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Date: Mon, 15 Aug 2016 13:25:22 -0500
From: Josh Poimboeuf <jpoimboe@redhat.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andy Lutomirski <luto@amacapital.net>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>,
        X86 ML <x86@kernel.org>,
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        Frederic Weisbecker <fweisbec@gmail.com>,
        Byungchul Park <byungchul.park@lge.com>,
        Nilay Vaish <nilayvaish@gmail.com>
Subject: Re: [PATCH v3 16/51] x86/32: put real return address on stack in
 entry code
Message-ID: <20160815182522.6vjn6aheuiw65oca@treble>
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On Mon, Aug 15, 2016 at 11:04:42AM -0700, H. Peter Anvin wrote:
> On 08/15/16 08:09, Josh Poimboeuf wrote:
> > On Sun, Aug 14, 2016 at 12:31:47AM -0700, Andy Lutomirski wrote:
> >> On Fri, Aug 12, 2016 at 7:28 AM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> >>> This standardizes the stacks of idle tasks to be consistent with other
> >>> tasks on 32-bit.
> >>
> >> It might be nice to stick a ud2 or 1: hlt; jmp 1b or similar
> >> afterwards to make it clear that initial_code can't return.
> > 
> > Yeah, I'll do something like that.
> > 
> 
> "Standardizing the stack" how?  A zero on the stack terminates the stack
> trace.

Instead of zero, user tasks have a real return address at that spot.
This makes idle tasks consistent with that, so we have a well defined
"end of stack".  Also it makes the stack trace more useful since it
shows what entry code was involved in calling into C.

-- 
Josh