Messages in this thread | | | From | Andy Lutomirski <> | Date | Tue, 1 Sep 2015 14:42:28 -0700 | Subject | Re: Why is irq_stack_union a union? |
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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
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