Messages in this thread | | | Date | Wed, 21 Oct 2009 11:00:53 -0700 | From | Arjan van de Ven <> | Subject | Re: Unnecessary overhead with stack protector. |
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On Wed, 21 Oct 2009 10:50:02 -0500 Eric Sandeen <sandeen@redhat.com> wrote:
> Ingo Molnar wrote: > > (Cc:-ed Arjan too.) > > > > * Dave Jones <davej@redhat.com> wrote: > > > >> 113c5413cf9051cc50b88befdc42e3402bb92115 introduced a change that > >> made CC_STACKPROTECTOR_ALL not-selectable if someone enables > >> CC_STACKPROTECTOR. > >> > >> We've noticed in Fedora that this has introduced noticable > >> overhead on some functions, including those which don't even have > >> any on-stack variables. > >> > >> According to the gcc manpage, -fstack-protector will protect > >> functions with as little as 8 bytes of stack usage. So we're > >> introducing a huge amount of overhead, to close a small amount of > >> vulnerability (the >0 && <8 case). > >> > >> The overhead as it stands right now means this whole option is > >> unusable for a distro kernel without reverting the above commit. > > > > Exactly what workload showed overhead, and how much? > > > > Ingo > > I had xfs blowing up pretty nicely; granted, xfs is not svelte but it > was never this bad before. >
do you have any indication that SP actually increases the stack footprint by that much? it's only a few bytes....
-- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org
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