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

[Magnus Ihse Bursie]

On 2015-09-17 14:48, Severin Gehwolf wrote:
> 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?

I can't really tell how the code behaves when additional patches I have 
not seen are laid on top of it. :-) However, I *can* see that in 
hotspot-spec.gmk ZERO_LIBARCH is *always* defined to have a value, so 
unless this is patched around as well, the "unknown" case will never be 
reached. Otoh, I'm not sure what that would mean either. The code is not 
likely to just happen to start running on an unknown architecture 
without some nontrivial effort. I just thought the code would do the 
same but more clearly if the fallback case just used 
OPENJDK_TARGET_CPU_LEGACY_LIB, instead of talking about zero and "unknown".

>
>> 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).
Ok, great! Thanks for your input.

/Magnus
>
> Cheers,
> Severin
>
>> /Magnus