x86: asm example use preprocessor + fix str length

1 files changed, 8 insertions, 7 deletions

diff --git a/src/arch/x86_64.md b/src/arch/x86_64.md
index 35fd9aa..38f40e1 100644
--- a/src/arch/x86_64.md
+++ b/src/arch/x86_64.md
@@ -331,34 +331,35 @@ Small assembler skeleton, ready to use with following properties:
 - gnu assembler [`gas`][gas_doc]
 - intel syntax
 ```x86asm
-# file: greet.s
+// file: greet.S
+#include <asm/unistd.h>
 
     .intel_syntax noprefix
 
     .section .text, "ax", @progbits
     .global _start
 _start:
-    mov rdi, 1                      # fd
+    mov rdi, 1                      # fd (stdout)
     lea rsi, [rip + greeting]       # buf
     mov rdx, [rip + greeting_len]   # count
-    mov rax, 1                      # write(2) syscall nr
+    mov rax, __NR_write             # write(2) syscall nr
     syscall
 
-    mov rdi, 0                      # exit code
+    mov rdi, __NR_exit              # exit code
     mov rax, 60                     # exit(2) syscall nr
     syscall
 
     .section .rdonly, "a", @progbits
 greeting:
-    .asciz "Hi ASM-World!\n"
+    .ascii "Hi ASM-World!\n"
 greeting_len:
     .int .-greeting
 ```
-> Syscall numbers are defined in `/usr/include/asm/unistd.h`.
+> Files with `.S` suffix are pre-processed, while files with `.s` suffix are not.
 
 To compile and run:
 ```bash
-> gcc -o greet greet.s -nostartfiles -nostdlib && ./greet
+> gcc -o greet greet.S -nostartfiles -nostdlib && ./greet
 Hi ASM-World!
 ```