Avoid stdio in SIGINT handler

* admin/merge-gnulib (GNULIB_MODULES): Add ignore-value.
* lib/gnulib.mk, m4/gnulib-comp.m4: Regenerate.
* lib/ignore-value.h: New file, from gnulib.
* src/keyboard.c: Include it.
(write_stdout, read_stdin): New functions.
(handle_interrupt): Use them instead of printf and getchar,
and avoid fflush when handling signals.

1 files changed, 47 insertions, 26 deletions

diff --git a/src/keyboard.c b/src/keyboard.c
index fcafd0bc9a1..6bdfc1aa084 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -64,6 +64,8 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include <unistd.h>
 #include <fcntl.h>
 
+#include <ignore-value.h>
+
 #ifdef HAVE_WINDOW_SYSTEM
 #include TERM_HEADER
 #endif /* HAVE_WINDOW_SYSTEM */
@@ -10206,6 +10208,21 @@ deliver_interrupt_signal (int sig)
   deliver_process_signal (sig, handle_interrupt_signal);
 }
 
+/* Output MSG directly to standard output, without buffering.  Ignore
+   failures.  This is safe in a signal handler.  */
+static void
+write_stdout (char const *msg)
+{
+  ignore_value (write (STDOUT_FILENO, msg, strlen (msg)));
+}
+
+/* Read a byte from stdin, without buffering.  Safe in signal handlers.  */
+static int
+read_stdin (void)
+{
+  char c;
+  return read (STDIN_FILENO, &c, 1) == 1 ? c : EOF;
+}
 
 /* If Emacs is stuck because `inhibit-quit' is true, then keep track
    of the number of times C-g has been requested.  If C-g is pressed
@@ -10242,9 +10259,9 @@ handle_interrupt (bool in_signal_handler)
           sigemptyset (&blocked);
           sigaddset (&blocked, SIGINT);
           pthread_sigmask (SIG_BLOCK, &blocked, 0);
+          fflush (stdout);
         }
 
-      fflush (stdout);
       reset_all_sys_modes ();
 
 #ifdef SIGTSTP
@@ -10260,8 +10277,9 @@ handle_interrupt (bool in_signal_handler)
       /* Perhaps should really fork an inferior shell?
          But that would not provide any way to get back
          to the original shell, ever.  */
-      printf ("No support for stopping a process on this operating system;\n");
-      printf ("you can continue or abort.\n");
+      write_stdout ("No support for stopping a process"
+                    " on this operating system;\n"
+                    "you can continue or abort.\n");
 #endif /* not SIGTSTP */
 #ifdef MSDOS
       /* We must remain inside the screen area when the internal terminal
@@ -10272,46 +10290,49 @@ handle_interrupt (bool in_signal_handler)
          the code used for auto-saving doesn't cope with the mark bit.  */
       if (!gc_in_progress)
         {
-          printf ("Auto-save? (y or n) ");
-          fflush (stdout);
-          if (((c = getchar ()) & ~040) == 'Y')
+          write_stdout ("Auto-save? (y or n) ");
+          c = read_stdin ();
+          if ((c & 040) == 'Y')
             {
               Fdo_auto_save (Qt, Qnil);
 #ifdef MSDOS
-              printf ("\r\nAuto-save done");
-#else /* not MSDOS */
-              printf ("Auto-save done\n");
-#endif /* not MSDOS */
+              write_stdout ("\r\nAuto-save done");
+#else
+              write_stdout ("Auto-save done\n");
+#endif
             }
-          while (c != '\n') c = getchar ();
+          while (c != '\n')
+            c = read_stdin ();
         }
       else
         {
           /* During GC, it must be safe to reenable quitting again.  */
           Vinhibit_quit = Qnil;
+          write_stdout
+            (
 #ifdef MSDOS
-          printf ("\r\n");
-#endif /* not MSDOS */
-          printf ("Garbage collection in progress; cannot auto-save now\r\n");
-          printf ("but will instead do a real quit after garbage collection ends\r\n");
-          fflush (stdout);
+             "\r\n"
+#endif
+             "Garbage collection in progress; cannot auto-save now\r\n"
+             "but will instead do a real quit"
+             " after garbage collection ends\r\n");
         }
 
 #ifdef MSDOS
-      printf ("\r\nAbort?  (y or n) ");
-#else /* not MSDOS */
-      printf ("Abort (and dump core)? (y or n) ");
-#endif /* not MSDOS */
-      fflush (stdout);
-      if (((c = getchar ()) & ~040) == 'Y')
+      write_stdout ("\r\nAbort?  (y or n) ");
+#else
+      write_stdout ("Abort (and dump core)? (y or n) ");
+#endif
+      c = read_stdin ();
+      if ((c & ~040) == 'Y')
         emacs_abort ();
-      while (c != '\n') c = getchar ();
+      while (c != '\n')
+        c = read_stdin ();
 #ifdef MSDOS
-      printf ("\r\nContinuing...\r\n");
+      write_stdout ("\r\nContinuing...\r\n");
 #else /* not MSDOS */
-      printf ("Continuing...\n");
+      write_stdout ("Continuing...\n");
 #endif /* not MSDOS */
-      fflush (stdout);
       init_all_sys_modes ();
     }
   else