Enter longmode

Makefile

@@ -3,7 +3,7 @@ GCC_VERSION      := 11.2.0
 PREFIX           := ${PWD}/cross
 CROSS_BIN        := ${PREFIX}/bin
 BUILD_DIR        := ./build
-TARGET           := i686-elf
+TARGET           := x86_64-elf
 FONTS            := default8x16.o
 
 BUILD_DIR_ABS := $(abspath $(BUILD_DIR))
@@ -15,8 +15,8 @@ ISO_DIR := $(BUILD_DIR)/iso_dir
 CROSS_AS         := ${TARGET}-as
 CROSS_CC         := ${TARGET}-gcc
 CROSS_LD         := ${TARGET}-ld
-CFLAGS           := "-std=gnu99 -ffreestanding -O2 -Wall -Wextra -I$$PWD/kernel"
+CFLAGS           := "-ggdb -std=gnu99 -ffreestanding -O2 -Wall -Wextra -I$$PWD/kernel -mno-red-zone"
-LDFLAGS          := "-ffreestanding -O2 -nostdlib -lgcc"
+LDFLAGS          := "-ggdb -ffreestanding -O2 -nostdlib -lgcc"
 
 export PATH      := ${CROSS_BIN}:$(PATH)
 

fonts/Makefile

@@ -1,21 +1,24 @@
 OBJECTS_GZ  := $(patsubst %.o, /usr/share/kbd/consolefonts/%.psfu.gz, $(OBJECTS))
 OBJECTS_PSF := $(patsubst %.o, $(BUILD_DIR)/%.psfu, $(OBJECTS))
 SYMS_PREFIX := consolefonts
+OBJCOPY     := x86_64-elf-objcopy
+OBJTARGET   := elf64-x86-64
+BINARY_ARCH := i386:x86-64
 
 .PHONY: all
 all: $(BUILD_DIR)/$(OBJECTS)
 
 $(BUILD_DIR)/%.o: $(OBJECTS_PSF)
-	@objcopy \
+	@$(OBJCOPY) \
-		-O elf32-i386 \
+		-O $(OBJTARGET) \
-		-B i386 \
+		-B $(BINARY_ARCH) \
 		-I binary \
 		$< $@
 	@./gen_srd_file.sh \
 		$<.srd \
 		$< \
 		$(SYMS_PREFIX)
-	@objcopy \
+	@$(OBJCOPY) \
 		--redefine-syms $<.srd \
 		$@
 	@rm $<.srd

kernel/Makefile

@@ -1,5 +1,5 @@
 
-SOURCES_S := boot.s
+SOURCES_S := boot.s boot64.s
 OBJECTS_S := $(patsubst %.s, $(BUILD_DIR)/kernel/%.o, $(SOURCES_S))
 
 SOURCES_C := kernel.c
@@ -12,18 +12,21 @@ LINKER_LD := linker.ld
 all: $(BUILD_DIR)/kernel.bin
 
 $(BUILD_DIR)/kernel.bin: $(OBJECTS_S) $(OBJECTS_C) $(LINKER_LD)
-	@$(CROSS_CC) \
+	@x86_64-elf-ld \
+		-n \
 		-T $(LINKER_LD) \
-		$(LDFLAGS) \
 		$(OBJECTS_C) \
 		$(OBJECTS_S) \
 		$(EXTRA_OBJS) \
 		-o $@
+	@echo "Built $@"
 
 $(BUILD_DIR)/kernel/%.o: %.c $(SOURCES_C)
 	@mkdir -p $(dir $@)
 	@$(CROSS_CC) -c $< -o $@ $(CFLAGS)
+	@echo "Built $@"
 
 $(BUILD_DIR)/kernel/%.o: %.s $(SOURCES_S)
 	@mkdir -p $(dir $@)
 	@$(CROSS_AS) $< -o $@
+	@echo "Built $@"

kernel/boot.s

@@ -30,6 +30,7 @@ search for this signature in the first 8 KiB of the kernel file, aligned at a
 forced to be within the first 8 KiB of the kernel file.
 */
 .section .multiboot
+.code32
 .align 4
 .long MAGIC
 .long FLAGS
@@ -73,19 +74,56 @@ System V ABI standard and de-facto extensions. The compiler will assume the
 stack is properly aligned and failure to align the stack will result in
 undefined behavior.
 */
+
+/* GDT varibles */
+.set GDT_ZERO_ENTRY,         0x0
+.set GDT_EXECUTABLE_FLAG,    1<<43
+.set GDT_CODE_AND_DATA_FLAG, 1<<44
+.set GDT_PRESENT_FLAG,       1<<47
+.set GDT_64_BIT_FLAG,        1<<53
+.set GDT_FLAGS,              GDT_EXECUTABLE_FLAG | GDT_CODE_AND_DATA_FLAG | GDT_PRESENT_FLAG | GDT_64_BIT_FLAG
+
 .section .bss
-.align 16
+/* We will be using hugepages, so we will need only 3 page levels. */
+.align 4096
+page_table_l4:
+.skip 4096
+page_table_l3:
+.skip 4096
+page_table_l2:
+.skip 4096
+page_table_l3_framebuffer:
+.skip 4096
+page_table_l2_framebuffer:
+.skip 4096
 stack_bottom:
-.skip 16384 # 16 KiB
+.skip 4096 * 4
 stack_top:
 
