Enable ISIG control mode of termios after exit

The ISIG control mode is disabled in capture_keyboard_input(), but
it is not reset in reset_keyboard_input(). This inconsistency causes
default keyboard signal malfunctions (e.g., SIGINT from CTRL+C) after
exit. To fix this, the termios control flag is encapsulated in a
macro, TERMIOS_C_CFLAG and used in both capture_keyboard_input() and
reset_keyboard_input().

Author: ChinYikMing

uart.c

@@ -10,6 +10,23 @@
 #include "riscv.h"
 #include "riscv_private.h"
 
+/*
+ * The control mode flag for keyboard.
+ *
+ * ICANON: Enable canonical mode.
+ * ECHO: Echo input characters.
+ * ISIG: When any of the characters INTR, QUIT,
+ *       SUSP, or DSUSP are received, generate the
+ *       corresponding signal.
+ *
+ * It is essential to re-enable ISIG upon exit.
+ * Otherwise, the default signal handler will
+ * not catch the signal. E.g., SIGINT generated by
+ * CTRL + c.
+ *
+ */
+#define TERMIOS_C_CFLAG (ICANON | ECHO | ISIG)
+
 /* Emulate 8250 (plain, without loopback mode support) */
 
 #define U8250_INT_THRE 1
@@ -19,7 +36,7 @@ static void reset_keyboard_input()
     /* Re-enable echo, etc. on keyboard. */
     struct termios term;
     tcgetattr(0, &term);
-    term.c_lflag |= ICANON | ECHO;
+    term.c_lflag |= TERMIOS_C_CFLAG;
     tcsetattr(0, TCSANOW, &term);
 }
 
@@ -31,7 +48,7 @@ void capture_keyboard_input()
 
     struct termios term;
     tcgetattr(0, &term);
-    term.c_lflag &= ~(ICANON | ECHO | ISIG); /* Disable echo as well */
+    term.c_lflag &= ~TERMIOS_C_CFLAG; /* Disable echo as well */
     tcsetattr(0, TCSANOW, &term);
 }