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

[Jan Beulich <jbeulich@suse.com>]

On 11.01.2024 14:27, H.J. Lu wrote:
> On Thu, Jan 11, 2024 at 12:05 AM Jan Beulich <jbeulich@suse.com> wrote:
>>
>> 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).
> 
> Leave them as reserved.  We have plenty.

Hmm, the latter sentence doesn't fir what I meant: Why does / did
i386-reg.tbl not / never have those numbers? I could have seen that
they were there and then possibly have been purged, but even then
I would expect there a comment to have been left. So minimally what
I'd like to see / do is to add such comments.

Jan