+.section .rodata
+.align 4
+gdt64:
+.quad GDT_ZERO_ENTRY
+.set gdt64_code_segment, . - gdt64
+.quad GDT_FLAGS
+/*
+gdt64_data_entry:
+.set gdt64_data_segment, gdt64_data_entry - gdt64
+.quad (1<<44) | (1<<46) | (1<<41)
+*/
+gdt64_pointer:
+.word . - gdt64 - 1
+.quad gdt64
+
 /*
 The linker script specifies _start as the entry point to the kernel and the
 bootloader will jump to this position once the kernel has been loaded. It
 doesn't make sense to return from this function as the bootloader is gone.
 */
 .section .text
+.code32
 .global _start
+.extern long_mode_start
 .type _start, @function
 _start:
         /*
@@ -126,8 +164,12 @@ _start:
         since (pushed 0 bytes so far), so the alignment has thus been
         preserved and the call is well defined.
         */
-        pushl %ebx /* pass the Multiboot Info struct addr to kernel_main */
+        call setup_page_tables
-        call kernel_main
+        call setup_framebuffer_page_tables
+        call enable_paging
+
+        lgdt (gdt64_pointer)
+        ljmp $gdt64_code_segment, $long_mode_start
 
         /*
         If the system has nothing more to do, put the computer into an
@@ -150,3 +192,92 @@ Set the size of the _start symbol to the current location '.' minus its start.
 This is useful when debugging or when you implement call tracing.
 */
 .size _start, . - _start
+
+setup_page_tables:
+        movl $page_table_l3, %eax
+        orl $0b11, %eax           /* flags are present and writable */
+        movl %eax, page_table_l4 /* set page_table_l4 first entry to point to page_table_l3 */
+
+        /* Same for next level */
+        movl $page_table_l2, %eax
+        orl $0b11, %eax
+        movl %eax, page_table_l3
+
+        /* Huge pages of size 2 MiBs */
+        movl $0, %ecx
+.loop:
+
+        movl $0x200000, %eax
+        mul %ecx
+
+        /* present, writable, hugepage */
+        orl $0b10000011, %eax
+        movl %eax, page_table_l2(, %ecx, 8)
+
+        inc %ecx
+        cmp $512, %ecx
+        jne .loop
+
+        ret
+
+setup_framebuffer_page_tables:
+        /* Get the multiboot struct address */
+        movl %ebx, %edx
+
+        /*
+        Offset to the framebuffer member. framebuffer[31:0] bits
+        */
+        add $88, %edx
+        movl (%edx), %edx
+
+        /* L4 */
+        movl %edx, %ecx
+        shr $30, %ecx
+        and $0b111111111, %ecx
+
+        and $0xC0000000, %edx /* We will start mapping from this address */
+
+        movl $page_table_l2_framebuffer, %eax
+        orl $0b11, %eax
+        movl %eax, page_table_l3(, %ecx, 8)
+
+        /* Huge pages of size 2 MiBs */
+        movl $0, %ecx
+.loop2:
+
+        movl $0x200000, %eax
+        imul %ecx, %eax
+        orl %edx, %eax
+
+        /* present, writable, hugepage */
+        orl $0b10000011, %eax
+        movl %eax, page_table_l2_framebuffer(, %ecx, 8)
+
+        inc %ecx
+        cmp $512, %ecx
+        jne .loop2
+
+        ret
+
+enable_paging:
+        /* pass page table location to CR3 */
+        movl $page_table_l4, %eax
+        movl %eax, %cr3
+
+        /* Enable Physical Address Extension */
+        movl %cr4, %eax
+        orl $(1<<5), %eax
+        mov %eax, %cr4
+
+        /* Enable long mode */
+        mov $0xC0000080, %ecx
+        rdmsr
+        orl $(1<<8), %eax
+        wrmsr
+
+        /* Enable paging */
+        movl %cr0, %eax
+        orl $(1<<31), %eax
+        mov %eax, %cr0
+
+        ret

kernel/boot64.s

@@ -0,0 +1,18 @@
+.global long_mode_start
+.extern kernel_main
+
+.section .text
+.code64
+long_mode_start:
+  movw $0, %ax
+  movw %ax, %ss
+  movw %ax, %ds
+  movw %ax, %es
+  movw %ax, %fs
+  movw %ax, %gs
+
+  /* We should keep the pointer to mb, debug needed */
+  push %rbx /* Multiboot struct pointer */
+  mov %rbx, %rdi
+  call kernel_main
+  hlt

kernel/kernel.c

@@ -6,8 +6,8 @@
 #error "You are not using a cross-compiler, you will most certainly run into trouble"
 #endif
 
-#if !defined (__i386__)
+#if !defined (__x86_64__)
-#error "The kernel needs to be compiled with a ix86-elf compiler"
+#error "The kernel needs to be compiled with a x86_64-elf compiler"
 #endif
 
 /* graphics framebuffer */