Avoid interleaving stderr lines when shutting down

* src/emacs.c (shut_down_emacs) [!DOS_NT]: Avoid interleaving
to stderr in the usual case, by using a single write and by
appending a newline.
* src/sysdep.c (emacs_backtrace) [HAVE_BACKTRACE_SYMBOLS_FD]:
Omit newline since shut_down_emacs now does that.

2 files changed, 23 insertions, 17 deletions

diff --git a/src/emacs.c b/src/emacs.c
index 9c93748a0f5..ad661a081b5 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -2454,23 +2454,29 @@ shut_down_emacs (int sig, Lisp_Object stuff)
 
   /* If we are controlling the terminal, reset terminal modes.  */
 #ifndef DOS_NT
-  {
-    pid_t pgrp = getpgrp ();
-    pid_t tpgrp = tcgetpgrp (0);
-    if ((tpgrp != -1) && tpgrp == pgrp)
-      {
-        reset_all_sys_modes ();
-        if (sig && sig != SIGTERM)
-          {
-            static char const format[] = "Fatal error %d: ";
-            char buf[sizeof format - 2 + INT_STRLEN_BOUND (int)];
-            int buflen = sprintf (buf, format, sig);
-            char const *sig_desc = safe_strsignal (sig);
+  pid_t tpgrp = tcgetpgrp (STDIN_FILENO);
+  if (tpgrp != -1 && tpgrp == getpgrp ())
+    {
+      reset_all_sys_modes ();
+      if (sig && sig != SIGTERM)
+        {
+          static char const fmt[] = "Fatal error %d: %n%s\n";
+          char buf[max ((sizeof fmt - sizeof "%d%n%s\n"
+                         + 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);
-            emacs_write (STDERR_FILENO, sig_desc, strlen (sig_desc));
-          }
-      }
-  }
+          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);
+            }
+        }
+    }
 #else
   fflush (stdout);
   reset_all_sys_modes ();
diff --git a/src/sysdep.c b/src/sysdep.c
index 9301405943b..f7478253a35 100644
--- a/src/sysdep.c
+++ b/src/sysdep.c
@@ -2436,7 +2436,7 @@ emacs_backtrace (int backtrace_limit)
 
   if (npointers)
     {
-      emacs_write (STDERR_FILENO, "\nBacktrace:\n", 12);
+      emacs_write (STDERR_FILENO, "Backtrace:\n", 11);
       backtrace_symbols_fd (buffer, npointers, STDERR_FILENO);
       if (bounded_limit < npointers)
         emacs_write (STDERR_FILENO, "...\n", 4);