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Which registers are designated as callee-saved registers in the AAPCS?

easy📝 Conceptual Q2 of 15
ARM Architecture - Subroutines and Stack
Which registers are designated as callee-saved registers in the AAPCS?
AR4 to R11
BR0 to R3
CR12 and LR
DSP and PC
Step-by-Step Solution
Solution:

  1. Step 1: Recall callee-saved registers definition

    Callee-saved registers must be preserved by the called function if it uses them.

  2. Step 2: Identify callee-saved registers in AAPCS

    Registers R4 to R11 are callee-saved according to AAPCS.

  3. Final Answer:

    R4 to R11 are callee-saved registers -> Option A

  4. Quick Check:

    Callee-saved = R4-R11 [OK]
Quick Trick: Callee-saved are R4 to R11, caller-saved are R0 to R3 [OK]
Common Mistakes:
  • Mixing caller-saved with callee-saved
  • Including R0-R3 as callee-saved
  • Confusing LR with callee-saved

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