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Re: "Death To C"

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Robert Wessel <robertwessel2@yahoo.com> wrote:

(snip)
>> It's easy enough to implement safe arrays in another
>>> language, but they you lose the speed of raw writes to memory.

>>It's easy enough to bounds check but who does it?
 
> No it's really not.  C makes thorough bounds checking almost
> impossible.  You *can* check named (static/automatic) and allocated
> objects as a whole fairly easily (although with fairly high overhead,
> usually with some sort of fat pointer scheme), doing that within
> objects is nearly, if not actually, impossible while maintaining full
> C semantics.

Yes it has to be done for whole allocations, as that is the
way C defines what you can do with pointers. If that isn't good
enough, you just have to specifically allocate each object you
want checked.

In the OS/2 1.x days, I could easily do this, and with no additional
overhead.  (That is, no more than 80286 protected mode does for
far pointer access.)

Instead of calling malloc(), I directly called the OS/2 segment
allocator, allocating the exact length needed. Then supply a zero
offset and store into a pointer. The 80286 hardware traps access
to non-allocated segment selectors, and access past the end of
the allocated length for each segment. One thing not checked is
that offsets will wrap at 64K, and so could come back into the
actual segment. Then again, with 16 bit int, subscript calculation
itself could wrap. But you don't have to worry about overwriting
any other segment.

For the 80386, segments and segment selectors are still there,
and the Watcom C compiler will generate large model 32 bit code
(pointers have a 16 bit segment selector, and 32 bit offset).
It might be that OS/2 2.0 and up can use that, but pretty much
all the other OS expect to allocate one big segment (maybe two,
a code and a data segment).  No help in bounds checking.

-- glen

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"Death To C" Lynn McGuire <lmc@winsim.com> - 2015-05-04 14:41 -0500
  Re: "Death To C" Melzzzzz <mel@zzzzz.com> - 2015-05-04 22:16 +0200
    Re: "Death To C" Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-05-04 13:26 -0700
      Re: "Death To C" Melzzzzz <mel@zzzzz.com> - 2015-05-04 22:51 +0200
      Re: "Death To C" Bartc <bc@freeuk.com> - 2015-05-04 22:02 +0100
        Re: "Death To C" Melzzzzz <mel@zzzzz.com> - 2015-05-05 00:06 +0200
  Re: "Death To C" Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-05-04 13:22 -0700
    Re: "Death To C" Melzzzzz <mel@zzzzz.com> - 2015-05-04 22:41 +0200
      Re: "Death To C" Robert Wessel <robertwessel2@yahoo.com> - 2015-05-04 20:25 -0500
        Bounds checking in C (Was: "Death To C") gazelle@shell.xmission.com (Kenny McCormack) - 2015-05-05 02:15 +0000
          Re: Bounds checking in C (Was: "Death To C") BGB <cr88192@hotmail.com> - 2015-05-06 10:23 -0500
        Re: "Death To C" Les Cargill <lcargill99@comcast.com> - 2015-05-04 21:36 -0500
          Re: "Death To C" Robert Wessel <robertwessel2@yahoo.com> - 2015-05-05 01:01 -0500
            Re: "Death To C" Les Cargill <lcargill99@comcast.com> - 2015-05-05 12:23 -0500
          Re: "Death To C" CHIN Dihedral <dihedral88888@gmail.com> - 2015-05-05 03:06 -0700
        Re: "Death To C" Ian Collins <ian-news@hotmail.com> - 2015-05-05 17:43 +1200
          Re: "Death To C" Robert Wessel <robertwessel2@yahoo.com> - 2015-05-05 01:00 -0500
            Re: "Death To C" Robert Wessel <robertwessel2@yahoo.com> - 2015-05-05 01:13 -0500
              Re: "Death To C" Ian Collins <ian-news@hotmail.com> - 2015-05-05 19:15 +1200
                Re: "Death To C" Robert Wessel <robertwessel2@yahoo.com> - 2015-05-05 02:41 -0500
                Re: "Death To C" Ian Collins <ian-news@hotmail.com> - 2015-05-05 20:12 +1200
        Re: "Death To C" glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-05-05 06:48 +0000
        Re: "Death To C" Bartc <bc@freeuk.com> - 2015-05-05 10:57 +0100
          Re: "Death To C" asetofsymbols@gmail.com - 2015-05-05 16:53 -0700
          Re: "Death To C" Nobody <nobody@nowhere.invalid> - 2015-05-06 08:10 +0100
            Re: "Death To C" Bartc <bc@freeuk.com> - 2015-05-06 09:53 +0100
              Re: "Death To C" Richard Heathfield <rjh@cpax.org.uk> - 2015-05-06 13:49 +0100
                Re: "Death To C" Bartc <bc@freeuk.com> - 2015-05-06 14:29 +0100
                Re: "Death To C" Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-05-06 09:43 -0700
                Re: "Death To C" Bartc <bc@freeuk.com> - 2015-05-06 18:24 +0100
          Re: "Death To C" asetofsymbols@gmail.com - 2015-05-08 00:44 -0700
            Re: "Death To C" Bartc <bc@freeuk.com> - 2015-05-08 13:49 +0100
    Re: "Death To C" Bartc <bc@freeuk.com> - 2015-05-04 22:15 +0100
      Re: "Death To C" BGB <cr88192@hotmail.com> - 2015-05-08 09:09 -0500
    Re: "Death To C" Stephen Sprunk <stephen@sprunk.org> - 2015-05-04 16:18 -0500
    Re: "Death To C" Ian Collins <ian-news@hotmail.com> - 2015-05-05 12:49 +1200
  Re: "Death To C" raltbos@xs4all.nl (Richard Bos) - 2015-05-08 21:52 +0000
  Re: "Death To C" Merikissa <merikissa@no.spam.net> - 2015-05-10 04:04 +0300
  Re: "Death To C" "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-05-13 08:11 -0700
    Re: "Death To C" David Kleinecke <dkleinecke@gmail.com> - 2015-05-13 10:00 -0700
      Re: "Death To C" Bartc <bc@freeuk.com> - 2015-05-13 18:20 +0100
        Re: "Death To C" David Kleinecke <dkleinecke@gmail.com> - 2015-05-14 10:47 -0700
          Re: "Death To C" "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-05-14 11:09 -0700
          Re: "Death To C" Bartc <bc@freeuk.com> - 2015-05-15 19:21 +0100
            Re: "Death To C" David Kleinecke <dkleinecke@gmail.com> - 2015-05-16 09:10 -0700
              Re: "Death To C" Bartc <bc@freeuk.com> - 2015-05-16 20:45 +0100
                Re: "Death To C" David Kleinecke <dkleinecke@gmail.com> - 2015-05-17 09:38 -0700
        Re: "Death To C" raltbos@xs4all.nl (Richard Bos) - 2015-05-17 10:47 +0000
          Re: "Death To C" Bartc <bc@freeuk.com> - 2015-05-17 12:20 +0100
      Re: "Death To C" "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-05-13 10:24 -0700
        Re: "Death To C" David Brown <david.brown@hesbynett.no> - 2015-05-13 22:01 +0200
    Re: "Death To C" Nobody <nobody@nowhere.invalid> - 2015-05-14 07:48 +0100

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