RFR: 8250876: Build system preparation to macos on aarch64

[Kim Barrett]

> On Aug 1, 2020, at 3:24 AM, Vladimir Kempik <vkempik at azul.com> wrote:
> 
> Hello
> 
> Please review this change for JDK-8250876
> 
> This changeset adds support for macos/aarch64 into build system.
> It will allow to crosscompile for macos/aarch64 using intel mac as well.
> 
> This changeset does NOT address some arm specific issues in the macos related code, we plan to do that in s separate commit.
> 
> An example of configure to cross-compile for macos/arm64:
> 
> --with-boot-jdk=/path/to/java/ --with-build-jdk=/path/to/same/java/as/compiled  --disable-warnings-as-errors --with-jvm-variants=zero --openjdk-target=aarch64-apple-darwin --with-extra-cflags='-arch arm64' --with-extra-ldflags='-arch arm64 -F/Path/To/Folder/Containing/JNF_framework/' —with-extra-cxxflags='-arch arm64’
> 
> JNF.framework is missing arm64 part as of next macos release, but Apple has opensourced it. 
> 
> Fix to adlc were needed due to it using symbols from stdc++ and not linking to it, so it fails when doing make images.
> 
> The webrev: http://cr.openjdk.java.net/~vkempik/8250876/webrev.00/
> The bug: https://bugs.openjdk.java.net/browse/JDK-8250876
> 
> Testing: jdk/submit.
> 
> Thanks, Vladimir.

Coming late to the party, as I see this has already been pushed.  But
one thing caught my eye.

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  42   else ifeq ($(call isBuildOs, macosx), true)
  43     ADLC_LDFLAGS := -lc++

I'm surprised this is needed. I expected the C++ toolchain to
implicitly include that, the way g++ does.

If something like this really is needed, then it seems like it should
be ADLC_LIBS that should be modified, rather than ADLC_LDFLAGS.
Though I noticed there are currently no assignments to ADLC_LIBS.

I'm similarly surprised by this pre-existing bit in CoreLibraries.gmk:

$(eval $(call SetupJdkLibrary, BUILD_LIBJIMAGE, \
...
    LIBS_unix := -ljvm -ldl $(LIBCXX), \
    LIBS_macosx := -lc++, \

And that suggests a better place for all this (assuming its needed at
all) is in lib-std.m4, setting LIBCXX for macosx and using it where
needed.

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