From 452ad7813ddd6f95166ecc151db2f12b10745ab2 Mon Sep 17 00:00:00 2001
From: Sascha Tommasone <sascha@tommasone.me>
Date: Sat, 8 Jun 2024 18:12:30 +0200
Subject: [PATCH] [Assignment-5] added solution task 3 (syscalling)

---
 .../syscalling/code.asm                       | 53 ++++++++++++++++---
 1 file changed, 46 insertions(+), 7 deletions(-)

diff --git a/Assignment 5 - Software Security - Teil 1/syscalling/code.asm b/Assignment 5 - Software Security - Teil 1/syscalling/code.asm
index 6152f8d..374be3e 100644
--- a/Assignment 5 - Software Security - Teil 1/syscalling/code.asm	
+++ b/Assignment 5 - Software Security - Teil 1/syscalling/code.asm	
@@ -5,15 +5,54 @@
 %define O_CREAT     00000100o
 %define O_TRUNC     00001000o
 %define S_IRUSR     00000400o
-%define S_IWUSR     00000200o 
+%define S_IWUSR     00000200o
+
 
 section .data
-path: db "/home/user/nachricht", 0
-greeting: db "hidad!", 0
+    path: db "/home/user/nachricht", 0
+    greeting: db "hidad!", 0
 
+    ; https://stackoverflow.com/a/45386640
+    length equ $ - greeting ; Length of greeting message
+
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+; https://chromium.googlesource.com/chromiumos/docs/+/master/constants/syscalls.md#x86-32_bit;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 section .text
-global _start   
+global _start
 _start:
-    ;----------------------------------
-    nop ; <YOUR CODE HERE>
-    ; ------------ End of file ------------
+    call _open              ; open file
+    call _write             ; write to file
+    call _close             ; close file
+    call _exit              ; exit without errors
+
+; https://www.man7.org/linux/man-pages/man2/open.2.html
+_open:
+    mov eax, 0x05           ; syscall number for 'open'
+    mov ebx, path           ; pointer to the path string
+    mov ecx, O_CREAT        ; open the file if it doesn't exist
+    xor ecx, O_WRONLY       ; open the file in write-only mode
+    mov edx, S_IRUSR        ; permissions for the file
+    int 0x80                ; call kernel
+
+; https://man7.org/linux/man-pages/man2/write.2.html
+_write:
+    mov ebx, eax            ; file descriptor returned by 'open'
+    mov eax, 0x04           ; syscall number for 'write'
+    mov ecx, greeting       ; pointer to the greeting message
+    mov edx, length         ; length of the greeting message
+    sub edx, 0x01           ; length of the greeting message without null byte
+    int 0x80                ; call kernel
+
+; https://man7.org/linux/man-pages/man2/close.2.html
+_close:
+    mov eax, 0x06           ; syscall number for 'close'
+    int 0x80                ; call kernel
+
+; https://man7.org/linux/man-pages/man2/exit.2.html
+_exit:
+    mov eax, 1              ; syscall number for 'exit'
+    mov ebx, 0              ; exit status
+    int 0x80                ; call kernel
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;