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SubjectRe: 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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