From: "H. Peter Anvin" <hpa@zytor.com>
To: linux-kernel@vger.kernel.org
Subject: Re: AMD64: 64 bit kernel 32 bit userland - some pending questions
Date: Tue, 6 Jun 2006 21:08:26 -0700 (PDT) [thread overview]
Message-ID: <e65jfq$m6v$1@terminus.zytor.com> (raw)
In-Reply-To: 787b0d920606062011j21083e80v659228a7565ecfab@mail.gmail.com
Followup to: <787b0d920606062011j21083e80v659228a7565ecfab@mail.gmail.com>
By author: "Albert Cahalan" <acahalan@gmail.com>
In newsgroup: linux.dev.kernel
>
> The bigger problem is that 32-bit code has fewer CPU registers.
> (nobody has done an ILP32 ABI for long mode) This is slow.
>
The issue isn't the ABI, the issue is that the processor doesn't
support it, since some of the opcodes mean different things in 16-,
32- and 64-bit mode. The opcodes which access the high half of the
register sets (REX prefixes) in 64-bit mode are INC and DEC
instructions in 16- and 32-bit mode.
AMD was apparently considering adding a "REX32" mode at some point,
but rather predictably noone was interested enough to make it
worthwhile.
-hpa
next prev parent reply other threads:[~2006-06-07 4:08 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-06-07 3:11 AMD64: 64 bit kernel 32 bit userland - some pending questions Albert Cahalan
2006-06-07 4:08 ` H. Peter Anvin [this message]
-- strict thread matches above, loose matches on Subject: below --
2006-06-06 9:34 Thomas Glanzmann
2006-06-06 10:42 ` Andi Kleen
2006-06-06 10:49 ` Thomas Glanzmann
2006-06-06 11:51 ` Rafael J. Wysocki
2006-06-06 11:55 ` Andi Kleen
2006-06-06 11:56 ` Marcus Meissner
2006-06-06 12:11 ` Rafael J. Wysocki
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