[9] RFR (S): 8160527: Check for final instance field updates can be omitted

[Zoltán Majó]

Hi,


please review the patch for 8160527.

https://bugs.openjdk.java.net/browse/JDK-8160527

Problem: 8157181 added a check that verifies that final instance fields 
can be updated only by object initializer methods (as required by JVMS 
 >=7) [1].

Unfortunately, the newly added check can be circumvented due to constant 
pool caching: If the instance field update is executed in an <init> 
method first, the instruction updating the field is cached in the 
constant pool cache. Subsequent updates use the constant pool cache (and 
do not call into the VM where the check is executed). As a result, any 
method can update a final instance field if that field was first updated 
in an instance initializer (the method must be declared in the same 
class as the field, though).

John's comment in the bug description provides more detailed information 
on how the above can happen.


Solution: Do not cache putfield instructions to final instance fields if 
the verifier has detected that the field is updated in other methods 
than <init> (i.e., has_initialized_field_update() returns true for the 
field). Avoiding caching results in the field access being re-resolved 
until the offending access is attempted; then an exception is thrown. 
Avoiding caching must be done very infrequently, as offending code is 
rare (e.g., such code cannot be produced by javac).

I've also corrected a small mistake in the fix for 8157181 (the class 
name is printed in the error message instead of the method's name).

Webrev:
http://cr.openjdk.java.net/~zmajo/8160527/webrev.00/

Testing:
- JPRT (testset hotspot, incl. newly added test);
- verified that the newly added test triggers the problem with an 
unmodified VM.

Thank you!

Best regards,


Zoltan

[1] http://hg.openjdk.java.net/jdk9/hs-comp/hotspot/rev/c558d46c1af2#l11.76