OK, time for more geek-talk. I’ve spent a couple of late nights fussing with fat binaries, bundles, and mach-o architecture API’s to try and find a way to determine if an app is running in 64 bit mode. Surprisingly, I couldn’t just Google it and get an easy solution.

Looking at the darwin source, I found there’s a sysctl() token to get this information. This code will return the processor type (including the 64-bit flag). Note that it uses the sysctlbyname_with_pid() function in Apple’s Universal Binary Programming Guidelines:

cpu_type_t GetProcessArchitecture(pid_t pid)
{
    cpu_type_t cputype;
    size_t cpusz = sizeof(cputype);    

    // Default values
#if __i386__
    cputype = CPU_TYPE_X86;
#else
    cputype = CPU_TYPE_POWERPC;
#endif

    if (sysctlbyname_with_pid("sysctl.proc_cputype", pid,
                              &cputype, &cpusz, NULL, 0) == -1)
    {
        fprintf(stderr, "proc_cputype: sysctlbyname_with_pid failed:"
                "%s\n", strerror(errno));
    }
    return cputype;
}