1 files changed, 14 insertions, 0 deletions
diff --git a/src/exit/exit.c b/src/exit/exit.c
index a6869b37..ca11b9ad 100644
--- a/src/exit/exit.c
+++ b/src/exit/exit.c
@@ -1,6 +1,9 @@
 #include <stdlib.h>
 #include <stdint.h>
 #include "libc.h"
+#include "pthread_impl.h"
+#include "atomic.h"
+#include "syscall.h"
 
 static void dummy()
 {
@@ -26,6 +29,17 @@ weak_alias(libc_exit_fini, __libc_exit_fini);
 
 _Noreturn void exit(int code)
 {
+	/* Handle potentially concurrent or recursive calls to exit,
+	 * whose behaviors have traditionally been undefined by the
+	 * standards. Using a custom lock here avoids pulling in lock
+	 * machinery and lets us trap recursive calls while supporting
+	 * multiple threads contending to be the one to exit(). */
+	static volatile int exit_lock[1];
+	int tid =  __pthread_self()->tid;
+	int prev = a_cas(exit_lock, 0, tid);
+	if (prev == tid) a_crash();
+	else if (prev) for (;;) __syscall(SYS_pause);
+
 	__funcs_on_exit();
 	__libc_exit_fini();
 	__stdio_exit();