3 files changed, 61 insertions(+), 0 deletions(-)

A .gitignore
A forth.s
A makefile

@@ 1,2 @@
+*.o
+forth

@@ 1,57 @@
+; vi: ft=nasm
+
+; https://blog.rchapman.org/posts/Linux_System_Call_Table_for_x86_64/
+
+;
+
+global _start
+section .text
+%define SYS_READ 0
+%define SYS_WRITE 1
+%define SYS_EXIT 60
+
+%define STDIN 0
+%define STDOUT 1
+
+
+%define putchar(x) mov
+
+_start:
+
+repl:
+        mov rax, SYS_WRITE          ; write prompt
+        mov rdi, STDOUT
+        mov rsi, prompt
+        mov rdx, prompt_len
+        syscall
+
+        mov rax, SYS_READ           ; read
+        mov rdi, STDIN
+        mov rsi, buf_in
+        mov rdx, buf_len
+        syscall
+
+        mov rdx, rax ; length in rax
+        cmp rdx, 0
+        jz exit
+
+        ;; write
+        mov rax, SYS_WRITE          ; echo
+        mov rdi, STDOUT
+        mov rsi, buf_in
+        syscall
+
+        jmp repl                    ; loop
+
+exit:
+        mov rax, SYS_EXIT
+        mov rdi, 0
+        syscall
+
+section .bss
+        buf_in: resb 128
+        buf_len: equ $ - buf_in
+
+section .rodata
+        prompt: db "> "
+        prompt_len: equ $ - prompt

@@ 1,2 @@
+all:
+	nasm -f elf64 -o forth.o forth.s && ld -o forth forth.o