第17章-x86-64寄存器

不同的CPU都能够解释的机器语言的体系称为指令集架构（ISA，Instruction Set Architecture），也可以称为指令集（instruction set）。Intel将x86系列CPU之中的32位CPU指令集架构称为IA-32，IA是“Intel Architecture”的简称，也可以称为i386、x86-32。AMD等于Intell提出了x86系列的64位扩展，所以由AMD设计的x86系列的64位指令集架构称为AMD64。后来Intel在自己的CPU中加入和AMD64几乎相同的指令集，称为Intel 64的指令集。AMD64和Intel 64可以统称为x86-64。

x86-64的所有寄存器都是与机器字长（数据总线位宽）相同，即64位的，x86-64将x86的8个32位通用寄存器扩展为64位（eax、ebx、ecx、edx、eci、edi、ebp、esp），并且增加了8个新的64位寄存器（r8-r15），在命名方式上，也从”exx”变为”rxx”，但仍保留”exx”进行32位操作，下表描述了各寄存器的命名和作用。

描述	32位	64位
通用寄存器组	eax	rax
	ecx	rcx
	edx	rdx
	ebx	rbx
	esp	rsp
	ebp	rbp
	esi	rsi
	edi	rdi
	-	r8~r15
浮点寄存器组	st0~st7	st0~st7
XMM寄存器组	XMM0~XMM7	XMM0~XMM15

其中的%esp与%ebp有特殊用途，用来保存指向程序栈中特定位置的指针。

另外还有eflags寄存器，通过位来表示特定的含义，如下图所示。

在HotSpot VM中，表示寄存器的类都继承自AbstractRegisterImpl类，这个类的定义如下：

源代码位置：hotspot/src/share/vm/asm/register.hpp

class AbstractRegisterImpl;

typedef AbstractRegisterImpl* AbstractRegister;

class AbstractRegisterImpl {

 protected:

  int value() const  { return (int)(intx)this; }

};

AbstractRegisterImpl类的继承体系如下图所示。

另外还有个ConcreteRegisterImpl类也继承了AbstractRegisterImpl，这个灰与C2编译器的实现有关，这里不做过多讲解。

1、RegisterImpl类

RegisterImpl类用来表示通用寄存器，类的定义如下：

源代码位置：cpu/x86/vm/register_x86.hpp

// 使用Register做为RegisterImpl的简称

class RegisterImpl;

typedef RegisterImpl* Register;

class RegisterImpl: public AbstractRegisterImpl {

 public:

  enum {

    number_of_registers      = 16,

    number_of_byte_registers = 16

  };

  // ...

};

对于64位来说，通用寄存器的位宽为64位，也可以将eax、ebx、ecx和edx的一部分当作8位寄存器来使用，所以可以存储字节的寄存器数量为4。

在HotSpot VM中定义寄存器，如下：

源代码位置：hotspot/src/cpu/x86/vm/register_x86.hpp

CONSTANT_REGISTER_DECLARATION(Register, noreg, (-1)); // noreg_RegisterEnumValue = ((-1))

CONSTANT_REGISTER_DECLARATION(Register, rax,    (0)); // rax_RegisterEnumValue = ((0))

CONSTANT_REGISTER_DECLARATION(Register, rcx,    (1)); // rcx_RegisterEnumValue = ((1))

CONSTANT_REGISTER_DECLARATION(Register, rdx,    (2)); // rdx_RegisterEnumValue = ((2))

CONSTANT_REGISTER_DECLARATION(Register, rbx,    (3)); // rbx_RegisterEnumValue = ((3))

CONSTANT_REGISTER_DECLARATION(Register, rsp,    (4)); // rsp_RegisterEnumValue = ((4))

CONSTANT_REGISTER_DECLARATION(Register, rbp,    (5)); // rbp_RegisterEnumValue = ((5))

CONSTANT_REGISTER_DECLARATION(Register, rsi,    (6)); // rsi_RegisterEnumValue = ((6))

CONSTANT_REGISTER_DECLARATION(Register, rdi,    (7)); // rdi_RegisterEnumValue = ((7))

CONSTANT_REGISTER_DECLARATION(Register, r8,     (8)); // r8_RegisterEnumValue = ((8))

CONSTANT_REGISTER_DECLARATION(Register, r9,     (9)); // r9_RegisterEnumValue = ((9))

CONSTANT_REGISTER_DECLARATION(Register, r10,   (10)); // r10_RegisterEnumValue = ((10))

CONSTANT_REGISTER_DECLARATION(Register, r11,   (11)); // r11_RegisterEnumValue = ((11))

CONSTANT_REGISTER_DECLARATION(Register, r12,   (12)); // r12_RegisterEnumValue = ((12))

CONSTANT_REGISTER_DECLARATION(Register, r13,   (13)); // r13_RegisterEnumValue = ((13))

