linux-kernel - Re: Various x86 syscall mechanisms

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Date:	Fri, 20 Jun 2008 19:00:33 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Roland McGrath <roland@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Various x86 syscall mechanisms

H. Peter Anvin wrote:
> The reason is that not all 64-bit processors (i.e. K8) support a 
> 32-bit sysenter in long mode (i.e. with a 64-bit kernel.)

OK, so compat 32-bit processes would use syscall in that case, even if 
they wouldn't on a 32-bit kernel?

>   sysenter is *always* entered from the vdso, since the return address 
> is lost and this is also where a 64-bit kernel can put a syscall.
>
> There is no reason we couldn't do syscall for 32-bit native, but the 
> only processor that would benefit would be K7, and that's far enough 
> in the past that I don't think anyone cares enough.

OK, good.

> Note that long mode syscall is different from protected mode syscall, 
> even in 32-bit compatibility mode.  The long mode variant is a lot saner.

You mean that syscall arriving in long mode ring0 is saner than syscall 
arriving in protected mode ring0?

    J
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