Subroutine call convention (AAPCS) in ARM Architecture - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to identify the register used for the first argument in AAPCS.

ARM Architecture

The first argument to a subroutine is passed in register [1] according to AAPCS.

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Ar4

Br12

Cr0

Dr7

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing argument registers with callee-saved registers.

Assuming arguments start from r4 or higher.

In the ARM Architecture Procedure Call Standard (AAPCS), the first argument is passed in register r0.

2fill in blank

medium

Complete the code to specify how many registers are used for passing arguments in AAPCS.

ARM Architecture

AAPCS uses up to [1] registers to pass arguments before using the stack.

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A2

B8

C6

D4

Attempts:

3 left

💡 Hint

Common Mistakes

Assuming all arguments are passed in registers.

Confusing the number of argument registers with total registers.

AAPCS specifies that up to 4 registers (r0 to r3) are used to pass arguments. Additional arguments are passed on the stack.

3fill in blank

hard

Fix the error in the statement about callee-saved registers in AAPCS.

ARM Architecture

Registers [1] to r7 are callee-saved according to AAPCS.

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Ar1

Br4

Cr0

Dr3

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing caller-saved and callee-saved registers.

Assuming r0 is callee-saved.

In AAPCS, registers r4 to r7 are callee-saved, meaning the called function must preserve their values.

4fill in blank

hard

Fill both blanks to complete the rule about the stack pointer and link register in AAPCS.

ARM Architecture

The [1] register holds the return address, and the [2] register points to the top of the stack.

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Alr

Bpc

Csp

Dr0

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the program counter (pc) with the link register (lr).

Confusing general-purpose registers with special registers.

The lr (link register) holds the return address, and the sp (stack pointer) points to the top of the stack in AAPCS.

5fill in blank

hard

Fill all three blanks to complete the dictionary comprehension that maps argument registers to their usage in AAPCS.

ARM Architecture

arg_registers = [1]: 'first', [2]: 'second', [3]: 'third'}

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Ar0

Br1

Cr2

Dr3

Attempts:

3 left

💡 Hint

Common Mistakes

Using registers out of order.

Including registers beyond the third argument.

According to AAPCS, r0 is the first argument register, r1 the second, and r2 the third.