Got GDT working

kernel/include/gdt.h

@@ -3,24 +3,6 @@
 
 #include <kernel.h>
 
-/*
- * Entries:
- * 0 Null desc.
- * 1 Kernel code desc.
- * 2 Kernel data desc.
- * 3 SYSENTER
- * 4 SYSEXIT
- * 5 User code desc.
- * 6 User data desc.
- * 7 Task State Segment
- */
-#define GDT_ENTRIES	8
-#define GDT_KERNEL_CODE	0x28
-#define GDT_KERNEL_DATA	0x30
-#define GDT_USER_CODE	0x50
-#define GDT_USER_DATA	0x48
-#define GDT_TSS		0x50
-
 /*
  * Segment selector explanation (why kcode is 0x08?)
  *
@@ -47,13 +29,39 @@
 #define SEGMENT_SEL(_priv, _tab, _i)\
 	(uint16_t)(((_i) << 3) | ((_tab) << 2) | (_priv))
 
+/*
+ * Entries:
+ * 0 Null desc.
+ * 1 Kernel code desc.
+ * 2 Kernel data desc.
+ * 3 User code desc.
+ * 4 User data desc.
+ * 5 Task State Segment
+ */
+#define GDT_ENTRIES	6
+#define GDT_NULL	SEGMENT_SEL(0, 0, 0)
+#define GDT_KERNEL_CODE	SEGMENT_SEL(0, 0, 1)
+#define GDT_KERNEL_DATA	SEGMENT_SEL(0, 0, 2)
+#define GDT_USER_CODE	SEGMENT_SEL(3, 0, 3)
+#define GDT_USER_DATA	SEGMENT_SEL(3, 0, 4)
+#define GDT_TSS		SEGMENT_SEL(0, 0, 5)
+
+#define GDT_DESC(_lim, _base, _acc, _flag) (struct gdt_entry){\
+	.limit 		= (_lim) & 0xffff,\
+	.baseLow	= (uint16_t)(_base),\
+	.baseMid	= (uint8_t)((_base) >> 16),\
+	.access		= (_acc),\
+	.flags		= (_flag << 4) | (((_lim) >> 16) & 0x0f),\
+	.baseHigh	= (uint8_t)((_base) >> 24),\
+}
+
 struct gdt_entry {
 	uint16_t limit;
 	uint16_t baseLow;
-	uint8_t baseMid;
+	uint8_t	 baseMid;
-	uint8_t access;
+	uint8_t  access;
-	uint8_t granulatiry;
+	uint8_t  flags;		// low 4 bits are 4 msbs of limit, high 4 bits are flags
-	uint8_t baseHigh;
+	uint8_t  baseHigh;
 } __packed;
 
 struct gdt_pointer {
@@ -61,15 +69,6 @@ struct gdt_pointer {
 	uint32_t base;
 } __packed;
 
-struct tss_entry {
-	uint16_t length;
-	uint16_t baseLow;
-	uint8_t baseMid;
-	uint8_t flags1;
-	uint8_t flags2;
-	uint8_t baseHigh;
-} __packed;
-
 struct tss_pointer {
 	uint16_t link;
 	uint16_t __reserved0;
@@ -90,7 +89,6 @@ struct tss_pointer {
 	uint32_t edx;
 	uint32_t ebx;
 	uint32_t esp;
-	uint32_t ebs;
 	uint32_t ebp;
 	uint32_t esi;
 	uint32_t edi;
@@ -112,11 +110,6 @@ struct tss_pointer {
 	uint32_t ssp;
 } __packed;
 
-struct gdt_entries {
-	struct gdt_entry descriptors[GDT_ENTRIES - 1]; // Subtract one for TSS
-	struct tss_entry tss;
-};
-
 int gdt_init(void);
 
 #endif

kernel/include/kernel.h

@@ -73,6 +73,7 @@ typedef int32_t		intptr_t;
  * Linker defined values
  */
 extern uint32_t __kernel_start, __kernel_end;
+extern uint32_t __kernel_stack_top, __kernel_stack_bottom;
 
 /*
  * Logging and errors
@@ -82,7 +83,10 @@ extern uint32_t __kernel_start, __kernel_end;
 #define pr_dbg(_s)	printk("[debug] %s\n", (_s))
 #define pr_wrn(_s)	printk("[warning] %s\n", (_s))
 #define pr_err(_s)	printk("[error] %s\n", (_s))
-#define panic(_s)	printk("[panic] %s\n", (_s))
+#define panic(_s)	do {\
+		printk("[panic] %s\n", (_s));\
+		while (1) __asm__ volatile ("cli; hlt");\
+	} while (0)
 #define BUG()		panic("BUG()")
 #define WARN()		pr_wrn("WARN()")
 #define BUG_ON(_e)	((_e) ? BUG() : NULL)

kernel/linker.ld

@@ -32,6 +32,13 @@ SECTIONS {
 		*(COMMON)
 		*(.bss)
 	} : data
+
+	/* Stack */
+	. = ALIGN(16);
+	__kernel_stack_bottom = .;
+	. += 16K;
+	__kernel_stack_top = .;
+
 	__kernel_end = .;
 
 	/DISCARD/ : {

kernel/src/entry.s

@@ -17,20 +17,22 @@ multiboot:
 	dd FLAGS
 	dd CHECK
 
-section .bss
-align 16
 
 ; Initialize stack
-stack_bottom:
+section .bss
+align 16
+global __kernel_stack_top
+global __kernel_stack_bottom
+__kernel_stack_bottom:
 	resb 16384
-stack_top:
+__kernel_stack_top:
 
