Memory Dump and Live Memory Visualization and Picture Extraction

NEW! The updated version of Dump2Picture is available: http://www.dumpanalysis.org/dump2picture

This is a reprint of several articles with permission from Memory Dump Analysis Anthology, Volume 1.

As the first step towards Memory Dump Tomography (Memory Dump Analysis Anthology, Volume 1, page 522) we created a small program that interprets a memory dump as a picture. We can visualize crash dumps with it. The tool is available for free download.

Simply run it from the command prompt and specify full paths to a dump file and an output BMP file. The memory dump file will be converted by default into true color, 32 bits-per-pixel bitmap. We can specify other values: 8, 16 and 24.

C:\Dump2Picture>Dump2Picture.exe
Dump2Picture version 1.0
Written by Dmitry Vostokov, 2007
Usage: Dump2Picture dumpfile bmpfile [8|16|24|32]

For example:

C:\Dump2Picture>Dump2Picture.exe MEMORY.DMP MEMORY.BMP 8
Dump2Picture version 1.0
Written by Dmitry Vostokov, 2007
MEMORY.BMP
MEMORY.DMP
1 file(s) copied.

Below are some screenshots of bitmap files created by the tool. We can think about them as visualized kernel or user address spaces.

Vista kernel memory dump (8 bits-per-pixel):

Vista kernel memory dump (16 bits-per-pixel):

Vista kernel memory dump (24 bits-per-pixel):

Vista kernel memory dump (32 bits-per-pixel):

Notepad process user memory dump (8 bits-per-pixel):

Notepad process user memory dump (16 bits-per-pixel):

Notepad process user memory dump (24 bits-per-pixel):

Notepad process user memory dump (32 bits-per-pixel):

Mspaint process user memory dump (32 bits-per-pixel):

Mspaint process user memory dump after loading "Toco Toucan.jpg" from Vista Sample Pictures folder (32 bits-per-pixel):

Dump2Picture can be used to explore memory leaks visually. We created the following small program in Visual C++ that leaks 64Kb every second:

#include "stdafx.h"
#include <windows.h>
int _tmain(int argc, _TCHAR* argv[])
{
  while (true)
  {
    printf("%x\n", (UINT_PTR)malloc(0xFFFF));
    Sleep(1000);
  }
  return 0;
}

Then we sampled 3 dumps at 7Mb, 17Mb and 32Mb process virtual memory size and converted them as 16 bits-per-pixel bitmaps. On the pictures below we can see that the middle black memory area grows significantly. Obviously malloc function allocates zeroed memory and therefore we see black color.

7Mb process memory dump:

17Mb process memory dump:

32Mb process memory dump:

If we zoom in the black area we would see the following pattern:

Colored lines inside are heap control structures that are created for every allocated block of memory. If this is correct then allocating smaller memory blocks would create a hatched pattern. And this is true indeed. The following program leaks 256 byte memory blocks:

#include "stdafx.h"
#include <windows.h>

int _tmain(int argc, _TCHAR* argv[])
{
  while (true)
  {
    printf("%x\n", (UINT_PTR)malloc(0xFF));
    Sleep(1000/0xFF);
  }
  return 0;
}

The corresponding process memory picture and zoomed heap area are the following:

Making allocations 4 times smaller makes heap area to look hatched, and zoomed picture is more densely packed by heap control structures:

#include "stdafx.h"
#include <windows.h>

int _tmain(int argc, _TCHAR* argv[])
{
  while (true)
  {
    printf("%x\n", (UINT_PTR)malloc(0xFF/4));
    Sleep((1000/0xFF)/4);
  }
  return 0;
}

Here is another example. One service was increasing its memory constantly. The crash dump picture shows huge hatched dark region in the middle:

and if we zoom in this region:

Because the pattern and allocation size look uniform it could be the true heap memory leak for some operation that allocates constant size buffers. After opening the dump and looking at heap segments that had grown the most we see the same allocation size indeed:

