[9] RFR(S): 8139150: ClassVerifier frees exception message while it's still in use

[Tobias Hartmann]

Hi Harold,

thanks for the review.

On 08.10.2015 18:17, harold seigel wrote:
> I think we should backport the fix to 8u.

Okay, I'll push the fix into hs-comp and backport it as soon as it passed nightly testing.

Best,
Tobias

> 
> Harold
> 
> On 10/8/2015 12:08 PM, Daniel D. Daugherty wrote:
>> On 10/8/15 9:38 AM, Tobias Hartmann wrote:
>>> Hi,
>>>
>>> please review the following patch.
>>>
>>> https://bugs.openjdk.java.net/browse/JDK-8139150
>>> http://cr.openjdk.java.net/~thartmann/8139150/webrev.00/
>>
>> src/share/vm/classfile/stackMapTable.cpp
>>     No comments.
>>
>> Thumbs up!
>>
>> Did a quick audit and I don't see any other calls to
>> class_format_error() with the same issue.
>>
>> This bug is very old. That ResourceMark came from here:
>>
>> $ sp -r1.17 src/share/vm/classfile/stackMapTable.cpp
>> src/share/vm/classfile/SCCS/s.stackMapTable.cpp:
>>
>> D 1.17 05/06/20 17:21:50 mingyao 18 17  00015/00008/00446
>> MRs:
>> COMMENTS:
>> Fixed 6275215, VM fails on StackMapTable jcod tests (VerifyError)
>> Fixed 6275199, VM fails on StackMapTable jcod tests
>> Fixed 6275153, VM fails on StackMapTable tests
>>
>> And the code looked like this:
>>
>> 187a185,194
>> >     if (offset >= _code_length ||
>> >         _code_data[offset] != ClassVerifier::NEW_OFFSET) {
>> >       ResourceMark rm(THREAD);
>> >       Exceptions::fthrow(
>> >         THREAD_AND_LOCATION,
>> >         vmSymbolHandles::java_lang_ClassFormatError(),
>> >         "StackMapTable format error: bad offset for Uninitialized"
>> >       );
>> >       return NULL;
>> >     }
>>
>>
>> The class_format_error() call came from here:
>>
>> D 1.21 06/04/13 11:43:50 km88527 23 22  00064/00108/00360
>> MRs:
>> COMMENTS:
>> fixed 6402717: Error verifying java.lang.Error causes VM to exit silently due to stack overflow
>>
>> and the code changed to look like this:
>>
>>     if (offset >= _code_length ||
>>         _code_data[offset] != ClassVerifier::NEW_OFFSET) {
>>       ResourceMark rm(THREAD);
>>       _verifier->class_format_error(
>>         "StackMapTable format error: bad offset for Uninitialized");
>>       return NULL;
>>     }
>>
>> This fix should probably be backported... but I would
>> check with Harold...
>>
>> Dan
>>
>>
>>>
>>> Problem:
>>> If class verification fails in StackMapReader::parse_verification_type(), ClassVerifier::class_format_error() is invoked to pass the error message. The method allocates a new string and saves it in ClassVerifier::_message. The problem is that the caller creates a new ResourceMark that leads to _message being deallocated after return. However, later in Verifier::verify() we call ClassVerifier::exception_message() to get the message and pass it on.
>>>
>>> Solution:
>>> We should not create a ResourceMark here. There is a top level ResourceMark in Verifier::verify() that will take care of freeing the memory allocated in ClassVerifier::class_format_error().
>>>
>>> Tested with JPRT and the failing testcase.
>>>
>>> Thanks,
>>> Tobias
>>
>