From: Eli Zaretskii <eliz@gnu.org>
Date: Thu, 28 Aug 2014 16:26:39 +0000 (+0300)
Subject: Fix bug #18339 with segfault when $ is typed into empty LaTeX buffer.
X-Git-Tag: emacs-24.3.94~72
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=74910c5d074b4173bd0469ca4e315e9deac78718;p=emacs.git

Fix bug #18339 with segfault when $ is typed into empty LaTeX buffer.
Back-ported from trunk revision-id: 2014-08-27T19:40:54Z!eliz@gnu.org

 src/syntax.c (scan_lists): Don't examine positions before BEGV.
---

diff --git a/src/ChangeLog b/src/ChangeLog
index 8ca95025019..b3744eb8b6e 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,8 @@
+2014-08-28  Eli Zaretskii  <eliz@gnu.org>
+
+	* syntax.c (scan_lists): Don't examine positions before BEGV.
+	(Bug#18339)
+
 2014-08-25  Eli Zaretskii  <eliz@gnu.org>
 
 	* conf_post.h (_GL_EXECINFO_INLINE) [MSDOS]: Don't define.
diff --git a/src/syntax.c b/src/syntax.c
index 0ee48bb3725..5e697d350ff 100644
--- a/src/syntax.c
+++ b/src/syntax.c
@@ -2859,10 +2859,13 @@ scan_lists (EMACS_INT from, EMACS_INT count, EMACS_INT depth, bool sexpflag)
 	    case Smath:
 	      if (!sexpflag)
 		break;
-	      temp_pos = dec_bytepos (from_byte);
-	      UPDATE_SYNTAX_TABLE_BACKWARD (from - 1);
-	      if (from != stop && c == FETCH_CHAR_AS_MULTIBYTE (temp_pos))
-		DEC_BOTH (from, from_byte);
+	      if (from > BEGV)
+		{
+		  temp_pos = dec_bytepos (from_byte);
+		  UPDATE_SYNTAX_TABLE_BACKWARD (from - 1);
+		  if (from != stop && c == FETCH_CHAR_AS_MULTIBYTE (temp_pos))
+		    DEC_BOTH (from, from_byte);
+		}
 	      if (mathexit)
 		{
 		  mathexit = 0;