Re: local arrays and stack

From	David Brown <david.brown@hesbynett.no>
Newsgroups	comp.lang.c
Subject	Re: local arrays and stack
Date	2015-03-24 20:01 +0100
Organization	A noiseless patient Spider
Message-ID	<mesc85$thj$1@dont-email.me> (permalink)
References	(3 earlier) <i0nvgahdv9uuetqfqg60eee3ln1jct1720@4ax.com> <de0fc18d-1589-4947-aabe-687cb44ad38d@googlegroups.com> <1cf3bb4e-12d0-4482-ac76-2f3906d210b2@googlegroups.com> <merjqe$gok$1@dont-email.me> <mes6tb$729$1@speranza.aioe.org>

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On 24/03/15 18:29, glen herrmannsfeldt wrote:
> David Brown <david.brown@hesbynett.no> wrote:
>> On 24/03/15 12:01, fir wrote:
>
> (snip)
>
>>> 2) making sure that given range ram area is unocuppied/avaliable
>>>     [there may be a biggest problem here]
>
>> No.
>
>> It is the OS's task to ensure that the stack given to the program
>> is in ram that does not overlap or collide with other memory.
>
> I don't believe that the "definition of OS" includes that statement.
> It is nice of an OS to do that, and good ones might.

In the context of the systems under discussion here (Linux and Windows), 
the OS does that.  But you are right - while it is an expected part of a 
"big" OS that keeps tasks carefully separated, it will certainly not be 
the case in small embedded OS's.

>
> A system with protected memory has to protect each task from others,
> but not from itself.

The OS is given a higher level of trust - tasks are "protected" from the 
OS in that they can expect the OS code to behave correctly.  But the OS 
and other tasks need protected from user-level tasks because they should 
continue to work even if a task misbehaves.

(Again, this does not apply in cases where there is no memory protection 
hardware, or in a small embedded where /all/ tasks are expected to 
behave correctly.)

>
>>> 3) pin up physical pages
>
>> No, that is certainly not the responsibility of the compiler!
>> Again, it is the OS (along with the MMU) that is responsible
>> for the memory mapping.
>
> So not required on systems without an MMU?

In the case of Linux/Windows, yes.

>
>> Of course, an OS may decide that the size of a program's stack is fixed,
>> or require some additional calls (like __chkstk_ms) to change the stack
>> size.  But the /compiler/ does not determine the memory mapping.
>
> And the compiler/linker might decide that the stack size is fixed.
> It is then the responsibility of the program to stay within that size.
>

It might add additional limits, but usually (at least when possible on 
the target cpu and OS) it is more efficient for the compiler-generated 
code to act as though the stack is unlimited, and for the MMU (or on 
some cpus, a stack limit register) to handle out-of-bounds errors.

