Hello World with RISC-V

Writing Hello World in RISC-V Assembly.

Why Hello World

Hello World is traditionally the first program that people write when starting a new computer programming language. RISC-V is no different.

Basically following the code on Stephen Smiths Blog but adding a second message of Hello Again.

Stephen has written a good book on RISC-V Assembly Language Programming (although sadly missing RVV commands, so I hope there will be a 2nd edition to add these).

On with the code. Just use vim, or your favourite text editor, to create the assembly source code file: hello.s

hello.s

.global _start # Provide program starting address to linker

# Setup the parameters to print hello world

# and then call Linux to do it.

_start:	
		addi a0, x0, 1		# 1 = StdOut
		la a1, helloworld	# load address of helloworld
		addi a2, x0, 13		# length of our string
		addi a7, x0, 64		# linux write system call
		ecall				# Call linux to output the string

		addi a0, x0, 1		# 1 = StdOut
		la a1, helloagain	# load address of helloagain
		addi a2, x0, 13		# length of our string
		addi a7, x0, 64		# linux write system call
		ecall				# Call linux to output the string

# Setup the parameters to exit the program
# and then call Linux to do it.

		addi a0, x0, 0		# Use 0 return code
		addi a7, x0, 93		# Service command code 93 terminates
		ecall				# Call linux to terminate the program

.data
helloworld: .ascii “Hello World!n”
helloagain: .ascii “Hello Again!n”

Assemble and Run

				as -mno-relax -o hello.o hello.s
				ld -o hello hello.o
				./hello

Mission Accomplished

And there we have it, you now have a functioning RISC-V Hello World. Its not much, but its a good step to see that your assembly toolchain is working.