iOS 64-bit architecture 使用objc_msgSend要小心

在iOS64-bit下，使用objc_msgSend直接调用方法会造成崩溃，报错xc_bad_access，具体原因看苹果文档https://developer.apple.com/library/ios/documentation/General/Conceptual/CocoaTouch64BitGuide/ConvertingYourAppto64-Bit/ConvertingYourAppto64-Bit.html

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, the

doSomething: 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_msgSend function 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); }

大致就是，OBJC_EXPORT id objc_msgSend(id self, SEL op, …)最后的参数需要声明类型，所以使用应该像这样

void (*objcMsgSend)(id,SEL,id) = (void *)objc_msgSend;
objcMsgSend(plugin, selector, cmd);