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[PATCH 2/6] x86/MPX: fix address size handling

Jan Beulich JBeulich@suse.com
Tue Oct 8 15:20:00 GMT 2013 
>>> 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.
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