[oe] [meta-java][PATCH] openjdk-8: make GCC6 happy

[Patrick Ohly]

Dan McGregor <danismostlikely <at> gmail.com> writes:
> From: Daniel McGregor <daniel.mcgregor <at> vecima.com>
> 
> GCC 6 sets the default C++ standard to C++14 and introduces dead store
> elimination by default. OpenJDK 8 is not ready for either of these
> changes, so set the C++ standard back to gnu++98 and disable dead
> store elimination.
> 
> Switched to using --with-extra-cflags, cxxflags, and ldflags. The added
> patch fixes building when using those flags, and are needed to get
> CFLAGS into the JDK build in the native case.

Has anyone tested this on a host system where gcc is still 4.x, like 4.9.2
on Debian Wheezy?

I'm finding that -fno-lifetime-dse is also getting passed to the gcc used
for compiling native binaries (obviously in openjdk-8-native, but also for
some helper executables in openjdk-8). This then breaks the compilation
because older gcc rejects that flag.

I've briefly toyed with the patch below which worked for openjdk-8-native,
but not for openjdk-8. I'm just going to work around it by staying on gcc
5.x and clearing these extra flags.

I'm not familiar enough with the openjdk-8 build process to propose a better
solution, but perhaps someone else has an idea?

diff --git a/meta-java/recipes-core/openjdk/openjdk-8-common.inc
b/meta-java/recipes-core/openjdk/openjdk-8-common.inc
index dd3d397..060d828 100644
--- a/meta-java/recipes-core/openjdk/openjdk-8-common.inc
+++ b/meta-java/recipes-core/openjdk/openjdk-8-common.inc
@@ -237,6 +237,25 @@ EXTRA_OECONF_append = "\
         --with-update-version=${OPENJDK_UPDATE_VERSION} \
 "
 
-CFLAGS_append = " -fno-lifetime-dse -fno-delete-null-pointer-checks"
-CXXFLAGS_append = " -fno-lifetime-dse -fno-delete-null-pointer-checks"
+# GCC 6 sets the default C++ standard to C++14 and introduces dead store
+# elimination by default. OpenJDK 8 is not ready for either of these
+# changes.
+FLAGS_GCC6 = "-fno-lifetime-dse -fno-delete-null-pointer-checks"
+
+# All supported cross compilers support the compiler flags that were
+# added to make compilation with gcc6 work. But the host compiler for
+# native compilation is a different story: it may be too old (for example,
+# gcc 4.9.2 on Debian Wheezy). In that case we need to check what the
+# version is and unset the flags when gcc is not yet GCC 6.
+python () {
+    if d.getVar('PN', True).endswith('-native'):
+        import re, subprocess
+        version = subprocess.check_output(d.expand('${CC}
--version').split()).decode('utf-8')
+        m = re.search(r'^gcc.* (\d+)(\.\d+)*$', version, re.MULTILINE)
+        if m and int(m.group(1)) < 6:
+            d.setVar('FLAGS_GCC6', '')
+}
+
+CFLAGS_append = " ${FLAGS_GCC6}"
+CXXFLAGS_append = " ${FLAGS_GCC6}"
 CXX_append = " -std=gnu++98"

Bye, Patrick