From: Andy Lutomirski <luto@amacapital.net>
To: Brian Gerst <brgerst@gmail.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
X86 ML <x86@kernel.org>, Steven Rostedt <rostedt@goodmis.org>,
Andi Kleen <andi@firstfloor.org>
Subject: Re: Why is irq_stack_union a union?
Date: Tue, 1 Sep 2015 14:42:28 -0700 [thread overview]
Message-ID: <CALCETrVME33SKP9sURj5S_1sFmLH5csHCHBJZppCLY3uncXrOA@mail.gmail.com> (raw)
In-Reply-To: <CAMzpN2hDmLyW2rC6kA2xc609t2LRAAZrSRb5gf+D=Ami30jCCg@mail.gmail.com>
On Mon, Aug 31, 2015 at 8:55 PM, Brian Gerst <brgerst@gmail.com> wrote:
> On Mon, Aug 31, 2015 at 6:01 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>> On Mon, Aug 31, 2015 at 2:47 PM, Brian Gerst <brgerst@gmail.com> wrote:
>>> On Mon, Aug 31, 2015 at 5:00 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>>>> Why not just a struct? Also, why is this all tangled up in gsbase initialization?
>>>
>>> It has to do with the fact that the GCC stackprotector is hardcoded to
>>> look for the canary at %gs:40. Since we also use %gs for the percpu
>>> segment, we have to make sure that the canary is placed at the start
>>> of the percpu section. Overlaying it onto the bottom of the IRQ stack
>>> and was the most convenient way to do it, with a side benefit that
>>> overflowing the stack will trip the canary.
>>
>> Would a struct not make more sense, then?
>
> Why would it? A union shows the overlay better.
I guess you're thinking of it as an overlay and I'm thinking of it as
the layout being the IRQ stack directly above the stack canary.
--Andy
>
> --
> Brian Gerst
--
Andy Lutomirski
AMA Capital Management, LLC
prev parent reply other threads:[~2015-09-01 21:42 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-31 21:00 Why is irq_stack_union a union? Andy Lutomirski
2015-08-31 21:47 ` Brian Gerst
2015-08-31 22:01 ` Andy Lutomirski
2015-09-01 3:55 ` Brian Gerst
2015-09-01 21:42 ` Andy Lutomirski [this message]
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