descriptor

Block中的descriptor描述符，决定了Block有哪些额外的属性和具体定义。

Block_private.h

中的，3种Block_descriptor：Block_descriptor_1、Block_descriptor_2、Block_descriptor_3

#define BLOCK_DESCRIPTOR_1 1
struct Block_descriptor_1 {
    uintptr_t reserved;
    uintptr_t size;
};

#define BLOCK_DESCRIPTOR_2 1
struct Block_descriptor_2 {
    // requires BLOCK_HAS_COPY_DISPOSE
    void (*copy)(void *dst, const void *src);
    void (*dispose)(const void *);
};

#define BLOCK_DESCRIPTOR_3 1
struct Block_descriptor_3 {
    // requires BLOCK_HAS_SIGNATURE
    const char *signature;
    const char *layout;     // contents depend on BLOCK_HAS_EXTENDED_LAYOUT
};

struct Block_layout {
    void *isa;
    volatile int32_t flags; // contains ref count
    int32_t reserved; 
    void (*invoke)(void *, ...);
    struct Block_descriptor_1 *descriptor;
    // imported variables
};

合并后，就是前面Block详细定义所整理的：

// merged new layout
struct Block_descriptor {
    // Block_descriptor_1
    uintptr_t reserved;
    uintptr_t size;

    // Block_descriptor_2
    // requires BLOCK_HAS_COPY_DISPOSE
    void (*copy)(void *dst, const void *src);
    void (*dispose)(const void *);

    // Block_descriptor_3
    // requires BLOCK_HAS_SIGNATURE
    const char *signature;
    const char *layout;     // contents depend on BLOCK_HAS_EXTENDED_LAYOUT
};

TODO：

• Block_descriptor_1、Block_descriptor_2、Block_descriptor_3
  • 【整理】iOS逆向心得：Block中Block_descriptor_1、Block_descriptor_2、Block_descriptor_3的计算逻辑和位置