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openvswitch/configure.ac
Ben Pfaff 538919d3a6 configure: Disable strict aliasing. 
The C standard allows compilers to do type-based alias analysis, which
means that the compiler is allowed to assume that pointers to objects of
different types are pointers to different objects.  For example, a compiler
may assume that "uint16_t *a" and "uint32_t *b" point to different and
nonoverlapping locations because the pointed-to types are different.  This
can lead to surprising "optimizations" with compilers that by default do
this kind of analysis, which includes GCC and Clang.

The one escape clause that the C standard gives us is that character types
must be assumed to alias any other object.  We've always tried to use this
escape clause to avoid problems with type-based alias analysis in the past.
I think that we should continue to try to do this in the future.  It's hard
to tell what compiler we might want to use in the future, and one never
knows what kind of control that compiler allows over alias analysis.

However, recently I helped another developer debug a nasty and confusing
issue, which turned out to be the result of a surprising compiler
optimization due to alias analysis.  I've seen enough of these that I don't
think it's worthwhile to risk more problems than we have to.  Thus, this
commit turns off type-based alias analysis in GCC and Clang.

Linus Torvalds thinks that type-base alias analysis is not sane, at least
as GCC implements it: https://lkml.org/lkml/2003/2/26/158

The GCC manual says that -Wstrict-aliasing is only effective without
-fno-strict-aliasing, otherwise I'd keep -Wstrict-aliasing also.

Indications are that MSVC doesn't do type-based alias analysis by default.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Jarno Rajahalme <jrajahalme@nicira.com>
2014-10-01 08:46:06 -07:00

