.m

#include <assert.h>
#include <stdbool.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/sysctl.h>

static bool AmIBeingDebugged(void)
// Returns true if the current process is being debugged (either
// running under the debugger or has a debugger attached post facto).
{
int junk;
int mib[4];
struct kinfo_proc info;
size_t size;
// Initialize the flags so that, if sysctl fails for some bizarre
// reason, we get a predictable result.
info.kp_proc.p_flag = 0;
// Initialize mib, which tells sysctl the info we want, in this case
// we're looking for information about a specific process ID.
mib[0] = CTL_KERN;
mib[1] = KERN_PROC;
mib[2] = KERN_PROC_PID;
mib[3] = getpid();
// Call sysctl.
size = sizeof(info);
junk = sysctl(mib, sizeof(mib) / sizeof(*mib), &info, &size, NULL, 0);
assert(junk == 0);
// We're being debugged if the P_TRACED flag is set.
return ( (info.kp_proc.p_flag & P_TRACED) != 0 );
}