Re: Segments

On Wed, 22 Jan 2025 22:44:45 GMT, scott@slp53.sl.home (Scott Lurndal)
wrote:

mitchalsup@aol.com (MitchAlsup1) writes:

On Wed, 22 Jan 2025 20:00:30 +0000, Scott Lurndal wrote:
>

mitchalsup@aol.com (MitchAlsup1) writes:

On Wed, 22 Jan 2025 14:58:04 +0000, Scott Lurndal wrote:

(MitchAlsup1)

>

On a Linux machine, you can find the last envp[*] entry and subtract
SP from it.

>
I would discourage programmers from relying on that for any reason
whatsoever.   The aux vectors are pushed before the envp entries.

>
This brings into question what is "on" the stack ?? to be included
in the measurement of stack size.
>
Only user data ??
Data that is present when control arrives ??
Could <equivalent> CRT0 store SP at arrival ??
>
I think we have an illdefined measurement !!

>
Everything between the base address of the stack
and the limit address of the stack.  The kernel exec(2)
family system calls will allocate the initial
stack region (with guard pages to handle extension)
and populate it with the AUX, ENVP and ARG vectors
before invoking the CRT in usermode.

>
So, how does one find the base (highest address on the stack) ??
in a way that works on every system capable of running C-code ??

>
It's not something that a programmer generally would need, or want to
do. 

https://plover.com/~mjd/misc/hbaker-archive/CheneyMTA.html

or any problem requiring potentially unbounded recursion.

However, if the OS they're using has a guard page to prevent
stack underflow, one could write a subroutine which accesses
page-aligned addresses towards the beginning of the stack
region (anti the direction of growth) until a
SIGSEGV is delivered.