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Re: Memory corruption problem

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In message <575802fd6cNews03@avisoft.f9.co.uk>
          Martin <News03@avisoft.f9.co.uk> wrote:

> On 16 Nov in article <dd0dec5757.Alan.Adams@ArmX6.adamshome.org.uk>,
>    Alan Adams <alan@adamshome.org.uk> wrote:
>> In message <5757e90ea1News03@avisoft.f9.co.uk>
>>           Martin <News03@avisoft.f9.co.uk> wrote:
>>> On 16 Nov in article <2e86dd5757.Alan.Adams@ArmX6.adamshome.org.uk>,
>>>    Alan Adams <alan@adamshome.org.uk> wrote:

> [Snip]

>>> However, if you use indirection operators !?$ it is possible that
>>> something that *should* be within your wimpslot is not. It is
>>> possible to validate write addresses?

>> There are a huge number of indirection operaions, not least among
>> the ring buffers used in the network communications. My suspicion
>> is that somewhere among them a completely invalid address is being
>> produced.

>>> If your applications use memory that is outside your slot
>>> (probably RMA?) then overrunning a block, or writing to the wrong
>>> address, can have predictable unpredictable results. Again, is it
>>> possible to validate writes?

>> I'm not using RMA

> Where is the memory you *should* be using?
> Are you using lots of individually allocated blocks?
> Or are you using your own Heap to manage blocks?

Individual blocks

> If there are a multiplicity of writes that cannot be verified, can
> you add a guard word at the end of each block, and check they are
> valid as often as possible?

I'm doing that for the ring buffers, to guard against overruns. 
However I don't think this is an overrun, more likely a miscalculated 
pointer, which could be absolutely anywhere in the address space.

It would be nice to have proper memory protection - I grew up with VMS 
which would produce "access violation" when this happened, and a stack 
dump to show you how you got to it. Unfortunately putting reportstack 
in the error handler is useless, because the call stack has already 
gone.

>> I'm wondering whether a high-vector build would help. If the disk
>> and socket data areas are protected, it would catch such invalid
>> writes. I'm on an ARMX6, and I don't know immediately whether
>> there is a high-vector build available. I seem to recall that
>> there is.

> Not sure if one is available ... but anyway, the HV build only
> protects what was in 'Zero page' which probably excludes disk &
> socket areas.

I've upgraded to 5.25, which made no difference. I don't think it's 
high-vector though - how can I tell?

-- 
Alan Adams, from Northamptonshire
alan@adamshome.org.uk
http://www.nckc.org.uk/

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Memory corruption problem Alan Adams <alan@adamshome.org.uk> - 2018-11-16 13:15 +0000
  Re: Memory corruption problem Martin <News03@avisoft.f9.co.uk> - 2018-11-16 15:21 +0000
    Re: Memory corruption problem Alan Adams <alan@adamshome.org.uk> - 2018-11-16 15:53 +0000
      Re: Memory corruption problem Martin <News03@avisoft.f9.co.uk> - 2018-11-16 20:04 +0000
        Re: Memory corruption problem Alan Adams <alan@adamshome.org.uk> - 2018-11-16 22:38 +0000
          Re: Memory corruption problem Martin <News03@avisoft.f9.co.uk> - 2018-11-16 23:46 +0000
  Re: Memory corruption problem David Buck <dbuckhome@gmail.com> - 2018-11-16 23:15 -0800
    Re: Memory corruption problem Alan Adams <alan@adamshome.org.uk> - 2018-11-17 12:21 +0000
      Re: Memory corruption problem Alan Adams <alan@adamshome.org.uk> - 2018-11-17 13:10 +0000
        Re: Memory corruption problem Martin <News03@avisoft.f9.co.uk> - 2018-11-17 19:01 +0000
          Re: Memory corruption problem Alan Adams <alan@adamshome.org.uk> - 2018-11-17 21:04 +0000
        Re: Memory corruption problem Erik G <noreply123@xs4all.nl> - 2018-11-24 20:17 +0100
    Re: Memory corruption problem "John Williams (News)" <UCEbin@tiscali.co.uk> - 2018-11-17 12:26 +0000
    Re: Memory corruption problem David Higton <dave@davehigton.me.uk> - 2018-11-17 20:59 +0000

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