Stack size set on icon ignored on 3.2.2.1

[ross]

Originally Posted by a/b

As I said, he is recasting upper and lower to ULONG*, so when a pointer subtraction happens the result is also normalized.
If you inc/dec (++/--) a ULONG pointer, it's increased/decreased by 4, not by 1. M68K asm works the same way (predec/postinc are the operand size, not 1).
Use void*, char*, (un)signed byte* or similar instead of ULONG* (or multiply total by sizeof(ULONG) after subtraction) to get the size in bytes.

Yep, I would have used similar code:

	ULONG upper, lower, total;

    // For CLI tasks, stack bounds are determined differently
    if (currentTask->pr_CLI) {
 ..
    } else {
        upper = (ULONG)currentTask->pr_Task.tc_SPUpper;
        lower = (ULONG)currentTask->pr_Task.tc_SPLower;
        total = upper - lower;
    }

Maybe coder fooled by this warning in types.h?

  /*  WARNING: APTR was redefined for the V36 Includes!  APTR is a   */
 /*  32-Bit Absolute Memory Pointer.  C pointer math will not	    */
/*  operate on APTR --	use "ULONG *" instead.			   */
...
typedef void *		APTR;	    /* 32-bit untyped pointer */
...
typedef unsigned long	ULONG;	    /* unsigned 32-bit quantity */

Sorry for the invasion, this is not my section

[meynaf]

To make it short, subtracting two ULONG pointers in C will give result in number of ULONGs, not in number of bytes.

[Nightfox]

Thanks for the feedback. I’ll rework it on the weekend. Sorry about this bug

[nocash]

Why is the amiga os requiring users to specify stack sizes in icons or command line?

I mean, if I would write a program that needs 32Kbyte stack, then I would allocate that memory, or pre-allocate it in bss segment, and then redirect the stack pointer to that memory area... or is there something in the os that prevents doing that?

[Thomas Richter]

Originally Posted by nocash

Why is the amiga os requiring users to specify stack sizes in icons or command line?

A good question, and in general, the user cannot know how much stack an application requires. From 3.1.4 onwards, authors can specify a stack size in their programs as simple as that:

 UBYTE stack[]="$STACK:32768";

and this will ensure that the program receives 32K stack minimum.

Originally Posted by nocash

I mean, if I would write a program that needs 32Kbyte stack, then I would allocate that memory, or pre-allocate it in bss segment, and then redirect the stack pointer to that memory area... or is there something in the os that prevents doing that?

That is in general not recommendable. First of all, you should *also* denote the stack for your program in the task structure (task->tc_Lower and task->tc_Upper) and second, that prevents the user for enlarging the stack should it be necessary because some Os patches between your program and the Os enlarge the size of the stack your program requires. Thus, always leave the flexibility of the stack to the user, but also provide a reasonable default stack size. The above stack-cookie defines a lower bound for the stack, but it can always be overridden by a larger size.

[Rotareneg]

Originally Posted by nocash

Why is the amiga os requiring users to specify stack sizes in icons or command line?

If I remember right it's a relic of its Tripos origins, something to do with BCPL I think?

[Thomas Richter]

Originally Posted by Rotareneg

If I remember right it's a relic of its Tripos origins, something to do with BCPL I think?

Not really. The 68K does not have a MMU, and thus cannot detect if the stack overruns. Thus, unlike in unix operating systems, the Os cannot assist in automatically extending the stack when necessary. You find similar constructions in MacOs, sometimes even weirder ones where you even need to specify the maximum heap a program takes - in the icon of the program.

[Nightfox]

The stack size calculation bug is now fixed in version 1.4.5 which I just released.

Thanks for your assistance everyone. I'll be more careful with pointer arithmetic from now on!

And yep AmigaGPT does use the stack cookie "$STACK:32768" to increase the stack if required but as mentioned, it requires AmigaOS 3.1.4 for that to work. If anyone is using an older version of AmigaOS, they will get a warning if the stack is too small. This would most likely happen if launched from CLI, since the AmigaGPT icon has 32768 set as stack so if launched from Workbench the stack should be automatically set.