Bugs item #1545668, was opened at 2006-08-24 05:14 Message generated for change (Comment added) made by jackjansen You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1545668&group_id=5470
Please note that this message will contain a full copy of the comment thread, including the initial issue submission, for this request, not just the latest update. >Category: Python Interpreter Core Group: Python 2.4 Status: Open Resolution: None Priority: 5 Submitted By: Jack Howarth (jwhowarth) >Assigned to: Nobody/Anonymous (nobody) Summary: gcc trunk (4.2) exposes a signed integer overflows Initial Comment: While building python 2.4.3 with the current gcc trunk (soon to be 4.2), I uncovered a signed integer overflows bug in Python with the help of one of the gcc developers. The bug I observed is documented in this gcc mailing list message... http://gcc.gnu.org/ml/gcc/2006-08/msg00436.html The gcc developer comments about its origin are in the messages... http://gcc.gnu.org/ml/gcc/2006-08/msg00434.html http://gcc.gnu.org/ml/gcc/2006-08/msg00442.html which in short says... It *is* a bug in python, here is the proof: https://codespeak.net/viewvc/vendor/cpython/Python-r243/dist/src/ Objects/intobject.c?revision=25647&view=markup Function * i_divmod*(*register* *long* x, *register* *long* y, the following lines: / /* (-sys.maxint-1)/-1 is the only overflow case. *// *if* (y == -1 && x < 0 && x == -x) *return* DIVMOD_OVERFLOW; If overflow is barred then x==-x may happen only when x==0. This conflicts with x<0, which means that the compiler may assume that x<0 && x==-x always yields false. This may allow the compiler to eliminate the whole if statement. Hence, clearly python is at fault. ---------------------------------------------------------------------- >Comment By: Jack Jansen (jackjansen) Date: 2006-08-24 11:14 Message: Logged In: YES user_id=45365 I don't think this is a mac-specific bug, and I'm also not really the right person to look into this... ---------------------------------------------------------------------- Comment By: Jack Howarth (jwhowarth) Date: 2006-08-24 06:13 Message: Logged In: YES user_id=403009 As suggested by another gcc developer in... http://gcc.gnu.org/ml/gcc/2006-08/msg00446.html ...the following patch eliminates the error when python is built with gcc trunk... --- Python-2.4.3/Objects/intobject.c.org 2006-08-23 23:49:33.000000000 -0400 +++ Python-2.4.3/Objects/intobject.c 2006-08-23 23:52:01.000000000 -0400 @@ -479,7 +479,7 @@ return DIVMOD_ERROR; } /* (-sys.maxint-1)/-1 is the only overflow case. */ - if (y == -1 && x < 0 && x == -x) + if (y == -1 && x < 0 && ((unsigned)x) == -(unsigned)x) return DIVMOD_OVERFLOW; xdivy = x / y; xmody = x - xdivy * y; This change allows python to completely pass its make check now when built with gcc trunk. ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1545668&group_id=5470 _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
