ARM SRS彙編指令的用法

SRS

Store Return State onto a stack.

Syntax

SRS{addr_mode}{cond} sp{!}, #modenum

SRS{addr_mode}{cond} #modenum{!}        ; This is a pre-UAL syntax

where:

addr_mode

is any one of the following:

IA

Increment address After each transfer

IB

Increment address Before each transfer (ARM only)

DA

Decrement address After each transfer (ARM only)

DB

Decrement address Before each transfer (Full Descending stack).

If addr_mode is omitted, it defaults to Increment After. You can also use stack oriented addressing mode suffixes, for example, when implementing stacks.

cond

is an optional condition code.

Note

cond is permitted only in Thumb code, using a preceding IT instruction. This is an unconditional instruction in ARM.

!

is an optional suffix. If ! is present, the final address is written back into the SP of the mode specified by modenum.

modenum

specifies the number of the mode whose banked SP is used as the base register. You must use only the defined mode numbers.

Operation

SRS stores the LR and the SPSR of the current mode, at the address contained in SP of the mode specified by modenum, and the following word respectively. Optionally updates SP of the mode specified by modenum. This is compatible with the normal use of the STM instruction for stack accesses.

Note

For full descending stack, you must use SRSFD or SRSDB.

Usage

You can use SRS to store return state for an exception handler on a different stack from the one automatically selected.

Notes

Where addresses are not word-aligned, SRS ignores the least significant two bits of the specified address.

The time order of the accesses to individual words of memory generated by SRS is not architecturally defined. Do not use this instruction on memory-mapped I/O locations where access order matters.

Do not use SRS in User and System modes because these modes do not have a SPSR.

Do not use SRS in Thumb-2EE.

SRS is not permitted in a non-secure state if modenum specifies monitor mode.

Architectures

This ARM instruction is available in ARMv6 and above.

This 32-bit Thumb instruction is available in ARMv6T2 and above, except the ARMv7-M architecture.

There is no 16-bit version of this instruction.

Example

R13_usr  EQU     16         SRSFD   sp,#R13_usr

See also

Concepts

Using the Assembler:

• Stack implementation using LDM and STM

• Processor modes, and privileged and unprivileged software execution.

Reference:

• LDM and STM