Messages in this thread | | | Date | Thu, 03 Sep 2009 13:45:54 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: [tip:x86/asm] x86/i386: Make sure stack-protector segment base is cache aligned |
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On 09/03/09 13:26, H. Peter Anvin wrote: > With the new zero-based percpu segment, it seems we should be able to > subsume the stack protector into the percpu segment and reference both > via %gs -- we just have to reserve the first 24 bytes of the segment, > and being able to reduce the number of segments we need in the kernel is > good for multiple reasons. > > Tejun - am I missing something why that would be hard or impossible? >
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). * The i386 percpu %fs base is offset by -__per_cpu_start from the percpu variables, so we can directly refer to %fs:per_cpu__foo. I'm not sure what it would take to unify i386 to use the same scheme as x86-64.
Neither looks insoluble.
J
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