wip: TSS added to the gdt and start to implement scheduler

headers/gdt.h

@@ -1,9 +1,10 @@
 #pragma once
 
+#include "tss.h"
 #include <stdint.h>
 
 #define GDT_ADDRESS 0xC0105040
-#define GDT_SIZE    7
+#define GDT_SIZE    8
 
 // https://wiki.osdev.org/Global_Descriptor_Table#GDTR
 struct gdt_descriptor {
@@ -11,6 +12,8 @@ struct gdt_descriptor {
 	uint32_t base;
 } __attribute__((packed));
 
+extern struct tss TSS;
+
 void init_gdt();
 
 #define GDT_FLAG_64BIT_MODE 0b0010
@@ -39,3 +42,4 @@ extern uint8_t gdt_entries[GDT_SIZE * 8];
 #define GDT_OFFSET_USER_CODE    0x20
 #define GDT_OFFSET_USER_DATA    0x28
 #define GDT_OFFSET_USER_STACK   0x30
+#define GDT_OFFSET_TSS          0x38

headers/task.h

@@ -0,0 +1,23 @@
+#pragma once
+
+#include "list.h"
+
+#include <stdint.h>
+
+enum status { ZOMBIE, THREAD, RUN };
+
+struct task {
+	uint32_t *esp;
+	uint32_t *esp0;
+	uint32_t *cr3;
+	uint16_t pid;
+	uint8_t status;
+	struct task *daddy;
+	struct task *child;
+	struct list **signals;
+	uint8_t owner_id;
+	struct task *next;
+};
+
+void scheduler(void);
+void switch_to_task(struct task *next_task);

headers/tss.h

@@ -0,0 +1,60 @@
+#pragma once
+
+#include <stdint.h>
+
+// _h fields are for the offset
+struct tss {
+	uint16_t link;
+	uint16_t link_h;
+
+	uint32_t esp0;
+	uint16_t ss0;
+	uint16_t ss0_h;
+
+	uint32_t esp1;
+	uint16_t ss1;
+	uint16_t ss1_h;
+
+	uint32_t esp2;
+	uint16_t ss2;
+	uint16_t ss2_h;
+
+	uint32_t cr3;
+	uint32_t eip;
+	uint32_t eflags;
+
+	uint32_t eax;
+	uint32_t ecx;
+	uint32_t edx;
+	uint32_t ebx;
+
+	uint32_t esp;
+	uint32_t ebp;
+
+	uint32_t esi;
+	uint32_t edi;
+
+	uint16_t es;
+	uint16_t es_h;
+
+	uint16_t cs;
+	uint16_t cs_h;
+
+	uint16_t ss;
+	uint16_t ss_h;
+
+	uint16_t ds;
+	uint16_t ds_h;
+
+	uint16_t fs;
+	uint16_t fs_h;
+
+	uint16_t gs;
+	uint16_t gs_h;
+
+	uint16_t ldt;
+	uint16_t ldt_h;
+
+	uint16_t trap;
+	uint16_t iomap;
+};

libbozo/headers/list.h

@@ -0,0 +1,6 @@
+#pragma once
+
+struct list {
+	void *content;
+	struct list *next;
+};

src/drivers/clock.c

@@ -6,13 +6,15 @@
 #include "kprintf.h"
 #include "memory.h"
 #include "sys/io.h"
+#include "task.h"
 
 #define PIT_CHANNEL0  0x40
 #define PIT_FREQUENCY 1193182
 #define PIT_COUNT     (65535 / 2)
 #define DELAY         (1000 / (PIT_FREQUENCY / PIT_COUNT))
 
-uint32_t counter = 0;
+uint32_t sleep_counter;
+uint32_t scheduler_counter;
 
 static void clock_handler(struct registers *regs);
 
@@ -36,12 +38,15 @@ void clock_init(struct registers *regs)
 static void clock_handler(struct registers *regs)
 {
 	(void)regs;
-	counter--;
+	if (scheduler_counter % 10)
+		scheduler();
+	scheduler_counter++;
+	sleep_counter--;
 }
 
 void sleep(uint64_t delay)
 {
-	counter = delay / DELAY;
-	while (counter)
+	sleep_counter = delay / DELAY;
+	while (sleep_counter)
 		;
 }

src/gdt/gdt.c

@@ -5,6 +5,7 @@
 
 extern void set_gdt(uint32_t gdt_ptr);
 
+struct tss TSS;
 uint8_t gdt_entries[GDT_SIZE * 8];
 struct gdt_descriptor *gdtr = (struct gdt_descriptor *)GDT_ADDRESS;
 
@@ -90,6 +91,9 @@ void init_gdt(void)
 		GDT_ACCESS_RW_READABLE_FOR_CODE_WRITABLE_FOR_DATA |
 		GDT_ACCESS_A_ACCESSED,
 	    GDT_FLAG_32BIT_MODE | GDT_FLAG_PAGE_MODE); // User stack
+	// TSS
+	set_gdt_entry_value(gdt_entries + GDT_OFFSET_TSS, (uint32_t)&TSS,
+	                    sizeof(struct tss) - 1, 0x89, 0);
 
 	set_gdt(((uint32_t)gdtr));
 }

src/kernel.c

@@ -41,7 +41,5 @@ void kernel_main(multiboot_info_t *mbd, uint32_t magic)
 	/*         "complex 8*unknown quantity -byte descriptor table. -- Troy "
 	 */
 	/*         "Martin 03:50, 22 March 2009 (UTC)\n"); */
-	/* terminal_putchar('A'); */
-	/* memset(display.buff, 255, 1024 * 1024); */
 	shell_init();
 }

src/multitasking/scheduler.c

@@ -0,0 +1,11 @@
+#include "task.h"
+
+struct task *current_task;
+
+void scheduler(void)
+{
+	struct task *it = current_task->next;
+	while (it->status != RUN)
+		it = it->next;
+	switch_to_task(it);
+}

src/multitasking/switch_to_task.s

@@ -0,0 +1,37 @@
+.intel_syntax noprefix
+
+.section .text
+	.global switch_to_task
+
+switch_to_task:
+	push ebx
+	push ebp
+	push edi
+	push esi
+
+	// save the current stack pointer to the old stack
+	mov [current_task], esp
+
+	// stack pointer + the 4 regs pushed
+	// and + 1 to get the argument (next task)
+	mov esi, [esp+(4+1)*4]
+	mov [current_task], esi
+	
+	mov esp, [current_task]
+	mov eax, [current_task+4]
+	mov ebx, [current_task+8]
+	mov [TSS + 4], eax
+	mov ecx, cr3
+
+	// if cr3 hasn't change, do nothing
+	cmp ecx, ebx
+	je .END 
+	mov cr3, ebx
+
+.END:
+	pop esi
+	pop edi
+	pop ebp
+	pop ebx
+
+	ret