FULL PRODUCT VERSION : java version " 1.7.0_21 " Java(TM) SE Runtime Environment (build 1.7.0_21-b11) Java HotSpot(TM) 64-Bit Server VM (build 23.21-b01, mixed mode) FULL OS VERSION : Linux xxx.xxx.xxx 2.6.18-128.1.6.el5 #1 SMP Tue Mar 24 12:05:57 EDT 2009 x86_64 x86_64 x86_64 GNU/Linux A DESCRIPTION OF THE PROBLEM : We have native code in our JVM. The native code uses signals. It attempts to call sigaction() where the signal >= 0x20. We LD_PRELOAD the libjsig.so library as documented. When the native code attempts to sigaction(0x2B) i.e. signal 0x2B, the JVM crashes. The problem is with the macro #define MAXSIGNUM 32 #define MASK(sig) ((unsigned int)1 << sig) In OpenJDK source file jsig.c. MASK() appears to assume that if sig>=0x20 then the result will be zero. But this is not correct. When shifting a 32-bit integer by a variable amount, the shift amount is masked by 0x1F before the shift happens. So ((unsigned int)1 << 0x2B) is the same as ((unsigned int)1 << 0x0B) and this results in an attempt to access beyond the end of the array sact[]. THE PROBLEM WAS REPRODUCIBLE WITH -Xint FLAG: Yes THE PROBLEM WAS REPRODUCIBLE WITH -server FLAG: Yes STEPS TO FOLLOW TO REPRODUCE THE PROBLEM : Write a JNI function that calls sigaction(0x2B) and run it while libjsig.so is LD_PRELOADed. EXPECTED VERSUS ACTUAL BEHAVIOR : The libjsig.so library should pass through the sigaction(0x2B) from its interceptor to the OS function. In fact, the JVM crashes. ERROR MESSAGES/STACK TRACES THAT OCCUR : This is the gdb stack trace: (gdb) whe #0 0x0000003d0960ce74 in __lll_lock_wait () from /lib64/libpthread.so.0 #1 0x0000003d09608874 in _L_lock_106 () from /lib64/libpthread.so.0 #2 0x0000003d096082e0 in pthread_mutex_lock () from /lib64/libpthread.so.0 #3 0x00002b30d520ea44 in signal_lock () from /home/murrap/jdk1.7.0_21/jre/lib/amd64/libjsig.so #4 0x00002b30d520ee40 in sigaction () from /home/murrap/jdk1.7.0_21/jre/lib/amd64/libjsig.so #5 0x00002b30d5ee606e in VMError::reset_signal_handlers () from /home/murrap/jdk1.7.0_21/jre/lib/amd64/server/libjvm.so #6 0x00002b30d5ee5b46 in VMError::report_and_die () from /home/murrap/jdk1.7.0_21/jre/lib/amd64/server/libjvm.so #7 0x00002b30d5d89370 in JVM_handle_linux_signal () from /home/murrap/jdk1.7.0_21/jre/lib/amd64/server/libjvm.so #8 <signal handler called> #9 0x00002b30d520eed7 in sigaction () from /home/murrap/jdk1.7.0_21/jre/lib/amd64/libjsig.so #10 0x00002aaab82eb6ee in Java_TestJNI_doSomething () from /home/murrap/jni/libTestJNI.so The thread hangs in sigaction() while attempting to acquire a lock that is already held at frame #9 by the application native code. REPRODUCIBILITY : This bug can be reproduced always. ---------- BEGIN SOURCE ---------- This is the native code. You'd need to construct a caller in java: #include <stdio.h> #include <jni.h> #define __USE_GNU #include <signal.h> #include <sys/ucontext.h> void sig_handler(int sig, siginfo_t *info, ucontext_t *context) { int thrNum; printf( " HANDLER (1) " ); // Move forward RIP to skip failing instruction context->uc_mcontext.gregs[REG_RIP] += 6; } JNIEXPORT void JNICALL Java_TestJNI_doSomething(JNIEnv *env, jclass klass, jint val) { struct sigaction act; struct sigaction oact; pthread_attr_t attr; stack_t stack; act.sa_flags = SA_ONSTACK|SA_RESTART|SA_SIGINFO; sigfillset(&act.sa_mask); act.sa_handler = SIG_DFL; act.sa_sigaction = (void (*)())sig_handler; sigaction(0x20+SIGSEGV, &act, &oact); printf( " doSomething(%d) " , val); printf( " old handler = %p " , oact.sa_handler); } ---------- END SOURCE ---------- CUSTOMER SUBMITTED WORKAROUND : There is no solution for this problem except a modification of the behaviour of jsig.c.
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