How do I mmap a _particular_ region in memory?

Question

I have a program. I want it to be able to mmap a particular region of memory over different runs.

1. I have the source code of the program. C/C++
2. I control how the program is compiled. gcc
3. I control how the program is linked. gcc
4. I control how the program is run (Linux).

I just want to have this particular region of memory, say 0xabcdabcd to 0xdeadbeef that I mmap to a particular file. Is there anyway to guarantee this? (I have to somehow make sure that other things aren't loaded into this particular region).

EDIT:

How do I make sure that nothing else takes this particular region in memory?

Answer 1

You need to do two things:

1. Specify the starting address as the first argument to mmap.
2. Include the MAP_FIXED flag.

For the starting address, you need to make sure it's a multiple of the pagesize. To get the pagesize, use the call sysconf(_SC_PAGESIZE) (that's the appropriate call on Linux, other platforms may be different).

Answer 2

Pass the address to map in addr . Try to get it on a 8KB boundary. You could try mlock() instead though.

Answer 3

You cannot make sure that nothing else takes that area of memory - first come, first served. However, as you need a particular part of the memory, I'm guessing that you have a pretty specialized environment, so you simply need to make sure that you are first (using start scripts)