master 1cc20535f87: Stop using printf %n

[Paul Eggert]

branch: master
commit 1cc20535f8730f49cd5d012313c1eaf0627d7216
Author: Paul Eggert <eggert@cs.ucla.edu>
Commit: Paul Eggert <eggert@cs.ucla.edu>

    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.
---
 src/emacs.c | 23 +++++++++++++++--------
 1 file 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);
            }
        }
     }