Re: [tip:x86/asm] x86/i386: Make sure stack-protector segment baseis cache aligned

From: H. Peter Anvin
Date: Thu Sep 03 2009 - 17:26:12 EST

On 09/03/2009 02:18 PM, Ingo Molnar wrote:
> * H. Peter Anvin <hpa@xxxxxxxxx> wrote:
>> On 09/03/2009 01:45 PM, Jeremy Fitzhardinge wrote:
>>> Two problems:
>>> * gcc generates %gs: references for stack-protector, but we use %fs
>>> for percpu data (because restoring %fs is faster if it's a null
>>> selector; TLS uses %gs). I guess we could use %fs if
>>> !CONFIG_CC_STACKPROTECTOR, or %gs if we are using it (though that
>>> has some fiddly ramifications for things like ptrace).
>> Well, by touching two segments we're getting the worst of both
>> worlds, so at least assuming some significant number of real-world
>> deployments use CC_STACKPROTECTOR, we really don't want to
>> pessimize that case too much.
> Fedora has stackprotector enabled so it's used in a widespread way.
> Ingo

I'm guessing most distros do, except perhaps embedded ones.

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