Handy hint: how to single step and breakpoint Zero's bytecode interpreter

[Andrew Haley]

Sometimes you need to set a breakpoint inside the JVM, to be triggered
when executing a particular method.  This is very tricky with Zero,
especially when the interpreter was compiled with full optimization.
This patch is a fairly lightweight way to do that.

If you set the environment variable JVM_TARGET_METHOD with your method
name and (optionally) the bytecode index, this will print the method
name, the BCI, and the contents of the expression stack:

java.util.HashMap.resize()[Ljava/util/HashMap$Node; 139
0x7fffae1a85e8
java.util.HashMap.resize()[Ljava/util/HashMap$Node; 141
0x7fffae1a85e8 0x7fffae1a8660

If you run HotSpot in GDB and place a breakpoint on the asm("nop")
this will print the location and stop the interpreter in the debugger.

http://cr.openjdk.java.net/~aph/c%2b%2binterpreter-breakpoint.patch

-- 
Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
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