From a183d55b692c334932b54d739f50f845fb97a4e8 Mon Sep 17 00:00:00 2001
From: mtgmonkey <mtgmonkey@nixos>
Date: Fri, 27 Jun 2025 04:10:26 -0400
Subject: [PATCH] init

---
 flake.lock   |  26 ++++++++++++
 flake.nix    |  11 +++++
 package.nix  |  30 +++++++++++++
 src/lib.asm  | 116 +++++++++++++++++++++++++++++++++++++++++++++++++++
 src/main.asm |  61 +++++++++++++++++++++++++++
 5 files changed, 244 insertions(+)
 create mode 100644 flake.lock
 create mode 100644 flake.nix
 create mode 100644 package.nix
 create mode 100644 src/lib.asm
 create mode 100644 src/main.asm

diff --git a/flake.lock b/flake.lock
new file mode 100644
index 0000000..3e3d586
--- /dev/null
+++ b/flake.lock
@@ -0,0 +1,26 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1750400657,
+        "narHash": "sha256-3vkjFnxCOP6vm5Pm13wC/Zy6/VYgei/I/2DWgW4RFeA=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "b2485d56967598da068b5a6946dadda8bfcbcd37",
+        "type": "github"
+      },
+      "original": {
+        "id": "nixpkgs",
+        "ref": "nixos-25.05",
+        "type": "indirect"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}
diff --git a/flake.nix b/flake.nix
new file mode 100644
index 0000000..95becdc
--- /dev/null
+++ b/flake.nix
@@ -0,0 +1,11 @@
+{
+  inputs = {
+    nixpkgs.url = "nixpkgs/nixos-25.05";
+  };
+  outputs = {nixpkgs, ...}: let
+    system = "x86_64-linux";
+    pkgs = nixpkgs.legacyPackages.${system};
+  in {
+    packages.${system}.default = pkgs.callPackage ./package.nix {};
+  };
+}
diff --git a/package.nix b/package.nix
new file mode 100644
index 0000000..fcdacf6
--- /dev/null
+++ b/package.nix
@@ -0,0 +1,30 @@
+{
+  lib,
+  stdenv,
+  nasm,
+  ...
+}:
+stdenv.mkDerivation {
+  name = "asm-test";
+  src = ./src;
+  nativeBuildInputs = [
+    nasm
+  ];
+  buildInputs = [
+  ];
+  configurePhase = ''
+  '';
+  buildPhase = ''
+    nasm -f elf main.asm
+    ld -m elf_i386 main.o -o main
+  '';
+  installPhase = ''
+    mkdir -p $out/bin
+    cp main $out/bin/main
+  '';
+
+  meta = {
+    license = lib.licenses.wtfpl;
+    mainProgram = "main";
+  };
+}
diff --git a/src/lib.asm b/src/lib.asm
new file mode 100644
index 0000000..d464f02
--- /dev/null
+++ b/src/lib.asm
@@ -0,0 +1,116 @@
+; ***************************
+; slen : String -> Int
+; calculates length of string
+; ***************************
+
+slen:
+  push ebx
+  mov ebx, eax
+
+slen_nextchar:
+  cmp byte [eax], 0
+  jz slen_finished
+  inc eax
+  jmp slen_nextchar
+
+slen_finished:
+  sub eax, ebx
+  pop ebx
+  ret
+
+; *********************
+; clear_bss : BSS -> IO
+; clears memory block
+; *********************
+
+clear_bss:
+  cmp byte [eax], 0
+  jz clear_bss_finished
+  mov [eax], byte 0
+  inc eax
+  jmp clear_bss
+
+clear_bss_finished:
+  ret
+
+; *******************************
+; scmp : String -> String -> Bool
+; compares 2 strings exactly
+; *******************************
+
+scmp:
+  push ecx
+
+scmp_nextchar:
+  mov cl, byte [ebx]
+  cmp byte [eax], cl
+  jnz scmp_bad
+  cmp byte [eax], 0
+  jz scmp_good
+  inc eax
+  inc ebx
+  jmp scmp_nextchar
+
+scmp_good:
+  mov eax, 0
+  jmp scmp_finished
+
+scmp_bad:
+  mov eax, 1
+
+scmp_finished:
+  pop ecx
+  ret
+
+; *********************
+; sprint : String -> IO
+; prints string
+; *********************
+
+sprint:
+  push edx
+  push ecx
+  push ebx
+  push eax
+  call slen
+
+  mov edx, eax
+  pop eax
+  mov ecx, eax
+  mov ebx, 1
+  mov eax, 4
+  int 80h
+
+  pop ebx
+  pop ecx
+  pop edx
+  ret
+
+; ***********************
+; sprintln : String -> IO
+; prints string + 0Ah
+; ***********************
+
+sprintln:
+  call sprint
+  push eax    ; initial
+
+  mov eax, 0Ah
+  push eax     ; linefeed
+  mov eax, esp ; esp is stack pointer
+  call sprint
+
+  pop eax ; linefeed
+  pop eax ; initial
+  ret
+
+; ************
+; exit : IO
+; exit program
+; ************
+
+exit:
+  mov ebx, 0
+  mov eax, 1
+  int 80h
+  ret
diff --git a/src/main.asm b/src/main.asm
new file mode 100644
index 0000000..c947b6d
--- /dev/null
+++ b/src/main.asm
@@ -0,0 +1,61 @@
+%include 'lib.asm'
+
+SECTION .data
+welcome_message db 'Welcome to this test program! It is experimental and very subject to change.', 0h
+prompt          db 'Enter a string to print: ', 0h
+exit_str        db 'exit', 0Ah, 0h
+
+SECTION .bss
+; resb ; 0001 byte
+; resw ; 0010 word
+; resd ; 0100 double word
+; resq ; 1000 quad word
+; rest ; 1010 ten bytes
+sinput: resb 255 ; 255 bytes
+
+SECTION .text
+global _start
+
+_start:
+  pop ecx ; number of arguments
+
+  pop eax ; dispose of first value, the exe
+  dec ecx
+
+  mov eax, welcome_message
+  call sprintln
+
+next_arg:
+  cmp ecx, 0h
+  jz prompt_loop
+  pop eax
+  call sprintln
+  dec ecx
+  jmp next_arg
+
+prompt_loop:
+  mov eax, prompt
+  call sprint
+
+  mov eax, sinput
+  call clear_bss
+
+  mov edx, 255    ; max bytes to read
+  mov ecx, sinput ; buffer
+  mov ebx, 0      ; (STDIN) where to read from
+  mov eax, 3      ; (SYS_READ)
+  int 80h
+
+  mov eax, sinput
+  mov ebx, exit_str
+  call scmp
+  cmp byte eax, 0
+  jz done
+
+  mov eax, sinput
+  call sprint
+
+  jmp prompt_loop
+
+done:
+  call exit