Save a memory block to disk

This article shows how to dump a a block of memory to a file, while debugging the program, without writing a debugging function into the program and without recompiling it.

Sample code 

int main()
{
    // buffer size
    int   bufferSize   = 1024;
    // create buffer
    void* buffer       = calloc(1, bufferSize);

    // set some bytes into the buffer
    memset(buffer, 0xAB, bufferSize);

    // release memory
    free(buffer);

    return 0;
}

Download

While this is a very simple piece of code, and writing a small function to save buffer contents to disk is not such a big deal, for a more complicated program ( thousands of lines of code ), if there isn’t already enough debugging code in place, we need to restart the debugging process every time that we add some new debugging code.

VSDebugPro extension offers a simple solution for this:

dumpmem
Dump memory utility.
------------------------------------------------------------------
Syntax: <dumpmem> <optional flags> <filename> <address> <size>
	EX: dumpmem c:\memdump.bin 0x00656789 200
	EX: dumpmem -f c:\memdump.bin 0x00656789 200
	Flags:
		  -f   - Force file overwrite.
		  -a   - Append to the file.
	<filename> - output filename
	<address>  - read address, must be a hex address / pointer, can be an expression
	<size>     - size in bytes, can be an expression
------------------------------------------------------------------
Steps to dump buffer contents to disk:
  1. Start debugging the program.
  2. Place a breakpoint at a carefully select point in code, where our data is available.
  3. Go to VSDebugPro menu and open Console.
  4. Dump buffer contents with the following command:
dumpmem buffer.bin buffer bufferSize

The dumpmem utility uses the Visual Studio C++ debugger interface to automatically evaluate the address of buffer and the size from bufferSize variable.

Dump buffer

References

HxD a free hex editor.