Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watmath!clyde!rutgers!rochester!ur-tut!sunybcs!boulder!hao!ames!ucbcad!ucbvax!hoser.berkeley.edu!bryce
From: bryce@hoser.berkeley.edu.UUCP
Newsgroups: comp.sys.amiga
Subject: Re: Dynamic Stack Allocation
Message-ID: <21484@ucbvax.BERKELEY.EDU>
Date: Wed, 28-Oct-87 01:20:41 EST
Article-I.D.: ucbvax.21484
Posted: Wed Oct 28 01:20:41 1987
Date-Received: Sat, 31-Oct-87 00:19:39 EST
References: <4585@zen.berkeley.edu> <21440@ucbvax.BERKELEY.EDU> <4314@well.UUCP>
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: bryce@hoser.berkeley.edu.UUCP (Bryce Nesbitt)
Organization: University of California at Berkeley
Lines: 106
Keywords: Stack, CLI, Workbench, Process, Task, Environment, Bogus, Schlage
Summary: Warning! Bogus information has been presented.


ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab) writes:
>bryce@hoser.berkeley.edu (Bryce Nesbitt) writes:
>
>> From C, simply get a pointer to your task with "FindTask(0L);" This returns
>> a pointer to struct Task from the exec/tasks.h include file.  tc_SPLower is
>> the lower bound of the stack tc_SPupper is the upper bound +2.
>
> Gee Byrce, I'm surprised you missed this.
> Yes, there are tc_SP{Upper,Lower} fields in the task control block,
> but these are not what DOS uses for the stack...
> ...To find out the size of the stack DOS allocated for you when your
> program was started, you say:
>	stacksize = ((struct Process *) FindTask (0L)) -> pr_StackSize;


Guess what Leo?  We are _both_ wrong!  So much for Samaritanism.

Actually we are both right.  Got that one figured out yet?


There is a not_so_subtle difference between the Workbench and the CLI.
pr_StackSize GIVES THE WRONG ANSWER!!  Better yet, pr_StackSize and
cli_DefaultStack, both declared as longs, are stored in different units!

I was so confused about the issue Leo brought up that only a sample
program saved me.  Try it from Workbench, "run" and direct CLI.  Set
a new stack number before each trial.

Take note of just who's stack pr_StackSize represents (Hint: It's not always
yours).  Take note that my solution will not work either.

(Also be on the lookout for a certain piece of commercial Amiga software that,
when run from the CLI, seems to use 8,000 more bytes than it needs to...
then complain to the programmer. :-)

/*
 * stack_test.c  27-Oct-87.  Bryce Nesbitt
 *
 * Created so I could have a clue.  Just how is that stacksize stuff saved?
 *
 * This program points out that CLI started programs will have the stacksize
 * from cli_DefaultStack.  This size is also saved at 4(a7) at startup... but
 * that is not available to a C program.  THE NORMAL TASK STRUCTURE REFERS TO
 * THE CLI PROCESSES' STACK... NOT THE ONE YOU ARE RUNNING ON!
 *
 * From the Workbench there is no cli_DefaultStack.  Here the normal task
 * structures take hold.
 *
 */
#include "exec/types.h"
#include "exec/tasks.h"
#include "libraries/dosextens.h"
#include "stdio.h"
struct Process *FindTask();

main()
{
register struct Process     *Process;
register FILE		    *Handle;
struct CommandLineInterface *CLI;

    if (!(Handle=fopen("con:0/11/250/128/Stack Window","a")))
	exit(20);	/* "a" is used so the window won't flicker */

    Process=FindTask(0L);

    if (CLI=(struct CommandLineInterface *)(Process->pr_CLI<<2))
	{
	if (CLI->cli_Background)
	    fprintf(Handle,"Background");
	else
	    fprintf(Handle,"Foreground");
	fprintf(Handle," CLI #%ld\n\n",Process->pr_TaskNum);

	fprintf(Handle,"cli_DefaultStack is: %ld\n\n",\
	       CLI->cli_DefaultStack<<2);
	}
    else
	{
	fprintf(Handle,"This is not a CLI process\n");
	fprintf(Handle,"Stack is %ld\n\n",Process->pr_StackSize);
	}

    /* Other useless information (we already know the stack size) */
    fprintf(Handle,"pr_StackSize     %ld\n",Process->pr_StackSize);
    fprintf(Handle,"pr_StackBase     $%lx\n\n",Process->pr_StackBase<<2);
    fprintf(Handle,"tc_SPLower       $%lx\n",Process->pr_Task.tc_SPLower);
    fprintf(Handle,"tc_SPUpper       $%lx\n",Process->pr_Task.tc_SPUpper);
    fprintf(Handle,"Upper-Lower      %ld\n\n",
	   (long)Process->pr_Task.tc_SPUpper-\
	   (long)Process->pr_Task.tc_SPLower);
    fprintf(Handle,"tc_SPReg         $%lx\n",Process->pr_Task.tc_SPReg);

    Delay(75L);     /* Be quick :-) */
    fprintf(Handle,"\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n");
		    /* Dramatic exit :-) */
    fclose(Handle);
}


|\ /|  . Ack! (NAK, SOH, EOT)
{o O} . bryce@hoser.berkeley.EDU -or- ucbvax!hoser!bryce
 (")
  U	"I never said you _could_, I merely said you _should_." -Humpty
	Dumpty