[Dwarf-Discuss] DWARF piece questions

[Andreas Arnez]

On Fri, Jan 27 2017, Robinson, Paul wrote:

>> So, from a DWARF perspective, you'd expect that all libraries shall be
>> recompiled when migrating from an older x86-64 CPU to a newer one that
>> has AVX-512?  Or, as in the z/Architecture case, from a zEC12 to a z13
>> system?  You don't consider it valid for old and new binaries to coexist
>> in the same program?
>
> I'd expect that the DWARF consumer will understand what the target for
> the original executable was, and interpret any DWARF expressions
> appropriately.
>
> My understanding is that AVX and AVX-512 were considered to expand the
> vector registers at the most-significant-bit end, not the LSB end.
> https://en.wikipedia.org/wiki/Advanced_Vector_Extensions
> This allows the same DWARF register numbers to be reused and counting
> bits from the LSB end works regardless of the register width.

Correct.  So DWARF happens to support this scenario without any
translation.  That's what I mean by *supporting* "register growth".

> I'm not able to find equivalent comparison of the z/Architecture
> models, but if they do something similar then it should all Just Work.

And that's the point: the first 16 vector registers of z13 are
expansions of the existing FP registers at the *LSB* end.  So,
unfortunately, it does not just work.

--
Andreas