fcbe2c-8436-7f0a-054f-24ef66f57b7a@virtuozzo.com>
Date:	Wed, 8 Jun 2016 16:28:57 +0300
From:	Dmitry Safonov <dsafonov@...tuozzo.com>
To:	Oleg Nesterov <oleg@...hat.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 06/07/2016 01:43 AM, Oleg Nesterov wrote:
> 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().
>

Thanks, the idea of dropping PR_REG_SIZE looks better than my patch!
I'll try to drop those macros for the next revision.

-- 
Regards,
Dmitry Safonov