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 ...).
diff --git a/Python/mystrtoul.c b/Python/mystrtoul.c
index 51553fb..0dda4be 100644
--- a/Python/mystrtoul.c
+++ b/Python/mystrtoul.c
@@ -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)) {
- errno = ERANGE;
- result = 0x7fffffff;
+ if (uresult <= (unsigned long)LONG_MAX) {
+ result = (long)uresult;
+ if (sign == '-')
+ result = -result;
}
-
- 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 = LONG_MAX;
+ }
return result;
}