Re: [PING][PATCH 2/2] Involve gdbarch in taking DWARF register pieces

[Pedro Alves <palves at redhat dot com>]

On 04/28/2016 05:51 PM, Andreas Arnez wrote:
> On Thu, Apr 28 2016, Pedro Alves wrote:
> 
>> I couldn't find any reference to "sub-register" in the codebase.
>> I'd assume it's something like "eax" being a sub part of "rax"
>> on x86-64.  But I'm not certain that's the case here?  On a machine with
>> vector registers, is a FP register really a chunk of the vector
>> register, or is it a real separate physical register?
> 
> It's exactly comparable with eax and rax.  Or consider the SSE registers
> xmm0-xmm15, which are embedded in their double-wide AVX counterparts
> ymm0-ymm15.  With z/Architecture, each 64-bit FP register is just a
> "chunk" ("sub-register" / "part" / "slice" / ...) of a 128-bit vector
> register.  The ASCII art in section 2.1 of this article illustrates
> this:
> 
>   https://sourceware.org/ml/gdb/2016-01/msg00013.html

Thanks, this helps a lot.

> 
> (BTW, I still didn't get much feedback on that article...)
> 
> And if there is a better (or wider used) term than "sub-register", I'll
> be happy to change the wording.

No, that's fine terminology.  I was just confused because I wasn't very
clear whether we're talking about completely different registers.
Thanks,
Pedro Alves