Kernel: move GDT initialization to boot.S

kernel/arch/i386/GDT.cpp

@@ -1,113 +0,0 @@
-#include <kernel/GDT.h>
-
-#include <stdint.h>
-
-namespace GDT
-{
-
-	union SegmentDesriptor
-	{
-		struct
-		{
-			uint16_t	limit_lo;
-			uint16_t	base_lo;
-			uint8_t		base_hi1;
-
-			uint8_t		type			: 4;
-			uint8_t		system			: 1;
-			uint8_t		DPL				: 2;
-			uint8_t		present			: 1;
-
-			uint8_t		limit_hi		: 4;
-			uint8_t		flags			: 4;
-
-			uint8_t		base_hi2;
-		} __attribute__((packed));
-		
-		struct
-		{
-			uint32_t low;
-			uint32_t high;
-		} __attribute__((packed));
-
-		SegmentDesriptor() : low(0), high(0) {}
-		SegmentDesriptor(uint32_t base, uint32_t limit, uint8_t access, uint8_t _flags)
-			: low(0), high(0)
-		{
-			set_base(base);
-			set_limit(limit);
-
-			high |= ((uint16_t)access) << 8;
-			flags = _flags;
-		}
-
-		void set_base(uint32_t base)
-		{
-			base_lo  =  base        & 0xFFFF;
-			base_hi1 = (base >> 16) & 0x00FF;
-			base_hi2 = (base >> 24) & 0x00FF;
-		}
-
-		void set_limit(uint32_t limit)
-		{
-			limit_lo =  limit        & 0xFFFF;
-			limit_hi = (limit >> 16) & 0x00FF;
-		}
-
-	} __attribute__((packed));
-
-	struct GDTR
-	{
-		uint16_t size;
-		void* address;
-	} __attribute__((packed));
-
-	static GDTR					s_gdtr;
-	static SegmentDesriptor		s_gdt[5];
-
-	extern "C" void load_gdt(void* gdt_ptr);
-	asm(
-	".global load_gdt;"
-	"load_gdt:"
-		"movl 4(%esp),%eax;"
-		"lgdt (%eax);"
-
-		"movw $0x10, %ax;"
-		"movw %ax, %ds;"
-		"movw %ax, %es;"
-		"movw %ax, %fs;"
-		"movw %ax, %gs;"
-		"movw %ax, %ss;"
-		"jmp  $0x08,$flush;"
-
-	"flush:"
-		"ret;"
-	);
-
-	void write_entry_raw(uint8_t segment, uint32_t low, uint32_t high)
-	{
-		uint8_t index = segment >> 3;
-		s_gdt[index].low = low;
-		s_gdt[index].high = high;
-	}
-
-	void write_entry(uint8_t segment, SegmentDesriptor descriptor)
-	{
-		write_entry_raw(segment, descriptor.low, descriptor.high);
-	}
-
-	void initialize()
-	{
-		s_gdtr.address = s_gdt;
-		s_gdtr.size = sizeof(s_gdt) - 1;
-
-		write_entry(0x00, { 0, 0x00000, 0x00, 0x0 }); // null
-		write_entry(0x08, { 0, 0xFFFFF, 0x9A, 0xC }); // kernel code
-		write_entry(0x10, { 0, 0xFFFFF, 0x92, 0xC }); // kernel data
-		write_entry(0x18, { 0, 0xFFFFF, 0xFA, 0xC }); // user code
-		write_entry(0x20, { 0, 0xFFFFF, 0xF2, 0xC }); // user data
-		
-		load_gdt(&s_gdtr);
-	}
-
-}

kernel/arch/i386/boot.S

@@ -29,6 +29,13 @@
 	g_kernel_cmdline:
 		.skip 4096
 
+	.global g_gdtr
+	g_gdtr:
+		.skip 2 + 4
+	.global g_gdt
+	g_gdt:
+		.skip 5 * 8
+
 	# Reserve memory for paging structures,
 	# we will identity map first 4 MiB
 
