We mostly see this on s390, but occasionally also on other platforms (eg x64).

s390, 15.10.20:

testMultipleCallsNoCheck start
Warning: SIGINT handler expected:libjvm.so+0x97a220 found:0x0000000000000001
Running in non-interactive shell, SIGINT handler is replaced by shell
Signal Handlers:
SIGSEGV: [libjvm.so+0x979a40], sa_mask[0]=11111111011111111101111111111110, sa_flags=SA_RESTART|SA_SIGINFO
SIGBUS: [libjvm.so+0x979a40], sa_mask[0]=11111111011111111101111111111110, sa_flags=SA_RESTART|SA_SIGINFO
SIGFPE: [libjvm.so+0x979a40], sa_mask[0]=11111111011111111101111111111110, sa_flags=SA_RESTART|SA_SIGINFO
SIGPIPE: [libjvm.so+0x979a40], sa_mask[0]=11111111011111111101111111111110, sa_flags=SA_RESTART|SA_SIGINFO
SIGXFSZ: [libjvm.so+0x979a40], sa_mask[0]=11111111011111111101111111111110, sa_flags=SA_RESTART|SA_SIGINFO
SIGILL: [libjvm.so+0x979a40], sa_mask[0]=11111111011111111101111111111110, sa_flags=SA_RESTART|SA_SIGINFO
SIGUSR2: [libjvm.so+0x9798f0], sa_mask[0]=00100000000000000000000000000000, sa_flags=SA_RESTART|SA_SIGINFO
SIGHUP: [libjvm.so+0x97a220], sa_mask[0]=11111111011111111101111111111110, sa_flags=SA_RESTART|SA_SIGINFO
SIGINT: SIG_IGN, sa_mask[0]=00000000000000000000000000000000, sa_flags=none
SIGTERM: [libjvm.so+0x97a220], sa_mask[0]=11111111011111111101111111111110, sa_flags=SA_RESTART|SA_SIGINFO
SIGQUIT: [libjvm.so+0x97a220], sa_mask[0]=11111111011111111101111111111110, sa_flags=EXPECT_WARNING_START 1
SA_RESTART|SA_SIGINFO
WARNING in native method: JNI call made without checking exceptions when required to from CallVoidMethod
at TestCheckedJniExceptionCheck.callJavaFromNative(Native Method)
at TestCheckedJniExceptionCheck.testMultipleCallsNoCheck(TestCheckedJniExceptionCheck.java:100)
at TestCheckedJniExceptionCheck.test(TestCheckedJniExceptionCheck.java:69)
at TestCheckedJniExceptionCheck.main(TestCheckedJniExceptionCheck.java:200)
EXPECT_WARNING_END
testMultipleCallsNoCheck end
testMultipleCallsCheck start
testMultipleCallsCheck end
testNestedSingleCallsNoCheck start
testNestedSingleCallsNoCheck end
testNestedSingleCallsCheck start
testNestedSingleCallsCheck end
testNestedMultipleCallsNoCheck start
EXPECT_WARNING_START 3
WARNING in native method: JNI call made without checking exceptions when required to from CallVoidMethod
at TestCheckedJniExceptionCheck.callJavaFromNative(Native Method)
at TestCheckedJniExceptionCheck.callableNestedMethod(TestCheckedJniExceptionCheck.java:142)
at TestCheckedJniExceptionCheck.callNestedJavaFromNative(Native Method)
at TestCheckedJniExceptionCheck.testNestedMultipleCallsNoCheck(TestCheckedJniExceptionCheck.java:126)
at TestCheckedJniExceptionCheck.test(TestCheckedJniExceptionCheck.java:74)
at TestCheckedJniExceptionCheck.main(TestCheckedJniExceptionCheck.java:200)
WARNING in native method: JNI call made without checking exceptions when required to from CallVoidMethod
at TestCheckedJniExceptionCheck.callNestedJavaFromNative(Native Method)
at TestCheckedJniExceptionCheck.testNestedMultipleCallsNoCheck(TestCheckedJniExceptionCheck.java:126)
at TestCheckedJniExceptionCheck.test(TestCheckedJniExceptionCheck.java:74)
at TestCheckedJniExceptionCheck.main(TestCheckedJniExceptionCheck.java:200)
WARNING in native method: JNI call made without checking exceptions when required to from CallVoidMethod
at TestCheckedJniExceptionCheck.callJavaFromNative(Native Method)
at TestCheckedJniExceptionCheck.callableNestedMethod(TestCheckedJniExceptionCheck.java:142)
at TestCheckedJniExceptionCheck.callNestedJavaFromNative(Native Method)
at TestCheckedJniExceptionCheck.testNestedMultipleCallsNoCheck(TestCheckedJniExceptionCheck.java:126)
at TestCheckedJniExceptionCheck.test(TestCheckedJniExceptionCheck.java:74)
at TestCheckedJniExceptionCheck.main(TestCheckedJniExceptionCheck.java:200)
EXPECT_WARNING_END
testNestedMultipleCallsNoCheck end
testNestedMultipleCallsCheck start
testNestedMultipleCallsCheck end
];
 stderr: []
 exitValue = 0

java.lang.RuntimeException: Unexpected warning at line 24

s390, 12.10.2019 (first occurrence AFAICS):

