From: "H.J. Lu" <hjl.tools@gmail.com>
To: Roland McGrath <mcgrathr@google.com>
Cc: binutils@sourceware.org
Subject: Re: [PATCH] i386-dis: fix decoding of reserved "prefetch" encodings
Date: Tue, 07 Aug 2012 18:23:00 -0000 [thread overview]
Message-ID: <CAMe9rOpbJuVwhv42ufxKipMxGSHU7QiDRrV9gUMkqdQv8cX+dQ@mail.gmail.com> (raw)
In-Reply-To: <CAB=4xhrEY+cWK4vTKzPr7njQrYEKi8VGSVcvjSy0UGZxLHwQXA@mail.gmail.com>
On Tue, Aug 7, 2012 at 10:52 AM, Roland McGrath <mcgrathr@google.com> wrote:
> On Tue, Aug 7, 2012 at 10:34 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> Those are marked as NOPs in AMD manual and reserved in Intel
>> manual. I don't like "prefetch(bad)". I can live with "nop/reserved".
>
> Can you cite the manuals you are looking at?
>
> I'm looking at http://support.amd.com/us/Processor_TechDocs/24594_APM_v3.pdf
> on page 254:
> The reserved PREFETCH types do not result in an invalid-opcode
> exception if executed. Instead, for forward compatibility with
> future processors that may implement additional forms of the
> PREFETCH instruction, all reserved PREFETCH types are implemented
> as synonyms of the basic PREFETCH type (the PREFETCH instruction
> with type 000b).
> That says they are prefetch, not nop. That's for the 0f 0d set.
>
> For 0f 18, the same AMD manual's Table A-7 (page 430, in the "Group 16"
> row) says "NOP[4]" for these excess encodings but the footnote is:
> 4. Reserved prefetch encodings are aliases to the /0 encoding
> (PREFETCH Exclusive) for future compatibility.
> So these Intel reserved opcodes are in fact also prefetch on AMD, not nop,
> despite the appearance of "NOP" in the table grid.
>
> So it seems to me the mnemonic ought to have "prefetch" in it somewhere.
> How about "prefetch/reserved"?
>
Since it is marked as NOP in AMD table, I prefer nop. As for aliasing
to PREFETCH Exclusive. It is just an implementation detail. A future
processor may alias them to a different NOP, not necessarily
PREFETCH Exclusive.
--
H.J.
next prev parent reply other threads:[~2012-08-07 18:00 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-06 22:51 Roland McGrath
2012-08-07 17:36 ` H.J. Lu
2012-08-07 18:00 ` Roland McGrath
2012-08-07 18:23 ` H.J. Lu [this message]
2012-08-08 7:07 ` Roland McGrath
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAMe9rOpbJuVwhv42ufxKipMxGSHU7QiDRrV9gUMkqdQv8cX+dQ@mail.gmail.com \
--to=hjl.tools@gmail.com \
--cc=binutils@sourceware.org \
--cc=mcgrathr@google.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).