main.m

#import <sys/sysctl.h>

static CFTimeInterval processStartTime() {
    size_t len = 4;
    int mib[len];
    struct kinfo_proc kp;

    sysctlnametomib("kern.proc.pid", mib, &len);
    mib[3] = getpid();
    len = sizeof(kp);
    sysctl(mib, 4, &kp, &len, NULL, 0);

    struct timeval startTime = kp.kp_proc.p_un.__p_starttime;
    return startTime.tv_sec + startTime.tv_usec / 1e6;
}

static CFTimeInterval sPreMainStartTimeRelative;

int main(int argc, char * argv[], char **envp) {
    CFTimeInterval absoluteTimeToRelativeTime =  CACurrentMediaTime() - [NSDate date].timeIntervalSince1970;
    sPreMainStartTimeRelative = processStartTime() + absoluteTimeToRelativeTime;
    // ...
}

// Call this function to get your final measurement
CFTimeInterval timeFromStartToNow() {
    return CACurrentMediaTime() - sPreMainStartTimeRelative;
}