Stack implementation using LDM and STM

The load and store multiple instructions can update the base register. For stack operations, the base register is usually the stack pointer, SP. This means that you can use these instructions to implement push and pop operations for any number of registers in a single instruction.

The load and store multiple instructions can be used with several types of stack:

Descending or ascending

The stack grows downwards, starting with a high address and progressing to a lower one (a descending stack), or upwards, starting from a low address and progressing to a higher address (an ascending stack).

Full or empty

The stack pointer can either point to the last item in the stack (a full stack), or the next free space on the stack (an empty stack).

To make it easier for the programmer, stack-oriented suffixes can be used instead of the increment or decrement, and before or after suffixes. Table 12 shows the stack-oriented suffixes and their equivalent addressing mode suffixes for load and store instructions.

Table 12. Stack-oriented suffixes and equivalent addressing mode suffixes

Stack-oriented suffixFor store or push instructionsFor load or pop instructions
FD (Full Descending stack)DB (Decrement Before)IA (Increment After)
FA (Full Ascending stack)IB (Increment Before)DA (Decrement After)
ED (Empty Descending stack)DA (Decrement After)IB (Increment Before)
EA (Empty Ascending stack)IA (Increment After)DB (Decrement Before)

Table 13 shows the load and store multiple instructions with the stack-oriented suffixes for the various stack types.

Table 13. Suffixes for load and store multiple instructions

Stack typeStoreLoad
Full descendingSTMFD (STMDB, Decrement Before)LDMFD (LDM, increment after)
Full ascendingSTMFA (STMIB, Increment Before)LDMFA (LDMDA, Decrement After)
Empty descendingSTMED (STMDA, Decrement After)LDMED (LDMIB, Increment Before)
Empty ascendingSTMEA (STM, increment after)LDMEA (LDMDB, Decrement Before)

For example:

    STMFD    sp!, {r0-r5}  ; Push onto a Full Descending Stack
    LDMFD    sp!, {r0-r5}  ; Pop from a Full Descending Stack

Note

The Procedure Call Standard for the ARM Architecture (AAPCS), and ARM and Thumb C and C++ compilers always use a full descending stack.

The PUSH and POP instructions assume a full descending stack. They are the preferred synonyms for STMDB and LDM with writeback.

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