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