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IAR compiler does not align stack on 8-byte boundary

Miro Samek

ARM ABI says that the stack should be 8-byte aligned, but the stack is sometimes aligned only to 4-byte boundary.

For example, I have the following simple busy-delay function:

void delay(int iter) {
   int volatile counter = 0;
   while (counter < iter) { // delay loop
       ++counter;
   }
}

This compiles with IAR EWARM 9.10.2 to the following disassembly:

SUB SP, SP, #0x4
...
ADD SP, SP, #0x4
BX LR

The problem is that after SUB SP,SP,4 the stack is misaligned (is aligned only to 4-byte boundary).

Why is this happening? Is this compliant with the ARM ABI? Are there any compiler options to control that?

Thanks a lot for explaining these questions!