Re: [PATCH 03/19] x86/dumpstack: remove unnecessary stack pointer arguments

From	Andy Lutomirski <luto@amacapital.net>
Newsgroups	linux.kernel
Subject	Re: [PATCH 03/19] x86/dumpstack: remove unnecessary stack pointer arguments
Date	2016-07-22 04:30 +0200
Message-ID	<rXynT-7XR-3@gated-at.bofh.it> (permalink)
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On Thu, Jul 21, 2016 at 6:41 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> On Thu, Jul 21, 2016 at 02:56:52PM -0700, Andy Lutomirski wrote:
>> On Thu, Jul 21, 2016 at 2:21 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>> > When calling show_stack_log_lvl() or dump_trace() with a regs argument,
>> > providing a stack pointer or frame pointer is redundant.
>> >
>>
>> > diff --git a/arch/x86/kernel/dumpstack_32.c b/arch/x86/kernel/dumpstack_32.c
>> > index 358fe1c..c533b8b 100644
>> > --- a/arch/x86/kernel/dumpstack_32.c
>> > +++ b/arch/x86/kernel/dumpstack_32.c
>> > @@ -122,7 +122,7 @@ void show_regs(struct pt_regs *regs)
>> >                 u8 *ip;
>> >
>> >                 pr_emerg("Stack:\n");
>> > -               show_stack_log_lvl(NULL, regs, &regs->sp, 0, KERN_EMERG);
>> > +               show_stack_log_lvl(NULL, regs, NULL, 0, KERN_EMERG);
>>
>> This is weird -- note the &.  You're at some risk of exposing a bug in
>> x86_32's kernel_stack_pointer() function, which is a mess.  (I don't
>> see why it's written the way it is -- the actual return stack pointer
>> given a pt_regs is quite well defined -- if regs->cs & 3 != 0, then
>> it's regs->sp, else it's &regs->sp.)
>>
>> That being said, this isn't a big deal, so:
>>
>> Reviewed-by: Andy Lutomirski <luto@kernel.org>
>>
>> If you want to make this all a bit more reliably on x86_32, you could
>> fix kernel_stack_pointer().
>
> Ok.  The whole '&regs->sp' thing threw me for a loop.  I have no idea
> what kernel_stack_pointer() is trying to do.  I just assumed it was
> correct.  I'll take a look at it and try to fix it in another patch.
>

On further inspection, it's probably correct except in cases of stack
overflow, so I wouldn't worry about it.  It's certainly
overcomplicated.

--Andy

Thread

[PATCH 03/19] x86/dumpstack: remove unnecessary stack pointer arguments Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-21 23:30 +0200
  Re: [PATCH 03/19] x86/dumpstack: remove unnecessary stack pointer arguments Andy Lutomirski <luto@amacapital.net> - 2016-07-22 00:00 +0200
    Re: [PATCH 03/19] x86/dumpstack: remove unnecessary stack pointer  arguments Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-22 03:50 +0200
      Re: [PATCH 03/19] x86/dumpstack: remove unnecessary stack pointer arguments Andy Lutomirski <luto@amacapital.net> - 2016-07-22 04:30 +0200
      Re: [PATCH 03/19] x86/dumpstack: remove unnecessary stack pointer arguments Brian Gerst <brgerst@gmail.com> - 2016-07-22 05:10 +0200

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