low-level objc runtime apis

.gitignore

*
!*.m
!Makefile

array.m

// To compile: gcc -o array array.m -lobjc -framework Foundation

#include <objc/runtime.h>
#include <dlfcn.h>
#include <stdio.h>

int main() {

  void *sdl_library = dlopen("/System/Library/Frameworks/Foundation.framework/Versions/Current/Foundation", RTLD_LAZY);
  if (sdl_library == NULL) {
    printf("Got dlopen error!\n");
  } else {
    printf("dlopen successful!\n");

    // Set up an NSAutoreleasePool
    Class nsautoreleasepool = objc_getClass("NSAutoreleasePool");
    id pool = class_createInstance(nsautoreleasepool, 0);
    SEL initSel = sel_registerName("init");
    id poolAfterInit = objc_msgSend(pool, initSel);

    // Create an NSMutableArray
    Class nsmutablearray = objc_getClass("NSMutableArray");

    // Regular way to create an NSMutableArray,
    // equivalent to [[NSMutableArray alloc] initWithCapacity: 10]
    id array = objc_msgSend(nsmutablearray, sel_registerName("alloc"));
    id arrayAfterInit = objc_msgSend(array, sel_registerName("initWithCapacity:"), 10);

    // Alternative, shorthand way of creating an NSMutableArray,
    // equivalent to [NSMutableArray arrayWithCapacity: 10]
    //id arrayAfterInit = objc_msgSend(nsmutablearray, sel_registerName("arrayWithCapacity:"), 10);

    // Add an NSString and the nsma class reference to the array
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"test");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), nsmutablearray);

    // Print out the length and debug printout
    NSLog(@"%d", objc_msgSend(arrayAfterInit, sel_registerName("count")));
    NSLog(@"%@", arrayAfterInit);
  }

  return 0;
}

block.m

#import <Foundation/Foundation.h>
#include <objc/runtime.h>
#include <Block.h>
#include <dlfcn.h>
#include <stdio.h>

int main() {

  void *sdl_library = dlopen("/System/Library/Frameworks/Foundation.framework/Versions/Current/Foundation", RTLD_LAZY);
  if (sdl_library == NULL) {
    printf("Got dlopen error!\n");
  } else {
    printf("dlopen successful!\n");

    // Set up an NSAutoreleasePool
    Class nsautoreleasepool = objc_getClass("NSAutoreleasePool");
    id pool = class_createInstance(nsautoreleasepool, 0);
    SEL initSel = sel_registerName("init");
    id poolAfterInit = objc_msgSend(pool, initSel);

    // Create an NSMutableArray
    Class nsmutablearray = objc_getClass("NSMutableArray");

    // Regular way to create an NSMutableArray,
    // equivalent to [[NSMutableArray alloc] initWithCapacity: 10]
    id array = objc_msgSend(nsmutablearray, sel_registerName("alloc"));
    id arrayAfterInit = objc_msgSend(array, sel_registerName("initWithCapacity:"), 10);

    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"a");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"b");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"c");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"d");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"e");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"f");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"g");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"h");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"i");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"j");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"k");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"l");

    id b = ^(id x, NSUInteger index, BOOL *stop){
      NSLog(@"%@", x);
    };

    NSLog(@"%@", b);

    objc_msgSend(arrayAfterInit, sel_registerName("enumerateObjectsUsingBlock:"), b);
  }

  return 0;
}

block2.m

#import <Foundation/Foundation.h>
#include <objc/runtime.h>
#include <Block.h>
#include <dlfcn.h>
#include <stdio.h>

struct __block_literal_1 {
  void *isa;
  int flags;
  int reserved; 
  void (*invoke)(struct __block_literal_1 *, id obj, NSUInteger idx, BOOL *stop);
  struct __block_descriptor_1 *descriptor;
};

// This is the regular C function we are turning into a Block.
void __block_invoke_1(struct __block_literal_1 *_block, id obj, NSUInteger idx, BOOL *stop) {
  NSLog(@"%d: %@", idx, obj);
}

static struct __block_descriptor_1 {
  unsigned long int reserved;
  unsigned long int Block_size;
} __block_descriptor_1 = { 0, sizeof(struct __block_literal_1) };


int main() {

  printf("sizeof(int): %lu\n", sizeof(int));
  printf("sizeof(void *): %lu\n", sizeof(void *));
  printf("sizeof(void (*)()): %lu\n", sizeof(void (*)()));
  printf("sizeof(struct __block_descriptor *): %lu\n", sizeof(struct __block_descriptor *));
  printf("sizeof(__block_literal_1): %lu\n", sizeof(struct __block_literal_1));
  printf("sizeof(__block_descriptor_1): %lu\n", sizeof(struct __block_descriptor_1));

  printf(" calculated: %lu\n", sizeof(void*)+sizeof(int)+sizeof(int)+sizeof(void (*)())+sizeof(struct __block_descriptor_1 *));


  void *sdl_library = dlopen("/System/Library/Frameworks/Foundation.framework/Versions/Current/Foundation", RTLD_LAZY);
  if (sdl_library == NULL) {
    printf("Got dlopen error!\n");
  } else {
    printf("dlopen successful!\n");

