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

[Jeremy Fitzhardinge <jeremy@goop.org>]

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.

    J