ARM汇编-指令是否等效？

Question

Is "stmdb r3!, {sp,lr}" equivalent to the sequence ?

1. str sp, [r3, #-4]!
2. str lr, [r3, #-4]!

And

Is "ldmia r0!, {sp,lr}" equivalent to the sequence ?

1. ldr sp, [r0], #4
2. ldr lr, [r0], #4

Answer 1

I misunderstood the stmdb functioning. The equivalent for "stmdb r3!, {sp,lr}", would be a swapped order "lr" first followed by "sp":

• str lr, [r3, #-4]!
• str sp, [r3, #-4]!

Thanks, Vijay

Answer 2

stmdb r3!, {sp,lr}

str sp, [r3, #-4]!

str lr, [r3, #-4]!

stmdb r3!, {sp,lr} - Store Multiple registers and Decrement address Before each transfer. r3 - base register and ! - write start r3 address + offcet into r3 back. DB - due to 4 stack type (Full Descending stack, Full Ascending stack, Empty Descending stack, Empty Ascending stack). With STM DB correspond to Full Descending stack. So sp - stack pointer and lr - link register store into memory addressed by r3 and r3 += sizeof(sp) + sizeof(ls). r3 += 8;

1. r3 point to some memory address.

2. r3 -= 8; (4 byte instruction) move r3 into lower memory address. Decrement r3.

3. Store order lr-first sp-second. Into r3-8 - lr will be stored and into r3-4 sp will be stored.

4. r3 - point to end (r3+=8);

str sp, [r3, #-4]! (pre-index variant) - store sp into r3-4 memory address and save r3-=4;

str lr, [r3, #-4]! - store lr into (r3-4)-4 and save r3-=4;

So stmdb r3!, {sp,lr} - into higher address lr situated. (str sp, [r3, #-4]!) + (str lr, [r3, #-4]!) lr located into higher address again.

Introducing ARM assembly language

ldmia r0!, {sp,lr} - load multiple increment after.

Get value from memory pointed by r0 and save it into sp. Get next value from memory and save into lr. r0 += 8;

ldr sp, [r0], #4 - load value from memory r0+4 into sp. ([r0], #4) - post-indexed variant first load and next edit r0, r0+=4.

ldr lr, [r0], #4 - load value from memory r0+4 into lr.

Into both variants value from higher memory was copied to lr.