    // Set up an NSAutoreleasePool
    Class nsautoreleasepool = objc_getClass("NSAutoreleasePool");
    id pool = class_createInstance(nsautoreleasepool, 0);
    SEL initSel = sel_registerName("init");
    id poolAfterInit = objc_msgSend(pool, initSel);

    // Create an NSMutableArray
    Class nsmutablearray = objc_getClass("NSMutableArray");

    // Regular way to create an NSMutableArray,
    // equivalent to [[NSMutableArray alloc] initWithCapacity: 10]
    id array = objc_msgSend(nsmutablearray, sel_registerName("alloc"));
    id arrayAfterInit = objc_msgSend(array, sel_registerName("initWithCapacity:"), 10);

    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"a");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"b");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"c");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"d");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"e");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"f");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"g");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"h");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"i");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"j");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"k");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"l");

    struct __block_literal_1 _block_literal = {
      &_NSConcreteStackBlock,
      //&_NSConcreteGlobalBlock,
      (1<<29),
      0,
      __block_invoke_1,
      &__block_descriptor_1
    };

    id b = (id)&_block_literal;

    NSLog(@"%@", b);

    objc_msgSend(arrayAfterInit, sel_registerName("enumerateObjectsUsingBlock:"), b);
  }

  return 0;
}

class_introspection.m

#include <objc/runtime.h>
#include <dlfcn.h>
#include <stdio.h>

int main(int argc, char **argv) {

  dlopen("/System/Library/Frameworks/Foundation.framework/Foundation", RTLD_LAZY);
  dlopen("/System/Library/Frameworks/AppKit.framework/AppKit", RTLD_LAZY);
  dlopen("/System/Library/Frameworks/Cocoa.framework/Cocoa", RTLD_LAZY);

  char * className = argc == 2 ? argv[1] : "NSMutableArray";
  Class NSMA = objc_getClass(className);

  if (!NSMA) {
    printf("Could not load Class: %s\n", className);
    return 1;
  }

  const char *name = class_getName(NSMA);
  printf("class_getName: %s\n", name);

  int version = class_getVersion(NSMA);
  printf("class_getVersion: %d\n", version);

  const char *weakIvarLayout = class_getWeakIvarLayout(NSMA);
  printf("class_getWeakIvarLayout: %s\n", weakIvarLayout);

  BOOL isMetaClass = class_isMetaClass(NSMA);
  printf("class_isMetaClass: %s\n", isMetaClass ? "yes" : "no");

  // get the metaclass
  id metaclass = NSMA->isa;
  isMetaClass = class_isMetaClass(metaclass);
  printf("class_isMetaClass(isa): %s\n", isMetaClass ? "yes" : "no");


  // Look up the Ivars
  unsigned int i = 0;
  unsigned int numIvars = 999999;
  Ivar *ivars = NULL;
  ivars = class_copyIvarList(NSMA, &numIvars);
  printf("\nNum ivars: %d\n", numIvars);
  for (; i<numIvars; i++) {
    Ivar ivar = ivars[i];
    const char *ivarName = ivar_getName(ivar);
    printf("  %s (%s)\n", ivarName, ivar_getTypeEncoding(ivar));
  }
  free(ivars);


  // Copy the Property List
  unsigned int numProps = 999999;
  objc_property_t *props = NULL;
  props = class_copyPropertyList(NSMA, &numProps);
  printf("\nNum props: %d\n", numProps);
  for (i=0; i<numProps; i++) {
  }
  free(props);


  // Copy Protocol List
  unsigned int numProtocols = 9999999;
  Protocol **ps = class_copyProtocolList(NSMA, &numProtocols);
  printf("\nNum Protocols: %d\n", numProtocols);
  for (i=0; i<numProtocols; i++) {
    Protocol *p = ps[i];
    printf("  %s\n", protocol_getName(p));
  }
  free(ps);

  // Copy Method List (instance methods)
  unsigned int numMethods = 99999999;
  Method * methods = NULL;
  methods = class_copyMethodList(NSMA, &numMethods);
  printf("\nNum Instance Methods: %d\n", numMethods);
  for (i=0; i<numMethods; i++) {
    Method m = methods[i];
    SEL name = method_getName(m);
    printf("  %s (%s)\n", sel_getName(name), method_getTypeEncoding(m));
  }
  free(methods);


