Question

Consider the ARM assembly code below. func1, func2, and func 3 are non-leaf functions. func 4 is a leaf function. The code is not shown for each function, but the comments indicate which registers are used within each function

Answer 1

The question pertains to ARM assembly language focusing on the register usage in non-leaf and leaf functions, with importance to ARM procedure call standard for register preservation and function arguments.

Step-by-step explanation:

The student's question relates to ARM assembly language, specifically the use of registers within non-leaf and leaf functions. A leaf function is a subroutine that does not make any further function calls, whereas a non-leaf function can call other functions and is therefore more complex in terms of stack usage and register saving. Registers are used by functions in assembly language for storing temporary data, passing arguments, returning values, and for other purposes dictated by the calling convention.

When writing assembly code, especially for ARM architectures, it is important to understand which registers are used and how they should be preserved across function calls. This concept adheres to the ARM procedure call standard (AAPCS), which guides which registers are to be saved across function calls (R4-R11) and which are used for passing function arguments (R0-R3).