 ; Entry point
 section .text
 global _start
 extern kmain
 _start:
-	mov esp, stack_top	; Setup stack
+	mov esp, __kernel_stack_top
 	push eax
 	push ebx
 	call kmain		; Call kernel main

kernel/src/gdt.c

@@ -2,22 +2,9 @@
 #include <string.h>
 #include <gdt.h>
 
-static struct gdt_entries gdt;
+static struct gdt_entry gdt[GDT_ENTRIES];
 static struct gdt_pointer gdtp;
 static struct tss_pointer tss;
-struct tss_pointer* tssp = &tss;
-
-void gdt_loadTss(struct tss_pointer* ptr) {
-	size_t addr = (size_t)ptr;
-
-	gdt.tss.baseLow = (uint16_t)addr;
-	gdt.tss.baseMid = (uint8_t)(addr >> 16);
-	gdt.tss.flags1 = 0x89;
-	gdt.tss.flags2 = 0;
-	gdt.tss.baseHigh = (uint8_t)(addr >> 24);
-	
-	__asm__ volatile ("ltr %0" : : "rm"(SEGMENT_SEL(0, 0, 7)));
-}
 
 void gdt_reload(void) {
 	__asm__ volatile (
@@ -37,66 +24,41 @@ void gdt_reload(void) {
 	);
 }
 
+void tss_reload(void) {
+	__asm__ volatile ("ltr %0" : : "rm"(GDT_TSS));
+	gdt[5].access |= 0x02;
+}
+
 int gdt_init(void) {
 	// Null descriptor (0)
-	gdt.descriptors[0].limit = 0;
+	gdt[0] = GDT_DESC(0, 0, 0, 0);
-	gdt.descriptors[0].baseLow = 0;
-	gdt.descriptors[0].baseMid = 0;
-	gdt.descriptors[0].access = 0;
-	gdt.descriptors[0].granulatiry = 0;
-	gdt.descriptors[0].baseHigh = 0;
 
 	// Kernel code (8)
-	gdt.descriptors[1].limit = 0xffff;
+	gdt[1] = GDT_DESC(0xfffff, 0, 0x9a, 0xc);
-	gdt.descriptors[1].baseLow = 0;
-	gdt.descriptors[1].baseMid = 0;
-	gdt.descriptors[1].access = 0x9a;
-	gdt.descriptors[1].granulatiry = 0xcf;
-	gdt.descriptors[1].baseHigh = 0;
 
 	// Kernel data (16)
-	gdt.descriptors[2].limit = 0xffff;
+	gdt[2] = GDT_DESC(0xfffff, 0, 0x92, 0xc);
-	gdt.descriptors[2].baseLow = 0;
-	gdt.descriptors[2].baseMid = 0;
-	gdt.descriptors[2].access = 0x90;
-	gdt.descriptors[2].granulatiry = 0xcf;
-	gdt.descriptors[2].baseHigh = 0;
 
-	// SYSENTER/SYSEXIT
+	// User code (24)
-	gdt.descriptors[3] = (struct gdt_entry){ 0 }; // (24)
+	gdt[3] = GDT_DESC(0xfffff, 0, 0xfa, 0xc);
-	gdt.descriptors[4] = (struct gdt_entry){ 0 }; // (32)
 
-	// User code (40)
+	// User data (32)
-	gdt.descriptors[5].limit = 0;
+	gdt[4] = GDT_DESC(0xfffff, 0, 0xf2, 0xc);
-	gdt.descriptors[5].baseLow = 0;
-	gdt.descriptors[5].baseMid = 0;
-	gdt.descriptors[5].access = 0xfa;
-	gdt.descriptors[5].granulatiry = 0x20;
-	gdt.descriptors[5].baseHigh = 0;
 
-	// User data (48)
+	// TSS (40)
-	gdt.descriptors[6].limit = 0;
+	memset(&tss, 0, sizeof(tss));
-	gdt.descriptors[6].baseLow = 0;
+	gdt[5] = GDT_DESC(sizeof(tss) - 1, (uint32_t)&tss, 0x89, 0x00);
-	gdt.descriptors[6].baseMid = 0;
+	tss.iopb = sizeof(struct tss_pointer);
-	gdt.descriptors[6].access = 0xf2;
+	tss.esp0 = __kernel_stack_top;
-	gdt.descriptors[6].granulatiry = 0;
+	tss.ss0 = GDT_KERNEL_DATA;
-	gdt.descriptors[6].baseHigh = 0;
 
-	// TSS (56)
+	// GDT Pointer
-	gdt.tss.length = 104;
+	gdtp.limit = sizeof(gdt) - 1;
-	gdt.tss.baseLow = 0;
-	gdt.tss.baseMid = 0;
-	gdt.tss.flags1 = 0x89;
-	gdt.tss.flags2 = 0;
-	gdt.tss.baseHigh = 0;
-
-	gdtp.limit = sizeof(struct gdt_entries) - 1;
 	gdtp.base = (uint32_t)&gdt;
 
 	gdt_reload();
+	tss_reload();
 
-	memset(tssp, 0, sizeof(struct tss_pointer));
-	gdt_loadTss(tssp);
 	return 0;
 }
 

kernel/src/kernel.c

@@ -27,7 +27,6 @@ void kmain(void* ptr, uint32_t magic) {
 	gdt_init();
 	// isr_init();
 	// pag_init();
-	while (1);
 
 	debugf("Basic initialization complete!\n");