RFR (S): 8210242: vmTestbase/nsk/stress/jni/jnistress001.java crashes with EXCEPTION_ACCESS_VIOLATION on windows-x86

David Holmes david.holmes at oracle.com
Thu Oct 25 11:32:03 UTC 2018

Thanks Lois!


On 25/10/2018 9:00 PM, Lois Foltan wrote:
> Looks good David.
> Lois
> On 10/25/2018 2:03 AM, David Holmes wrote:
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8210242
>> webrev: http://cr.openjdk.java.net/~dholmes/8210242/webrev/
>> The fundamental bug here was that a character array was copied without 
>> attempting to copy**/add a NUL terminating character so it formed a 
>> valid C string (char*). The array was passed to printf %s and by good 
>> fortune happened to have a NUL 99% of the time, occasionally had a 
>> junk character or two that would at least print okay on Linux etc but 
>> once in a blue moon would trigger an EXCEPTION_ACCESS_VIOLATION on 
>> windows-x86.
>> ** There's actually no guarantee the original array was itself 
>> NUL-terminated (hotspot does do so but the JNI spec does not require 
>> it) - but that's a cleanup for later - see below.
>> The fix I chose for that was to use %.*s and pass the actual length. 
>> The main reason I chose that was to reinforce that arrays need not be 
>> NUL-terminated and we should get out of that mind set when working 
>> with Java Strings and JNI. In doing that I factored an expression:
>> javachars->size[index]
>> (sometimes expressed as index-1 due to index being sneakily 
>> incremented in the middle of the code), into a local variable elem_len.
>> In addition, due to thinking it may be the cause of the problem, I 
>> introduced a utility function c_malloc to check malloc does not return 
>> NULL and to fail if it does. So all mallocs became c_malloc calls.
>> There is a lot of potential cleanup possible in this test and the 
>> others in Testbase/nsk/stress/jni/ but I had neither the time nor the 
>> inclination to clean up what is in places truly awful code. So I filed 
>> a follow RFE for someone else to do that cleanup:
>> https://bugs.openjdk.java.net/browse/JDK-8212961
>> Testing:
>>   - local testing showed corrupted names before the fix and no 
>> corruption afterwards
>>   - Windows specific testing showed 1 in 50 crash before and no 
>> crashes in 210 after
>> Thanks,
>> David

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