Re: [PATCH] use strnlen in pretty printer for "%.*s" (PR 81859)

[Martin Sebor <msebor at gmail dot com>]

On 08/16/2017 02:55 PM, David Malcolm wrote:
> On Wed, 2017-08-16 at 10:12 -0600, Martin Sebor wrote:
> > PR c/81859 - [8 Regression] valgrind error from
> > warn_about_normalization
> >
> > gcc/ChangeLog:
> >
> > 	PR c/81859
> > 	* pretty-print.c (pp_format): Use strnlen in %.*s to avoid
> > reading
> > 	past the end of an array.
> > 	(test_pp_format): Add test cases.
> >
> > Index: gcc/pretty-print.c
> > ===================================================================
> > --- gcc/pretty-print.c	(revision 251100)
> > +++ gcc/pretty-print.c	(working copy)
> > @@ -668,15 +668,11 @@ pp_format (pretty_printer *pp, text_info *text)
> >
> >  	    s = va_arg (*text->args_ptr, const char *);
> >
> > -	    /* Negative precision is treated as if it were
> > omitted.  */
> > -	    if (n < 0)
> > -	      n = INT_MAX;
> > +	    /* Append the lesser of precision and strlen (s)
> > characters
> > +	       from the array (which need not be a nul-terminated
> > string).
> > +	       Negative precision is treated as if it were
> > omitted.  */
> > +	    size_t len = n < 0 ? strlen (s) : strnlen (s, n);
> >
> > -	    /* Append the lesser of precision and strlen (s)
> > characters.  */
> > -	    size_t len = strlen (s);
> > -	    if ((unsigned) n < len)
> > -	      len = n;
> > -
> >  	    pp_append_text (pp, s, s + len);
> >  	  }
> >  	  break;
> > @@ -1438,6 +1434,13 @@ test_pp_format ()
> >    ASSERT_PP_FORMAT_2 ("A 12345678", "%c %x", 'A', 0x12345678);
> >    ASSERT_PP_FORMAT_2 ("hello world 12345678", "%s %x", "hello
> > world",
> >  		      0x12345678);
> > +
> > +  /* Not nul-terminated.  */
> > +  char arr[5] = { '1', '2', '3', '4', '5' };
> > +  ASSERT_PP_FORMAT_2 ("123", "%.*s", 3, arr);
> > +  ASSERT_PP_FORMAT_2 ("1234", "%.*s", -1, "1234");
> > +  ASSERT_PP_FORMAT_2 ("12345", "%.*s", 7, "12345");
> > +
>
> The other examples in this selftest append a trailing argument with a
> known bit pattern (0x12345678), to ensure that we're consuming
> arguments correctly.
>
> Please can you do the same for these tests.

Sure.  I committed the updated fix in r251157.

Martin