[aarch64-port-dev ] VAR_CPU_ARCH for ARM platforms

[Andrew Haley]

On 23/12/15 20:36, Bob Vandette wrote:
>> > This is not true of x86_64, which is a rather elaborate 64-bit
>> > extension of x86.
> One could say the same thing about armv8 versus armv7.

I don't think one could.  I suspect this exact architecture could have
been designed by some other company, and no-one would have suggested
it was related.  Maybe someone might have said "Ooh, it's very
ARM-ish," but that's all.  It's a clean sheet design, it's not just
wider with more registers.  (The floating-point units are very
similar, I'll grant you.)  In contrast, x86_64 is pretty much a
superset with even the same binary encodings for many instructions.

[ NB: ARMv8 identifies both the AArch32 and AArch64 instruction set
architectures.  AArch32 is a slightly extended ARM; AArch64 is all-
new. ]

> That really depends on your criteria for comparison.  I still
> believe we need a broad variable that identifies ARM varieties.

Maybe so.  I guess this would capture what they have in common with
each other that is different from other architectures.  But there
isn't much of that.

> Without this, when the aarch32 port is attempted there’s going to be
> a lot of extraneous checks required in the makefile for “if ARCH ==
> aarch32” || ARCH == arm in places that would not need to be changed
> simply because we didn’t use the existing variable for the purpose
> that I believe it was originally intended.

I totally agree about AArch32 and ARM.  It's the same thing: the
AArch32 project is just about creating ARM-open.  There definitely
should be a variable to cover those.

Andrew.