Execution problems with Atomic Operations on OpenJDK10 for ARM5 Soft Float

[David Holmes]

On 5/04/2018 11:26 AM, bren at juanantonio.info wrote:
> Good night David,
> 
> It is the first time that I report a Bug on OpenJDK and I didn´t receive 
> any notification so I didn´t know the status of the Issue that I reported.

Sorry about that. You should have received some form of notification.

> Many thanks with the link about the Platforms supported:
> http://www.oracle.com/technetwork/java/javase/documentation/jdk10certconfig-4417031.html 
> 
> 
> We will try to do Compilation with the solution.
> 
> --- a/src/hotspot/cpu/arm/vm_version_arm_32.cpp
> +++ b/src/hotspot/cpu/arm/vm_version_arm_32.cpp
> @@ -298,6 +298,15 @@
>       FLAG_SET_DEFAULT(UseUnalignedAccesses, false);
>     }
> 
> + if (arm_arch() == 5) {
> + if (FLAG_IS_DEFAULT(AssumeMP)) {
> + FLAG_SET_DEFAULT(AssumeMP, false);
> + else if (AssumeMP) {
> + warning("AssumeMP can not be true for ARMv5 as there is only 
> uniprocessor support");
> + FLAG_SET_DEFAULT(AssumeMP, false);
> + }
> + }
> +
>     _is_initialized = true;
>   }
> 
> Runtime workaround: java -XX:-AssumeMP
> 
> In our case, I would like to continue maintaining this support for the 
> Device.
> What is the advice that you could give us?

You would have to keep the local copy of your source code patched and 
produce your own builds. But if you also try to update with the mainline 
OpenJDK code then you will very soon hit problems. In fact I'd be very 
surprised if this works today, even if it builds, as we have not 
provided any updates to ARM32 in a long time. The only supported way to 
run on ARM32 is using the Zero interpreter as Adrian replied.

> What is AssumeMP?

Assume Multi-Processor.

When running on a MP system the VM has to use and generate code that 
provides the correct level of atomicity and memory consistency - none of 
which is necessary on a uniprocessor system. MP systems are the norm and 
in the rare case we issue the additional memory synchronization 
instructions they should be no-ops on a uniprocessor, so we are heading 
towards stripping out uniprocessor support and only build in MP support 
so that we don't need dynamic checks through the code to see if we are 
MP or not. Switching AssumeMP to true was the first step in that process 
(and avoided problems where the VM may be started with only one 
processor available but then had additional ones added later.)

In any case there has never been any support for ARMv5 multiprocessors.

Cheers,
David

> For education, this device is pretty interesting for the whole Java 
> community, this is the reason.


> I will inform with the results.
> 
> Many thanks in advance.
> 
> Cheers
> 
> Juan Antonio
> 
> El 2018-04-05 00:12, David Holmes escribió:
>> Hi,
>>
>> This was already reported as:
>>
>> https://bugs.openjdk.java.net/browse/JDK-8200580
>>
>> to which I have responded and closed the bug as this is not a
>> supported platform.
>>
>> As per the bug report this may be due to the change to AssumeMP to be
>> true, but there is no MP support for ARMv5.
>>
>> David
>>
>> On 4/04/2018 8:29 PM, bren at juanantonio.info wrote:
>>> Good morning,
>>>
>>> Mi name is Juan Antonio Breña Moral, I am developing a set of Java 
>>> libraries for Lego Mindstorms EV3, an ARM5 robotics device and 
>>> recently, we build OpenJDK 9 with success but with OpenJDK 10, we 
>>> have found some problems when we execute some Java programs.
>>>
>>> Repository to build OpenJDK 9/10 for ARM5 Soft Float:
>>> https://github.com/ev3dev-lang-java/openjdk-ev3
>>>
>>> To test the JVM, I am using the following repo to test the VM:
>>> https://github.com/ev3dev-lang-java/vmbenchmarks
>>>
>>> And this is the output with the error:
>>>
>>> robot at ev3dev:~$ java -jar benchmarks.jar -f 1
>>> WARNING: An illegal reflective access operation has occurred
>>> WARNING: Illegal reflective access by org.openjdk.jmh.util.Utils 
>>> (file:/home/robot/benchmarks.jar) to field java.io.Console.cs
>>> WARNING: Please consider reporting this to the maintainers of 
>>> org.openjdk.jmh.util.Utils
>>> WARNING: Use --illegal-access=warn to enable warnings of further 
>>> illegal reflective access operations
>>> WARNING: All illegal access operations will be denied in a future 
>>> release
>>> =============== DEBUG MESSAGE: Atomic load(jlong) unsupported on this 
>>> platform ================
>>>
>>> =============== DEBUG MESSAGE: Atomic store(jlong) unsupported on 
>>> this platform ================
>>>
>>>
>>> =============== DEBUG MESSAGE: Atomic load(jlong) unsupported on this 
>>> platform ================
>>>
>>> [thread 4430 also had an error]
>>> [error occurred during error reporting ((null)), id 0xe0000000]
>>>
>>> =============== DEBUG MESSAGE: Atomic store(jlong) unsupported on 
>>> this platform ================
>>>
>>>
>>> [error occurred during error reporting (printing fatal error 
>>> message), id 0xe0000000]
>>>
>>> =============== DEBUG MESSAGE: Atomic store(jlong) unsupported on 
>>> this platform ================
>>>
>>>
>>> [error occurred during error reporting (printing type of error), id 
>>> 0xe0000000]
>>>
>>> =============== DEBUG MESSAGE: Atomic store(jlong) unsupported on 
>>> this platform ================
>>>
>>>
>>> [error occurred during error reporting (printing stack bounds), id 
>>> 0xe0000000]
>>>
>>> =============== DEBUG MESSAGE: Atomic store(jlong) unsupported on 
>>> this platform ================
>>>
>>>
>>> [error occurred during error reporting (printing native stack), id 
>>> 0xe0000000]
>>>
>>> =============== DEBUG MESSAGE: Atomic store(jlong) unsupported on 
>>> this platform ================
>>>
>>>
>>> [error occurred during error reporting (printing Java stack), id 
>>> 0xe0000000]
>>>
>>> =============== DEBUG MESSAGE: Atomic store(jlong) unsupported on 
>>> this platform ================
>>>
>>>
>>> [error occurred during error reporting (printing target Java thread 
>>> stack), id 0xe0000000]
>>>
>>> =============== DEBUG MESSAGE: Atomic store(jlong) unsupported on 
>>> this platform ================
>>>
>>>
>>> [error occurred during error reporting (printing siginfo), id 
>>> 0xe0000000]
>>>
>>> =============== DEBUG MESSAGE: Atomic store(jlong) unsupported on 
>>> this platform ================
>>>
>>>
>>> [error occurred during error reporting (CDS archive access warning), 
>>> id 0xe0000000]
>>>
>>> =============== DEBUG MESSAGE: Atomic store(jlong) unsupported on 
>>> this platform ================
>>>
>>>
>>> [error occurred during error reporting (printing register info), id 
>>> 0xe0000000]
>>>
>>> =============== DEBUG MESSAGE: Atomic store(jlong) unsupported on 
>>> this platform ================
>>>
>>>
>>> [Too many errors, abort]
>>> Aborted
>>>
>>> I think that in OpenJDK10 changed something in compare to OpenJDK9 in 
>>> relation to ARM5 support.
>>>
>>> Any idea?
>>>
>>> Many thanks in advance.
>>>
>>> Cheers
>>>
>>> Juan Antonio
>>>