RFR 8202210: jlink uses little-endian for big-endian cross-compilation targets

[Aleksey Shipilev]

Hi,

I was doing the exercise of cross-compiling from x86_64 to most OpenJDK arches, and we have
discovered the bug with endianness. Right now, compiling big-endian s390x target on little-endian
x86_64 host produces the modules blob that cannot be read on real s390x.

It seems to be a simple overlook in image building, and we should pass target-cpu endianness to
jlink. During the build, jlink is called twice: first for the interim image build, then for the
final image build. In cross-compilation, it seems only the final image build should take target-cpu
endianness.

(Aside: what is our backporting policy for build system bugs? Would love to make the jdk10 backport
for this)

Bug:
  https://bugs.openjdk.java.net/browse/JDK-8202210

Fix:

diff -r 5d2da44780ac make/Images.gmk
--- a/make/Images.gmk	Wed Apr 25 10:38:07 2018 +0200
+++ b/make/Images.gmk	Wed Apr 25 10:55:04 2018 +0200
@@ -117,7 +117,7 @@

 JLINK_TOOL := $(JLINK) -J-Djlink.debug=true \
     --module-path $(IMAGES_OUTPUTDIR)/jmods \
-    --endian $(OPENJDK_BUILD_CPU_ENDIAN) \
+    --endian $(OPENJDK_TARGET_CPU_ENDIAN) \
     --release-info $(BASE_RELEASE_FILE) \
     --order-resources=$(call CommaList, $(JLINK_ORDER_RESOURCES)) \
     --dedup-legal-notices=error-if-not-same-content \

Testing: x86_64 build, s390x cross-compiled build

Thanks,
-Aleksey