Re: Assuming types for PC

[Pedro Alves <palves@redhat.com>]

On 06/11/2013 10:21 AM, Pedro Alves wrote:
>>>  Overall I think the test is too strict.  If you think the use of "long 
>>> long" is unfortunate for the PC, then an artificial type might be created 
>>> internally within GDB specifically for the PC, similarly to what we do 
>>> e.g. for IEEE 754 data types and floating-point registers in some cases.
>>
>> An artificial type like that probably is the way to go.
> 
> I agree.  Something like the GDB equivalent of:
> 
>   typedef void * ptr64 __attribute ((mode(DI)));
> 
> (That worked last time I tried it on x32, probably works on MIPS too.)
> 

BTW, this whole issue is really a special case of an ABI register name
colliding with a machine register name.  A similar example came up when GDB
was made to expose whole set of x86 general purpose registers.  Specifically
the $rsp/$rsp/$sp, where $sp (16-bit) collides with desire to use $sp
to refer to stack pointer.  An alternative idea I thrown out back then,
would be to always leave $pc/$sp/$fp as the ABI version of the registers,
and in case the machine has real registers by that name, expose those with
an alternative naming, like e.g., $_pc/$_sp/$_fp.  These would have the
machine's full width.

On i686, you'd get:
 32-bit pointer $pc, 16-bit integer $ip, 32-bit pointer $eip.
 32-bit pointer $sp, 16-bit integer $_sp, 32-bit pointer $esp.
 32-bit pointer $fp, 16-bit integer $bp, 32-bit pointer $ebp.

On x32, you'd get:
 32-bit pointer $pc, 16-bit integer $ip, 32-bit pointer $eip, 64-bit integer $rip.
 32-bit pointer $sp, 16-bit integer $_sp, 32-bit pointer $esp, 64-bit integer $rsp.
 32-bit pointer $fp, 16-bit integer $bp, 32-bit pointer $ebp, 64-bit integer $rbp.

On x86_64 (-m64), you'd get
 64-bit pointer $pc, 16-bit integer $ip, 32-bit integer $eip, 64-bit pointer $rip.
 64-bit pointer $sp, 16-bit integer $_sp, 32-bit integer $esp, 64-bit pointer $rsp.
 64-bit pointer $fp, 16-bit integer $bp, 32-bit integer $ebp, 64-bit pointer $rbp.

On MIPS n32, you'd get:
 32-bit pointer $pc, 64-bit integer $_pc/$rNN.
 32-bit pointer $sp, 64-bit integer $_sp/$rNN.
 32-bit pointer $fp, 64-bit integer $_fp/$rNN.

(the _ variants probably would be raw from any arch bit manipulation).

(I'm not really sure which solution I prefer.)

-- 
Pedro Alves