arch/i386: Boot to kernel main() with proper initial segmentation/paging setup
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@ -18,39 +18,128 @@
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51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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.global start /* making entry point visible to linker */
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#include <arch/segmentation.h>
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/* setting up the Multiboot header - see GRUB docs for details */
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.set ALIGN, 1<<0 /* align loaded modules on page boundaries */
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.set MEMINFO, 1<<1 /* provide memory map */
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.set FLAGS, ALIGN | MEMINFO /* this is the Multiboot 'flag' field */
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.set MAGIC, 0x1BADB002 /* 'magic number' lets bootloader find the header */
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.set CHECKSUM, -(MAGIC + FLAGS) /* checksum required */
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#define KERNEL_START_VIRTUAL 0xc0000000
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#define KERNEL_START_PAGE (KERNEL_START_VIRTUAL >> 22)
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#define virt_to_phys(addr) (addr - KERNEL_START_VIRTUAL)
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#define STACK_SIZE 0x4000 /* 16k */
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/* setup multiboot header */
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#define ALIGN (1<<0) /* align loaded modules on page boundaries */
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#define MEMINFO (1<<1) /* provide memory map */
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#define FLAGS (ALIGN | MEMINFO) /* this is the Multiboot 'flag' field */
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#define MAGIC 0x1BADB002 /* 'magic number' lets bootloader find the header */
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#define CHECKSUM (-(MAGIC + FLAGS)) /* checksum required */
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.align 4
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.long MAGIC
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.long FLAGS
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.long CHECKSUM
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/* reserve initial kernel stack space */
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.set STACKSIZE, 0x4000 /* that is, 16k. */
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.align 32
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.lcomm stack, STACKSIZE /* reserve 16k stack on a doubleword boundary */
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.comm mbd, 4 /* we will use this in i386_main */
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.comm magic, 4 /* we will use this in i386_main */
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/*
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* Kernel entry in assembly for i386 architecture. This handles saving off
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* multiboot information, setting up initial page tables to map the kernel to
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* where it is linked against, ensures segmentation is setup right (large segments
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* over entire address range), and finally jumps to the kernel's main() function
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* in C.
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*/
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.global start
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start:
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movl $(stack + STACKSIZE), %esp /* set up the stack */
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movl %eax, magic /* Multiboot magic number */
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movl %ebx, mbd /* Multiboot data structure */
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movl %eax, virt_to_phys(magic) /* Save off multiboot magic number */
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movl %ebx, virt_to_phys(mbd) /* Save off multiboot data structure */
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call i386_main /* call kernel proper */
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movl $virt_to_phys(init_page_dir), %eax /* load page directory base register */
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movl %eax, %cr3
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cli
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movl %cr4, %eax
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orl $0x00000010, %eax /* set PSE bit for 4mb pages */
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movl %eax, %cr4
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movl %cr0, %eax
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orl $0x80000000, %eax /* set PG bit to enable paging */
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movl %eax, %cr0
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lea paging_enabled, %eax
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jmp *%eax
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paging_enabled:
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movl $0, init_page_dir /* unmap identity mapping and invalidate */
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invlpg 0
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movl $(stack + STACK_SIZE), %esp /* set up the stack */
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/* setup two large kernel segments over entire 4gb address range */
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pushl $initial_gdt /* setup the pointer to the GDT */
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pushw $(INITIAL_GDT_SIZE-1)
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lgdt (%esp)
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addl $6, %esp
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ljmp $SEGMENT_SELECTOR_KERNEL_CS, $gdt_reload /* long jump to set %cs */
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gdt_reload:
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/* reset remaining segment registers */
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movl $SEGMENT_SELECTOR_KERNEL_DS, %eax
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movl %eax, %ds
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movl %eax, %es
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movl %eax, %fs
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movl %eax, %gs
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movl %eax, %ss
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call main /* call kernel proper */
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cli
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hang:
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hlt /* halt machine should kernel return */
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jmp hang
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hlt /* halt machine should kernel return */
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jmp hang
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.globl atags_ptr
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.section .init
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/* Note: if the offsets into the GDT change, they must be updated in arch/segmentation.h */
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.set INITIAL_GDT_SIZE, 8*6
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initial_gdt:
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.long 0x00000000 /* 0x00 intentionally empty */
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.long 0x00000000
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.long 0x00000000 /* 0x08 TODO TSS */
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.long 0x00000000
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.long 0x0000ffff /* 0x10 kernel code segment (%cs) */
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.long 0x00cf9a00
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.long 0x0000ffff /* 0x18 kernel data segment (%ds) */
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.long 0x00cf9200
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.long 0x0000ffff /* 0x20 userspace code segment (%cs) */
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.long 0x00cffa00
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.long 0x0000ffff /* 0x28 userspace data segment (%ds) */
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.long 0x00cff200
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.align 0x1000
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init_page_dir:
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/* This page directory entry identity-maps the first 4MB of the 32-bit physical address space.
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All bits are clear except the following:
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bit 7: PS The kernel page is 4MB.
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bit 1: RW The kernel page is read/write.
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bit 0: P The kernel page is present.
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This entry must be here -- otherwise the kernel will crash immediately after paging is
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enabled because it can't fetch the next instruction! It's ok to unmap this page later. */
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.long 0x00000083
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.rept (KERNEL_START_PAGE - 1)
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.long 0 /* Pages before kernel space. */
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.endr
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/* This page directory entry defines a 4MB page containing the kernel. */
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.long 0x00000083
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.rept (1024 - KERNEL_START_PAGE - 1)
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.long 0 /* Pages after the kernel image. */
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.endr
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/* reserve initial kernel stack space */
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.align 32
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.lcomm stack, STACK_SIZE /* reserve stack space on a doubleword boundary */
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/* place to store multiboot header information */
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.global mbd
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.comm mbd, 4 /* we will use this in i386_main */
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.global magic
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.comm magic, 4 /* we will use this in i386_main */
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/* TODO FIXME remove this - needs fix to dependencies first */
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.global atags_ptr
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atags_ptr:
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.word 0
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.long 0
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