RFR 8146984: SIGBUS: bool Method::has_method_vptr(const void*)+0xc
coleen.phillimore at oracle.com
Sat Jan 30 14:39:02 UTC 2016
I've moved the SafeFetch to has_method_vptr as suggested and retested.
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!
>> 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
>> 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
> 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.
>>> bug link https://bugs.openjdk.java.net/browse/JDK-8146984
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