RFR (XS) JDK-8041918: BootstrapMethods attribute cannot be empty

Lois Foltan lois.foltan at oracle.com
Fri May 9 14:51:00 UTC 2014

On 5/9/2014 10:27 AM, harold seigel wrote:
> Hi Lois,
> Could TestEmptyBootstrapMethodsAttr.java, just check for 
> "java.lang.ClassFormatError"?  Then the test would not break if the 
> rest of the message changed.

Hi Harold,

Thanks for the review.  I can do that, but would prefer not to.  It 
allows the test to verify specifically the boundary condition of an 
attribute_length of 2.  If the message is changed in the future, it 
would be pretty obvious why the test is failing.

> I think the .jcod files need copyright statements.  Also, could you 
> add a small comment about what each one does.

Will do.

> Thanks, Harold
> On 5/9/2014 10:22 AM, Lois Foltan wrote:
>> Hello,
>> Please review the following fix:
>> Webrev:
>>     http://cr.openjdk.java.net/~lfoltan/bug_jdk8041918/
>> Bug: BootstrapMethods attribute cannot be empty
>>     https://bugs.openjdk.java.net/browse/JDK-8041918
>> Summary of fix:
>> JVMS 8, section 4.7.23 details the BootstrapMethods attribute. In 
>> particular, page 155, describes the "attribute length" field of a 
>> BootstrapMethods attribute by documenting, "the value of the 
>> attribute_length item indicates the length of the attribute, 
>> excluding the initial six bytes."  Thus, a valid BootstrapMethod 
>> attribute could have an empty bootstrap_methods table where the 
>> num_bootstrap_methods field is equal to zero.  This situation would 
>> set the attribute_length legitimately to 2.  The class format check 
>> within ClassFileParser::parse_classfile_bootstrap_methods_attribte() 
>> must check for attribute_byte_length to be greater than or equal to 
>> the sizeof(u2). This check was added post JDK 8, an empty 
>> bootstrap_methods table was accepted by JDK 8 without generating a 
>> ClassFormatError.  Thank you to Harold Seigel for helping to figure 
>> out the .jcod files to yield a reproducer for this bug.
>> Tests:
>>     Hotspot's jtreg tests, JCK lang & vm, JDK lang & util, 
>> vm.quick.testlist
>> Thank you,
>> Lois

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