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# Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013, 2014 Nicira, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at:
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
AC_PREREQ(2.63)
AC_INIT(openvswitch, 2.3.90, bugs@openvswitch.org)
AC_CONFIG_SRCDIR([datapath/datapath.c])
AC_CONFIG_MACRO_DIR([m4])
AC_CONFIG_AUX_DIR([build-aux])
AC_CONFIG_HEADERS([config.h])
AC_CONFIG_TESTDIR([tests])
AM_INIT_AUTOMAKE
AC_PROG_CC_C99
AM_PROG_CC_C_O
AC_PROG_CPP
AC_PROG_MKDIR_P
AC_PROG_FGREP
AC_PROG_EGREP
AC_ARG_VAR([PERL], [path to Perl interpreter])
AC_PATH_PROG([PERL], perl, no)
if test "$PERL" = no; then
AC_MSG_ERROR([Perl interpreter not found in $PATH or $PERL.])
fi
AM_MISSING_PROG([AUTOM4TE], [autom4te])
AC_USE_SYSTEM_EXTENSIONS
AC_C_BIGENDIAN
AC_SYS_LARGEFILE
LT_INIT([disable-shared])
m4_pattern_forbid([LT_INIT]) dnl Make autoconf fail if libtool is missing.
AC_SEARCH_LIBS([pow], [m])
AC_SEARCH_LIBS([clock_gettime], [rt])
AC_SEARCH_LIBS([timer_create], [rt])
AC_SEARCH_LIBS([pthread_sigmask], [pthread])
AC_FUNC_STRERROR_R
OVS_CHECK_ESX
OVS_CHECK_WIN32
OVS_CHECK_VISUAL_STUDIO_DDK
OVS_CHECK_COVERAGE
OVS_CHECK_NDEBUG
OVS_CHECK_NETLINK
OVS_CHECK_OPENSSL
OVS_CHECK_LOGDIR
OVS_CHECK_PYTHON
OVS_CHECK_PYTHON_COMPAT
OVS_CHECK_DOT
OVS_CHECK_IF_PACKET
OVS_CHECK_IF_DL
OVS_CHECK_STRTOK_R
AC_CHECK_DECLS([sys_siglist], [], [], [[#include <signal.h>]])
AC_CHECK_MEMBERS([struct stat.st_mtim.tv_nsec, struct stat.st_mtimensec],
[], [], [[#include <sys/stat.h>]])
AC_CHECK_MEMBERS([struct ifreq.ifr_flagshigh], [], [], [[#include <net/if.h>]])
AC_CHECK_FUNCS([mlockall strnlen getloadavg statvfs getmntent_r])
AC_CHECK_HEADERS([mntent.h sys/statvfs.h linux/types.h linux/if_ether.h stdatomic.h])
AC_CHECK_HEADERS([net/if_mib.h], [], [], [[#include <sys/types.h>
#include <net/if.h>]])
OVS_CHECK_PKIDIR
OVS_CHECK_RUNDIR
OVS_CHECK_DBDIR
OVS_CHECK_BACKTRACE
OVS_CHECK_VALGRIND
OVS_CHECK_SOCKET_LIBS
OVS_CHECK_XENSERVER_VERSION
OVS_CHECK_GROFF
OVS_CHECK_GNU_MAKE
OVS_CHECK_TLS
OVS_CHECK_ATOMIC_LIBS
OVS_CHECK_GCC4_ATOMICS
OVS_CHECK_ATOMIC_ALWAYS_LOCK_FREE(1)
OVS_CHECK_ATOMIC_ALWAYS_LOCK_FREE(2)
OVS_CHECK_ATOMIC_ALWAYS_LOCK_FREE(4)
OVS_CHECK_ATOMIC_ALWAYS_LOCK_FREE(8)
OVS_CHECK_POSIX_AIO
OVS_CHECK_PTHREAD_SET_NAME
OVS_CHECK_LINUX_HOST
AX_FUNC_POSIX_MEMALIGN
OVS_CHECK_INCLUDE_NEXT([stdio.h string.h])
AC_CONFIG_FILES([lib/stdio.h lib/string.h])
OVS_ENABLE_OPTION([-Wall])
OVS_ENABLE_OPTION([-Wextra])
OVS_ENABLE_OPTION([-Wno-sign-compare])
OVS_ENABLE_OPTION([-Wpointer-arith])
OVS_ENABLE_OPTION([-Wformat-security])
OVS_ENABLE_OPTION([-Wno-format-zero-length])
OVS_ENABLE_OPTION([-Wswitch-enum])
OVS_ENABLE_OPTION([-Wunused-parameter])
OVS_ENABLE_OPTION([-Wbad-function-cast])
OVS_ENABLE_OPTION([-Wcast-align])
OVS_ENABLE_OPTION([-Wstrict-prototypes])
OVS_ENABLE_OPTION([-Wold-style-definition])
OVS_ENABLE_OPTION([-Wmissing-prototypes])
OVS_ENABLE_OPTION([-Wmissing-field-initializers])
OVS_ENABLE_OPTION([-Wthread-safety])
OVS_ENABLE_OPTION([-fno-strict-aliasing])
OVS_CONDITIONAL_CC_OPTION([-Wno-unused], [HAVE_WNO_UNUSED])
OVS_CONDITIONAL_CC_OPTION([-Wno-unused-parameter], [HAVE_WNO_UNUSED_PARAMETER])
OVS_ENABLE_WERROR
OVS_ENABLE_SPARSE
AC_ARG_VAR(KARCH, [Kernel Architecture String])
AC_SUBST(KARCH)
OVS_CHECK_LINUX
OVS_CHECK_DPDK
OVS_CHECK_PRAGMA_MESSAGE
AC_SUBST([OVS_CFLAGS])
AC_SUBST([OVS_LDFLAGS])
AC_CONFIG_FILES(Makefile)
AC_CONFIG_FILES(datapath/Makefile)
AC_CONFIG_FILES(datapath/linux/Kbuild)
AC_CONFIG_FILES(datapath/linux/Makefile)
AC_CONFIG_FILES(datapath/linux/Makefile.main)
AC_CONFIG_FILES(tests/atlocal)
dnl This makes sure that include/openflow gets created in the build directory.
AC_CONFIG_COMMANDS([include/openflow/openflow.h.stamp])
AC_CONFIG_COMMANDS([utilities/bugtool/dummy], [:])
m4_ifdef([AM_SILENT_RULES], [AM_SILENT_RULES])
AC_OUTPUT
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