[8u] RFR: JDK-8164041: support old pre-c++11 toolchains and ucLibc

[Edward Nevill]

Hi Andrey,

This build fine for me now on my Samsung Chromebook. Thanks for
updating this.

For the future we might like to dynamically generate such code rather
than building it statically. This would enable VMs built on one system
to run on another without the need for having separate binaries for
both. However this is an exercise for another date.

Looks good to push,
Ed.


On Thu, 2016-08-25 at 08:40 +0000, Andrey Petushkov wrote:
> Hi Ed, All,
> 
> Please consider the updated patch which should allow to build for
> ARMv6
> prior to revision K. Here
> http://cr.openjdk.java.net/~apetushkov/8164041/webrev.01/
> Please note that at first it's attempted to use the inline assembly
> and
> only if not not possible the fallback is done to gcc intrinsics. The
> reason
> is that we know that assembly is more robust. Unfortunately due to
> differences in set of macros defined by different toolchains the
> selection
> condition in the #if look really crazy. I've tried to check every
> single
> symbol which could mean ldrexd is available, since I've met the case
> when
> only __ARM_ARCH_6ZK__ is defined and nothing else. If you're aware
> that
> it's guaranteed that some of checks are redundant please let me know
> 
> Thanks,
> Andrey
>