FRAME ADDRESS

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5.5.1. FRAME ADDRESS

The FRAME ADDRESS directive describes how to calculate the canonical frame address for following instructions. You can only use it in functions with FUNCTION and ENDFUNC or PROC and ENDP directives.

Syntax

FRAME ADDRESS reg[,offset]

where:

reg: is the register on which the canonical frame addressis to be based. This is sp unless the function uses a separate frame pointer.
offset: is the offset of the canonical frame address from reg. If offset is zero, you can omit it.

Usage

Use FRAME ADDRESS if your code alters which register the canonical frame address is based on, or if it changes the offset of the canonical frame address from the register. You must use FRAME ADDRESS immediately after the instruction that changes the calculation of the canonical frame address.

Note

If your code uses a single instruction to save registers and alter the stack pointer, you can use FRAME PUSH instead of using both FRAME ADDRESS and FRAME SAVE (see FRAME PUSH).

If your code uses a single instruction to load registers and alter the stack pointer, you can use FRAME POP instead of using both FRAME ADDRESS and FRAME RESTORE (see FRAME POP).

Example

_fn     FUNCTION        ; CFA (Canonical Frame Address) is value
                        ; of sp on entry to function
        PUSH    {r4,fp,ip,lr,pc}
        FRAME PUSH {r4,fp,ip,lr,pc}
        SUB     sp,sp,#4            ; CFA offset now changed
        FRAME ADDRESS sp,24         ; - so we correct it
        ADD     fp,sp,#20
        FRAME ADDRESS fp,4          ; New base register
        ; code using fp to base call-frame on, instead of sp

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