Fixes ability to load multiple user application at a same time.

Author: scopeInfinity

memory_layout.md

@@ -8,5 +8,7 @@
 | 0x7F00    | 0x7FFF    | 256B      | SHARED STATIC MEMORY for real_mode library    |
 | 0x8000    | 0xB1FF    | 12.5KB    | BOOT LOADER STAGE 2                           |
 | 0xC000    | 0x10200   | -         | KERNEL                                        |
-| 0x20000   | fill      | -         | Application                                   |
+| 0x20000   | 0x2FFFF   | -         | Application 0                                 |
+| 0x30000   | 0x3FFFF   | -         | Application 1                                 |
+...
 | -         | 0xFFFFF   | -         | 20-bit memory limit                           |

src/kernel/process.asm

@@ -8,24 +8,33 @@ global call_main
         push ebp
         mov ebp, esp
 
-        mov eax, [ebp + 0x8]         ; (argc)
-        mov ebx, [ebp + 0xc]         ; (argv)
+        mov eax, [ebp + 0x10]         ; (argc)
+        mov eax, [ebp + 0x14]         ; (argv)
+
+        ; bx and cx are used below.
+        mov ebx, [ebp + 0x08]         ; (CS)
+        mov ecx, [ebp + 0x0c]         ; (DS)
 
         mov eax, esp
         mov [kernel_saved_stack_top], eax
 
+
         ; Preparing for exec.
 
-        mov ax, 0x30
-        mov es, ax
-        mov ss, ax
-        mov ds, ax
-        mov fs, ax
-        mov gs, ax
+        ; Assigning DS and stuff.
+        mov es, cx
+        mov ss, cx
+        mov ds, cx
+        mov fs, cx
+        mov gs, cx
 
         mov eax, 0xFFFF
-        mov esp, eax
-        call 0x28:0x0000
+
+        ; far jump to main()
+        mov [farjmp_location+4], bx
+        xor ebx, ebx
+        mov [farjmp_location], ebx
+        call far [farjmp_location]
         ; eax should contain the program return value.
 
         ; Returned from exec.
@@ -45,4 +54,6 @@ global call_main
         ret
 
 [SECTION .data]
-    kernel_saved_stack_top  db  '    '
+    kernel_saved_stack_top  db  '    '
+    farjmp_location dd 0
+                    dw 0

src/kernel/process.c

@@ -24,7 +24,6 @@ void process_handler_init() {
 
 int process_reserve_new_id() {
     // Only one process can at a time for now.
-    return 0;
     // id: application id, 0-based
     for (int i = 0; i < MAX_PROCESS; ++i) {
         if(process_availability[i]) {
@@ -40,10 +39,10 @@ int process_free_id(int id) {
 }
 
 int process_new_allocated_memory(int id) {
-    return MEMORY_LOCATION_APP+0x10000;
+    return MEMORY_LOCATION_APP+0x10000*id;
 }
 
-extern int call_main(int argc, char *argv[]);
+extern int call_main(int cs, int ds, int argc, char *argv[]);
 
 int process_exec(int sector_index, int sector_count) {
     int id = process_reserve_new_id();
@@ -78,9 +77,17 @@ int process_exec(int sector_index, int sector_count) {
 
     int relative_address = memory_location-MEMORY_LOCATION_KERNEL;
     print_log("App loaded at 0x%x, relative_address: 0x%x: %x...",
-        MEMORY_LOCATION_APP, relative_address,
+        memory_location, relative_address,
         *(int*)relative_address);
-    int exit_code = call_main(0, 0);
+
+    int code_segment = idt_cs_entry*sizeof(struct GDTEntry);
+    int data_segment = idt_ds_entry*sizeof(struct GDTEntry);
+    int argc = 0;
+    int argv = 0;
+    print_log("call_main(0x%x, 0x%x, %d, %d)", code_segment, data_segment, argc, argv);
+
+    int exit_code = call_main(code_segment, data_segment, argc, argv);
+
     process_free_id(id);
     io_low_flush();
     return exit_code;