testMultipleCallsNoCheck start
Warning: SIGINT handler EXPECT_WARNING_START 1
expected:libjvm.so+0x10b05a8 found:0x0000000000000001
Running in non-interactive shell, SIGINT handler is replaced by shell
Signal Handlers:
SIGSEGV: [libjvm.so+0x10af5f8], sa_mask[0]=11111111011111111101111111111110, sa_flags=SA_RESTART|SA_SIGINFO
SIGBUS: [libjvm.so+0x10af5f8], sa_mask[0]=11111111011111111101111111111110, sa_flags=SA_RESTART|SA_SIGINFO
SIGFPE: [libjvm.so+0x10af5f8], sa_mask[0]=11111111011111111101111111111110, sa_flags=SA_RESTART|SA_SIGINFO
SIGPIPE: [libjvm.so+0x10af5f8], sa_mask[0]=11111111011111111101111111111110, sa_flags=SA_RESTART|SA_SIGINFO
SIGXFSZ: [libjvm.so+0x10af5f8], sa_mask[0]=11111111011111111101111111111110, sa_flags=SA_RESTART|SA_SIGINFO
SIGILL: [libjvm.so+0x10af5f8], sa_mask[0]=11111111011111111101111111111110, sa_flags=SA_RESTART|SA_SIGINFO
SIGUSR2: [libjvm.so+0x10af410], sa_mask[0]=00100000000000000000000000000000, sa_flags=SA_RESTART|SA_SIGINFO
SIGHUP: [libjvm.so+0x10b05a8], sa_mask[0]=11111111011111111101111111111110, sa_flags=SA_RESTART|SA_SIGINFO
SIGINT: SIG_IGN, sa_mask[0]=00000000000000000000000000000000, sa_flags=none
SIGTERM: [libjvm.so+0x10b05a8], sa_mask[0]=11111111011111111101111111111110, sa_flags=SA_RESTART|SA_SIGINFO
SIGQUIT: [libjvm.so+0x10b05a8], sa_mask[0]=11111111011111111101111111111110, sa_flags=SA_RESTART|SA_SIGINFO
WARNING in native method: JNI call made without checking exceptions when required to from CallVoidMethod
at TestCheckedJniExceptionCheck.callJavaFromNative(Native Method)
at TestCheckedJniExceptionCheck.testMultipleCallsNoCheck(TestCheckedJniExceptionCheck.java:100)
at TestCheckedJniExceptionCheck.test(TestCheckedJniExceptionCheck.java:69)
at TestCheckedJniExceptionCheck.main(TestCheckedJniExceptionCheck.java:200)
EXPECT_WARNING_END
testMultipleCallsNoCheck end
testMultipleCallsCheck start
testMultipleCallsCheck end
testNestedSingleCallsNoCheck start
testNestedSingleCallsNoCheck end
testNestedSingleCallsCheck start
testNestedSingleCallsCheck end
testNestedMultipleCallsNoCheck start
EXPECT_WARNING_START 3
WARNING in native method: JNI call made without checking exceptions when required to from CallVoidMethod
at TestCheckedJniExceptionCheck.callJavaFromNative(Native Method)
at TestCheckedJniExceptionCheck.callableNestedMethod(TestCheckedJniExceptionCheck.java:142)
at TestCheckedJniExceptionCheck.callNestedJavaFromNative(Native Method)
at TestCheckedJniExceptionCheck.testNestedMultipleCallsNoCheck(TestCheckedJniExceptionCheck.java:126)
at TestCheckedJniExceptionCheck.test(TestCheckedJniExceptionCheck.java:74)
at TestCheckedJniExceptionCheck.main(TestCheckedJniExceptionCheck.java:200)
WARNING in native method: JNI call made without checking exceptions when required to from CallVoidMethod
at TestCheckedJniExceptionCheck.callNestedJavaFromNative(Native Method)
at TestCheckedJniExceptionCheck.testNestedMultipleCallsNoCheck(TestCheckedJniExceptionCheck.java:126)
at TestCheckedJniExceptionCheck.test(TestCheckedJniExceptionCheck.java:74)
at TestCheckedJniExceptionCheck.main(TestCheckedJniExceptionCheck.java:200)
WARNING in native method: JNI call made without checking exceptions when required to from CallVoidMethod
at TestCheckedJniExceptionCheck.callJavaFromNative(Native Method)
at TestCheckedJniExceptionCheck.callableNestedMethod(TestCheckedJniExceptionCheck.java:142)
at TestCheckedJniExceptionCheck.callNestedJavaFromNative(Native Method)
at TestCheckedJniExceptionCheck.testNestedMultipleCallsNoCheck(TestCheckedJniExceptionCheck.java:126)
at TestCheckedJniExceptionCheck.test(TestCheckedJniExceptionCheck.java:74)
at TestCheckedJniExceptionCheck.main(TestCheckedJniExceptionCheck.java:200)
EXPECT_WARNING_END
testNestedMultipleCallsNoCheck end
testNestedMultipleCallsCheck start
testNestedMultipleCallsCheck end
];
 stderr: []
 exitValue = 0

java.lang.RuntimeException: Unexpected warning at line 24
at TestCheckedJniExceptionCheck.checkOuputForCorrectWarnings(TestCheckedJniExceptionCheck.java:171)