nasfmt

Code formatter for NASM x86-64 assembly.

Install

$ cargo install nasfmt

Usage

Format a file in place:

$ nasfmt file.s

Format multiple files in place:

$ nasfmt file1.s file2.s file3.s

Check formatting without modifying files (exits 1 with a diff if changes are needed):

$ nasfmt --check tests/resources/main.s
--- tests/resources/main.s
+++ tests/resources/main.s
@@ -103,9 +103,9 @@
     syscall
     cmp     rax, 0
     jle     no_input_connected
-    movzx   rax, byte [input_char] ; Convert ASCII to integer
-    sub   rax, '0'
-    cmp      rax, 1                    ; Check lower bound
+    movzx   rax, byte [input_char]    ; Convert ASCII to integer
+    sub     rax, '0'
+    cmp     rax, 1                    ; Check lower bound
     jl      invalid_input
     cmp     rax, 9                    ; Check upper bound
     jg      invalid_input

What it does

• Normalises mnemonics, registers, and size prefixes to lowercase (MOV RAX → mov rax), or uppercase if the --upper flag is passed
• Aligns operands and comments consistently within each instruction block
• Ensures labels appear on their own line
• Standardises spacing inside memory operands ([rbp-8] → [rbp - 8])
• Leaves user-defined symbol names and string literals untouched

Reference

• NASM documentation