Introduction¶

varm is an educational ARM-like virtual machine for learning assembly programming.

Why varm?¶

• Safe: Bugs crash the VM, not your system

• Simple: ~20 instructions vs. hundreds on real ARM

• Portable: Runs anywhere with a C compiler

Registers¶

varm has 16 registers (r0-r15):

• r0-r12: General purpose

• r13 (sp): Stack pointer

• r14 (lr): Link register

• r15 (pc): Program counter

Memory Layout¶

• Text (0x20): Executable code

• Data (0x10000): Variables

First Program¶

.text
mov r0, #42
mov r7, #1
swi

Build and run:

vasm program.vasm -o program.vm
varm program.vm

Key Instructions¶

• mov rd, #imm: Move value to register

• add rd, rn, rm: Addition

• sub rd, rn, rm: Subtraction

• mul rd, rn, rm: Multiplication

• swi: Syscall (I/O, exit)

• ldr rd, =label: Load label address

• ldr rd, [rn]: Load from memory

See Instruction Set for the full instruction set.