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

[David Holmes]

Hi Harold,

On 4/03/2017 12:22 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.

A couple of nits - feel free to ignore:

  311       case 19:
  312       case 20: {

Shouldn't these have symbolic names defined?

---

  388   short bad_constant = class_bad_constant_seen();
  389   if (bad_constant != 0) {
  390     // Either a CONSTANT_Module or CONSTANT_Package entry was 
found in the constant
  391     // pool.  So, stop parsing and return.  The caller will decide 
whether to throw
  392     // NCDFE if it finds ACC_MODULE in the class's access_flags or 
throw CFE for
  393     // the bad constant pool entry.
  394     assert((bad_constant == 19 || bad_constant == 20) && 
_major_version >= JAVA_9_VERSION,
  395            "Unexpected bad constant pool entry");
  396     return;
  397   }

I don't think we need the detailed comments or the assertion here. As 
part of generalizing this it could just be:

if (class_bad_constant_seen() != 0) {
   // a bad CP entry has been detected previously so
   // stop parsing and just return;
   return;
}

Thanks,
David
-----

> 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
>>>>
>>
>