RFR 8146984: SIGBUS: bool Method::has_method_vptr(const void*)+0xc

[Coleen Phillimore]

I've moved the SafeFetch to has_method_vptr as suggested and retested.

http://cr.openjdk.java.net/~coleenp/8146984.02/webrev/

Thanks,
Coleen

On 1/29/16 11:58 AM, Coleen Phillimore wrote:
>
>
> On 1/29/16 11:02 AM, Daniel D. Daugherty wrote:
>> On 1/29/16 5:46 AM, Coleen Phillimore wrote:
>>> Summary: Add address check and use SafeFetchN for Method* vptr 
>>> access when Method* may be bad pointer.
>>>
>>> Tested with RBT and failing test case (reproduced 1 in 100 times) 
>>> with fatal in the 'return's in the change to verify.
>>>
>>> open webrev at http://cr.openjdk.java.net/~coleenp/8146984/
>>
>> This one caught my eye because it has to do with sampling...
>
> I should mention sampling in all my RFRs then!
>>
>> src/share/vm/oops/method.cpp
>>     The old code checked "!is_metaspace_object()" and used
>>     has_method_vptr((const void*)this).
>>
>>     The new code skips the "!is_metaspace_object()" check even after 
>> sanity
>>     checking the pointer, but you don't really explain why that's OK.
>
> is_metaspace_object is a very expensive check.   It has to traverse 
> all the metaspace mmap chunks.   The new code is more robust in that 
> it sanity checks the pointer first but uses Safefetch to get the vptr.
>
>
>>
>>     The new code also picks up parts of Method::has_method_vptr() which
>>     makes me wonder if that's the right place for the fix. Won't other
>>     callers to Method::has_method_vptr() be subject to the same crashing
>>     mode? Or was the crashing mode only due to the 
>> "!is_metaspace_object()"
>>     check...
>
> I should have moved the SafeFetch in to the has_method_vptr.  I can't 
> remember why I copied it now.  It crashed because the pointer was in 
> metaspace (is_metaspace_object returned true) but wasn't aligned, but 
> the pointer could come from anywhere.
>
> Thanks,   I'll test out this fix and resend it.
> Coleen
>
>>
>> Dan
>>
>>
>>> bug link https://bugs.openjdk.java.net/browse/JDK-8146984
>>>
>>> Thanks,
>>> Coleen
>>>
>>
>