  // Copy Method List (class methods)
  numMethods = 0;
  methods = NULL;
  methods = class_copyMethodList(metaclass, &numMethods);
  printf("\nNum Class Methods: %d\n", numMethods);
  for (i=0; i<numMethods; i++) {
    Method m = methods[i];
    SEL name = method_getName(m);
    printf("  %s (%s)\n", sel_getName(name), method_getTypeEncoding(m));
  }
  free(methods);

  // get superclass
  Class superclass = NSMA;
  printf("\nWalking inheritance chain:\n");
  printf("  %s\n", name);
  unsigned int numClasses = 0;
  do {
    printf("  ");
    numClasses++;
    superclass = class_getSuperclass(superclass);
    for (i=0; i<numClasses; i++) {
      printf("  ");
    }
    printf("↳ %s\n", class_getName(superclass));
  } while(superclass);


  return 0;
}

copyProtocolList.m

#include <objc/runtime.h>
#include <dlfcn.h>
#include <stdio.h>

int main(int argc, char **argv) {

  dlopen("/System/Library/Frameworks/Foundation.framework/Versions/Current/Foundation", RTLD_LAZY);

  unsigned int i, n;
  Protocol **ps = NULL;

  ps = objc_copyProtocolList(&n);
  printf("Num Protocols: %d\n", n);


  // Do stuff with `classes`
  for (i=0; i<n; i++) {
    Protocol *p = ps[i];
    printf("%s\n", protocol_getName(p));
  }

  free(ps);

  return 0;
}

getClassList.m

// To compile: gcc -o getClassList getClassList.m -lobjc -framework Foundation

#import <Foundation/Foundation.h>
#include <objc/runtime.h>
#include <dlfcn.h>
#include <stdio.h>

int main(int argc, char **argv) {

  dlopen("/System/Library/Frameworks/Foundation.framework/Foundation", RTLD_LAZY);
  dlopen("/System/Library/Frameworks/AppKit.framework/AppKit", RTLD_LAZY);

  int i = 0;
  int numClasses;
  Class * classes = NULL;

  numClasses = objc_getClassList(NULL, 0);
  printf("Num classes: %d\n", numClasses);

  if (numClasses > 0 ) {
    classes = malloc(sizeof(Class) * numClasses);
    numClasses = objc_getClassList(classes, numClasses);

    // Do stuff with `classes`
    for (i=0; i<numClasses; i++) {
      Class c = classes[i];
      printf("%s\n", class_getName(c));
    }

    free(classes);
  }

  return 0;
}

hello.m

// To compile: gcc -o hello hello.m -lobjc

#include <objc/runtime.h>
#include <dlfcn.h>
#include <stdio.h>

int main() {

  void *sdl_library = dlopen("/System/Library/Frameworks/Foundation.framework/Versions/Current/Foundation", RTLD_LAZY);
  if (sdl_library == NULL) {
    printf("Got dlopen error!\n");
  } else {
    printf("dlopen successful!\n");

    // Set up an NSAutoreleasePool
    Class nsautoreleasepool = objc_getClass("NSAutoreleasePool");
    id pool = class_createInstance(nsautoreleasepool, 0);
    SEL initSel = sel_registerName("init");
    id poolAfterInit = objc_msgSend(pool, initSel);

    // Set up a NSString with the contents "Hello World" from a C string
    Class nsstring = objc_getClass("NSString");
    SEL stringUTF8sel = sel_registerName("stringWithUTF8String:");
    id hello = objc_msgSend(nsstring, stringUTF8sel, "Hello World\n");

    // Print it back out as a C string
    printf("%s", (char *)objc_msgSend(hello, sel_registerName("UTF8String")));
  }

  return 0;
}

Makefile

CC = gcc
SRC_FILES = $(wildcard *.m)
OUT_FILES = $(SRC_FILES:.m=)

.PHONY: all
all: $(OUT_FILES)

%: %.m
	$(CC) -g -lobjc -framework Foundation -o $@ $<

.PHONY: clean
clean:
	rm -f $(OUT_FILES)
	rm -rf $(SRC_FILES:.m=.dSYM)

scriptingbridge.m

// To compile: gcc -o scriptingbridge scriptingbridge.m -lobjc -framework Foundation

#import <Foundation/Foundation.h>
#include <objc/runtime.h>
#include <dlfcn.h>
#include <stdio.h>

int main(int argc, char **argv) {

  dlopen("/System/Library/Frameworks/Foundation.framework/Versions/Current/Foundation", RTLD_LAZY);
  dlopen("/System/Library/Frameworks/ScriptingBridge.framework/Versions/Current/ScriptingBridge", RTLD_LAZY);

