Re: WIP: Register doco

Jim Blandy
2002-07-24T04:17:23Z

Andrew Cagney <ac131313@ges.redhat.com> writes:
> > I'm still trying to get a handle on your intent, though. In a case
> > like MIPS III (an ISA with 64-bit registers) running o32 (an ABI which
> > only uses the lower 32 bits of each register), would you suggest that
> > printing registers in the usual way should show the full 64 bits of
> > the register, or only the lower 32 bits?
>
> 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.