syscalls: implement read syscall

grubshit/aaa.asm

@@ -1,33 +1,45 @@
 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)
+    file_path db '/ebalo/huy.txt', 0        ; File path
+    message   db 'Hello, World from KatauOS!', 10, 0  ; Message with newline
+    message_len equ $ - message - 1         ; Length excluding null terminator
+
+section .bss
+    buffer resb 256           ; Buffer for reading file content
+    read_count resd 1         ; Store bytes read count
 
 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
+    ; Reopen file for reading
+    mov eax, 5                ; sys_open
+    mov ebx, file_path
+    mov ecx, 0                ; O_RDONLY
+    mov edx, 0                ; Mode (unused)
+    int 0x80
+    mov edi, eax              ; Save new descriptor
 
-    ; 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
+    ; Read file content
+    mov eax, 3                ; sys_read
+    mov ebx, edi
+    mov ecx, buffer
+    mov edx, 256
+    int 0x80
+    mov [read_count], eax     ; Save bytes read count
 
-    ; Close the file
-    mov eax, 6              ; System call number for sys_close
-    mov ebx, edi            ; File descriptor
-    int 0x80                ; Invoke system call
+    ; Write to stdout
+    mov eax, 4                ; sys_write
+    mov ebx, 1                ; stdout
+    mov ecx, buffer
+    mov edx, [read_count]     ; Use actual bytes read
+    int 0x80
 
-    ; Exit the program
-    mov eax, 1              ; System call number for sys_exit
-    xor ebx, ebx            ; Return status 0
-    int 0x80                ; Invoke system call
+    ; Close file
+    mov eax, 6                ; sys_close
+    mov ebx, edi
+    int 0x80
+
+    ; Exit
+    mov eax, 1                ; sys_exit
+    xor ebx, ebx              ; Return 0
+    int 0x80