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Re: Return of the Overlays!

From Grant Edwards <invalid@invalid.invalid>
Newsgroups comp.arch.embedded
Subject Re: Return of the Overlays!
Date 2026-01-14 21:00 +0000
Organization PANIX Public Access Internet and UNIX, NYC
Message-ID <10k904m$4h$1@reader2.panix.com> (permalink)
References <10k6mhf$3hfn8$1@dont-email.me> <10k8uuq$2ep0$1@gal.iecc.com>

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On 2026-01-14, John Levine <johnl@taugh.com> wrote:
> According to Don Y  <blockedofcourse@foo.invalid>:
>>But, there is nothing in the traditional build process that
>>ensures references from "some point" in the code don't refer
>>back to some *other* point (that you thought you were done with).
>
> Depends on your tools.

Indeed, it's pretty simple to do something like that with gcc and
binutils.  You can link each "chunk" separately so that it exposes
only a few (or even no) global symbols.

Then you link those chunks together to build an executable, you know
there's a very limited (or empty) set of "connections" between
them. However, that set of possible connections is static and doesn't
change over time the way it does when you swap overlays in/out.

I do this regularly to eliminate the possibilty of accidental name
collisions and so that I know exactly what functions can by called by
"others" outside a chunk/module.

That's not quite the same as overlays, because all the chunks/modules
are resident in memory all the time, and there might be multiple
threads active in various different chunks at any point in time --
even though they can't access each other's functions or variables.

--
Grant

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Thread

Return of the Overlays! Don Y <blockedofcourse@foo.invalid> - 2026-01-13 17:03 -0700
  Re: Return of the Overlays! George Neuner <gneuner2@comcast.net> - 2026-01-14 01:11 -0500
    Re: Return of the Overlays! Don Y <blockedofcourse@foo.invalid> - 2026-01-14 13:39 -0700
      Re: Return of the Overlays! George Neuner <gneuner2@comcast.net> - 2026-01-15 03:06 -0500
        Re: Return of the Overlays! Don Y <blockedofcourse@foo.invalid> - 2026-01-15 03:25 -0700
          Re: Return of the Overlays! George Neuner <gneuner2@comcast.net> - 2026-01-17 01:23 -0500
  Re: Return of the Overlays! John Levine <johnl@taugh.com> - 2026-01-14 20:39 +0000
    Re: Return of the Overlays! Grant Edwards <invalid@invalid.invalid> - 2026-01-14 21:00 +0000
      Re: Return of the Overlays! Don Y <blockedofcourse@foo.invalid> - 2026-01-14 18:55 -0700
    Re: Return of the Overlays! Don Y <blockedofcourse@foo.invalid> - 2026-01-14 18:48 -0700
  Re: Return of the Overlays! Don Y <blockedofcourse@foo.invalid> - 2026-01-25 01:46 -0700
    Re: Return of the Overlays! Don Y <blockedofcourse@foo.invalid> - 2026-01-25 02:10 -0700

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