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[PATCH] genmodes: remove misleading use of strncpy


Found by inspection.
Seeing this strncpy use without the usual following NUL-termination,
my reflex was that it was a buffer overrun candidate, but then I
realized this is gcc, so that's not very likely.
Looking a little harder, I saw the preceding strlen >= sizeof buf test,
which means there is no risk of overrun.

That preceding test means the use of strncpy is misleading, since
with that there is no risk of the name being too long for the buffer,
and hence no reason to use strncpy.
One way to make the code clearer is to use strcpy, as done below.
An alternative is to use memcpy (buf, m->name, strlen (m->name) + 1).

Ok to commit?

2012-04-19  Jim Meyering  <meyering@redhat.com>

	genmodes: remove misleading use of strncpy
	* genmodes.c (make_complex_modes): Avoid unnecessary use of strncpy.
	We verified above that the string(including trailing NUL) fits in buf,
	so just use strcpy.


diff --git a/gcc/genmodes.c b/gcc/genmodes.c
index 8b6f5bc..f786258 100644
--- a/gcc/genmodes.c
+++ b/gcc/genmodes.c
@@ -1,15 +1,15 @@
 /* Generate the machine mode enumeration and associated tables.
-   Copyright (C) 2003, 2004, 2005, 2006, 2007, 2010
+   Copyright (C) 2003, 2004, 2005, 2006, 2007, 2010, 2012
    Free Software Foundation, Inc.

 This file is part of GCC.

 GCC is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free
 Software Foundation; either version 3, or (at your option) any later
 version.

 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
 WARRANTY; without even the implied warranty of MERCHANTABILITY or
 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 for more details.
@@ -442,27 +442,27 @@ make_complex_modes (enum mode_class cl,
       if (strlen (m->name) >= sizeof buf)
 	{
 	  error ("%s:%d:mode name \"%s\" is too long",
 		 m->file, m->line, m->name);
 	  continue;
 	}

       /* Float complex modes are named SCmode, etc.
 	 Int complex modes are named CSImode, etc.
          This inconsistency should be eliminated.  */
       if (cl == MODE_FLOAT)
 	{
 	  char *p, *q = 0;
-	  strncpy (buf, m->name, sizeof buf);
+	  strcpy (buf, m->name);
 	  p = strchr (buf, 'F');
 	  if (p == 0)
 	    q = strchr (buf, 'D');
 	  if (p == 0 && q == 0)
 	    {
 	      error ("%s:%d: float mode \"%s\" has no 'F' or 'D'",
 		     m->file, m->line, m->name);
 	      continue;
 	    }

 	  if (p != 0)
 	    *p = 'C';
 	  else
--
1.7.10.208.gb4267


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