__LP64__

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/// https://github.com/llvm/llvm-project/
if (TI.getPointerWidth(0) == 64 && TI.getLongWidth() == 64
      && TI.getIntWidth() == 32) {
    Builder.defineMacro("_LP64");
    Builder.defineMacro("__LP64__");
}

if (TI.getPointerWidth(0) == 32 && TI.getLongWidth() == 32
    && TI.getIntWidth() == 32) {
    Builder.defineMacro("_ILP32");
    Builder.defineMacro("__ILP32__");
}
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// Target properties.
if (!getTriple().isOSWindows() && getTriple().isArch64Bit()) {
    Builder.defineMacro("_LP64");
    Builder.defineMacro("__LP64__");
}

  • 这里可能会有一点疑惑：为什么isArch64Bit 就认为是__LP64__?

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    bool Triple::isArch64Bit() const {
        // 大概意思应该是：获取 pointer 占用的 bit 数
        // 接着看下文中对 LP64 的说明
        return getArchPointerBitWidth(getArch()) == 64;
    }

  • LP64 其实就是 long integers 和 pointers 是 64 bits

  • 除了 LP64 之外，还有 LLP64、ILP64、SILP64、ILP32 等

  • 值得注意的是： 也有在64位处理器上使用ILP32数据模型，该数据模型减小了代码大小，并减小了包含指针的数据结构的大小，所以造成的结果就是地址空间会小很多(这里应该是指操作系统给应用进程分配的虚拟内存空间)。对于某些嵌入式系统来说，ILP32 是一个不错的选择。已在Apple Watch Series 4 / 5中使用。

data models
Data model short int long long long pointer
LLP64 16 32 32 64 64
LP64 16 32 64 64 64
ILP64 16 64 64 64 64
SILP64 64 64 64 64 64
ILP32 16 32 32 64 32

__ARM_ARCH_7K__

  • isWatchABI
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// Unfortunately, __ARM_ARCH_7K__ is now more of an ABI descriptor. The CPU
// happens to be Cortex-A7 though, so it should still get __ARM_ARCH_7A__.
if (getTriple().isWatchABI())
    Builder.defineMacro("__ARM_ARCH_7K__", "2");

SUPPORT_PACKED_ISA

  • 在iOS中采用__LP64__数据模型；
    • 即：# define SUPPORT_PACKED_ISA 1
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// Define SUPPORT_PACKED_ISA=1 on platforms that store the class in the isa 
// field as a maskable pointer with other data around it.
#if (!__LP64__  ||  TARGET_OS_WIN32  ||  \
     (TARGET_OS_SIMULATOR && !TARGET_OS_IOSMAC))
#   define SUPPORT_PACKED_ISA 0
#else
#   define SUPPORT_PACKED_ISA 1
#endif
  • 在isa_t中使用到了ISA_BITFIELD
  • ISA_BITFIELD 定义在 SUPPORT_PACKED_ISA 内
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union isa_t {
    isa_t() { }
    isa_t(uintptr_t value) : bits(value) { }

    Class cls;
    uintptr_t bits;
#if defined(ISA_BITFIELD)
    struct {
        ISA_BITFIELD;  // defined in isa.h
    };
#endif
};
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#if SUPPORT_PACKED_ISA

# if __arm64__
#   define ISA_MASK        0x0000000ffffffff8ULL
#   define ISA_MAGIC_MASK  0x000003f000000001ULL
#   define ISA_MAGIC_VALUE 0x000001a000000001ULL
#   define ISA_BITFIELD                                                      \
      uintptr_t nonpointer        : 1;                                       \
      uintptr_t has_assoc         : 1;                                       \
      uintptr_t has_cxx_dtor      : 1;                                       \
      uintptr_t shiftcls          : 33; /*MACH_VM_MAX_ADDRESS 0x1000000000*/ \
      uintptr_t magic             : 6;                                       \
      uintptr_t weakly_referenced : 1;                                       \
      uintptr_t deallocating      : 1;                                       \
      uintptr_t has_sidetable_rc  : 1;                                       \
      uintptr_t extra_rc          : 19
#   define RC_ONE   (1ULL<<45)
#   define RC_HALF  (1ULL<<18)
# elif __x86_64__

    ......

# endif

// SUPPORT_PACKED_ISA
#endif

SUPPORT_INDEXED_ISA

  • # define SUPPORT_INDEXED_ISA 1 主要针对 watchOS
  • 在 iOS 中 # define SUPPORT_INDEXED_ISA 0
  • 注意点:
    • __arm64__ 代表的是CPU架构
    • LP64 代表的采用哪种数据模型（可以回看文章首部关不LP64的说明）
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// Define SUPPORT_INDEXED_ISA=1 on platforms that store the class in the isa 
// field as an index into a class table.
// Note, keep this in sync with any .s files which also define it.
// Be sure to edit objc-abi.h as well.
#if __ARM_ARCH_7K__ >= 2  ||  (__arm64__ && !__LP64__)
#   define SUPPORT_INDEXED_ISA 1
#else
#   define SUPPORT_INDEXED_ISA 0
#endif

SUPPORT_NONPOINTER_ISA

  • 与isa指针类型有关系
  • SUPPORT_NONPOINTER_ISA=1: 非单纯指针类型的isa
  • iOS中 SUPPORT_INDEXED_ISA 0，SUPPORT_PACKED_ISA 1
    • # define SUPPORT_NONPOINTER_ISA 1
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// Define SUPPORT_NONPOINTER_ISA=1 on any platform that may store something
// in the isa field that is not a raw pointer.
#if !SUPPORT_INDEXED_ISA  &&  !SUPPORT_PACKED_ISA
#   define SUPPORT_NONPOINTER_ISA 0
#else
#   define SUPPORT_NONPOINTER_ISA 1
#endif