CONSTANT_REGISTER_DECLARATION(Register, r14,   (14)); // r14_RegisterEnumValue = ((14))

CONSTANT_REGISTER_DECLARATION(Register, r15,   (15)); // r15_RegisterEnumValue = ((15))

宏CONSTANT_REGISTER_DECLARATION定义如下：

源代码位置：hotspot/src/share/vm/asm/register.hpp

#define CONSTANT_REGISTER_DECLARATION(type, name, value)   \

  extern const type name;                                  \

  enum { name##_##type##EnumValue = (value) }

经过宏扩展后如下：

extern const Register  rax;

enum { rax_RegisterEnumValue = ((0)) }

extern const Register  rcx;

enum { rcx_RegisterEnumValue = ((1)) }

extern const Register  rdx;

enum { rdx_RegisterEnumValue = ((2)) }

extern const Register  rbx;

enum { rbx_RegisterEnumValue = ((3)) }

extern const Register  rsp;

enum { rsp_RegisterEnumValue = ((4)) }

extern const Register  rbp;

enum { rbp_RegisterEnumValue = ((5)) }

extern const Register  rsi;

enum { rsi_RegisterEnumValue = ((6)) }

extern const Register  rsi;

enum { rdi_RegisterEnumValue = ((7)) }

extern const Register  r8;

enum { r8_RegisterEnumValue = ((8)) }

extern const Register  r9;

enum { r9_RegisterEnumValue = ((9)) }

extern const Register  r10;

enum { r10_RegisterEnumValue = ((10)) }

extern const Register  r11;

enum { r11_RegisterEnumValue = ((11)) }

extern const Register  r12;

enum { r12_RegisterEnumValue = ((12)) }

extern const Register  r13;

enum { r13_RegisterEnumValue = ((13)) }

extern const Register  r14;

enum { r14_RegisterEnumValue = ((14)) }

extern const Register  r15;

enum { r15_RegisterEnumValue = ((15)) }

如上的枚举类给寄存器指定了一个常量值。

在cpu/x86/vm/register_definitions_x86.cpp文件中定义的寄存器如下：

const Register  noreg = ((Register)noreg_RegisterEnumValue)

const Register  rax =   ((Register)rax_RegisterEnumValue)

const Register  rcx =   ((Register)rcx_RegisterEnumValue)

const Register  rdx =   ((Register)rdx_RegisterEnumValue)

const Register  rbx =   ((Register)rbx_RegisterEnumValue)

const Register  rsp =   ((Register)rsp_RegisterEnumValue)

const Register  rbp =   ((Register)rbp_RegisterEnumValue)

const Register  rsi =   ((Register)rsi_RegisterEnumValue)

const Register  rdi =   ((Register)rdi_RegisterEnumValue)

const Register  r8 =  ((Register)r8_RegisterEnumValue)

const Register  r9 =  ((Register)r9_RegisterEnumValue)

const Register  r10 = ((Register)r10_RegisterEnumValue)

const Register  r11 = ((Register)r11_RegisterEnumValue)

const Register  r12 = ((Register)r12_RegisterEnumValue)

const Register  r13 = ((Register)r13_RegisterEnumValue)

const Register  r14 = ((Register)r14_RegisterEnumValue)

const Register  r15 = ((Register)r15_RegisterEnumValue)

当我们需要使用通用寄存器时，通过rax、rcx等变量引用就可以了。

2、FloatRegisterImpl

在HotSpot VM中，使用FloatRegisterImpl来表示浮点寄存器，此类的定义如下：

源代码位置：hotspot/src/cpu/x86/vm/register_x86.hpp

// 使用FloatRegister做为简称

class FloatRegisterImpl;

typedef FloatRegisterImpl* FloatRegister;

class FloatRegisterImpl: public AbstractRegisterImpl {

 public:

  enum {

    number_of_registers = 8

  };

  // ...

}

浮点寄存器有8个，分别是st0~st7，这是8个80位寄存器。

这里需要注意的是，还有一种寄存器MMX，MMX并非一种新的寄存器，而是借用了80位浮点寄存器的低64位，也就是说，使用MMX指令集，会影响浮点运算！

3、MMXRegisterImpl

MMX 为一种 SIMD 技术，即可通过一条指令执行多个数据运算，共有8个64位寄存器（借用了80位浮点寄存器的低64位），分别为mm0 – mm7，他与其他普通64位寄存器的区别在于通过它的指令进行运算，可以同时计算2个32位数据，或者4个16位数据等等，可以应用为图像处理过程中图形颜色的计算。

MMXRegisterImpl类的定义如下：

class MMXRegisterImpl;

typedef MMXRegisterImpl* MMXRegister;

MMX寄存器的定义如下：

CONSTANT_REGISTER_DECLARATION(MMXRegister, mnoreg , (-1));

