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SUBS pc, lr

Exception return, without popping anything from the stack.

Syntax

SUBS{cond} pc, lr, #imm ; A32 and T32 code

MOVS{cond} pc, lr ; A32 and T32 code

op1S{cond} pc, Rn, #imm ; A32 code only and is deprecated

op1S{cond} pc, Rn, Rm {, shift} ; A32 code only and is deprecated

op2S{cond} pc, #imm ; A32 code only and is deprecated

op2S{cond} pc, Rm {, shift} ; A32 code only and is deprecated

where:

op1

is one of ADC, ADD, AND, BIC, EOR, ORN, ORR, RSB, RSC, SBC, and SUB.

op2

is one of MOV and MVN.

cond

is an optional condition code.

imm

is an immediate value. In T32 code, it is limited to the range 0-255. In A32 code, it is a flexible second operand.

Rn

is the first general-purpose source register. Arm deprecates the use of any register except LR.

Rm

is the optionally shifted second or only general-purpose register.

shift

is an optional condition code.

Usage

SUBS pc, lr, #imm subtracts a value from the link register and loads the PC with the result, then copies the SPSR to the CPSR.

You can use SUBS pc, lr, #imm to return from an exception if there is no return state on the stack. The value of #imm depends on the exception to return from.

Notes

SUBS pc, lr, #imm writes an address to the PC. The alignment of this address must be correct for the instruction set in use after the exception return:

  • For a return to A32, the address written to the PC must be word-aligned.
  • For a return to T32, the address written to the PC must be halfword-aligned.
  • For a return to Jazelle, there are no alignment restrictions on the address written to the PC.

No special precautions are required in software to follow these rules, if you use the instruction to return after a valid exception entry mechanism.

In T32, only SUBS{cond} pc, lr, #imm is a valid instruction. MOVS pc, lr is a synonym of SUBS pc, lr, #0. Other instructions are undefined.

In A32, only SUBS{cond} pc, lr, #imm and MOVS{cond} pc, lr are valid instructions. Other instructions are deprecated.

CAUTION:

Do not use these instructions in User mode or System mode. The assembler cannot warn you about this.

Availability

This 32-bit instruction is available in A32 and T32.

The 32-bit T32 instruction is not available in the Arm®v7‑M architecture.

There is no 16-bit version of this instruction in T32.

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