linux-kernel - Re: [PATCH] xtensa: improve stack dumping

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Message-ID: <20191107143810.oon6bj7dc7xqcyxe@pathway.suse.cz>
Date:   Thu, 7 Nov 2019 15:38:10 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Max Filippov <jcmvbkbc@...il.com>
Cc:     Joe Perches <joe@...ches.com>,
        "open list:TENSILICA XTENSA PORT (xtensa)" 
        <linux-xtensa@...ux-xtensa.org>, Chris Zankel <chris@...kel.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Dmitry Safonov <dima@...sta.com>
Subject: Re: [PATCH] xtensa: improve stack dumping

On Wed 2019-11-06 16:21:51, Max Filippov wrote:
> On Wed, Nov 6, 2019 at 2:34 PM Joe Perches <joe@...ches.com> wrote:
> > > @@ -512,10 +510,12 @@ void show_stack(struct task_struct *task, unsigned long *sp)
> > >       for (i = 0; i < kstack_depth_to_print; i++) {
> > >               if (kstack_end(sp))
> > >                       break;
> > > -             pr_cont(" %08lx", *sp++);
> > > +             sprintf(buf + (i % 8) * 9, " %08lx", *sp++);
> > >               if (i % 8 == 7)
> > > -                     pr_cont("\n");
> > > +                     pr_info("%s\n", buf);
> > >       }
> > > +     if (i % 8)
> > > +             pr_info("%s\n", buf);
> >
> > Could this be done using hex_dump_to_buffer
> > by precalculating kstack_end ?
> 
> I've got this, but it doesn't look very attractive to me:
> 
> void show_stack(struct task_struct *task, unsigned long *sp)
> {
>         unsigned long *stack;
>         int len;
> 
>         if (!sp)
>                 sp = stack_pointer(task);
>         stack = sp;
> 
>         len = min((-(unsigned long)stack) & (THREAD_SIZE - 4),
>                   kstack_depth_to_print * 4ul);
> 
>         pr_info("Stack:\n");
> 
>         for (; len > 0; len -= 32) {
>                 char buf[9 * 8 + 1];
> 
>                 hex_dump_to_buffer(sp, min(len, 32), 32, 4,
>                                    buf, sizeof(buf), false);
>                 pr_info(" %08lx:  %s\n", (unsigned long)sp, buf);
>                 sp += 8;
>         }

I wonder if the cycle actually could get replaced by a single call:

	print_hex_dump(KERN_INFO, "", DUMP_PREFIX_OFFSET,
		       16, 1, sp, len, false);

print_hex_dump() currently does not allow to print 8 bytes per-line.
Either 16 is acceptable or hex_dump() function could be updated.

Best Regards,
Petr