替换所有block的实现

main.m

//
//  main.m
//  TestObjc
//
//  Created by Skifary on 14/03/2018.
//  Copyright © 2018 skifary. All rights reserved.
//

#import <Foundation/Foundation.h>

#import "fishhook.h"

typedef struct __block_impl {
    void *isa;
    int Flags;
    int Reserved;
    void *FuncPtr;
}__block_impl;

static void (*orig_func)(void *v ,int i, NSString *str);

void hookFunc(void *v ,int i, NSString *str) {
    NSLog(@"%d,%@", i, str);
    orig_func(v,i,str);
}

void HookBlockToPrintArguments(id blk) {
    __block_impl *ptr = (__bridge __block_impl *)blk;
    orig_func = ptr->FuncPtr;
    ptr->FuncPtr = &hookFunc;
}

#pragma mark - 第三题实现部分

static id (*orig_objc_retainBlock)(id);

id hook_objc_retainBlock(id blk) {
    
    id retainBlk = orig_objc_retainBlock(blk);
    
    // 因为retain会多次调动
    // 这里可以给blk添加一个属性 如果被hook过就不用继续hook
    // 因为这里只是一个测试例子 就不做这么麻烦了
    if (true) {
        HookBlockToPrintArguments(blk);
    }
    return retainBlk;
}

void HookEveryBlockToPrintArguments() {
    rebind_symbols((struct rebinding[1]){{"objc_retainBlock", hook_objc_retainBlock, (void *)&orig_objc_retainBlock}}, 1);
}

int main(int argc, const char * argv[]) {

    HookEveryBlockToPrintArguments();
    
    void (^blk)(int, NSString *) = ^void(int i, NSString *str) {
        NSLog(@"original invoke");
    };

    blk(1,@"aaa");
    
    return 0;
}

第三题：

原理，block在每次赋值的时候都会调用retain函数，所以说，利用fishhook hook了block的retain函数objc_retainBlock，在第二题的基础上在hook每一个block对象即可

static void (*orig_func)(void *v ,int i, NSString *str);

应该是下面的声明把

static void (* orig_objc_retainBlock)(void *v ,int i, NSString *str);

这里可以给blk添加一个属性 如果被hook过就不用继续hook，那么问题来了。。如何给一个void *添加属性呢？

objc_retainBlock实际上就是_Block_Copy方法，这个方法是这么定义的：

void *_Block_copy(const void *arg) {
    struct Block_layout *aBlock;

    if (!arg) return NULL;
    
    // The following would be better done as a switch statement
    aBlock = (struct Block_layout *)arg;
    if (aBlock->flags & BLOCK_NEEDS_FREE) {
        // latches on high
        latching_incr_int(&aBlock->flags);
        return aBlock;
    }
    else if (aBlock->flags & BLOCK_IS_GLOBAL) {
        return aBlock;
    }
    else {
        // Its a stack block.  Make a copy.
        struct Block_layout *result = malloc(aBlock->descriptor->size);
        if (!result) return NULL;
        memmove(result, aBlock, aBlock->descriptor->size); // bitcopy first
        // reset refcount
        result->flags &= ~(BLOCK_REFCOUNT_MASK|BLOCK_DEALLOCATING);    // XXX not needed
        result->flags |= BLOCK_NEEDS_FREE | 2;  // logical refcount 1
        _Block_call_copy_helper(result, aBlock);
        // Set isa last so memory analysis tools see a fully-initialized object.
        result->isa = _NSConcreteMallocBlock;
        return result;
    }
}