Request for review: 8000797: NPG: is_pseudo_string_at() doesn't work (original) (raw)

serguei.spitsyn at oracle.com serguei.spitsyn at oracle.com
Thu Feb 21 11:16:25 PST 2013

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.phillimore at oracle.com <mailto:coleen.phillimore at oracle.com>> wrote:

Summary: Add JVMCONSTANTPseudoString in place of JVMCONSTANTObject 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 JVMCONSTANTPseudoString. 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 sethaspseudostring. 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 hasinvokedynamic for that matter. haspreresolution 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 "CONSTANTPLACEHOLDER42" (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 JVMCONSTANTPseudoString (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

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