RFR: 8248238: Implementation of JEP: Windows AArch64 Support

[Erik Joelsson]

On Fri, 18 Sep 2020 20:32:36 GMT, Erik Joelsson <erikj at openjdk.org> wrote:

>> This is a continuation of https://mail.openjdk.java.net/pipermail/aarch64-port-dev/2020-August/009566.html
>>  
>> Changes since then:
>> * We've improved the write barrier as suggested by Andrew [1]
>> * The define-guards around R18 have been changed to `R18_RESERVED`. This will be enabled for Windows only for now but
>>   will be required for the upcoming macOS+Aarch64 [2] port as well.
>> * We've incorporated https://github.com/openjdk/jdk/pull/154 by @AntonKozlov in our PR for now and built the
>>   Windows-specific CPU feature detection on top of it.
>> 
>> [1] https://mail.openjdk.java.net/pipermail/aarch64-port-dev/2020-August/009597.html
>> [2] https://openjdk.java.net/jeps/8251280
>
> make/autoconf/toolchain.m4 line 902:
> 
>> 900:           BUILD_DEVKIT_TOOLCHAIN_PATH="$BUILD_DEVKIT_ROOT/bin"
>> 901:         fi
>> 902:         UTIL_PREPEND_TO_PATH([PATH],$BUILD_DEVKIT_TOOLCHAIN_PATH)
> 
> Here is a problem. In our linux cross compile build, we rely on the PATH being completely overwritten with the paths
> from the devkit here. Otherwise the UTIL_REQUIRE_PROGS may find /usr/bin/cc before $BUILD_DEVKIT_TOOLCHAIN_PATH/gcc.
> This is the reason my linux-aarch64 (cross compile) build failed. The system installed cc was too old to recognize
> the -stdc=c++14 argument.

I assume you need the rest of the PATH on Windows.

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PR: https://git.openjdk.java.net/jdk/pull/212