Re: [PATCH] opcodes: i386: fix dw2_regnum data type in reg_entry

[Jan Beulich <jbeulich@suse.com>]

On 11.01.2024 08:59, Kong, Lingling wrote:
> 
> 
>> -----Original Message-----
>> From: Jan Beulich <jbeulich@suse.com>
>> Sent: Thursday, January 11, 2024 3:43 PM
>> To: Kong, Lingling <lingling.kong@intel.com>
>> Cc: binutils@sourceware.org; Indu Bhagat <indu.bhagat@oracle.com>; Cui, Lili
>> <lili.cui@intel.com>; H.J. Lu <hjl.tools@gmail.com>; Hu, Lin1
>> <lin1.hu@intel.com>
>> Subject: Re: [PATCH] opcodes: i386: fix dw2_regnum data type in reg_entry
>>
>> On 11.01.2024 02:35, Kong, Lingling wrote:
>>>
>>>
>>>> -----Original Message-----
>>>> From: Jan Beulich <jbeulich@suse.com>
>>>> Sent: Tuesday, January 9, 2024 4:25 PM
>>>> To: Indu Bhagat <indu.bhagat@oracle.com>; Cui, Lili
>>>> <lili.cui@intel.com>; H.J. Lu <hjl.tools@gmail.com>; Kong, Lingling
>>>> <lingling.kong@intel.com>; Hu, Lin1 <lin1.hu@intel.com>
>>>> Cc: binutils@sourceware.org
>>>> Subject: Re: [PATCH] opcodes: i386: fix dw2_regnum data type in
>>>> reg_entry
>>>>
>>>> On 09.01.2024 02:12, Indu Bhagat wrote:
>>>>> The DWARF register numbers for the APX EGRPs start with 130.  The
>>>>> data type holding the same currently is signed char.
>>>>>
>>>>> ChangeLog:
>>>>> 	* opcodes/i386-opc.h (reg_entry): Bump to signed short.
>>>>
>>>> So yes, something needs doing. But there are further questions to be
>>>> raised to the original authors: Was the code tested at all in this
>>>> regard? Why do numbers start at 130, when according to i386-reg.tbl
>>>> 128 and 129 are unused (and would hence be more natural to [also] use)?
>>>
>>> This is because for some historical reasons, some numbers(126-129) have been
>> agreed to be reserved.
>>> Details can be found in https://groups.google.com/g/x86-64-
>> abi/c/GS8LZf5nQFk.
>>
>> I'm sorry, there are no details there. There's merely mention of these four being
>> reserved, without supplying any reason (historical or not).
> 
> Sorry, you could see https://gitlab.com/x86-psABIs/x86-64-ABI/-/commit/6207f9a2c0645f20a7ec591a09e4c382b1675784
> There are reserved  for Intel MPX (Memory Protection Extensions) provides 4 128-bit wide bound registers (reg{bnd0} - reg{bnd3}).

Then why aren't these marked that way? The commit introducing them to
opcodes used Dw2Inval, and it was never changed from that (i.e. there
wasn't even deliberate undoing with respective justification).

Jan