Detecting if iOS app is run in debugger

Question

I set up my application to either send debugging output to console or a log file. Now, I\'d like to decide with in the code whether

• it is run in the debugger

Answer 1

There's a function from Apple to detect whether a program is being debugged in the Technical Q&A 1361 (entry in Mac library and entry in iOS library; they are identical).

Code from the Technical Q&A:

#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 );
}

Also pay attention to this note at the end of the Q&A:

Important: Because the definition of the kinfo_proc structure (in <sys/sysctl.h>) is conditionalized by __APPLE_API_UNSTABLE, you should restrict use of the above code to the debug build of your program.

Answer 2

It is possible to instruct the debugger to set environment variables when it launches a process it is about to debug. This can be done in Xcode by going to the menu item Product->Edit Scheme. Then under the Debug scheme's Arguments tab add a new environment variable. The variable should be named "debugger" with the value "true". Then the following code snippet can be used to determine if the debugger launched your process:

NSDictionary* env = [NSProcessInfo processInfo].environment;

if ([env[@"debugger"] isEqual:@"true"]) {
    NSLog(@"debugger yes");
}
else {
    NSLog(@"debugger no");
}

Answer 3

Why not using conditional compilation block in Swift?

     #if DEBUG
        // Do something.
     #endif

Any objection?

You can define if you want a runtime constant

#if DEBUG
public let IS_RUNNING_IN_DEBUGGER: Bool = true
#else
public let IS_RUNNING_IN_DEBUGGER: Bool = false
#endif

The same approach can be used in Objc & more.

Answer 4

For me this piece of swift-code works perfectly:

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

Answer 5

I usually go for a much more simple solution; is the binary compiled with optimizations?

A debug build is not optimized, and logs are nice. A release build should have optimizations and not as many logs. You can check for this with the __OPTIMIZE__ symbol.

For logging I use this setup for logg-functions:

#ifdef __OPTIMIZE__ 
  #define CWLog(...)
  #define CWLogDebug(...)
  #define CWLogInfo(...)
#else
  #define CWLog(...) NSLog(__VA_ARGS__)
  #define CWLogDebug( s, ... ) NSLog( @"DEBUG <%p %@:(%d)> %@", self, [[NSString stringWithUTF8String:__FILE__] lastPathComponent], __LINE__, [NSString stringWithFormat:(s), ##__VA_ARGS__] )
  #ifndef LOG_INFO
    #define CWLogInfo(...)
  #else
    #define CWLogInfo( s, ... ) NSLog( @"INFO <%p %@:(%d)> %@", self, [[NSString stringWithUTF8String:__FILE__] lastPathComponent], __LINE__, [NSString stringWithFormat:(s), ##__VA_ARGS__] )
  #endif
#endif
#define CWLogWarning( s, ... ) NSLog( @"WARNING <%p %@:(%d)> %@", self, [[NSString stringWithUTF8String:__FILE__] lastPathComponent], __LINE__, [NSString stringWithFormat:(s), ##__VA_ARGS__] )
#define CWLogError( s, ... ) NSLog( @"ERROR <%p %@:(%d)> %@", self, [[NSString stringWithUTF8String:__FILE__] lastPathComponent], __LINE__, [NSString stringWithFormat:(s), ##__VA_ARGS__] )

Answer 6

Based off an answer in a duplicate thread that was for Objective-C as well and showed how HockeyApp-iOS does it, here's a Swift 5 version:

let isDebuggerAttached: Bool = {
    var debuggerIsAttached = false

    var name: [Int32] = [CTL_KERN, KERN_PROC, KERN_PROC_PID, getpid()]
    var info: kinfo_proc = kinfo_proc()
    var info_size = MemoryLayout<kinfo_proc>.size

    let success = name.withUnsafeMutableBytes { (nameBytePtr: UnsafeMutableRawBufferPointer) -> Bool in
        guard let nameBytesBlindMemory = nameBytePtr.bindMemory(to: Int32.self).baseAddress else { return false }
        return -1 != sysctl(nameBytesBlindMemory, 4, &info/*UnsafeMutableRawPointer!*/, &info_size/*UnsafeMutablePointer<Int>!*/, nil, 0)
    }

    // The original HockeyApp code checks for this; you could just as well remove these lines:
    if !success {
        debuggerIsAttached = false
    }

    if !debuggerIsAttached && (info.kp_proc.p_flag & P_TRACED) != 0 {
        debuggerIsAttached = true
    }

    return debuggerIsAttached
}()