Thread

local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-22 01:51 -0700
  local arrays and stack asetofsymbols@gmail.com - 2015-03-22 02:23 -0700
  Re: local arrays and stack Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-03-22 13:22 -0700
    Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-23 01:55 -0700
  Re: local arrays and stack Xcott Craver <xcottcraver@gmail.com> - 2015-03-22 15:07 -0700
    Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-23 01:50 -0700
      Re: local arrays and stack Robert Wessel <robertwessel2@yahoo.com> - 2015-03-23 04:26 -0500
        Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-23 06:53 -0700
        Re: local arrays and stack Xcott Craver <xcottcraver@gmail.com> - 2015-03-23 07:29 -0700
          Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-23 08:34 -0700
          Re: local arrays and stack Robert Wessel <robertwessel2@yahoo.com> - 2015-03-23 19:57 -0500
          Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-24 04:01 -0700
            Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-24 04:37 -0700
            Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-24 13:04 +0100
              Re: local arrays and stack glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-03-24 17:29 +0000
                Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-24 20:01 +0100
        Re: local arrays and stack Keith Thompson <kst-u@mib.org> - 2015-03-23 08:24 -0700
          Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-23 08:42 -0700
            Re: local arrays and stack Bartc <bc@freeuk.com> - 2015-03-23 16:07 +0000
              Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-23 09:15 -0700
              Re: local arrays and stack Keith Thompson <kst-u@mib.org> - 2015-03-23 09:16 -0700
                Re: local arrays and stack Bartc <bc@freeuk.com> - 2015-03-23 16:34 +0000
                Re: local arrays and stack Xcott Craver <xcottcraver@gmail.com> - 2015-03-23 10:12 -0700
                Re: local arrays and stack Bartc <bc@freeuk.com> - 2015-03-23 17:44 +0000
                Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-23 11:47 -0700
                Re: local arrays and stack Xcott Craver <xcottcraver@gmail.com> - 2015-03-23 12:06 -0700
                Re: local arrays and stack Bartc <bc@freeuk.com> - 2015-03-23 20:25 +0000
                Re: local arrays and stack Xcott Craver <xcottcraver@gmail.com> - 2015-03-23 14:10 -0700
                Re: local arrays and stack Bartc <bc@freeuk.com> - 2015-03-23 22:22 +0000
                Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-23 23:57 -0700
                Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-24 10:28 +0100
                Re: local arrays and stack Bartc <bc@freeuk.com> - 2015-03-24 10:44 +0000
                Re: local arrays and stack Martin Shobe <martin.shobe@yahoo.com> - 2015-03-24 06:38 -0500
                Re: local arrays and stack Martin Shobe <martin.shobe@yahoo.com> - 2015-03-24 09:57 -0500
                Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-24 13:22 +0100
                Re: local arrays and stack Bartc <bc@freeuk.com> - 2015-03-25 16:07 +0000
                Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-25 17:42 +0100
                Re: local arrays and stack Bartc <bc@freeuk.com> - 2015-03-25 19:06 +0000
                Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-25 12:26 -0700
                Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-25 13:20 -0700
                Re: local arrays and stack Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-03-25 12:28 -0700
                Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-25 21:45 +0100
                Re: local arrays and stack Keith Thompson <kst-u@mib.org> - 2015-03-25 12:50 -0700
                Re: local arrays and stack Bartc <bc@freeuk.com> - 2015-03-25 22:33 +0000
                Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-25 23:57 +0100
                Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-25 21:42 +0100
                Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-25 09:55 -0700
                Re: local arrays and stack Keith Thompson <kst-u@mib.org> - 2015-03-25 12:36 -0700
                Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-25 13:04 -0700
                Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-25 21:52 +0100
                Re: local arrays and stack Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-03-25 15:18 -0700
                Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-26 00:02 +0100
                Re: local arrays and stack Melzzzzz <mel@zzzzz.com> - 2015-03-26 00:47 +0100
                Re: local arrays and stack Mel <mel@zzzzz.com> - 2015-03-24 14:58 +0100
                Re: local arrays and stack Xcott Craver <xcottcraver@gmail.com> - 2015-03-24 06:58 -0700
                Re: local arrays and stack Keith Thompson <kst-u@mib.org> - 2015-03-23 14:34 -0700
                Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-24 10:16 +0100
                Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-24 09:55 +0100
                Re: local arrays and stack Noob <root@127.0.0.1> - 2015-03-24 10:23 +0100
                Re: local arrays and stack Tim Rentsch <txr@alumni.caltech.edu> - 2015-03-24 12:18 -0700
                Re: local arrays and stack Keith Thompson <kst-u@mib.org> - 2015-03-24 13:42 -0700
                Re: local arrays and stack Tim Rentsch <txr@alumni.caltech.edu> - 2015-03-25 08:47 -0700
            Re: local arrays and stack Xcott Craver <xcottcraver@gmail.com> - 2015-03-23 09:32 -0700
              Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-23 09:57 -0700
              Re: local arrays and stack Keith Thompson <kst-u@mib.org> - 2015-03-23 10:37 -0700
                Re: local arrays and stack Xcott Craver <xcottcraver@gmail.com> - 2015-03-23 10:49 -0700
                Re: local arrays and stack Keith Thompson <kst-u@mib.org> - 2015-03-23 12:48 -0700
                Re: local arrays and stack jt@toerring.de (Jens Thoms Toerring) - 2015-03-23 22:29 +0000
                Re: local arrays and stack James Kuyper <jameskuyper@verizon.net> - 2015-03-23 19:03 -0400
                Re: local arrays and stack jt@toerring.de (Jens Thoms Toerring) - 2015-03-23 23:36 +0000
                Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-24 02:17 -0700
                Re: local arrays and stack Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-03-23 11:56 -0700
          Re: local arrays and stack Robert Wessel <robertwessel2@yahoo.com> - 2015-03-23 20:00 -0500
            Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-24 10:39 +0100

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