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Re: Indexing one past the end of array?

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"Oliver S." <Follow.Me@gmx.net> writes:
>> Elsewhere, I've read that on embedded systems memory can be allocated 
>> right up to the end of memory, and therefore such indexes are invalid 
>> (but I cannot remember where).
>> So, is it always legal to calculate one past the end of an array or 
>> allocated memory?
>> [1] https://lwn.net/Articles/278137/
>
>Userspace has its addresses ussually in the lower part of the logical
>address-space, so addresses calculated to be above an array would never
>wrap-around.
>In kernel-space addresses could wrap-around but I think a proper ker-
>nel would reserve a reasonable amount of memory at top of the logical
>address-space so that a past-the-end-pointer would maximally point
>into that area and not wrap around.

Most of them mark the first page of the virtual address space as
not-present to catch inadvertent wrapping behavior.

On the physical address side, both ARM and Intel will use unsigned modulo
arithmetic, so addresses will simply wrap.

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Indexing one past the end of array? Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2019-10-06 04:02 +0800
  Re: Indexing one past the end of array? Keith Thompson <kst-u@mib.org> - 2019-10-05 13:13 -0700
    Re: Indexing one past the end of array? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-05 22:01 +0100
      Re: Indexing one past the end of array? Keith Thompson <kst-u@mib.org> - 2019-10-05 14:35 -0700
      Re: Indexing one past the end of array? Richard Damon <Richard@Damon-Family.org> - 2019-10-05 19:00 -0400
        Re: Indexing one past the end of array? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-10-06 08:05 -0700
      Re: Indexing one past the end of array? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-10-06 06:36 -0700
        Re: Indexing one past the end of array? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-06 16:31 +0100
    Re: Indexing one past the end of array? Richard Damon <Richard@Damon-Family.org> - 2019-10-05 17:10 -0400
      Re: Indexing one past the end of array? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-10-06 07:40 -0700
  Re: Indexing one past the end of array? Mateusz Viste <mateusz@wont.tell> - 2019-10-05 20:26 +0000
  Re: Indexing one past the end of array? chad <cdalten@gmail.com> - 2019-10-05 16:55 -0700
  Re: Indexing one past the end of array? "Oliver S." <Follow.Me@gmx.net> - 2019-10-06 15:50 +0200
  Re: Indexing one past the end of array? "Oliver S." <Follow.Me@gmx.net> - 2019-10-06 17:04 +0200
    Re: Indexing one past the end of array? scott@slp53.sl.home (Scott Lurndal) - 2019-10-07 13:32 +0000
      Re: Indexing one past the end of array? "Oliver S." <Follow.Me@gmx.net> - 2019-10-07 17:23 +0200

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