RFR 8175383: JVM should throw NCDFE if ACC_MODULE and CONSTANT_Module/Package are set

harold seigel harold.seigel at oracle.com
Fri Mar 3 14:22:20 UTC 2017


Please review this updated webrev for JDK-8175383: 

This webrev contains a simplified fix and simplified tests based on 
reviewers' previous suggestions on how to improve this fix.

Thanks, Harold

On 3/1/2017 8:20 AM, harold seigel wrote:
> Hi David,
> Thanks for your input.  Please see comments in-line.
> On 2/28/2017 10:50 PM, David Holmes wrote:
>> Hi Harold,
>> On 27/02/2017 11:48 PM, harold seigel wrote:
>>> Hi,
>>> Please review this fix to throw NoClassDefFoundError exceptions, 
>>> instead
>>> of ClassFormatError exceptions, for version 53 or greater class files
>>> that have ACC_MODULE set in their access_flags and one or more constant
>>> pool entries of CONSTANT_Module or CONSTANT_Package (19 or 20). The JVM
>>> parses the constant pool before parsing the access_flags.  So, it needs
>>> to save the fact that the constant pool contained an entry of 19 or 20.
>>> Then, after checking for ACC_Module in the access_flags, decide which
>>> exception to throw.
>> That is truly awful! - and that's not a reflection on you or your 
>> code :)
> I'll discuss this with Alex.  Perhaps the JVM Spec requirement is more 
> flexible than what I implemented.
>> This kind of approach doesn't scale - what happens when we have new 
>> rules in 10 for classfile version >=54? There are too many special 
>> cases.
>> Really - and this is I concede out-of-scope for this stage of 9 and 
>> this bug - we need to separate the structural parsing errors from the 
>> logical errors, so we can do the main parsing and then all the 
>> convoluted "if version >= 53 and has_constant_module and 
>> has_acc_module ..." logic.
> This sounds like a good enhancement for JDK-10.
>>> To summarize the desired behavior:
>>>    For class file versions < 53 throw CFE for any bad constant pool
>>>    entry regardless of access_flags.
>>>    For class file versions >= 53 throw NCDFE for a bad constant pool
>>>    entry of 19 or 20 and ACC_Module set in access_flags.
>>>    For class file versions >= 53 throw CFE for a bad constant pool
>>>    entry of 19 or 20 and ACC_Module not set in access_flags.
>>>    For class file versions >= 53 throw CFE for a bad constant pool
>>>    entry other than 19 or 20 regardless of access_flags.
>>> The reasoning behind this is that constant pool entries 19 and 20 are
>>> only valid when ACC_Module is set.  So, if ACC_Module is set then
>>> constant pool entries 19 and 20 are technically valid and CFE should 
>>> not
>>> be thrown.  Instead, a NCDFE is thrown because of ACC_Module.
>>> I moved the check for ACC_MODULE out of verify_legal_class_modifiers()
>>> for the following reason.  Suppose there's a CONSTANT_Module entry in
>>> the constant pool and suppose verify_legal_class_modifiers() throws a
>>> CFE for a reason unrelated to ACC_MODULE.  That could be considered a
>>> bug because the CFE should be thrown with a message describing the bad
>>> CONSTANT_Module entry, not the bad access_flags.  If it does not matter
>>> which CFE gets thrown then the ACC_MODULE check could be moved back 
>>> into
>>> verify_legal_class_modifiers().
>> I prefer the ACC_MODULE check where it was so that we don't duplicate 
>> the logic. I'm not aware of anything that gives precedence to one CFE 
>> over another, or how anyone could legitimately complain about the 
>> behaviour either way.
> If no one objects then I'll move the ACC_MODULE check back into 
> verify_legal_class_modifiers().  It will simplify the change.
>>> Open webrev:
>>> http://cr.openjdk.java.net/~hseigel/bug_8175383/webrev/index.html
>> Functional changes okay modulo what I already said.
>> For the tests ... I find the use of asm very cumbersome, and prefer 
>> using jcods myself. That aside, can you not factor out the custom 
>> classloader so that it only has to be written once? It can take the 
>> name of the class to treat specially as a constructor arg, and the 
>> exception message checking can go around the loadClass call instead 
>> of the defineClass call.
> I agree that asm is very cumbersome but I couldn't use jcod or jasm 
> because they don't support constant pool items of 19 or 20. I'll look 
> into factoring out the custom classloader.
> Thanks, Harold
>> Thanks,
>> David
>>> JBS Bug: https://bugs.openjdk.java.net/browse/JDK-8175383
>>> The fix was tested with the JCK lang and vm tests, the JTreg hotspot,
>>> java/io, java/lang, java/util and other tests, the RBT tier2 -tier5
>>> tests, the colocated and non-colocated NSK tests, and with JPRT.
>>> Thanks, Harold

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