On 2/20/13 11:59 AM, Coleen Phillimore wrote:
On 2/20/2013 2:51 PM, John Rose wrote:
On Feb 20, 2013, at 10:20 AM, Coleen Phillimore
<coleen.phillim...@oracle.com <mailto:coleen.phillim...@oracle.com>>
wrote:
Summary: Add JVM_CONSTANT_PseudoString in place of
JVM_CONSTANT_Object and use this tag to distinguish patched pseudo
strings. The original string is retained if it was present.
This is reasonable; it is a good cleanup. If you can propose a name
better than "PseudoString" I'm all ears.
If the string is really meaningless, maybe it can be deleted and we
don't need this JVM_CONSTANT_PseudoString. The only reason I kept
"String" in the name is because I thought the string would have some
meaning to be preserved.
Consider getting rid of set_has_pseudo_string. That flag was present
(IIRC) only to tell the GC that there might be non-perm oops in the
constant pool. Do we still need that?
I'd be happy to. I noticed it wasn't being used. Neither is
_has_invokedynamic for that matter. _has_preresolution does do
something.
I'm not sure how class file reconstitution for pseudo-strings is
going to work, but I thought it was prudent to leave the Symbol* in
the slot for the patched 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
InvokerBytecodeGenerator::constantPlaceholder).
Maybe there isn't a way or API to reconstitute an anonymous class. I
don't know if there is. I'm not sure how to reconstitute a normal
class in the first place. Maybe Serguei can comment. If this class
cannot be reconsitituted, I'll change this to remove the string in the
patched case and won't need JVM_CONSTANT_PseudoString (and the
constant for Object can be removed too).
Reconstitution of the ConstantPool is needed for both the JVMTI
GetConstantPool() and RetransformClasses().
Finally, it goes to the ConstantPool::copy_cpool_bytes().
This is the place that has to be fixed:
ConstantPool.cpp:
int ConstantPool::copy_cpool_bytes(int cpool_size,
. . .
case JVM_CONSTANT_String: {
*bytes = JVM_CONSTANT_String;
Symbol* sym = unresolved_string_at(idx);
idx1 = tbl->symbol_to_value(sym);
assert(idx1 != 0, "Have not found a hashtable entry");
Bytes::put_Java_u2((address) (bytes+1), idx1);
DBG(char *str = sym->as_utf8());
DBG(printf("JVM_CONSTANT_String: idx=#%03hd, %s", idx1, str));
break;
}
I think, the John's suggestion for odd strings should work here.
Something like:
if (sym == NULL) {
str = "CONSTANT_PLACEHOLDER_42";
}
I will file a bug on this.
Thanks,
Serguei
Thanks!
Coleen
— John
