RFR: 8282828: CDS uncompressed oops archive is not deterministic

[Ioi Lam]

On Fri, 29 Apr 2022 22:50:45 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> During `java -Xshare:dump -XX:-UseCompressedOops`, the location of the Java heap is chosen by the OS. Due to Address Space Layout Randomization, the heap will always start at a different location. This causes the archive for uncompressed oops ($JAVA_HOME/lib/server/classes_nocoops.jsa) to be non-deterministic.
> 
> The fix is to patch the archived object pointers to make it look like the heap starts at a fixed address -- I chose 0x10000000, but the exact value doesn't really matter.
> 
> At runtime, the object pointers will be patched again according to the real location of the heap.
> 
> Tested with tiers 1-5. I am running builds-tier5 several times to test the xxx-cmp-baseline builds.

src/hotspot/share/cds/heapShared.cpp line 184:

> 182:   // Do not call p->identity_hash() as that will update the
> 183:   // object header.
> 184:   return primitive_hash(cast_from_oop<intptr_t>(p));

This fix doesn't affect the contents of the archive, but it's necessary to avoid incorrect output from `-Xlog:cds+map=trace`.

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PR: https://git.openjdk.java.net/jdk/pull/8478