Bug #1608: use -fwrapv when GCC supports it. This is important, newer

GCC versions may optimize away overflow buffer overflow checks without
this option!  Thanks to Ismail Donmez.  No thanks to the GCC devs.

Misc/ACKS

@@ -161,6 +161,7 @@ Yves Dionne
 Daniel Dittmar
 Walter Drwald
 Jaromir Dolecek
+Ismail Donmez
 Dima Dorfman
 Cesar Douady
 Dean Draayer

Misc/NEWS

@@ -177,6 +177,10 @@ Documentation
 Build
 -----
 
+- Bug #1608: use -fwrapv when GCC supports it.  This is important,
+  newer GCC versions may optimize away overflow buffer overflow checks
+  without this option!
+
 - Allow simultaneous installation of 32-bit and 64-bit versions
   on 64-bit Windows systems.
 

README

@@ -282,19 +282,6 @@ on these platforms without the special directions mentioned here,
 submit a documentation bug report to SourceForge (see Bug Reports
 above) so we can remove them!)
 
-GCC 4.1,
-GCC 4.2: There is a known incompatibility between Python and GCC,
-         where GCC 4.1 and later uses an interpretation of C 
-         different to earlier GCC releases in an area where the C 
-         specification has undefined behaviour (namely, integer arithmetic 
-         involving -sys.maxint-1).
-
-	 As a consequence, compiling Python with GCC 4.1/4.2 is not
-	 recommended. It is likely that this problem will be resolved
-	 in future Python releases. As a work-around, it seems that
-	 adding -fwrapv to the compiler options restores the earlier
-	 GCC behaviour.
-
 Unix platforms: If your vendor still ships (and you still use) Berkeley DB
         1.85 you will need to edit Modules/Setup to build the bsddb185
         module and add a line to sitecustomize.py which makes it the

configure.in

@@ -757,6 +757,10 @@ then
         if test "$CC" != 'g++' ; then
 	    STRICT_PROTO="-Wstrict-prototypes"
 	fi
+        # For gcc 4.x we need to use -fwrapv so lets check if its supported
+        if "$CC" -v --help 2>/dev/null |grep -- -fwrapv > /dev/null; then
+           WRAP="-fwrapv"
+        fi
 	case $ac_cv_prog_cc_g in
 	yes)
 	    if test "$Py_DEBUG" = 'true' ; then
@@ -764,7 +768,7 @@ then
 		# debug builds.
 		OPT="-g -Wall $STRICT_PROTO"
 	    else
-		OPT="-g -O3 -Wall $STRICT_PROTO"
+		OPT="-g $WRAP -O3 -Wall $STRICT_PROTO"
 	    fi
 	    ;;
 	*)