[vbox-dev] Memory initialization

[Michal Necasek]

What does "shutdown the guest system/start again the guest system" mean? Shut down the VM and start it again? Or reboot the guest OS without terminating the VM? 


In either case, I'd recommend dumping the VM's memory right after the VM is reset (when it's executing firmware). Are the artifacts there at that point? 


Running with --dbg just shows the VM debugger UI, it does not change the VM's behavior. 



- Michal 

----- Original Message ----- 
From: b38911 at gmail.com 
To: michal.necasek at oracle.com 
Sent: Tuesday, July 30, 2019 11:13:05 AM GMT +01:00 Amsterdam / Berlin / Bern / Rome / Stockholm / Vienna 
Subject: Re: [vbox-dev] Memory initialization 



Hi Michal. 


Sure, I'll try to explain better what I mean: 


- start virtualbox and start a Windows 10 guest system (allocating let's say 4GB of RAM) 
- start a specific software in the guest, which, after its exits, leave some artefacts in RAM (like a specific portion of code in unallocated memory). So far, so good, nothing strange. 
- shutdown the guest system 
- start again the guest system 
- looking into the RAM (dumping it), I still see the same artefacts, even if I didn't ran the same software as before. Like if the allocated RAM (still 4GB) was not re-initialized to 0 


This make sense if the initial allocation does not set memory to 0 (or something else), since I'm not rebooting the host, so for sure these artefacts are still in the host memory. 
If you say that this is reset should be done, I'll try to re-run a set of tests, may be I'm missing something. Consider that I'm running the VM with --dbg option, not sure if this change something. 


Thanks and let me know if you need more details on this. 
Thanks 
c 



Il giorno mar 30 lug 2019 alle ore 10:11 Michal Necasek < michal.necasek at oracle.com > ha scritto: 



Can you provide a simple reproduction scenario? What does one have to 
do to see this? 

A VM reset should clear memory. A caveat is that a given guest OS may 
not perform a full reset but only a soft reboot, which does not clear 
memory. 

- Michal 

On 7/28/2019 10:15 PM, b38911 wrote: 
> Hello all. 
> 
> I was suggested to post my question here. 
> 
> Here my doubt: 
> 
> I noticed this behavior, which is probably expected: dumping the RAM of 
> a guest (with ".pgmphystofile" command) I saw that the memory is not 
> initialized between virtual powercycle, like if there was a real 
> powerdown. Sometimes, between restarts of the guest (with a shutdown and 
> then a restart), I find some memory artifacts belonging to processes 
> that shouldn't be there. 
> I assume this happens because I'm not restarting the host system, so 
> probably the RAM is just remapped, but not initialized. This is a bit 
> annoying in some case, especially if you are using the system for 
> testing purposes. 
> 
> Is there a way to force the guest to initialize the allocated RAM to 
> zero (or something else), in order to emulate a real powerdown-powerup? 
> Thanks for your help. 
> 
> cips 
> 
> _______________________________________________ 
> vbox-dev mailing list 
> vbox-dev at virtualbox.org 
> https://www.virtualbox.org/mailman/listinfo/vbox-dev 

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