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

From: Jeremy Fitzhardinge
Date: Fri Sep 04 2009 - 12:04:36 EST

On 09/03/09 22:06, Tejun Heo wrote:
>>> Heh... here's a naive and hopeful plan. How about we beg gcc
>>> developers to allow different segment register and offset in newer gcc
>>> versions and then use the same one when building with the new gcc?
>>> This should solve the i386 problem too. It would be the best as we
>>> get to keep the separate segment register from the userland. Too
>>> hopeful?
>> I think it's possible to set the register in more recent gcc. Doing the
>> sane thing and having a symbol for an offset is probably worse.
> I was thinking about altering the build process so that we can use sed
> to substitute %gs:40 with %fs:40 while compiling. If it's already
> possible to override the register in more recent gcc, no need to go
> into that horror.

Ideally we'd like to get rid of the constant offset too. If we could
change it to %[fg]s:__gcc_stack_canary_offset on both 32-bit and 64-bit,
it would give us a lot more flexibility. __gcc_stack_canary_offset
could be weakly defined to 20/40 for backwards compatibility, but we
could override it to point to a normal percpu variable.

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