RFR (S) 8008678: JSR 292: constant pool reconstitution must support pseudo strings

[Coleen Phillimore]

Serguei,
I had a quick look at this.  I was wondering if we could make the 
pseudo_string_map conditional in ConstantPool and not make all classes 
pay in footprint for this field?  The same thing probably could be done 
for operands too.  There are flags that you can set to conditionally add 
a pointer to base() in this function.

Typical C++ would subclass ConstantPool to add InvokeDynamicConstantPool 
fields, but this is not typical C++ so the trick we use is like the one 
in ConstMethod.   I think it's worth doing in this case.

Thanks,
Coleen

On 11/26/14, 3:59 AM, serguei.spitsyn at oracle.com wrote:
> Please, review the fix for:
>   https://bugs.openjdk.java.net/browse/JDK-8008678
>
>
> Open webrev:
> http://cr.openjdk.java.net/~sspitsyn/webrevs/2014/hotspot/8008678-JVMTI-pseudo.1/ 
>
>
>
> Summary:
>    The pseudo-strings are currently not supported in reconstitution of 
> constant pool.
>
>    This is an explanation from John Rose about what the pseudo-strings 
> are:
>
>    "We still need "live" oop constants pre-linked into the constant 
> pool of bytecodes which
>     implement some method handles. We use the anonymous class 
> pseudo-string feature for that.
>     The relevant code is here:
> http://hg.openjdk.java.net/jdk8/jdk8/jdk/file/tip/src/share/classes/java/lang/invoke/InvokerBytecodeGenerator.java 
>
>     These oops are what "pseudo-strings" are.
>     The odd name refers to the fact that, even though they are random 
> oops, they appear in the constant pool
>     where one would expect (because of class file syntax) to find a 
> string."
>      ...
>     If you really wanted to reconstitute a class file for an anonymous 
> class, and
>     if that class has oop patching (pseudo-strings), you would need 
> either to (a) reconstitute the patches array
>     handed to Unsafe.defineAnonymousClass, or (b) accept whatever odd 
> strings were there first, as an approximation.
>     The "odd strings" are totally insignificant, and are typically 
> something like "CONSTANT_PLACEHOLDER_42"
>     (see java/lang/invoke/InvokerBytecodeGenerator.java)."
>
>
>    Reconstitution of the ConstantPool is needed for both the JVMTI 
> GetConstantPool() and RetransformClasses().
>    Finally, it goes to the ConstantPool::copy_cpool_bytes().
>
>    The problem is that a pseudo-string is a patched string that does 
> not have
>    a reference to the string symbol anymore:
>        unresolved_string_at(idx) == NULL
>
>    The fix is to create and fill in a map from JVM_CONSTANT_String cp 
> index to the JVM_CONSTANT_Utf8 cp index
>    to be able to restore this assotiation in the 
> JvmtiConstantPoolReconstituter.
>
> Testing:
>   Run:
>    - java/lang/instrument tests
>    - new jtreg test (see webrev) that was written by Filipp Zhinkin
>
>
> Thanks,
> Serguei