Re: tor callgrinds

[Christopher Layne <clayne@xxxxxxxxxxxx>]

On Fri, Feb 16, 2007 at 09:19:51PM -0500, Watson Ladd wrote:
> I couldn't help but notice a strncpy in the diagrams. That's
> inefficient, and insecure. The reason is that strncpy fills the entire
> rest of the  target string with \x00 but might not do it if the sizes
> differ. Use strlcpy instead! It's almost a drop in replacement, faster,
> and more secure.
> Thanks,
> Watson Ladd
> 
> 

Without the visualizer itself it can be difficult to find the context just
by looking at a snapshot.

It's mainly being called from _tor_strndup(), from what I can see, which
specifically notes:

/** Allocate and return a new string containing the first <b>n</b>
 * characters of <b>s</b>.  If <b>s</b> is longer than <b>n</b>
 * characters, only the first <b>n</b> are copied.  The result is
 * always NUL-terminated.  (Like strndup(s,n), but never returns
 * NULL.)
 */
char *
_tor_strndup(const char *s, size_t n DMALLOC_PARAMS)
{
  char *dup;
  tor_assert(s);
  dup = _tor_malloc((n+1) DMALLOC_FN_ARGS);
  /* Performance note: Ordinarily we prefer strlcpy to strncpy.  But
   * this function gets called a whole lot, and platform strncpy is
   * much faster than strlcpy when strlen(s) is much longer than n.
   */
  strncpy(dup, s, n);
  dup[n]='\0';
  return dup;
}

-cl