Segmentation fault caused by the wrong use of %ebx register
-----------------------------------------------------------

If your compiler seems to work well, assembly code looks
right and even the compiled program does the job
correctly but segfaults instead of exiting cleanly,
you should check if you use the EBX register.
It might segfault on some systems and work well on
others. The segfaulting behaviour has been seen
at least in a Pentinkulma workstation but it's appearance
seems to be quite flaky.

If you happen to trace the program with gdb, you'll
notice the segfault occurs after exiting your own code,
in the C-library function _dl_pagesize() which is called
from __libc_start_main(). At least this was the case
in the observed situation. YMMV.

The EBX register is mentioned to be callee-saved [1].
This means that it's value should be reset to original
value before exiting a function that uses it.
The specification is propably GCC and glibc specific.

A simple example of full function framework:

main:
        pushl   %ebp
        movl    %esp, %ebp
        pushl   %ebx

; user code here

        popl    %ebx
	movl	%ebp, %esp
	popl	%ebp
        leave
        ret

Notice the operations with %ebx.
This is the GCC way of doing things. Remember to keep the stack
pointer (%esp) on the right track so the right values are popped.

There are other registers that too have to be reset to original
values if they are changed. See [1].
On the other hand these registers can be assumed to hold their
values across function calls.

[1] http://en.tldp.org/HOWTO/Assembly-HOWTO/linux.html