libc: Block and ignore appropriate signals in system()

libc/include/signal.h

@@ -8,6 +8,8 @@
 
 typedef int sig_atomic_t;
 
+#define SIG_ERR (__simple_sighandler_t)(-3)
+
 #ifdef __cplusplus
 extern "C"
 {
@@ -19,6 +21,9 @@ extern "C"
     int sigaction(int signo, const struct sigaction* act, struct sigaction* oldact);
 #pragma GCC pop_options
 
+    /* Change the current thread's signal disposition for a specific signal. */
+    __simple_sighandler_t signal(int signo, __simple_sighandler_t handler);
+
     /* Send a signal to a specific process. */
     int kill(pid_t pid, int signo);
 

libc/src/signal.cpp

@@ -13,6 +13,18 @@ extern "C"
         __errno_return(rc, int);
     }
 
+    __simple_sighandler_t signal(int signo, __simple_sighandler_t handler)
+    {
+        struct sigaction act, oldact;
+        act.sa_handler = handler;
+        sigemptyset(&act.sa_mask);
+        act.sa_flags = 0;
+
+        if (sigaction(signo, &act, &oldact) < 0) return SIG_ERR;
+
+        return oldact.sa_handler;
+    }
+
     int kill(pid_t pid, int signo)
     {
         long rc = syscall(SYS_kill, pid, signo);

libc/src/stdlib.cpp

@@ -191,9 +191,6 @@ extern "C"
             return S_ISREG(st.st_mode);
         }
 
-        // FIXME: During the execution of system(), SIGCHLD will be blocked, and SIGINT and SIGQUIT will be ignored, in
-        // the process that calls system().
-
         pid_t child = fork();
         if (child == 0)
         {
@@ -203,9 +200,21 @@ extern "C"
 
         if (child < 0) return -1;
 
+        sigset_t set, oldset;
+        sigemptyset(&set);
+        sigaddset(&set, SIGCHLD);
+        sigprocmask(SIG_BLOCK, &set, &oldset);
+
+        auto old_int = signal(SIGINT, SIG_IGN);
+        auto old_quit = signal(SIGQUIT, SIG_IGN);
+
         int status;
         waitpid(child, &status, 0);
 
+        sigprocmask(SIG_SETMASK, &oldset, nullptr);
+        signal(SIGINT, old_int);
+        signal(SIGQUIT, old_quit);
+
         return status;
     }