Created attachment 155955 [details]
sysctl-overflow.diff

Here's a part of 'sysctl vm.mvtotal' output on my 10.0/amd64
machine:

  % sysctl vm.vmtotal
  [...]
  Virtual Memory:         (Total: 1654588K Active: 1536668K)
  [...]

If on the other hand, when I try to retrieve the same data via
sysctl(3), I get different total virtual memory:

  % cat >test.c <<'EOF'
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/sysctl.h>
#include <sys/vmmeter.h>

int main() {
    struct vmtotal vt = {0};
    size_t vtlen = sizeof(vt);
    if (sysctlbyname("vm.vmtotal", &vt, &vtlen, NULL, 0) != 0)
        return -1;
    ssize_t pagesize = getpagesize()/1024;
    printf("vm.vmtotal.t_vm = %zd pages (%zd kB)\n",
            (ssize_t)vt.t_vm,
            pagesize*vt.t_vm);
    return 0;
}
'EOF'
  % c99 test.c && ./a.out
  vm.vmtotal.t_vm = 1074154446 pages (4296617784 kB)

As you can see, the actual data coming out of sysctl(3) is
4296617784K, not 1654588K as sysctl(8) says. This is because
sysctl(8) has a multiplication overflow in the 'S_vmtotal'
function [1] when the number of pages ('t_vm') is multiplied by
the page size ('pageKilo').

I'm attaching a (completely untested) patch to fix this problem;
apply this patch to 'sbin/sysctl/sysctl.c'.

[1] http://svnweb.freebsd.org/base/head/sbin/sysctl/sysctl.c?revision=278654&view=markup#l530