調用objc_msgSend方法在64位下崩潰解決方法

以前一直在非64位機器下測試一切正常的程序，在iPhone5s下平白無故崩潰。崩潰的位置是調用objc_msgSend時出現。通過一番辛苦搜索終於發現蘋果官網上有一段這樣的描述：

Dispatch Objective-C Messages Using the Method Function’s Prototype

An exception to the casting rule described above is when you are calling the objc_msgSend function or any other similar functions in the Objective-C runtime that send messages. Although the prototype for the message functions has a variadic form, the method function that is called by the Objective-C runtime does not share the same prototype. The Objective-C runtime directly dispatches to the function that implements the method, so the calling conventions are mismatched, as described previously. Therefore you must cast the objc_msgSend function to a prototype that matches the method function being called.

Listing 2-14 shows the proper form for dispatching a message to an object using the low-level message functions. In this example, thedoSomething: method takes a single parameter and does not have a variadic form. It casts the objc_msgSend function using the prototype of the method function. Note that a method function always takes an id variable and a selector as its first two parameters. After the objc_msgSendfunction is cast to a function pointer, the call is dispatched through that same function pointer.

Listing 2-14  Using a cast to call the Objective-C message sending functions

- (int) doSomething:(int) x { ... }
- (void) doSomethingElse {
   int (*action)(id, SEL, int) = (int (*)(id, SEL, int)) objc_msgSend;
   action(self, @selector(doSomething:), 0);
}

 

貌似是說不能直接使用objc_msgSend的原型方法來匿名調用，不然會出現異常。結果嘗試了上面的方法強制轉換成必定的方法後，再次運行沒有崩潰了，Luck!!

原文來自：https://developer.apple.com/library/ios/documentation/General/Conceptual/CocoaTouch64BitGuide/ConvertingYourAppto64-Bit/ConvertingYourAppto64-Bit.html

 

補充說明（2015-8-5）：

對於返回結構體的方法，若是使用objc_msgSend進行調用是會拋出異常EXC_BAD_ACCESS：

CGSize (*action)(id, SEL, int) = (CGSize (*)(id, SEL, int)) objc_msgSend;
CGSize size = action(self, @selector(doSomething:), 0);

這樣的作法是有可能會出現崩潰問題的（可是不必定每一個程序都必然會出現），通過查看官方文檔發現，objc_msgSend有一個擴展版本objc_msgSend_stret，是專門用於處理返回結構體的狀況，所以把代碼改成以下所示便可解決問題：

CGSize (*action)(id, SEL, int) = (CGSize (*)(id, SEL, int)) objc_msgSend_stret;
CGSize size = action(self, @selector(doSomething:), 0);

注：此調整隻有在armv7架構下須要進行調整，若是包含arm64則不須要。