[PATCH] openjdk/zero: only use FPU opcodes if FPU is available (original) (raw)

Andrew Haley aph at redhat.com
Wed Jun 23 05:32:07 PDT 2010

On 06/23/2010 09:29 AM, Gary Benson wrote:

Sebastian Andrzej Siewior wrote:

* Gary Benson | 2010-06-22 09:47:51 [+0100]:

I'm happy with this patch if it allows Zero to build where it otherwise wouldn't, but be aware that without this code or some equivalent it will not be possible to pass the TCK with the build.

I've built the code with this patch and I saw no further problems. Can you please describe what you mean by " it will not be possible to pass the TCK with the build" ? It looks to me that it is just an optimization on s390 and powerpc (with FPU). Other Architectures like arm or mips are treated the same way. The TCK is the set of tests that checks whether or not a JVM is compatible with a specific version of Java. This little piece of assembler is there because the Java Language Specification [1] states that reads and writes of volatile long and volatile double fields must be atomic. If you remove that bit of code then what you build does not conform to the spec. It will work without it, but it's not certifyable. The reason ARM and 32-bit MIPS don't have that piece of assembler is that nobody has tried to certify them yet so nobody has written that piece of assembler for those platforms. Basically, if you just want to run stuff then it's ok to bypass that piece of assembler, but if you want to certify the builds for whatever reason then you will need to figure out some other way to do a 64-bit atomic copy.

Which is pretty easy:

static void atomic_copy64(volatile void *src, volatile void *dst) { pthread_mutex_lock(&the_mutex); *dst = *src; pthread_mutex_unlock(&the_mutex); }

... assuming that's the only place volatile doubles are ever touched.

Andrew.

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