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 06:03:33 UTC 2018

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:


(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:


   - 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


More information about the hotspot-runtime-dev mailing list