Metal ARM x04 - Function Calls (Lab Notes)

Project 4 is a bit smaller in implementaion size due to amount of reading I needed to do. Nevertheless, it consists of:

• Adding instructions to support actual function calls,
• Reading (in-progress) the ARM Procedure Call Standard,
• Started using Compiler Explorer for code generation comparison,
• Getting an emulator setup going via QEMU for toolchain-related tasks that aren't dependent on real hardware.

Work Completed

• Added support for BL/BX instructions to enable function calls and returns to/from a given function (which is just a label):

  BL &function
  ; [...]
  
  @function
    ; [...]
    BX LR
  

• Added PUSH {regs...} and POP {regs...} for stack management,

• Added define!(<identifier>, <hex_literal>) pseudo-instruction for definitions visible during assembly (but the define itself doesn't appear in the binary):

  define!(some-value, x11)
  ; [...]
  MOVS R0 $some-value
  

• Added mov!(<register>, <hex_literal>) pseudo-instruction for a little boilerplate reduction when generating plain MOVs.

Next Steps

I think this is enough foundation for creating a primitive-but-useful module system that isn't strictly "text-replace" based. That, combined with a small linker, will let me start writing actually reusable code. Onward!