ARM64各寄存器说明

详细参考：http://119.90.25.22/infocenter.arm.com/help/topic/com.arm.doc.ihi0055b/IHI0055B_aapcs64.pdf

There are thirty-one, 64-bit, general-purpose (integer) registers visible to the A64 instruction set; these are labeled

r0-r30. In a 64-bit context these registers are normally referred to using the names x0-x30; in a 32-bit context the

registers are specified by using w0-w30. Additionally, a stack-pointer register, SP, can be used with a restricted

number of instructions. Register names may appear in assembly language in either upper case or lower case. In

this specification upper case is used when the register has a fixed role in this procedure call standard. Table 2,

General purpose registers and AAPCS64 usage summarizes the uses of the general-purpose registers in this

standard. In addition to the general-purpose registers there is one status register (NZCV) that may be set and

read by conforming code.

SP The Stack Pointer.

r30 LR The Link Register.

r29 FP The Frame Pointer

r19…r28 Callee-saved registers

r18 The Platform Register, if needed; otherwise a temporary register.See notes.

r17 IP1 The second intra-procedure-call temporary register (can be used by call veneers and PLT code); at other times may be used as a temporary register.

r16 IP0 The first intra-procedure-call scratch register (can be used by call veneers and PLT code); at other times may be used as a temporary register.

r9…r15 Temporary registers

r8 Indirect result location register

r0…r7 Parameter/result registers

The first eight registers, r0-r7, are used to pass argument values into a subroutine and to return result values from

a function. They may also be used to hold intermediate values within a routine (but, in general, only between

subroutine calls).

Registers r16 (IP0) and r17 (IP1) may be used by a linker as a scratch register between a routine and any

subroutine it calls (for details, see §5.3.1.1, Use of IP0 and IP1 by the linker). They can also be used within a

routine to hold intermediate values between subroutine calls.

The role of register r18 is platform specific. If a platform ABI has need of a dedicated general purpose register to

carry inter-procedural state (for example, the thread context) then it should use this register for that purpose. If 

the platform ABI has no such requirements, then it should use r18 as an additional temporary register. The

platform ABI specification must document the usage for this register.

     Note Software developers creating platform-independent code are advised to avoid using r18 if at all possible.

Most compilers provide a mechanism to prevent specific registers from being used for general allocation;

portable hand-coded assembler should avoid it entirely. It should not be assumed that treating the

register as callee-saved will be sufficient to satisfy the requirements of the platform. Virtualization code

must, of course, treat the register as they would any other resource provided to the virtual machine.

A subroutine invocation must preserve the contents of the registers r19-r29 and SP.

In all variants of the procedure call standard, registers r16, r17, r29 and r30 have special roles. In these roles they

are labeled IP0, IP1, FP and LR when being used for holding addresses (that is, the special name implies

accessing the register as a 64-bit entity).

     Note The special register names (IP0, IP1, FP and LR) should be used only in the context in which they are

special. It is recommended that disassemblers always use the architectural names for the registers.

The NZCV register is a global condition flag register with the following properties:

 The N, Z, C and V flags are undefined on entry to and return from a public interface.