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Temporary fix for bug 4254 - a _lot_ of strict aliasing warnings

Ozkan Sezer

A horde of strict aliasing violation warnings are emitted from joystick
layer, and also from a few other places. This happens with gcc-4.4.7 on
Linux CentOS 6.10.  Some other sysjoystick would possibly have the same
warnings.

Attached my full log here. Example entry:
src/joystick/SDL_joystick.c: In function 'SDL_GetJoystickGUIDInfo':
src/joystick/SDL_joystick.c:1094: warning: dereferencing pointer '({anonymous})' does break strict-aliasing rules
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slouken committed Jun 9, 2019
1 parent 3176524 commit 1b73d578f3d60ddf3e6d33eeafd6e106a2aa8458
Showing with 68 additions and 1 deletion.
  1. +5 −0 CMakeLists.txt
  2. +39 −1 configure
  3. +24 −0 configure.ac
@@ -418,6 +418,11 @@ if(USE_GCC OR USE_CLANG)
endif()
endif()

check_c_compiler_flag(-fno-strict-aliasing HAVE_GCC_NO_STRICT_ALIASING)
if(HAVE_GCC_NO_STRICT_ALIASING)
list(APPEND EXTRA_CFLAGS "-fno-strict-aliasing")
endif()

check_c_compiler_flag(-Wdeclaration-after-statement HAVE_GCC_WDECLARATION_AFTER_STATEMENT)
if(HAVE_GCC_WDECLARATION_AFTER_STATEMENT)
check_c_compiler_flag(-Werror=declaration-after-statement HAVE_GCC_WERROR_DECLARATION_AFTER_STATEMENT)
fi
}

CheckNoStrictAliasing()
{
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GCC -fno-strict-aliasing option" >&5
$as_echo_n "checking for GCC -fno-strict-aliasing option... " >&6; }
have_gcc_no_strict_aliasing=no

save_CFLAGS="$CFLAGS"
CFLAGS="$save_CFLAGS -fno-strict-aliasing"
cat confdefs.h - <<_ACEOF >conftest.$ac_ext
/* end confdefs.h. */

int x = 0;

int
main ()
{


;
return 0;
}
_ACEOF
if ac_fn_c_try_compile "$LINENO"; then :

have_gcc_no_strict_aliasing=yes

fi
rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $have_gcc_no_strict_aliasing" >&5
$as_echo "$have_gcc_no_strict_aliasing" >&6; }
CFLAGS="$save_CFLAGS"

if test x$have_gcc_no_strict_aliasing = xyes; then
EXTRA_CFLAGS="$EXTRA_CFLAGS -fno-strict-aliasing"
fi
}

CheckStackBoundary()
{
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GCC -mpreferred-stack-boundary option" >&5


CheckWarnAll
CheckNoStrictAliasing

CheckEventSignals

CheckOpenGLESX11
CheckVulkan
CheckWayland
CheckLibUDev
CheckInputEvents
CheckLibUDev
CheckDBus
CheckIME
CheckIBus
@@ -1329,6 +1329,29 @@ CheckVisibilityHidden()
fi
}

dnl See if GCC's -fno-strict-aliasingis supported.
dnl Reference: https://bugzilla.libsdl.org/show_bug.cgi?id=4254
CheckNoStrictAliasing()
{
AC_MSG_CHECKING(for GCC -fno-strict-aliasing option)
have_gcc_no_strict_aliasing=no

save_CFLAGS="$CFLAGS"
CFLAGS="$save_CFLAGS -fno-strict-aliasing"
AC_TRY_COMPILE([
int x = 0;
],[
],[
have_gcc_no_strict_aliasing=yes
])
AC_MSG_RESULT($have_gcc_no_strict_aliasing)
CFLAGS="$save_CFLAGS"

if test x$have_gcc_no_strict_aliasing = xyes; then
EXTRA_CFLAGS="$EXTRA_CFLAGS -fno-strict-aliasing"
fi
}

dnl See if GCC's -mpreferred-stack-boundary is supported.
dnl Reference: http://bugzilla.libsdl.org/show_bug.cgi?id=1296
CheckStackBoundary()
@@ -3263,6 +3286,7 @@ AS_HELP_STRING([--enable-foregrounding-signal], [number to use for magic foregro

dnl Do this on all platforms, before everything else (other things might want to override it).
CheckWarnAll
CheckNoStrictAliasing

dnl Do this for every platform, but for some it doesn't mean anything, but better to catch it here anyhow.
CheckEventSignals

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