add diagnostic counters for handled segfaults

ddprof-lib/src/main/cpp/counters.h

@@ -55,7 +55,9 @@
     X(CODECACHE_RUNTIME_STUBS_SIZE_BYTES, "codecache_runtime_stubs_size_bytes") \
     X(AGCT_NOT_REGISTERED_IN_TLS, "agct_not_registered_in_tls") \
     X(AGCT_NOT_JAVA, "agct_not_java") \
-    X(AGCT_NATIVE_NO_JAVA_CONTEXT, "agct_native_no_java_context")
+    X(AGCT_NATIVE_NO_JAVA_CONTEXT, "agct_native_no_java_context") \
+    X(HANDLED_SIGSEGV_SAFEFETCH, "handled_sigsegv_safefetch") \
+    X(HANDLED_SIGSEGV_WALKVM, "handled_sigsegv_walkvm")
 #define X_ENUM(a, b) a,
 typedef enum CounterId : int {
     DD_COUNTER_TABLE(X_ENUM) DD_NUM_COUNTERS

ddprof-lib/src/main/cpp/profiler.cpp

@@ -849,6 +849,7 @@ void Profiler::segvHandler(int signo, siginfo_t* siginfo, void* ucontext) {
         // Skip the fault instruction, as if it successfully loaded NULL
         frame.pc() += length;
         frame.retval() = 0;
+        Counters::increment(HANDLED_SIGSEGV_SAFEFETCH);
         return;
     }
 
@@ -857,6 +858,7 @@ void Profiler::segvHandler(int signo, siginfo_t* siginfo, void* ucontext) {
         // Act as if the load returned default_value argument
         frame.pc() += length;
         frame.retval() = frame.arg1();
+        Counters::increment(HANDLED_SIGSEGV_SAFEFETCH);
         return;
     }
 

ddprof-lib/src/main/cpp/stackWalker.cpp

@@ -424,6 +424,7 @@ int StackWalker::walkVM(void* ucontext, ASGCT_CallFrame* frames, int max_depth)
 void StackWalker::checkFault() {
     VMThread* vm_thread = VMThread::current();
     if (vm_thread != NULL && sameStack(vm_thread->exception(), &vm_thread)) {
+        Counters::increment(HANDLED_SIGSEGV_WALKVM);
         longjmp(*(jmp_buf*)vm_thread->exception(), 1);
     }
 }