From: "Jan Beulich" <JBeulich@suse.com>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: <kirill.yukhin@intel.com>,"Binutils" <binutils@sourceware.org>
Subject: Re: [PATCH 2/6] x86/MPX: fix address size handling
Date: Wed, 09 Oct 2013 07:30:00 -0000 [thread overview]
Message-ID: <5255221C02000078000F9DD2@nat28.tlf.novell.com> (raw)
In-Reply-To: <CAMe9rOo82eK4oS8YAPKS0DDRktyiCUc16OqxDH4ujihKjmA7vA@mail.gmail.com>
>>> On 08.10.13 at 17:32, "H.J. Lu" <hjl.tools@gmail.com> wrote:
> On Tue, Oct 8, 2013 at 8:20 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>>>> On 08.10.13 at 17:15, "H.J. Lu" <hjl.tools@gmail.com> wrote:
>>> On Tue, Oct 8, 2013 at 7:41 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>>> While address overrides are ignored in 64-bit mode (and hence shouldn't
>>>> result in an error), trying to use 16-bit addressing is documented to
>>>> result in #UD, and hence the assembler should reject the attempt.
>>>>
>>>> gas/
>>>> 2013-10-08 Jan Beulich <jbeulich@suse.com>
>>>>
>>>> * tc-i386.c (md_assemble): Alter address size checking for MPX
>>>> instructions.
>>>>
>>>> --- 2013-10-07/gas/config/tc-i386.c
>>>> +++ 2013-10-07/gas/config/tc-i386.c
>>>> @@ -3549,10 +3549,15 @@ md_assemble (char *line)
>>>> if (i.bnd_prefix && !i.tm.opcode_modifier.bndprefixok)
>>>> as_bad (_("expecting valid branch instruction after `bnd'"));
>>>>
>>>> - if (i.tm.cpu_flags.bitfield.cpumpx
>>>> - && flag_code == CODE_64BIT
>>>> - && i.prefix[ADDR_PREFIX])
>>>> - as_bad (_("32-bit address isn't allowed in 64-bit MPX instructions."));
>>>
>>> It is done on purpose. When 32-bit address prefix in 64-bit is ignored,
>>> MPX doesn't work correctly for x32.
>>
>> I don't understand: It _is_ being ignored by the hardware as per
>> the documentation. So x32 need to get along with that. Maybe
>> an example would help, so I could understand why you think
>> this _needs_ to be an error...
>>
>
> X32 won't work with MPX since hardware assumes pointer
> size is always 64 bit in 64-bit mode with or without address
> size prefix. MPX depends on correct pointer size to work.
> I don't want people to use MPX in x32 by accident.
This seems even more odd - why would x32 be excluded from
using MPX? Again - an example might help, as my understanding
so far was that the implicit zero extension of results of 32-bit
operations should guarantee the half width pointers to be quite
fine to use as full width values (i.e. in other memory operands
I don't see why you would want to use 32-bit addressing either,
except when the wraparound case matters, as might e.g. be
the case with EIP-relative addressing).
And in any case - the assembler shouldn't enforce policy, it
should only enforce architectural restrictions.
Bottom line - I continue to be convinced that the diagnostic
we talk about here ought to be a warning, not an error (at
least by default).
Jan
next prev parent reply other threads:[~2013-10-09 7:30 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-08 14:36 [PATCH 0/6] x86: various MPX fixes Jan Beulich
2013-10-08 14:41 ` [PATCH 1/6] x86/MPX: testsuite adjustments Jan Beulich
2013-10-08 14:41 ` [PATCH 2/6] x86/MPX: fix address size handling Jan Beulich
2013-10-08 15:15 ` H.J. Lu
2013-10-08 15:20 ` Jan Beulich
2013-10-08 15:32 ` H.J. Lu
2013-10-09 7:30 ` Jan Beulich [this message]
2013-10-09 15:45 ` H.J. Lu
2013-10-10 12:27 ` Jan Beulich
2013-10-10 15:18 ` H.J. Lu
2013-10-08 14:42 ` [PATCH 3/6] x86/MPX: suppress base/index swapping in Intel mode for bndmk, bndldx, and bndstx Jan Beulich
2013-10-08 15:16 ` H.J. Lu
2013-10-08 15:23 ` Jan Beulich
2013-10-08 15:34 ` H.J. Lu
2013-10-08 16:00 ` Jan Beulich
2013-10-08 16:19 ` H.J. Lu
2013-10-09 7:15 ` acceptance rules (was: Re: [PATCH 3/6] x86/MPX: suppress base/index swapping ...) Jan Beulich
2013-10-09 16:45 ` H.J. Lu
2013-10-08 14:43 ` [PATCH 4/6] x86/MPX: bndmk, bndldx, and bndstx only allow a memory operand Jan Beulich
2013-10-08 15:28 ` H.J. Lu
2013-10-09 7:24 ` Jan Beulich
2013-10-09 15:17 ` H.J. Lu
2013-10-08 14:43 ` [PATCH 5/6] x86/MPX: fix operand size handling Jan Beulich
2013-10-08 15:45 ` H.J. Lu
2013-10-09 7:36 ` Jan Beulich
2013-10-09 15:51 ` H.J. Lu
2013-10-10 13:14 ` Jan Beulich
2013-10-10 15:14 ` H.J. Lu
2013-10-12 15:58 ` H.J. Lu
2013-10-12 17:12 ` H.J. Lu
2013-10-08 14:44 ` [PATCH 6/6] x86/MPX: bndmk, bndldx, and bndstx don't allow RIP-relative addressing Jan Beulich
2013-10-08 16:13 ` H.J. Lu
2013-10-09 7:40 ` Jan Beulich
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=5255221C02000078000F9DD2@nat28.tlf.novell.com \
--to=jbeulich@suse.com \
--cc=binutils@sourceware.org \
--cc=hjl.tools@gmail.com \
--cc=kirill.yukhin@intel.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).