0:000> !.\w2kfre\ntsdexts.heap -h 5
HEAPEXT: Unable to get address of NTDLL!NtGlobalFlag.
Index Address Name Debugging options enabled
1: 00140000
2: 00240000
3: 00310000
4: 00330000
5: 00370000
Segment at 00370000 to 00380000 (00010000 bytes committed)
Segment at 01680000 to 01780000 (00100000 bytes committed)
Segment at 019C0000 to 01BC0000 (00200000 bytes committed)
Segment at 01BC0000 to 01FC0000 (00400000 bytes committed)
Segment at 01FC0000 to 027C0000 (00800000 bytes committed)
Segment at 027C0000 to 037C0000 (01000000 bytes committed)
Segment at 037C0000 to 057C0000 (02000000 bytes committed)

Segment at 057C0000 to 097C0000 (00155000 bytes committed)
...
...
...
057B96E0: 01048 . 01048 [07] - busy (1030), tail fill
057BA728: 01048 . 01048 [07] - busy (1030), tail fill
057BB770: 01048 . 01048 [07] - busy (1030), tail fill
057BC7B8: 01048 . 01048 [07] - busy (1030), tail fill
057BD800: 01048 . 01048 [07] - busy (1030), tail fill
057BE848: 01048 . 01048 [07] - busy (1030), tail fill
057BF890: 01048 . 00770 [14] free fill
Heap entries for Segment07 in Heap 370000
057C0040: 00040 . 01048 [07] - busy (1030), tail fill
057C1088: 01048 . 01048 [07] - busy (1030), tail fill
057C20D0: 01048 . 01048 [07] - busy (1030), tail fill
057C3118: 01048 . 01048 [07] - busy (1030), tail fill
057C4160: 01048 . 01048 [07] - busy (1030), tail fill
057C51A8: 01048 . 01048 [07] - busy (1030), tail fill
...
...
...

An alternative to converting memory dumps to picture files is to save a memory range to a binary file and then convert it to a BMP file. Thus we can view the particular DLL or driver mapped into address space, heap or pool region, including live memory:

To save a memory range to a file use WinDbg .writemem command:

.writemem d2p-range.bin 00800000 0085e000

or

.writemem d2p-range.bin 00400000 L20000

We wrote a WinDbg script that saves a specified memory range and then calls a shell script that automatically converts the saved binary file to a BMP file and then runs a picture viewer registered for .bmp extension.

The WinDbg script code (mempicture.txt):

.writemem d2p-range.bin ${$arg1} ${$arg2}
.if (${/d:$arg3})
{
  .shell -i- mempicture.cmd d2p-range ${$arg3}
}
.else
{
  .shell -i- mempicture.cmd d2p-range
}

The shell script (mempicture.cmd):

dump2picture %1.bin %1.bmp %2
%1.bmp

Because WinDbg installation folder is assumed to be the default directory for both scripts and Dump2Picture.exe they should be copied to the same folder where windbg.exe is located. On our system it is

C:\Program Files\Debugging Tools for Windows

Both scripts are now included in Dump2Picture package available for free download.

To call the script from WinDbg use the following command:

$$>a< mempicture.txt Range [bits-per-pixel]

where Range can be in Address1 Address2 or Address Lxxx format, bits-per-pixel can be 8, 16, 24 or 32. By default it is 32.

For example, we loaded a complete Windows x64 memory dump and visualized HAL (hardware abstraction layer) module:

kd> lm
start end module name
fffff800`00800000 fffff800`0085e000 hal
fffff800`01000000 fffff800`0147b000 nt
fffff97f`ff000000 fffff97f`ff45d000 win32k
...
...
...

kd> $$>a< mempicture.txt fffff800`00800000 fffff800`0085e000
Writing 5e001 bytes...

C:\Program Files\Debugging Tools for Windows>dump2picture d2p-range.bin d2p-range.bmp

Dump2Picture version 1.1
Written by Dmitry Vostokov, 2007

d2p-range.bmp
d2p-range.bin
1 file(s) copied.

C:\Program Files\Debugging Tools for Windows>d2p-range.bmp
<.shell waiting 10 second(s) for process>
.shell: Process exited
kd>

and Windows Picture and Fax Viewer application was launched and displayed the following picture: