Re: WIP: Register doco

Andrew Cagney
2002-07-24T16:09:01Z

>> Sorry, I'm again lost. I earlier wrote (note edits):
>>
>> ``No, ABI. For instance mipsIII and o32. The o32 ABI thinks
>> registers have 32 bits yet the real register has 64 bits. This gives
>> two [cooked] views of the same [raw] register. When o32 debug info
>> indicates a value in two adjacent [cooked] registers, it is refering
>> to 32 bit and not 64 bit registers.''
>>
>> I'm not discussing which of these should be printed since that is
>> outside of the scope of this discussion.
>
>
> (Sorry, the `what would this print' is a distraction.)
>
> Suppose I have a program compiled to the o32 ABI which has a 64-bit
> variable that the debug info says is in $a0. I'm running it on a MIPS
> III machine. This means that half of my variable is in the low 32
> bits of $a0, and the the other half is in the low 32 bits of $a1.
>
> So, when you say that cooked registers are "ABI registers", are you
> saying that, in the cooked register set, $a0 and $a1 would be 32-bit
> registers, even though we're executing a 64-bit instruction set?
> Having the register sizes disagree with the actual instructions being
> executed is what seems like a bad idea to me.

As I pointed out in the above, there are two cooked $a0's. One is 32
bits and one is 64 bits. With regard to which should be user visible, I
wrote:

``(Should user visible registers be displayed according to the
underlying ISA or ABI is an item for debate. It has never been
specified and I suspect in part because GDB, prior to
gdbarch_register_read/write, couldn't handle both.)''

It was in paren because I want to first fix the regcache (and its doco).
That debate can be left to when someone has the cycles spare for
fixing it.

enjoy,
Andrew