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Stack implementation using LDM and STM

You can use the LDM and STM instructions to implement pop and push operations respectively. You use a suffix to indicate the stack type.

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. The following table shows the stack-oriented suffixes and their equivalent addressing mode suffixes for load and store instructions:

Table 4-1 Stack-oriented suffixes and equivalent addressing mode suffixes

Stack-oriented suffix For store or push instructions For 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)

The following table shows the load and store multiple instructions with the stack-oriented suffixes for the various stack types:

Table 4-2 Suffixes for load and store multiple instructions

Stack type Store Load
Full descending STMFD (STMDB, Decrement Before) LDMFD (LDM, increment after)
Full ascending STMFA (STMIB, Increment Before) LDMFA (LDMDA, Decrement After)
Empty descending STMED (STMDA, Decrement After) LDMED (LDMIB, Increment Before)
Empty ascending STMEA (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

The Procedure Call Standard for the ARM Architecture (AAPCS), and armcc 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.