On Wednesday, Apr 2, 2003, at 22:08 US/Pacific, Robert Plantz wrote: On Wednesday, April 2, 2003, at 07:10 PM, Justin Walker wrote: tisdagen den 1 april 2003 kl 05.54 skrev Jim Magee: Out of curiosity, I've always wondered why the ABI grows the stack downwards. It seems to be just as easy to grow it upwards, which would make buffer overflows much harder, if not impossible. Habit, mostly, I think. Most of this stuff grew up on PDP11's, and the PDP11 architecture gave downward growing stacks (among other things, interrupts and subroutine calls predecremented stack pointers; and the register specifiers in instructions made it easy to 'comply' with that mode of operation). With modernXXXmore recent architectures like PowerPC where a stack is more ABI than ISA, you can, as it were, go either way (:-}). Perhaps I'm being too simplistic, but if I wanted to make maximum use of memory, I would store my program code at one end and start my stack at the other, then let them grow toward each other. That is too simplistic. The main issue is that large chunks of address space are "reserved" for shared libraries and shared data segemnts. In addition, your private data segment has to go somewhere as well. There are a lot of claims on that single, linear, array of memory. Regards, Justin -- Justin C. Walker, Curmudgeon-At-Large * Institute for General Semantics | When LuteFisk is outlawed | Only outlaws will have | LuteFisk *--------------------------------------*-------------------------------* _______________________________________________ darwin-kernel mailing list | darwin-kernel@lists.apple.com Help/Unsubscribe/Archives: http://www.lists.apple.com/mailman/listinfo/darwin-kernel Do not post admin requests to the list. They will be ignored.