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In the ARM Architecture Procedure Call Standard (AAPCS), which register is used to hold the return value of a function?

easy📝 Conceptual Q1 of 15
ARM Architecture - Subroutines and Stack
In the ARM Architecture Procedure Call Standard (AAPCS), which register is used to hold the return value of a function?
AR0
BR4
CLR
DSP
Step-by-Step Solution
Solution:

  1. Step 1: Understand the role of registers in AAPCS

    The AAPCS defines specific registers for passing arguments and return values. R0 to R3 are used for arguments and return values.

  2. Step 2: Identify the register for return values

    R0 is used to hold the return value of a function as per AAPCS.

  3. Final Answer:

    R0 is used to hold the return value -> Option A

  4. Quick Check:

    Return value register = R0 [OK]
Quick Trick: Return values are in R0 register by convention [OK]
Common Mistakes:
  • Confusing LR with return value register
  • Using SP as return value register
  • Assuming R4 holds return value

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