  // Set up an NSAutoreleasePool
  Class nsautoreleasepool = objc_getClass("NSAutoreleasePool");
  id pool = class_createInstance(nsautoreleasepool, 0);
  SEL initSel = sel_registerName("init");
  id poolAfterInit = objc_msgSend(pool, initSel);

  // Create an instance of the local iTunes installation
  Class sbapplication = objc_getClass("SBApplication");
  id itunes = objc_msgSend(sbapplication, sel_registerName("applicationWithBundleIdentifier:"), @"com.apple.iTunes");

  // Is iTunes running?
  id running = objc_msgSend(itunes, sel_registerName("isRunning"));
  NSLog(@"iTunes Running: %d", running);

  // Print out the name of the iTunes application
  id name = objc_msgSend(itunes, sel_registerName("name"));
  NSLog(@"Name: %@", name);

  // Print out the current volume
  NSInteger curVol = (NSInteger) objc_msgSend(itunes, sel_registerName("soundVolume"));
  NSLog(@"Current Volume: %d", curVol);

  // If an argument was passed, assume it's an integer and set iTunes' volume
  if (argc > 1) {
    NSInteger volToSet = atoi(argv[1]);
    objc_msgSend(itunes, sel_registerName("setSoundVolume:"), volToSet);
    NSLog(@"Set Volume to: %d", volToSet);
  }

  return 0;
}

sizeof.m

// To compile: gcc -o array array.m -lobjc -framework Foundation

#import <Foundation/Foundation.h>
#include <objc/runtime.h>
#include <dlfcn.h>
#include <stdio.h>

int main() {

  void *sdl_library = dlopen("/System/Library/Frameworks/Foundation.framework/Versions/Current/Foundation", RTLD_LAZY);
  if (sdl_library == NULL) {
    printf("Got dlopen error!\n");
  } else {
    printf("dlopen successful!\n");
  }

  printf("sizeof(Class): %lu\n", sizeof(Class));
  printf("sizeof(Method): %lu\n", sizeof(Method));
  printf("sizeof(unsigned long int): %lu\n", sizeof(unsigned long int));
  printf("sizeof(struct int, void*): %lu\n", sizeof(struct test { int test; void * ptr; }));
  printf("sizeof(struct int, int, void*): %lu\n", sizeof(struct test2 { int test; int test2; void * ptr; }));
  printf("sizeof(struct void*, int, int, void*): %lu\n", sizeof(struct test3 { void *ptr2; int test2; void * ptr; }));

  return 0;
}

uncaughtException.m

#include <objc/runtime.h>
#include <objc/objc-exception.h>
#include <dlfcn.h>
#include <stdio.h>

void uncaughtExceptionHandler (id exception) {
  fprintf(stderr, "Inside uncaughtException handler!!!!\n");
  fprintf(stderr, "Exception Type: %s\n", (const char *)objc_msgSend(objc_msgSend(exception, sel_registerName("name")), sel_registerName("UTF8String")));
  fprintf(stderr, "Exception Reason: %s\n", (const char *)objc_msgSend(objc_msgSend(exception, sel_registerName("reason")), sel_registerName("UTF8String")));
}


int main() {

  void *sdl_library = dlopen("/System/Library/Frameworks/Foundation.framework/Versions/Current/Foundation", RTLD_LAZY);
  if (sdl_library == NULL) {
    printf("Got dlopen error!\n");
  } else {
    printf("dlopen successful!\n");

    // Set up an NSAutoreleasePool
    Class nsautoreleasepool = objc_getClass("NSAutoreleasePool");
    id pool = class_createInstance(nsautoreleasepool, 0);
    SEL initSel = sel_registerName("init");
    id poolAfterInit = objc_msgSend(pool, initSel);


    // Set up an uncaughtException handler
    objc_setUncaughtExceptionHandler((objc_uncaught_exception_handler)uncaughtExceptionHandler);


    // Intentionally throw an exception, by sending a bad selector to an object
    Class nsobject = objc_getClass("NSObject");
    SEL badSel = sel_registerName("badSelector");
    objc_msgSend(nsobject, badSel);
  }

  return 0;
}

Realise this was created a long time ago but is a really useful resource.

objc_msgSend appears to have a odd definition where the params are just inserted wherever. Do you know if it's possible to send parameters gradually to an object by repeatedly sending objc_msgSend() (or some other function) for parameters instead?

id itunesPre = objc_msgSend(sbapplication, sel_registerName("applicationWithBundleIdentifier:"));
id itunes = objc_msgSend(itunesPre, @"com.apple.iTunes")

Additionally, do you know how to send a named parameter?