From 1b73d578f3d60ddf3e6d33eeafd6e106a2aa8458 Mon Sep 17 00:00:00 2001 From: Sam Lantinga Date: Sat, 8 Jun 2019 18:32:29 -0700 Subject: [PATCH] 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 --- CMakeLists.txt | 5 +++++ configure | 40 +++++++++++++++++++++++++++++++++++++++- configure.ac | 24 ++++++++++++++++++++++++ 3 files changed, 68 insertions(+), 1 deletion(-) diff --git a/CMakeLists.txt b/CMakeLists.txt index 89b4aa361..e80d27563 100644 --- a/CMakeLists.txt +++ b/CMakeLists.txt @@ -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) diff --git a/configure b/configure index 7e21bed34..d0bb5b0ff 100755 --- a/configure +++ b/configure @@ -19396,6 +19396,43 @@ $as_echo "$have_gcc_fvisibility" >&6; } 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 @@ -24334,6 +24371,7 @@ fi CheckWarnAll +CheckNoStrictAliasing CheckEventSignals @@ -24402,8 +24440,8 @@ case "$host" in CheckOpenGLESX11 CheckVulkan CheckWayland - CheckLibUDev CheckInputEvents + CheckLibUDev CheckDBus CheckIME CheckIBus diff --git a/configure.ac b/configure.ac index b76c4d25b..0f637ea8f 100644 --- a/configure.ac +++ b/configure.ac @@ -1329,6 +1329,29 @@ CheckVisibilityHidden() fi } +dnl See if GCC's -fno-strict-aliasingis supported. +dnl Reference: https://bugzilla.libsdl.org/show_bug.cgi?id=4254 +CheckNoStrictAliasing() +{ + AC_MSG_CHECKING(for GCC -fno-strict-aliasing option) + have_gcc_no_strict_aliasing=no + + save_CFLAGS="$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