From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Brian Gerst <brgerst@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] x86-64: Unify x86_*_percpu() functions.
Date: Sat, 27 Dec 2008 22:03:35 +1100 [thread overview]
Message-ID: <49560B87.8090407@goop.org> (raw)
In-Reply-To: <1230052506-5041-2-git-send-email-brgerst@gmail.com>
Brian Gerst wrote:
> Merge the 32-bit and 64-bit versions of these functions. Unlike 32-bit,
> the segment base is the current cpu's PDA instead of the offset from the
> original per-cpu area. This is because GCC hardcodes the stackprotector
> canary at %gs:40. Since the assembler is incapable of relocating against
> multiple symbols, the code ends up looking like:
>
> movq $per_cpu__var, reg
> subq $per_cpu__pda, reg
> movq %gs:(reg), reg
>
> This is still atomic since the offset is a constant (just calculated at
> runtime) and not dependant on the cpu number.
>
Yeah, it's a real pity we can't convince the linker to do this simple
computation as a single %gs:ADDR addressing mode. On the other hand, if
the compiler can reuse the computation of %reg 2-3 times, then the
generated code could well end up being denser.
J
next prev parent reply other threads:[~2008-12-27 11:03 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-12-23 17:15 [PATCH 1/3] x86-64: Convert the PDA to percpu Brian Gerst
2008-12-23 17:15 ` [PATCH 2/3] x86-64: Unify x86_*_percpu() functions Brian Gerst
2008-12-23 17:15 ` [PATCH 3/3] x86-64: Move cpu number from PDA to per-cpu and consolidate with 32-bit Brian Gerst
2008-12-27 11:03 ` Jeremy Fitzhardinge [this message]
2008-12-27 11:09 ` [PATCH 2/3] x86-64: Unify x86_*_percpu() functions Ingo Molnar
2008-12-27 11:20 ` Jeremy Fitzhardinge
2008-12-27 10:41 ` [PATCH 1/3] x86-64: Convert the PDA to percpu Ingo Molnar
2008-12-27 15:30 ` Brian Gerst
2008-12-27 15:53 ` Ingo Molnar
2008-12-27 17:16 ` Brian Gerst
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