RFR (s) 8135298: Fix zero builds for "unknown" architectures on linux.

[Severin Gehwolf]

Hi,

On Thu, 2015-09-17 at 10:50 +0200, Magnus Ihse Bursie wrote:
> I'm not sure this code does what you think it does. At least when 
> building from the top-level makefile, ZERO_LIBARCH will always be
> set, 
> so the "unknown" case will not be reached.

CC'ing Matthias as we're not really building on any platform not
listed in platform.m4.

Looking at common/autoconf/platform.m4 (line 20 onwards) where VAR_CPU
seems to be defined, then used as OPENJDK_TARGET_CPU and then as
OPENJDK_TARGET_CPU_LEGACY_LIB and yet again as ZERO_LIBARCH. It may be
true for all the CPUs listed in platform.m4. I can only speculate, but
some distributions still build on more platforms than listed there
(Debian?). So if some distribution patches that code to support a
specific arch, what happens then? Has this been considered when you
wrote the above?

> Also, I'd like to hijacking this thread slightly, sorry about that.
> :)
> 
> When rewriting the Hotspot makefiles, I've been wondering if it
> would 
> not make more sense to consider "zero" to be a different
> architecture, 
> rather than a different "flavor" (like minimal1), as it is treated
> right 
> now. This patch seems to align with the treatment of zero as an 
> architecture. Just as an open question, do you think that would make
> sense?

A Zero (interpreter only) JVM has the goal to be (easily) built on
many (any?) architectures. There can be Zero on x86_64, on arm32, etc.
I don't think it makes sense to treat Zero as an architecture itself.
To me it being a variant/flavor kind of build is correct (depending on
what the definition of a variant/flavor build is exactly).

Cheers,
Severin

> /Magnus