ultra-tiny 1kB docker images

.gitignore

*.o
hello
a.out
hex 

README.md

Ultra-tiny 1kB Docker Image

$ docker images |grep tiny-hello
tiny-hello                                    latest                21d5b79018bb        2 minutes ago       952B

Dockerfile

FROM alpine:latest as builder
WORKDIR /build
RUN apk update && \
    apk add nasm make binutils
COPY .  ./
RUN make hello

FROM scratch
WORKDIR /
COPY --from=builder /build/hello .
CMD ["/hello"]

hello.asm

; Define variables in the data section
SECTION .DATA
	hello:     db 'Hello world!',10
	helloLen:  equ $-hello

; Code goes in the text section
SECTION .TEXT
	GLOBAL _start 

kernel:
	int	80h	; Call kernel
	ret
	
	
_start:
	mov eax,4            ; 'write' system call = 4
	mov ebx,1            ; file descriptor 1 = STDOUT
	mov ecx,hello        ; string to write
	mov edx,helloLen     ; length of string to write
	call kernel              ; call the kernel

	; Terminate program
	mov eax,1            ; 'exit' system call
	mov ebx,0            ; exit with error code 0
	call kernel              ; call the kernel

hex.asm

%include	'system.inc'

section	.data
hex	db	'0123456789ABCDEF'
buffer	db	0, 0, ' '

section	.text
global	_start
_start:
	; read a byte from stdin
	push	dword 1
	push	dword buffer
	push	dword stdin
	sys.read
	add	esp, byte 12
	or	eax, eax
	je	.done

	; convert it to hex
	movzx	eax, byte [buffer]
	mov	edx, eax
	shr	dl, 4
	mov	dl, [hex+edx]
	mov	[buffer], dl
	and	al, 0Fh
	mov	al, [hex+eax]
	mov	[buffer+1], al

	; print it
	push	dword 3
	push	dword buffer
	push	dword stdout
	sys.write
	add	esp, byte 12
	jmp	short _start

.done:
	push	dword 0
	sys.exit

Makefile

hello.o: hello.asm
	nasm -f elf64 $< -o $@

hello: hello.o
	ld $< -o $@

system.inc

%define	stdin	0
%define	stdout	1
%define	stderr	2

%define	SYS_nosys	0
%define	SYS_exit	1
%define	SYS_fork	2
%define	SYS_read	3
%define	SYS_write	4
; [etc...]

section	.text
align 4
access.the.bsd.kernel:
	int	80h
	ret
	
%macro	system	1
	mov	eax, %1
	call	access.the.bsd.kernel
%endmacro

%macro	sys.exit	0
	system	SYS_exit
%endmacro

%macro	sys.fork	0
	system	SYS_fork
%endmacro

%macro	sys.read	0
	system	SYS_read
%endmacro

%macro	sys.write	0
	system	SYS_write
%endmacro

; [etc...]