psx: free allocated memory at exit.

Kalen Hall reported that Valgrind detected a memory leak associated
with a multi-threaded program linked against libcap and libpsx.

  https://bugzilla.kernel.org/show_bug.cgi?id=215551

I've been unable to validate this myself with valgrind (likely holding
it wrong), but did explore psx for allocated memory and via fprintf's
convinced myself that this change should pair all calloc()s with a
corresponding free().

Signed-off-by: Andrew G. Morgan <morgan@kernel.org>
diff --git a/psx/psx.c b/psx/psx.c
index 6b669ae..1876978 100644
--- a/psx/psx.c
+++ b/psx/psx.c
@@ -29,6 +29,26 @@
 
 #include "psx_syscall.h"
 
+#ifdef _PSX_DEBUG_MEMORY
+
+static void *_psx_calloc(const char *file, const int line,
+			 size_t nmemb, size_t size) {
+    void *ptr = calloc(nmemb, size);
+    fprintf(stderr, "psx:%d:%s:%d: calloc(%ld, %ld) -> %p\n", gettid(),
+	    file, line, (long int)nmemb, (long int)size, ptr);
+    return ptr;
+}
+
+static void _psx_free(const char *file, const int line, void *ptr) {
+    fprintf(stderr, "psx:%d:%s:%d: free(%p)\n", gettid(), file, line, ptr);
+    return free(ptr);
+}
+
+#define calloc(a, b)  _psx_calloc(__FILE__, __LINE__, a, b)
+#define free(a)       _psx_free(__FILE__, __LINE__, a)
+
+#endif /* def _PSX_DEBUG_MEMORY */
+
 /*
  * psx_load_syscalls() can be weakly defined in dependent libraries to
  * provide a mechanism for a library to optionally leverage this psx
@@ -177,6 +197,7 @@
  * Some forward declarations for the initialization
  * psx_syscall_start() routine.
  */
+static void _psx_cleanup(void);
 static void _psx_prepare_fork(void);
 static void _psx_fork_completed(void);
 static void _psx_forked_child(void);
@@ -240,6 +261,7 @@
 
     psx_confirm_sigaction();
     psx_do_registration(); /* register the main thread. */
+    atexit(_psx_cleanup);
 
     psx_tracker.initialized = 1;
 }
@@ -420,7 +442,7 @@
     pthread_sigmask(SIG_SETMASK, &orig_sigbits, NULL);
 
     /*
-     * Allow the rest of the psx system carry on as per normal.
+     * Allow the rest of the psx system to carry on as per normal.
      */
     psx_new_state(_PSX_EXITING, _PSX_IDLE);
 }
@@ -700,6 +722,26 @@
 }
 
 /*
+ * _psx_cleanup its called when the program exits. It is used to free
+ * any memory used by the thread tracker.
+ */
+static void _psx_cleanup(void) {
+    registered_thread_t *ref, *next;
+
+    /*
+     * We enter the exiting state. Unlike exiting a single thread we
+     * never leave this state since this cleanup is only done at
+     * program exit.
+     */
+    psx_new_state(_PSX_IDLE, _PSX_EXITING);
+
+    for (ref = psx_tracker.root; ref; ref = next) {
+	next = ref->next;
+	psx_do_unregister(ref);
+    }
+}
+
+/*
  * Change the PSX sensitivity level. If the threads appear to have
  * diverged in behavior, this can cause the library to notify the
  * user.