+/*
+ * Are we in system call entry or in syscall exit?
+ *
+ * This bit is set after all syscall entry processing is done.
+ * Therefore, this bit will be set when next ptrace stop occurs,
+ * which should be syscall exit stop. Other stops which are possible
+ * directly after syscall entry (death, ptrace event stop)
+ * are simpler and handled without calling trace_syscall(), therefore
+ * the places where TCB_INSYSCALL can be set but we aren't in syscall stop
+ * are limited to trace(), this condition is never observed in trace_syscall()
+ * and below.
+ * The bit is cleared after all syscall exit processing is done.
+ * User-generated SIGTRAPs and post-execve SIGTRAP make it necessary
+ * to be very careful and NOT set TCB_INSYSCALL bit when they are encountered.
+ * TCB_WAITEXECVE bit is used for this purpose (see below).
+ *
+ * Use entering(tcp) / exiting(tcp) to check this bit to make code more readable.
+ */
+#define TCB_INSYSCALL 00004