Fixes bug 1296 - SDL_SetVideoMode crashes because of unaligned MOVAPS instruction

t.grundner@goto3d.de 2011-09-01 03:59:17 PDT
I figured out what is going on. GCC 4.5.2 assumes the stack is 16 byte aligned
by default. Therefore there are no AND alignment corrections necessary if we
wish to align a stack variable to a 16 byte boundary. That is bad if your OS
ABI is not 16 byte aligned. Windows 32 bit stacks are 4 byte aligned. This
results in the above mentioned SIGSEGV. This is also no problem if I compile
both SDL.dll and my app with MingW because MinGW/GCC inserts a

        andl    $-16, %esp

instruction right in the beginning of the main function. So at least the stack
of the thread calling the main function is 16 byte aligned. But as soon as I
start to use the SDL.dll from an application not compiled by MinGW there is no
ANDL safing my app.

However there is a GCC option that can change the default stack alignment:

        -mpreferred-stack-boundary=num

Setting num=2 assumes a the stack is aligned to a 4 byte boundary. This results
in GCC inserting the necessary

        andl    $-16, %esp

into SDL_FillRect. Rebuilding SDL with

       ./configure "CFLAGS=-mpreferred-stack-boundary=2 -g -O3"

solved the problem.

IMHO this should also be a problem on Solaris.

The following links contain further information:

http://gcc.gnu.org/onlinedocs/gcc-4.5.2/gcc/i386-and-x86_002d64-Options.html#i386-and-x86_002d64-Options

http://www.agner.org/optimize/calling_conventions.pdf

1 files changed, 67 insertions, 0 deletions

diff --git a/configure b/configure
index 28d8e28f..db88edb4 100755
--- a/configure
+++ b/configure
@@ -20593,6 +20593,70 @@ echo "${ECHO_T}$have_gcc_fvisibility" >&6; }
     fi
 }
 
+CheckStackBoundary()
+{
+    { echo "$as_me:$LINENO: checking for GCC -mpreferred-stack-boundary option" >&5
+echo $ECHO_N "checking for GCC -mpreferred-stack-boundary option... $ECHO_C" >&6; }
+    have_gcc_preferred_stack_boundary=no
+
+    save_CFLAGS="$CFLAGS"
+    CFLAGS="$save_CFLAGS -mpreferred-stack-boundary=2"
+    cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+
+    int x = 0;
+
+int
+main ()
+{
+
+
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval "echo \"\$as_me:$LINENO: $ac_try_echo\"") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+
+    have_gcc_preferred_stack_boundary=yes
+
+else
+  echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+    { echo "$as_me:$LINENO: result: $have_gcc_preferred_stack_boundary" >&5
+echo "${ECHO_T}$have_gcc_preferred_stack_boundary" >&6; }
+    CFLAGS="$save_CFLAGS"
+
+    if test x$have_gcc_preferred_stack_boundary = xyes; then
+        EXTRA_CFLAGS="$EXTRA_CFLAGS -mpreferred-stack-boundary=2"
+    fi
+}
+
+
 CheckWarnAll()
 {
     { echo "$as_me:$LINENO: checking for GCC -Wall option" >&5
@@ -24695,6 +24759,9 @@ fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
     { echo "$as_me:$LINENO: result: $have_wince" >&5
 echo "${ECHO_T}$have_wince" >&6; }
+
+    # This fixes Windows stack alignment with newer GCC
+    CheckStackBoundary
 }
 
 CheckDIRECTX()