From: A DOT D DOT Brown AT bradford DOT ac DOT uk
Subject: Re: Chaining real-mode interrupts
To: bdavidson AT ra DOT isisnet DOT com (Bill Davidson)
Date: Thu, 27 Apr 1995 11:45:25 +0100 (BST)
Cc: eliz AT is DOT elta DOT co DOT il, djgpp AT sun DOT soe DOT clarkson DOT edu

> As for my own code, I tried the -S option to gcc and looked over the 
> resulting assembler (also had -O2 in there).  I noticed that in my 
> handler function, where it called memset() and where it called 
> _go32_dpmi_simulate_fcall_iret(), there was no cleaning-up of the stack 
> on return.  I confess that I am not up on 386+ assembler (I learned 8088 
> assembler then switched to C); I think the 'leave' command does the stack 
> cleanup (?), but it still looked wrong to me, especially in a handler 
> function.  So I recompiled the module without any optimization, relinked, 
> and the program ran pretty good.  The keyboard handler still seems to be 
> a problem, but at least I am getting some (unstable) results!

I think you'll find there is something like:

pushl %ebp
movl %esp, %ebp

at the top of the function.  The leave instruction, at the end of the function,
evaluates to:

movl %ebp, %esp
popl %ebp

So, any pushes that are done after the first two instructions (for local
variables) are effectivly elminated at the end of the function with the
leave.

Alistair
-- 
EMAIL: A DOT D DOT Brown AT bradford DOT ac DOT uk