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

[Jan Beulich <jbeulich@suse.com>]

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).

Jan