Re: RFA: New port: ia64-hp-openvms - the stub

[Tristan Gingold <gingold at adacore dot com>]

On Feb 24, 2012, at 11:46 AM, Pedro Alves wrote:

>>>>>> +#if 1
>>>>>> +      /* What a mess.  Gdb and linux expects bsp to point after the current
>>>>>> +         register frame.  Adjust.  */
>>>>> 
>>>>> What does this mean?  Are we committing to a hack that will make our
>>>>> lives hard when we want to fix it?
>>>> 
>>>> I have updated the comment.  Currently, ia64-tdep.c follows the Linux convention, and we don't want to change that.  So the BSP has to be adjusted.
>>> 
>>> Why don't we want to change it?
>> 
>> I think it's too late.  That would be a change in gdbserver and other stubs, so it would break compatibility.  
> 
> We have ways to make it happen without breaking other stubs.  The question is what is the
> right thing to do.

I am not sure that modifying the convention of BSP is the right thing to do.

> Is this really Linux specific?  We have ia64 hpux support as well.

AFAIU, hpux also follows the Linux convention.

> I take it libunwind must follow the same convention as well, and I hope a libunwind
> built on a Linux host doesn't behave different from a libunwind built on a
> different host.

That's correct.  libunwind convention matches the VMS one, and therefore ia64-tdep.c has to translate the convention.
See for example the case of UNW_IA64_AR_BSP in ia64-tdep.c:ia64_access_reg.

> The adjustment in the VMS stubs isn't that complex.
> 
> Hopefully it'll still be simple with infcalls in the game.  :-)  afaics, you're
> not undoing the adjustment on writes.

Correct. Writing this register is used only to implement inferior call, which is not yet implemented.  The user will never modify it
directly, as this value cannot be changed without modifying other registers.  HPUX even don't allow to modify it (for not so bad reasons).
Welcome in ia64 world!

Tristan.