CONSTANT_REGISTER_DECLARATION(MMXRegister, mmx0 , ( 0));

CONSTANT_REGISTER_DECLARATION(MMXRegister, mmx1 , ( 1));

CONSTANT_REGISTER_DECLARATION(MMXRegister, mmx2 , ( 2));

CONSTANT_REGISTER_DECLARATION(MMXRegister, mmx3 , ( 3));

CONSTANT_REGISTER_DECLARATION(MMXRegister, mmx4 , ( 4));

CONSTANT_REGISTER_DECLARATION(MMXRegister, mmx5 , ( 5));

CONSTANT_REGISTER_DECLARATION(MMXRegister, mmx6 , ( 6));

CONSTANT_REGISTER_DECLARATION(MMXRegister, mmx7 , ( 7));

宏扩展后如下：

extern const MMXRegister  mnoreg;

enum { mnoreg_MMXRegisterEnumValue = ((-1)) }

extern const MMXRegister  mmx0;

enum { mmx0_MMXRegisterEnumValue = (( 0)) }

extern const MMXRegister  mmx1;

enum { mmx1_MMXRegisterEnumValue = (( 1)) }

extern const MMXRegister  mmx2;

enum { mmx2_MMXRegisterEnumValue = (( 2)) }

extern const MMXRegister  mmx3;

enum { mmx3_MMXRegisterEnumValue = (( 3)) }

extern const MMXRegister  mmx4;

enum { mmx4_MMXRegisterEnumValue = (( 4)) }

extern const MMXRegister  mmx5;

enum { mmx5_MMXRegisterEnumValue = (( 5)) }

extern const MMXRegister  mmx6;

enum { mmx6_MMXRegisterEnumValue = (( 6)) }

extern const MMXRegister  mmx7;

enum { mmx7_MMXRegisterEnumValue = (( 7)) }

MMX Pentium以及Pentium II之后的CPU中有从mm0到mm7共8个64位寄存器。但实际上MMX寄存器和浮点数寄存器是共用的，即无法同时使用浮点数寄存器和MMX寄存器。　　

cpu/x86/vm/register_definitions_x86.cpp文件中定义的寄存器变量如下：

const MMXRegister  mnoreg = ((MMXRegister)mnoreg_MMXRegisterEnumValue)

const MMXRegister  mmx0 =   ((MMXRegister)mmx0_MMXRegisterEnumValue)

const MMXRegister  mmx1 =   ((MMXRegister)mmx1_MMXRegisterEnumValue)

const MMXRegister  mmx2 =   ((MMXRegister)mmx2_MMXRegisterEnumValue)

const MMXRegister  mmx3 =   ((MMXRegister)mmx3_MMXRegisterEnumValue)

const MMXRegister  mmx4 =   ((MMXRegister)mmx4_MMXRegisterEnumValue)

const MMXRegister  mmx5 =   ((MMXRegister)mmx5_MMXRegisterEnumValue)

const MMXRegister  mmx6 =   ((MMXRegister)mmx6_MMXRegisterEnumValue)

const MMXRegister  mmx7 =   ((MMXRegister)mmx7_MMXRegisterEnumValue)

当我们需要使用MMX寄存器时，通过mmx0、mmx1等变量引用就可以了。

4、XMMRegisterImpl类

XMM寄存器是SSE指令用的寄存器。Pentium iii以及之后的CPU中提供了xmm0到xmm7共8个128位宽的XMM寄存器。另外还有个mxcsr寄存器，这个寄存器用来表示SSE指令的运算状态的寄存器。在HotSpot VM中，通过XMMRegisterImpl类来表示寄存器。这个类的定义如下：

源代码位置：hotspot/src/share/x86/cpu/vm/register_x86.hpp

// 使用XMMRegister寄存器做为简称

class XMMRegisterImpl;

typedef XMMRegisterImpl* XMMRegister;

class XMMRegisterImpl: public AbstractRegisterImpl {

 public:

  enum {

    number_of_registers = 16

  };

  ...

}

XMM寄存器的定义如下：

CONSTANT_REGISTER_DECLARATION(XMMRegister, xnoreg , (-1));

CONSTANT_REGISTER_DECLARATION(XMMRegister, xmm0 ,   ( 0));

CONSTANT_REGISTER_DECLARATION(XMMRegister, xmm1 ,   ( 1));

CONSTANT_REGISTER_DECLARATION(XMMRegister, xmm2 ,   ( 2));

CONSTANT_REGISTER_DECLARATION(XMMRegister, xmm3 ,   ( 3));

CONSTANT_REGISTER_DECLARATION(XMMRegister, xmm4 ,   ( 4));

CONSTANT_REGISTER_DECLARATION(XMMRegister, xmm5 ,   ( 5));

CONSTANT_REGISTER_DECLARATION(XMMRegister, xmm6 ,   ( 6));

