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 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) |
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 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
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.
See also
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