Detect if Swift app is being run from Xcode

Question

I would like to programmatically determine if the iOS app is being run directly from XCode (either in the simulator or on a tethered device). I've tried the -D DEBUG solution described here, but when I then disconnect from Xcode and re-run the app, it still thinks it's in debug mode. I think what I'm looking for is a Swift version of this function

#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 );
}

Answer 1

Clarification: Your C code (and the Swift version below) checks if the program is run under debugger control, not if it's being run from Xcode. One can debug a program outside of Xcode (by calling lldb or gdb directly) and one can run a program from Xcode without debugging it (if the “Debug Executable” checkbox in the scheme setting is off).

---

You could simply keep the C function and call it from Swift. The recipes given in How do I call Objective-C code from Swift? apply to pure C code as well.

But it is actually not too complicated to translate that code to Swift:

func amIBeingDebugged() -> Bool {
    // Buffer for "sysctl(...)" call's result.
    var info = kinfo_proc()
    // Counts buffer's size in bytes (like C/C++'s `sizeof`).
    var size = MemoryLayout.stride(ofValue: info)
    // Tells we want info about own process.
    var mib : [Int32] = [CTL_KERN, KERN_PROC, KERN_PROC_PID, getpid()]
    // Call the API (and assert success).
    let junk = sysctl(&mib, UInt32(mib.count), &info, &size, nil, 0)
    assert(junk == 0, "sysctl failed")
    // Finally, checks if debugger's flag is present yet.
    return (info.kp_proc.p_flag & P_TRACED) != 0
}

Update for Swift 5 (Xcode 10.7): strideofValue and the related functions do not exist anymore, they have been replaced by MemoryLayout.stride(ofValue:).

Remarks:

• kinfo_proc() creates a fully initialized structure with all fields set to zero, therefore setting info.kp_proc.p_flag = 0 is not necessary.
• The C int type is Int32 is Swift.
• sizeof(info) from the C code has to be strideOfValue(info) in Swift to include the structure padding. With sizeofValue(info) the above code always returned false in the Simulator for 64-bit devices. This was the most difficult part to figure out.

Swift 2 logic:

func amIBeingDebugged() -> Bool {
    var info = kinfo_proc()
    var mib : [Int32] = [CTL_KERN, KERN_PROC, KERN_PROC_PID, getpid()]
    var size = strideofValue(info)
    let junk = sysctl(&mib, UInt32(mib.count), &info, &size, nil, 0)
    assert(junk == 0, "sysctl failed")
    return (info.kp_proc.p_flag & P_TRACED) != 0
}

Answer 2

For those looking for a simpler solution - this works perfectly:

func isDebuggerAttached() -> Bool {
    return getppid() != 1
}