Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!seismo!rochester!PT!b.gp.cs.cmu.edu!ralf
From: ralf@b.gp.cs.cmu.edu (Ralf Brown)
Newsgroups: comp.sys.ibm.pc
Subject: Re: signal() for Turbo C
Message-ID: <88@b.gp.cs.cmu.edu>
Date: Thu, 27-Aug-87 21:13:00 EDT
Article-I.D.: b.88
Posted: Thu Aug 27 21:13:00 1987
Date-Received: Sun, 30-Aug-87 03:05:01 EDT
References: <1009@bsu-cs.UUCP> <2670002@hpsrla.HP.COM> <1059@bsu-cs.UUCP>
Organization: Carnegie-Mellon University, CS/RI
Lines: 45

In article <1059@bsu-cs.UUCP> dhesi@bsu-cs.UUCP (Rahul Dhesi) writes:
>In article <2670002@hpsrla.HP.COM> darrylo@hpsrla.HP.COM (Darryl Okahata) 
>writes about my signal() for Turbo C:
>>	[...]
>
>When I tested the signal() handler code, I did run out of stack space.
>Then I initialized _stklen to a bigger value and the program ran
>correctly.  So any shortage of stack space is occurring simply because
>the Turbo C stack is not big enough.  The default stack, if you don't
>create _stklen, is only 128 bytes, which is peanuts.
NO!  The default stack length is 4096 bytes (there is a module in the 
library whose sole purpose is to define _stklen).  The 128 bytes is the
initial startup stack, which gets moved as soon as C0.ASM figures out
where to place it.  No matter what value you give _stklen, the startup
stack stays 128 bytes.

>Also note that I believe that the small model start-up code for Turbo C
>does not properly handle _stklen to set a bigger stack.  I changed and
>recompiled the startup module for the small memory model to fix this
>apparent bug.  I made the following changes in C0.ASM:

Actually, the bug is in determining how much memory to allocate to the
program.  The problem is that when less than 64K is available in tiny
model, the code does not use all available memory, but only 
CODE+DATA+minSTACK, where minSTACK is 256 bytes.  My fix for this
(posted some time ago) is to change the two lines in C0.ASM between
the two "ja ExcessOfMemory" statements to
	mov	di,bp
	cmp	bp,bx
DI contains the amount to allocate, BP contains the amount available, and BX
contains the minimum amount needed.  (Which is too little, because it only
allocates 256 bytes for the stack).

Note that this patch can also be applied to the .COM file, as the 
instructions are the same size as those they replace.

>-- 
>Rahul Dhesi         UUCP:  {ihnp4,seismo}!{iuvax,pur-ee}!bsu-cs!dhesi

-- 
-=-=-=-=-=-=-=-= {harvard,seismo,ucbvax}!b.gp.cs.cmu.edu!ralf =-=-=-=-=-=-=-=-
ARPAnet: RALF@B.GP.CS.CMU.EDU            BITnet: RALF%B.GP.CS.CMU.EDU@CMUCCVMA
AT&Tnet: (412) 268-3053 (school)         FIDOnet: Ralf Brown at 129/31
	        DISCLAIMER?  Who ever said I claimed anything? 
"I do not fear computers.  I fear the lack of them..." -- Isaac Asimov