[8u] RFR backport of JDK-8144732: VM_HeapDumper hits assert with bad dump_len

[Andrew Hughes]

On 06/11/2019 18:07, Hohensee, Paul wrote:
> I found http://jperfanal.sourceforge.net/java.hprof.txt, which is a thread stack dump that references 1.0.1, is dated Dec 30, 2001, and the dump output is copyright 1998. So 1.0.1 is probably from 1998.
> 
> I found a file format spec at http://hg.openjdk.java.net/jdk6/jdk6/jdk/raw-file/tip/src/share/demo/jvmti/hprof/manual.html#mozTocId848088. It's from Java 6, so 1.0.2 was supported then. I also found
> 
> https://bugs.openjdk.java.net/browse/JDK-6305542: HPROF binary format needs to support large dumps
> 
> for Java 6, and
> 
> https://bugs.openjdk.java.net/browse/JDK-6313381: HPROF: agent should generate version 1.0.2 for large heaps
> 
> which updated the hprof agent to generate 1.0.2 format files for heaps > 4gb in Java 6, and
> 
> https://bugs.openjdk.java.net/browse/JDK-6313383: SA: Update jmap to support HPROF binary format "JAVA PROFILE 1.0.2"
> 
> which was shipped in 8u25 in 2014.
> 
> So, JDKs/JREs starting with Java 6 can read 1.0.2 files, and the SA can read them starting with 8u25. I don't think we need to worry about using Java 5 to read files generated by Java 8, and the SA is good to go for 8.
> 
> Paul
> 

Thanks for the through research. My concern is not so much whether the
format can be read, as whether it is expected on small heap dumps.
JDK-6313383 also says "For compatibility it would be best if jmap
continued to generate a 1.0.1 format for smaller heaps (<2GB for example).".

I think this may warrant a CSR.

Thanks,
-- 
Andrew :)

Senior Free Java Software Engineer
Red Hat, Inc. (http://www.redhat.com)

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