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Subject: Re: [PATCH v3 16/51] x86/32: put real return address on stack in
 entry code
To: Josh Poimboeuf <jpoimboe@redhat.com>
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Cc: Andy Lutomirski <luto@amacapital.net>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>,
        X86 ML <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Steven Rostedt <rostedt@goodmis.org>, Brian Gerst <brgerst@gmail.com>,
        Kees Cook <keescook@chromium.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Byungchul Park <byungchul.park@lge.com>,
        Nilay Vaish <nilayvaish@gmail.com>
From: "H. Peter Anvin" <hpa@zytor.com>
Message-ID: <495f58c1-d1f3-6259-1786-d1fc2e154587@zytor.com>
Date: Mon, 15 Aug 2016 12:22:33 -0700
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On 08/15/16 11:25, Josh Poimboeuf wrote:
> 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.
> 

So how is the stack terminated, and does things like kdb and kgdb need
modifications?  Or is there now a stack termination above the struct
pt_regs?

	-hpa