hauntsaninja · Mar 4, 2023 · Sep 14, 2022 · Sep 14, 2022 · Sep 14, 2022 · Sep 16, 2022
diff --git a/Misc/NEWS.d/next/Build/2022-09-14-10-38-15.gh-issue-96821.Zk2a9c.rst b/Misc/NEWS.d/next/Build/2022-09-14-10-38-15.gh-issue-96821.Zk2a9c.rst
@@ -0,0 +1,2 @@
+Explicitly mark C modules that need defined signed integer overflow,
+and set up machinery for ``-fstrict-overflow``.
@@ -2080,6 +2080,34 @@ case $CC in
         fi
 esac
 
+# Historically, some of our code assumed that signed integer overflow
+# is defined behaviour via twos-complement.  Prepare some flags so that
+# we can mark the modules that still do so.
+_SAVE_VAR([CFLAGS])
+CFLAGS="-fstrict-overflow -fno-strict-overflow"
+AC_CACHE_CHECK([if $CC supports -fstrict-overflow and -fno-strict-overflow],
+               [ac_cv_cc_supports_fstrict_overflow],
+  AC_COMPILE_IFELSE(
+    [
+      AC_LANG_PROGRAM([[]], [[]])
+    ],[
+      STRICT_OVERFLOW_CFLAGS="-fstrict-overflow"
+      NO_STRICT_OVERFLOW_CFLAGS="-fno-strict-overflow"
+    ],[
+      STRICT_OVERFLOW_CFLAGS=""
+      NO_STRICT_OVERFLOW_CFLAGS=""
+    ])
+)
+_RESTORE_VAR([CFLAGS])
+
+AC_MSG_CHECKING(for --with-strict-overflow)
+AC_ARG_WITH(strict-overflow,
+  AS_HELP_STRING(
+    [--with-strict-overflow],
+    [choose between -fstrict-overflow or -fno-strict-overflow (default is no for backwards compatibility)]),,
+  with_strict_overflow=no)
+AC_MSG_RESULT($with_strict_overflow)
+
 # Check if CC supports -Og optimization level
 _SAVE_VAR([CFLAGS])
 CFLAGS="-Og"
@@ -2110,15 +2138,8 @@ if test "${OPT-unset}" = "unset"
 then
     case $GCC in
     yes)
-        # For gcc 4.x we need to use -fwrapv so lets check if its supported
-        if "$CC" -v --help 2>/dev/null |grep -- -fwrapv > /dev/null; then
-           WRAP="-fwrapv"
-        fi
-
         if test -n "${cc_is_clang}"
         then
-            # Clang also needs -fwrapv
-            WRAP="-fwrapv"
             # bpo-30104: disable strict aliasing to compile correctly dtoa.c,
             # see Makefile.pre.in for more information
             CFLAGS_ALIASING="-fno-strict-aliasing"
@@ -2129,7 +2150,7 @@ then
 	    if test "$Py_DEBUG" = 'true' ; then
 		OPT="-g $PYDEBUG_CFLAGS -Wall"
 	    else
-		OPT="-g $WRAP -O3 -Wall"
+		OPT="-g -O3 -Wall"
 	    fi
 	    ;;
 	*)
@@ -2244,6 +2265,10 @@ AC_DEFUN([PY_CHECK_CC_WARNING], [
 ])
 
 # tweak BASECFLAGS based on compiler and platform
+AS_VAR_IF([with_strict_overflow], [yes],
+          [BASECFLAGS="$BASECFLAGS $STRICT_OVERFLOW_CFLAGS"],
+          [BASECFLAGS="$BASECFLAGS $NO_STRICT_OVERFLOW_CFLAGS"])
+
 case $GCC in
 yes)
     CFLAGS_NODIST="$CFLAGS_NODIST -std=c11"
@@ -7230,7 +7255,7 @@ PY_STDLIB_MOD_SIMPLE([_posixsubprocess])
 PY_STDLIB_MOD_SIMPLE([_queue])
 PY_STDLIB_MOD_SIMPLE([_random])
 PY_STDLIB_MOD_SIMPLE([select])
-PY_STDLIB_MOD_SIMPLE([_struct])
+PY_STDLIB_MOD_SIMPLE([_struct], [$NO_STRICT_OVERFLOW_CFLAGS])
 PY_STDLIB_MOD_SIMPLE([_typing])
 PY_STDLIB_MOD_SIMPLE([_xxsubinterpreters])
 PY_STDLIB_MOD_SIMPLE([_zoneinfo])
@@ -7244,7 +7269,7 @@ PY_STDLIB_MOD([_posixshmem],
   [$POSIXSHMEM_CFLAGS], [$POSIXSHMEM_LIBS])
 
 dnl needs libm
-PY_STDLIB_MOD_SIMPLE([audioop], [], [$LIBM])
+PY_STDLIB_MOD_SIMPLE([audioop], [$NO_STRICT_OVERFLOW_CFLAGS], [$LIBM])
 PY_STDLIB_MOD_SIMPLE([_statistics], [], [$LIBM])
 PY_STDLIB_MOD_SIMPLE([cmath], [], [$LIBM])
 PY_STDLIB_MOD_SIMPLE([math], [], [$LIBM])
@@ -7305,7 +7330,7 @@ PY_STDLIB_MOD([_crypt],
   [$LIBCRYPT_CFLAGS], [$LIBCRYPT_LIBS])
 PY_STDLIB_MOD([_ctypes],
   [], [test "$have_libffi" = yes],
-  [$LIBFFI_CFLAGS], [$LIBFFI_LIBS])
+  [$NO_STRICT_OVERFLOW_CFLAGS $LIBFFI_CFLAGS], [$LIBFFI_LIBS])
 PY_STDLIB_MOD([_curses],
   [], [test "$have_curses" != "no"],
   [$CURSES_CFLAGS], [$CURSES_LIBS]
@@ -7355,7 +7380,7 @@ PY_STDLIB_MOD([_hashlib], [], [test "$ac_cv_working_openssl_hashlib" = yes],
   [$OPENSSL_INCLUDES], [$OPENSSL_LDFLAGS $OPENSSL_LDFLAGS_RPATH $LIBCRYPTO_LIBS])
 
 dnl test modules
-PY_STDLIB_MOD([_testcapi], [test "$TEST_MODULES" = yes])
+PY_STDLIB_MOD([_testcapi], [test "$TEST_MODULES" = yes], [], [$NO_STRICT_OVERFLOW_CFLAGS])
 PY_STDLIB_MOD([_testinternalcapi], [test "$TEST_MODULES" = yes])
 PY_STDLIB_MOD([_testbuffer], [test "$TEST_MODULES" = yes])
 PY_STDLIB_MOD([_testimportmultiple], [test "$TEST_MODULES" = yes], [test "$ac_cv_func_dlopen" = yes])
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Explicitly mark C modules that need defined signed integer overflow,
		and set up machinery for ``-fstrict-overflow``.