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Re: [PATCH 2/6] x86/MPX: fix address size handling
- From: "Jan Beulich" <JBeulich at suse dot com>
- To: "H.J. Lu" <hjl dot tools at gmail dot com>
- Cc: <kirill dot yukhin at intel dot com>,"Binutils" <binutils at sourceware dot org>
- Date: Tue, 08 Oct 2013 16:20:35 +0100
- Subject: Re: [PATCH 2/6] x86/MPX: fix address size handling
- Authentication-results: sourceware.org; auth=none
- References: <5254349502000078000F9A3D at nat28 dot tlf dot novell dot com> <525435BC02000078000F9A51 at nat28 dot tlf dot novell dot com> <CAMe9rOrZuQRgcaUNgex=MDFjKYxsJimK1aCMqzEyM2XbZXCo4w at mail dot gmail dot com>
>>> 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...
Jan
>> + if (i.tm.cpu_flags.bitfield.cpumpx)
>> + {
>> + if (flag_code == CODE_64BIT && i.prefix[ADDR_PREFIX])
>> + as_warn (_("32-bit addressing is ignored in 64-bit MPX
> instructions"));
>> + else if (flag_code != CODE_16BIT
>> + ? i.prefix[ADDR_PREFIX]
>> + : i.mem_operands && !i.prefix[ADDR_PREFIX])
>> + as_bad (_("16-bit addressing isn't allowed in MPX instructions"));
>> + }
>>
>> /* Insert BND prefix. */
>> if (add_bnd_prefix
>>
>>
>>
>
>
>
> --
> H.J.