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

George Triantafillou george.triantafillou at oracle.com
Fri Mar 3 15:37:09 UTC 2017

Hi Harold,

One typo:

313         // Record that an error occured in these two cases but keep 
parsing so
                                       should be "occurred".

Otherwise, it looks good.


On 3/3/2017 9:22 AM, harold seigel wrote:
> Hi,
> Please review this updated webrev for JDK-8175383: 
> http://cr.openjdk.java.net/~hseigel/bug_8175383.2/webrev/index.html
> 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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