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Re: heap memory indexed as an array

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nobody@example.org (Scott) writes:
>On Wed, 20 Mar 2019 16:43:53 GMT, scott@slp53.sl.home (Scott Lurndal)
>wrote:
>
>>nobody@example.org (Scott) writes:
>>>On Wed, 20 Mar 2019 04:40:25 GMT, Spiros Bousbouras <spibou@gmail.com>
>>>wrote:
>>>
>>>>But you don't get to do error checking either and if there isn't enough
>>>>memory to allocate the array , the programme will probably crash with an
>>>>uninformative error message.
>>>
>>>Well, maybe. On some contemporary operating systems, a malloc return
>>>value of non-null does not guarantee that the allocated memory
>>>actually exists. It can appear to succeed, and only explodes when you
>>>try to write to that phantom memory -- and there's no way to trap that
>>>fault in C.
>>
>>Correction, no "standard C" method.   One may always catch SIGSEGV.
>
>Agreed, one may do so, *if* the signal is sent. Seg fault happens when
>you hit memory that isn't yours, but in the case of overcommit, the
>page *is* yours, it just doesn't have any memory behind it.

Some unix will send SIGBUS in this case, but most will send SIGSEGV.

> My
>experiences here are brief and not conclusive at all, but when I wrote
>a test program to really push the issue, the result was crashing the
>entire OS more often than not, with no (catchable) signal ever sent to
>my process.

You'd have to point out which OS.   The feature originated, IIRC, with
IBM's AIX in the 80's.

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heap memory indexed as an array sinbad <sinbad.sinbad@gmail.com> - 2019-03-19 20:05 -0700
  Re: heap memory indexed as an array Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2019-03-19 21:37 -0600
    Re: heap memory indexed as an array Spiros Bousbouras <spibou@gmail.com> - 2019-03-20 04:40 +0000
      Re: heap memory indexed as an array nobody@example.org (Scott) - 2019-03-20 15:56 +0000
        Re: heap memory indexed as an array scott@slp53.sl.home (Scott Lurndal) - 2019-03-20 16:43 +0000
          Re: heap memory indexed as an array fir <profesor.fir@gmail.com> - 2019-03-20 10:00 -0700
          Re: heap memory indexed as an array William Ahern <william@25thandClement.com> - 2019-03-20 15:07 -0700
            Re: heap memory indexed as an array fir is a sexy shemale <cdalten@gmail.com> - 2019-03-20 23:52 -0700
          Re: heap memory indexed as an array nobody@example.org (Scott) - 2019-03-21 16:50 +0000
            Re: heap memory indexed as an array scott@slp53.sl.home (Scott Lurndal) - 2019-03-21 17:23 +0000
              Re: heap memory indexed as an array nobody@example.org (Scott) - 2019-03-22 04:29 +0000
                OT: crashing malloc [was Re: heap memory indexed as an array] nobody@example.org (Scott) - 2019-03-23 15:27 +0000
                Re: heap memory indexed as an array Spiros Bousbouras <spibou@gmail.com> - 2019-03-23 19:24 +0000
                Re: heap memory indexed as an array Melzzzzz <Melzzzzz@zzzzz.com> - 2019-03-23 20:20 +0000
      Re: heap memory indexed as an array Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-03-21 22:35 -0700
  Re: heap memory indexed as an array Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-03-20 07:05 +0000
  Re: heap memory indexed as an array Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-03-20 12:12 +0000

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