Stop using printf %n

* src/emacs.c (shut_down_emacs): Don’t use printf’s "%n" format.
Android, MS-Windows, and OpenBSD don’t support it, and it’s easy
enough to do its equivalent by hand.

1 files changed, 15 insertions, 8 deletions

diff --git a/src/emacs.c b/src/emacs.c
index 80a013b68df..5a036554a87 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -2959,24 +2959,31 @@ shut_down_emacs (int sig, Lisp_Object stuff)
       reset_all_sys_modes ();
       if (sig && sig != SIGTERM)
         {
-          static char const fmt[] = "Fatal error %d: %n%s\n";
 #ifdef HAVE_HAIKU
           if (haiku_debug_on_fatal_error)
             debugger ("Fatal error in Emacs");
 #endif
-          char buf[max ((sizeof fmt - sizeof "%d%n%s\n"
+          /* Output a "Fatal error NUM: DESC\n" diagnostic with a single write,
+             but use multiple writes if the diagnosic is absurdly long
+             and likely couldn't be written atomically anyway.  */
+          static char const fmt[] = "Fatal error %d: ";
+          char buf[max ((sizeof fmt - sizeof "%d"
                          + INT_STRLEN_BOUND (int) + 1),
                         min (PIPE_BUF, MAX_ALLOCA))];
           char const *sig_desc = safe_strsignal (sig);
-          int nlen;
-          int buflen = snprintf (buf, sizeof buf, fmt, sig, &nlen, sig_desc);
-          if (0 <= buflen && buflen < sizeof buf)
-            emacs_write (STDERR_FILENO, buf, buflen);
+          size_t sig_desclen = strlen (sig_desc);
+          int nlen = sprintf (buf, fmt, sig);
+          if (nlen + sig_desclen < sizeof buf - 1)
+            {
+              char *p = mempcpy (buf + nlen, sig_desc, sig_desclen);
+              *p++ = '\n';
+              emacs_write (STDERR_FILENO, buf, p - buf);
+            }
           else
             {
               emacs_write (STDERR_FILENO, buf, nlen);
-              emacs_write (STDERR_FILENO, sig_desc, strlen (sig_desc));
-              emacs_write (STDERR_FILENO, fmt + sizeof fmt - 2, 1);
+              emacs_write (STDERR_FILENO, sig_desc, sig_desclen);
+              emacs_write (STDERR_FILENO, "\n", 1);
             }
         }
     }