Are memory addresses reported in valgrind absolute, physical addresses?

Question

While running an MPI program with valgrind using mpirun -np 3 valgrind test, I noticed that the addresses of malloc/calloc'ed arrays are sometimes identical for different processes. This would lead me to believe that the addresses reported by Valgrind are either not absolute or do not correspond to the physical memory addresses -- which would make sense, as it uses its own allocator. Could anyone confirm this, or tell me which trivial insight I'm missing here? Thank you.

The code:

#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>
#include <assert.h>

int main(int argc, char* argv[])
{
  int rank, nproc;
  /* first let MPI strip off its MPI stuff: */
  MPI_Init(&argc, &argv);
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  MPI_Comm_size(MPI_COMM_WORLD, &nproc);

  double* a;
  int n = 40;
  assert(a = calloc(n, sizeof(double)));
  printf("Rank %d: Address of a = %p\n",rank,a);
  free(a);
  MPI_Finalize();
  return 0;
}

Example output:

Rank 0: Address of a = 0x6dad300
Rank 1: Address of a = 0x67a8800
Rank 2: Address of a = 0x67a8800

Answer 1

In modern processors / operating systems, memory is mapped into the process space of a program. The program has no notion (or interest in) the actual physical memory address of the space it's using--only device drivers really have the need.