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From Geir Magnusson Jr <g...@pobox.com>
Subject Re: [drlvm] verification of classfile format
Date Thu, 06 Jul 2006 18:51:42 GMT

Gregory Shimansky wrote:
> On Thursday 06 July 2006 20:26 Geir Magnusson Jr wrote:
>> As part of the work surrounding the HARMONY-677 (r419557), getting DRLVM
>> to deal with Java5 classfile format,  I noticed that DRLVM doesn't
>> appear to give a hoot what version of the classfile it's chewing on.  It
>> just goes until something blows up.
> It does check the class file version in bootstrap class loader 
> (vm/vmcore/src/class_support/Class_File_Loader.cpp) and can throw 
> UnsupportedClassVersionError. The constant CLASSFILE_MAJOR_MAX is defined in 
> vm/vmcore/include/Class.h.

Ah ha.  I think I just skipped over class_parse() when reading through :)

>> I was comparing to j9, which gives a UnsupportedClassVersionError.
>> DRLVM should do the same of course, and it makes me worry what else it
>> outght to be doing - if we don't understand the version of the class
>> file, how can we read it dependably?
> For some reason I don't really know the constant was changed to 49 as if VM 
> did support class files of version 1.5. Maybe it was the first step to 
> support 1.5 classes :)

Well, that explains that.  Sorry about that.  My bad.  I've verified
that it works as expected (namely throws the UCVE on a v49 class w/
DRLVM set to v48)

>> I was reading down through j.l.ClassLoader and natives, and given the
>> dearth of comments, didn't quite grok where a good place to start doing
>> some verification would be...  Maybe I missed it.  Can anyone give me a
>> hint?
> I think it should happen in bootstrap class loader since it is the place where 
> class file parsing is done anyway. So the place is in VM native code, not 
> kernel classes.

It seems to be.  Just need some docs, and maybe some tests...


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