Re: Non-executable stack
Re: Non-executable stack
- Subject: Re: Non-executable stack
- From: Brian Tabone <email@hidden>
- Date: Thu, 3 Apr 2003 22:36:59 -0600
If I remember correctly, part of the reason that the stack grows down
from the top is to make it easier for both the stack and heap to grow.
Since both stack and heap can grow, it would be difficult to have them
be placed back to back in virtual memory. To do that, you would have to
make all addresses in either the stack or heap relative to some movable
starting point. That would be an address translation headache. Instead,
both have their starting points bound by fixed address regions. The
heap grows up, the stack grows down and they can grow until they
collide, which will occur when you have exhausted your VM space.
-Brian Tabone
On Thursday, April 3, 2003, at 12:08 AM, 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.
--Bob
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