syscalls: done with open, write, close syscalls

2025-06-20 23:06:01 +03:00
parent 4ccae473ca
commit bf7d96865a
4 changed files with 88 additions and 32 deletions
@@ -1,29 +1,33 @@
-section .text
-    global _start       ;must be declared for using gcc
-_start:                     ;tell linker entry point
-    mov edx, len    ;message length
-    mov ecx, msg    ;message to write
-    mov ebx, 1      ;file descriptor (stdout)
-    mov eax, 4      ;system call number (sys_write)
-    int 0x80        ;call kernel
-
-    mov eax, 1      ;system call number (sys_exit)
-    int 0x80        ;call kernel
-
-    mov eax, 4
-    mov ebx, 1
-    mov ecx, msg2
-    mov edx, len2
-    int 0x80
-
-    mov eax, 1
-    int 0x80
-
-    jmp $
-
 section .data
+    file_path db '/ebalo/huy.txt', 0        ; Specific file path, null-terminated
+    message   db 'Hello, World from KatauOS!', 10, 0    ; Message to write, with newline
+    message_len equ $ - message - 1        ; Length of message (14 bytes, excluding null)

-msg db  'Hello, world!',0x0 ;our dear string
-len equ $ - msg         ;length of our dear string
-msg2 db 'seems like KatauOS just executed this ELF-file!!',0x0
-len2 equ $ - msg2
+section .text
+    global _start
+
+_start:
+    ; Open the file
+    mov eax, 5              ; System call number for sys_open
+    mov ebx, file_path      ; Pointer to file path
+    mov ecx, 65             ; Flags: O_WRONLY (1) | O_CREAT (64)
+    mov edx, 0x1A4          ; Mode: 0644 (rw-r--r--)
+    int 0x80                ; Invoke system call
+    mov edi, eax            ; Save file descriptor in edi
+
+    ; Write to the file
+    mov eax, 4              ; System call number for sys_write
+    mov ebx, edi            ; File descriptor
+    mov ecx, message        ; Pointer to message
+    mov edx, message_len    ; Number of bytes to write
+    int 0x80                ; Invoke system call
+
+    ; Close the file
+    mov eax, 6              ; System call number for sys_close
+    mov ebx, edi            ; File descriptor
+    int 0x80                ; Invoke system call
+
+    ; Exit the program
+    mov eax, 1              ; System call number for sys_exit
+    xor ebx, ebx            ; Return status 0
+    int 0x80                ; Invoke system call