@@ -110,19 +117,7 @@ enable_sse:
 	movl %eax, %cr4
 	ret
 
-.global _start
+initialize_paging:
-.type _start, @function
-_start:
-	# Initialize stack and multiboot info
-	movl $stack_top, %esp
-	movl %eax, g_multiboot_magic
-	movl %ebx, g_multiboot_info
-
-	# Copy kernel command line to known location
-	call copy_kernel_commandline
-	call check_requirements
-	call enable_sse
-
 	# identity map first 4 MiB
 	movl $(0x00000000           + 0x83), boot_page_directory1 + 0
 	movl $(0x00200000           + 0x83), boot_page_directory1 + 8
@@ -142,14 +137,55 @@ _start:
 	orl $0x80000000, %ecx
 	movl %ecx, %cr0
 
-	# call global constuctors
+	ret
+
+initialize_gdt:
+	# setup gdt
+	movw $(5 * 8 - 1),	g_gdtr
+	movl $(g_gdt),		g_gdtr + 2
+	movl $(0x0000FFFF), g_gdt + 0x08
+	movl $(0x00CF9A00), g_gdt + 0x08 + 4
+	movl $(0x0000FFFF), g_gdt + 0x10
+	movl $(0x00CF9200), g_gdt + 0x10 + 4
+	movl $(0x0000FFFF), g_gdt + 0x18
+	movl $(0x00CFFA00), g_gdt + 0x18 + 4
+	movl $(0x0000FFFF), g_gdt + 0x20
+	movl $(0x00CFF200), g_gdt + 0x20 + 4
+	lgdt g_gdtr
+
+	# flush gdt
+	movw $0x10, %ax
+	movw %ax, %ds
+	movw %ax, %es
+	movw %ax, %fs
+	movw %ax, %gs
+	movw %ax, %ss
+	jmp $0x08, $flush
+flush:
+	ret
+
+
+.global _start
+.type _start, @function
+_start:
+	# Initialize stack and multiboot info
+	movl $stack_top, %esp
+	movl %eax, g_multiboot_magic
+	movl %ebx, g_multiboot_info
+
+	call copy_kernel_commandline
+	call check_requirements
+	call enable_sse
+
+	call initialize_paging
+	call initialize_gdt
+
 	call _init
 
 	# call to the kernel itself (clear ebp for stacktrace)
 	xorl %ebp, %ebp
 	call kernel_main
 
-	# call global destructors
 	call _fini
 
 system_halt:

kernel/arch/i386/make.config

@@ -7,7 +7,6 @@ KERNEL_ARCH_OBJS=		\
 $(ARCHDIR)/APIC.o		\
 $(ARCHDIR)/boot.o		\
 $(ARCHDIR)/CPUID.o		\
-$(ARCHDIR)/GDT.o		\
 $(ARCHDIR)/IDT.o		\
 $(ARCHDIR)/MMU.o		\
 $(ARCHDIR)/Panic.o		\

kernel/include/kernel/GDT.h

@@ -1,8 +1,44 @@
 #pragma once
 
+#include <stdint.h>
+
 namespace GDT
 {
 
-	void initialize();
+	union SegmentDesriptor
+	{
+		struct
+		{
+			uint16_t	limit_lo;
+			uint16_t	base_lo;
+			uint8_t		base_hi1;
+
+			uint8_t		type			: 4;
+			uint8_t		system			: 1;
+			uint8_t		DPL				: 2;
+			uint8_t		present			: 1;
+
+			uint8_t		limit_hi		: 4;
+			uint8_t		flags			: 4;
+
+			uint8_t		base_hi2;
+		} __attribute__((packed));
+		
+		struct
+		{
+			uint32_t low;
+			uint32_t high;
+		} __attribute__((packed));
+
+	} __attribute__((packed));
+
+	struct GDTR
+	{
+		uint16_t size;
+		void* address;
+	} __attribute__((packed));
+
+	extern "C" GDTR g_gdtr[];
+	extern "C" SegmentDesriptor g_gdt[];
 
 }

kernel/kernel/kernel.cpp

@@ -70,8 +70,6 @@ extern "C" void kernel_main()
 	kmalloc_initialize();
 	dprintln("kmalloc initialized");
 
-	GDT::initialize();
-	dprintln("GDT initialized");
 	IDT::initialize();
 	dprintln("IDT initialized");