[Vol-users] Problem reading mapped ranges in linux address spaces

Edwin Smulders edwin.smulders at gmail.com
Wed Jun 19 09:13:07 CDT 2013

Ahh, that is really too bad, I was pretty sure I had enough memory,
but I suppose swapping might occur at any moment, even with a good
amount of free memory.
Thanks for your answer, it's yet another issue I can include in my thesis :)

On 19 June 2013 16:08, Michael Hale Ligh <michael.hale at gmail.com> wrote:
> Hi Edwin,
> This is the effect of swapping. When you dump a vma region to disk, we
> zero-pad pages that are swapped to retain the original size and offsets in
> the vma region. You can call proc_as.is_valid_address(0x7faf9d9b0e9b) and if
> its False then the page containing that address is in the pagefile. You can
> also use proc_as.zread() instead of read() which will automatically zero-pad
> pages that are not memory resident.
> On Wed, Jun 19, 2013 at 9:15 AM, Edwin Smulders <edwin.smulders at gmail.com>
> wrote:
>> Hi all,
>> I am having a problem reading certain values in an address space. I
>> know for certain that the range I am trying to read is mapped, i.e.
>> there is a vma for it.
>> The specific range in this case is shown in the vma list as this:
>> 1206 0x00007faf9d98f000 0x00007faf9db4d000 r-x                   0x0
>>    8      1        241 /lib/x86_64-linux-gnu/libc-2.17.so
>> The offset in this range that I am trying to read is 0x21e9b =
>> 0x7faf9d9b0e9b
>> the call may look like this: proc_as.read(0x7faf9d9b0e9b, 10)
>> and it will return None, meaning it could not read that address.
>> Using the linux_dump_map I exported the whole range and there's a
>> pretty big empty (inaccessible) chunk in the middle, which appears as
>> 0-bytes in the export. I know for a fact that my libc does not have a
>> big area of 0-bytes, so this is pretty weird. It also works just fine
>> for other processes in the same dump (so using the same libc).
>> For research purposes I make my memory dumps with virtualbox, so I
>> don't think it's an issue with memory corruption; as far as i can
>> tell, virtualbox makes complete snapshots.
>> Does anyone know what might cause this problem?
>> Cheers,
>> Edwin
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