ARM Prolog and Epilog Coding Examples

Article
06/30/2006

The following code samples show ARM and THUMB prolog and epilog code.

ARM Prolog with frame in R11.

MOV    r12, r13        ; Save stack on entry if needed.
STMDB  r13!, {r0-r3}    ; As needed
STMDB  r13!, {r4-r12, r14}  ; As needed
SUB    r11, r12, #16    ; Sets frame past args
<stack link if needed>

ARM Prolog with no frame.

MOV    r12, r13
STMDB  r13!, {r0-r3}        ; As needed
STMDB  r13! {[r4-r12,]|[r13,]r14}  ; As needed
<stack link if needed>
<note: r12 is not used if the stack (r13) is the first register saved>

ARM Epilog with frame in R11.

<no stack unlink>
LDMDB  r11, {r4-r11, r13, r15}

ARM Epilog with no frame.

<stack unlink if needed>
LDMIA  r13, {r4-R11, r13, r15}

ARM Epilog with interworking return.

<stack unlink if needed>
LDMIA   r13, {r4-r11, r13, LR}
BX      LR

THUMB Prolog with no frame.

PUSH    {r0-r3}    ; As needed
PUSH    {r4-r7, LR}  ; As needed
SUB    SP, SP, #4  ; Stack link (as needed)

THUMB Epilog with no frame.

ADD    SP, SP, #4    ; Stack link (as needed)
POP    {r4-r7}      
POP    {r3}        ; POP link register into r3
ADD    SP, SP, #16    ; POP r0-r3 as needed
MOV    PC, r3

THUMB Prolog with frame in R7.

PUSH    {r0-r3}      ; As needed
PUSH    {r4-r7, LR}    ; As needed
SUB    SP, SP, #4    ; Stack link (as needed)
MOV    r7, SP      ; Set frame

THUMB Epilog with frame in R7.

MOV    r13, r7
ADD    SP, SP, #4    ; Stack unlink (as needed)
POP    {r4-r7}      
POP    {r3}        ; POP link register into r3
ADD    SP, SP, #16    ; POP r0-r3 as needed
MOV    PC, r3

THUMB Prolog with interworking return.
```
PUSH    {r4-r7, LR}
```

THUMB Prolog saving high registers.

PUSH    {r0-r3}      ; Save r0-r3 as needed
PUSH    {LR}
BL    __savegpr_9    ; Routine for saving {r4-r11}
SUB    SP, SP, #4    ; Stack link (as needed)

THUMB Epilog restoring high registers.

ADD    SP, SP, #4    ; Stack link (as needed)
BL    __restgpr_9
ADD    SP, SP, #16    ; POP r0-r3 as needed
BX    LR

THUMB Prolog with a large stack frame.

PUSH    {r7}  
LDR    r7, [PC, #20]
NEG    r7, r7
ADD    SP, r7

THUMB Epilog with a large stack frame.

LDR    r7, [PC, #4]
ADD    SP, r7
POP    {r7}
MOV    PC, LR

Save register routine.

__savegpr_9
  BX      PC
  NOP
  STMDB    SP!, {r4-r7, r9-r11}
  BX      LR

Restore register routine.

__restgpr_9
  MOV      r3, LR
  BX      PC
  LDMIA    SP!, {r4-r7, r9-r11, LR}
  BX      r3

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ARM Prolog and Epilog Coding Examples

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