RFR: 8220283: ZGC fails to build on GCC 4.4.7: ATTRIBUTE_ALIGNED compatibility issue

[Severin Gehwolf]

Hi,

In order to be able to build recent JDKs on CentOS 6/RHEL 6 we've
discovered that a few fixes would be needed in the codebase. One such
instance is being caused by ZGC's use of ATTRIBUTE_ALIGNED:

#define ATTRIBUTE_ALIGNED(x) __attribute__((aligned(x+0)))

Used as:

ZMarkStackList _published  ATTRIBUTE_ALIGNED(ZCacheLineSize);

This trips up GCC 4.4.7 with:

src/hotspot/share/gc/z/zMarkStack.hpp:77: error: requested alignment is not a constant

Although, 4.4.7 isn't a supported compiler version, the fix would be
this one-liner:

http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8220283/01/webrev/

Bug: https://bugs.openjdk.java.net/browse/JDK-8220283

Testing: tier1 tests on Linux x86_64, jdk/submit (ongoing)

Thoughts?

Thanks,
Severin