RFR(XS): 8155735: use strings instead of Symbol* in JVMCI exception stubs

[Tom Rodriguez]

> On Apr 29, 2016, at 8:55 AM, Roland Schatz <roland.schatz at oracle.com> wrote:
> 
> On 04/29/2016 05:27 PM, Tom Rodriguez wrote:
>> I think you need to handle the case where the symbol doesn’t exist.  lookup_symbol will return NULL if there’s no currently loaded symbol with that name which will lead to a SEGV later.  So you either need to throw an exception here or you should use
>> 
>> TempNewSymbol symbol = SymbolTable::new_symbol
> 
> SymbolTable::lookup should add it if it doesn't exist.

Sorry I was looking at the comment below lookup instead of above it.  It’s very odd that both of these exist though and new_symbol just forwards to lookup.

  static Symbol* new_symbol(const char* utf8_buffer, int length, TRAPS) {
  static Symbol* lookup(const char* name, int len, TRAPS);

I do think you want the TempNewSymbol though.

> 
>> and let new_exception throw an exception if the class named by symbol doesn’t exist.
> 
> throw_and_post_jvmti_exception will throw a `NoClassDefFoundError` when the exception class doesn't exist.
> 
> 
> Just to be sure, I tested this using graal. Temporarily passing in a wrong class name into the stub results in:
>> java.lang.NoClassDefFoundError: bla/java/lang/NullPointerException
>>        at com.oracle.graal.replacements.test.CompiledNullPointerExceptionTest.testSnippet(CompiledNullPointerExceptionTest.java:93)
>>        at jdk.vm.ci.hotspot.CompilerToVM.executeInstalledCode(Native Method)
>>        at jdk.vm.ci.hotspot.HotSpotNmethod.executeVarargs(HotSpotNmethod.java:100)
>>        at com.oracle.graal.compiler.test.GraalCompilerTest.executeActual(GraalCompilerTest.java:578)
>> […]

Thanks for checking.

tom

> 
> 
> - Roland
>