[Python-checkins] r50855 - in python/trunk: Misc/NEWS Python/mystrtoul.c

[Neal Norwitz]

This fixed the problem on amd64 linux with gcc 4.1.1.

On 7/26/06, tim.peters <python-checkins at python.org> wrote:
> Author: tim.peters
> Date: Thu Jul 27 03:14:53 2006
> New Revision: 50855
>
> Modified:
>    python/trunk/Misc/NEWS
>    python/trunk/Python/mystrtoul.c
> Log:
> Bug #1521947:  possible bug in mystrtol.c with recent gcc.
>
> In general, C doesn't define anything about what happens when
> an operation on a signed integral type overflows, and PyOS_strtol()
> did several formally undefined things of that nature on signed
> longs.  Some version of gcc apparently tries to exploit that now,
> and PyOS_strtol() could fail to detect overflow then.
>
> Tried to repair all that, although it seems at least as likely to me
> that we'll get screwed by bad platform definitions for LONG_MIN
> and/or LONG_MAX now.  For that reason, I don't recommend backporting
> this.
>
> Note that I have no box on which this makes a lick of difference --
> can't really test it, except to note that it didn't break anything
> on my boxes.
>
> Silent change:  PyOS_strtol() used to return the hard-coded 0x7fffffff
> in case of overflow.  Now it returns LONG_MAX.  They're the same only on
> 32-bit boxes (although C doesn't guarantee that either ...).
>
>
> Modified: python/trunk/Misc/NEWS
> ==============================================================================
> --- python/trunk/Misc/NEWS      (original)
> +++ python/trunk/Misc/NEWS      Thu Jul 27 03:14:53 2006
> @@ -12,6 +12,11 @@
>  Core and builtins
>  -----------------
>
> +- Bug #1521947: When checking for overflow, ``PyOS_strtol()`` used some
> +  operations on signed longs that are formally undefined by C.
> +  Unfortunately, at least one compiler now cares about that, so complicated
> +  the code to make that compiler happy again.
> +
>  - Bug #1524310: Properly report errors from FindNextFile in os.listdir.
>
>  - Patch #1232023: Stop including current directory in search
> @@ -37,7 +42,7 @@
>    mapping the faux "thread id" 0 to the current frame.
>
>  - Bug #1525447: build on MacOS X on a case-sensitive filesystem.
> -
> +
>
>  Library
>  -------
> @@ -88,7 +93,7 @@
>  Extension Modules
>  -----------------
>
> -- Bug #1471938: Fix curses module build problem on Solaris 8; patch by
> +- Bug #1471938: Fix curses module build problem on Solaris 8; patch by
>    Paul Eggert.
>
>  - Patch #1448199: Release interpreter lock in _winreg.ConnectRegistry.
>
> Modified: python/trunk/Python/mystrtoul.c
> ==============================================================================
> --- python/trunk/Python/mystrtoul.c     (original)
> +++ python/trunk/Python/mystrtoul.c     Thu Jul 27 03:14:53 2006
> @@ -195,10 +195,19 @@
>         return (unsigned long)-1;
>  }
>
> +/* Checking for overflow in PyOS_strtol is a PITA since C doesn't define
> + * anything about what happens when a signed integer operation overflows,
> + * and some compilers think they're doing you a favor by being "clever"
> + * then.  Python assumes a 2's-complement representation, so that the bit
> + * pattern for the largest postive signed long is LONG_MAX, and for
> + * the smallest negative signed long is LONG_MAX + 1.
> + */
> +
>  long
>  PyOS_strtol(char *str, char **ptr, int base)
>  {
>         long result;
> +       unsigned long uresult;
>         char sign;
>
>         while (*str && isspace(Py_CHARMASK(*str)))
> @@ -208,17 +217,20 @@
>         if (sign == '+' || sign == '-')
>                 str++;
>
> -       result = (long) PyOS_strtoul(str, ptr, base);
> +       uresult = PyOS_strtoul(str, ptr, base);
>
> -       /* Signal overflow if the result appears negative,
> -          except for the largest negative integer */
> -       if (result < 0 && !(sign == '-' && result == -result)) {
> +       if (uresult <= (unsigned long)LONG_MAX) {
> +               result = (long)uresult;
> +               if (sign == '-')
> +                       result = -result;
> +       }
> +       else if (sign == '-' && uresult == (unsigned long)LONG_MAX + 1) {
> +               assert(LONG_MIN == -LONG_MAX-1);
> +               result = LONG_MIN;
> +       }
> +       else {
>                 errno = ERANGE;
> -               result = 0x7fffffff;
> +               result = LONG_MAX;
>         }
> -
> -       if (sign == '-')
> -               result = -result;
> -
>         return result;
>  }
> _______________________________________________
> Python-checkins mailing list
> Python-checkins at python.org
> http://mail.python.org/mailman/listinfo/python-checkins
>