CONSTANT_REGISTER_DECLARATION(XMMRegister, xmm7 ,   ( 7));

CONSTANT_REGISTER_DECLARATION(XMMRegister, xmm8,      (8));

CONSTANT_REGISTER_DECLARATION(XMMRegister, xmm9,      (9));

CONSTANT_REGISTER_DECLARATION(XMMRegister, xmm10,    (10));

CONSTANT_REGISTER_DECLARATION(XMMRegister, xmm11,    (11));

CONSTANT_REGISTER_DECLARATION(XMMRegister, xmm12,    (12));

CONSTANT_REGISTER_DECLARATION(XMMRegister, xmm13,    (13));

CONSTANT_REGISTER_DECLARATION(XMMRegister, xmm14,    (14));

CONSTANT_REGISTER_DECLARATION(XMMRegister, xmm15,    (15));

经过宏扩展后为：

extern const XMMRegister  xnoreg;

enum { xnoreg_XMMRegisterEnumValue = ((-1)) }

extern const XMMRegister  xmm0;

enum { xmm0_XMMRegisterEnumValue = (( 0)) }

extern const XMMRegister  xmm1;

enum { xmm1_XMMRegisterEnumValue = (( 1)) }

extern const XMMRegister  xmm2;

enum { xmm2_XMMRegisterEnumValue = (( 2)) }

extern const XMMRegister  xmm3;

enum { xmm3_XMMRegisterEnumValue = (( 3)) }

extern const XMMRegister  xmm4;

enum { xmm4_XMMRegisterEnumValue = (( 4)) }

extern const XMMRegister  xmm5;

enum { xmm5_XMMRegisterEnumValue = (( 5)) }

extern const XMMRegister  xmm6;

enum { xmm6_XMMRegisterEnumValue = (( 6)) }

extern const XMMRegister  xmm7;

enum { xmm7_XMMRegisterEnumValue = (( 7)) }

extern const XMMRegister  xmm8;

enum { xmm8_XMMRegisterEnumValue = ((8)) }

extern const XMMRegister  xmm9;

enum { xmm9_XMMRegisterEnumValue = ((9)) }

extern const XMMRegister  xmm10;

enum { xmm10_XMMRegisterEnumValue = ((10)) }

extern const XMMRegister  xmm11;

enum { xmm11_XMMRegisterEnumValue = ((11)) }

extern const XMMRegister  xmm12;

enum { xmm12_XMMRegisterEnumValue = ((12)) }

extern const XMMRegister  xmm13;

enum { xmm13_XMMRegisterEnumValue = ((13)) }

extern const XMMRegister  xmm14;

enum { xmm14_XMMRegisterEnumValue = ((14)) }

extern const XMMRegister  xmm15;

enum { xmm15_XMMRegisterEnumValue = ((15)) }

在cpu/x86/vm/register_definitions_x86.cpp文件中定义的寄存器变量如下：

const XMMRegister  xnoreg = ((XMMRegister)xnoreg_XMMRegisterEnumValue)

const XMMRegister  xmm0 =   ((XMMRegister)xmm0_XMMRegisterEnumValue)

const XMMRegister  xmm1 =   ((XMMRegister)xmm1_XMMRegisterEnumValue)

const XMMRegister  xmm2 =   ((XMMRegister)xmm2_XMMRegisterEnumValue)

const XMMRegister  xmm3 =   ((XMMRegister)xmm3_XMMRegisterEnumValue)

const XMMRegister  xmm4 =   ((XMMRegister)xmm4_XMMRegisterEnumValue)

const XMMRegister  xmm5 =   ((XMMRegister)xmm5_XMMRegisterEnumValue)

const XMMRegister  xmm6 =   ((XMMRegister)xmm6_XMMRegisterEnumValue)

const XMMRegister  xmm7 =   ((XMMRegister)xmm7_XMMRegisterEnumValue)

const XMMRegister  xmm8 =   ((XMMRegister)xmm8_XMMRegisterEnumValue)

const XMMRegister  xmm9 =   ((XMMRegister)xmm9_XMMRegisterEnumValue)

const XMMRegister  xmm10 =  ((XMMRegister)xmm10_XMMRegisterEnumValue)

const XMMRegister  xmm11 =  ((XMMRegister)xmm11_XMMRegisterEnumValue)

const XMMRegister  xmm12 =  ((XMMRegister)xmm12_XMMRegisterEnumValue)

const XMMRegister  xmm13 =  ((XMMRegister)xmm13_XMMRegisterEnumValue)

const XMMRegister  xmm14 =  ((XMMRegister)xmm14_XMMRegisterEnumValue)

const XMMRegister  xmm15 =  ((XMMRegister)xmm15_XMMRegisterEnumValue)

当我们需要使用XMM寄存器时，直接通过xmm0、xmm1等变量引用就可以了。