Make kernel multiboot compatible
This commit is contained in:
Mathieu Maret
parent
2c251fa51c
commit
c1afe927cb
4
Makefile
4
Makefile
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@ -17,7 +17,7 @@ cobj=$(csrc:%.c=%.o)
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deps = $(csrc:%.c=%.d)
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kernel:$(asmobj) $(cobj) linker.ld
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$(CXX) $(LDFLAGS) $(cobj) $(asmobj) -o $@ -T linker.ld
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$(CC) -m32 -ffreestanding -nostdlib $(cobj) $(asmobj) -o $@ -T linker.ld
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fd.img: kernel
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dd if=/dev/zero of=$@ bs=512 count=2880
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@ -33,7 +33,7 @@ core/irq_handler.o:core/irq_handler.c
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$(AS) $(ASFLAGS) -o $@ $<
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test:kernel
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qemu-system-x86_64 -fda $<
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qemu-system-x86_64 -kernel $<
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clean:
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$(RM) kernel $(asmobj) $(cobj) $(deps)
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@ -0,0 +1,90 @@
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; Declare constants for the multiboot header.
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MBALIGN equ 1 << 0 ; align loaded modules on page boundaries
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MEMINFO equ 1 << 1 ; provide memory map
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FLAGS equ MBALIGN | MEMINFO ; this is the Multiboot 'flag' field
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MAGIC equ 0x1BADB002 ; 'magic number' lets bootloader find the header
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CHECKSUM equ -(MAGIC + FLAGS) ; checksum of above, to prove we are multiboot
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; Declare a multiboot header that marks the program as a kernel. These are magic
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; values that are documented in the multiboot standard. The bootloader will
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; search for this signature in the first 8 KiB of the kernel file, aligned at a
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; 32-bit boundary. The signature is in its own section so the header can be
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; forced to be within the first 8 KiB of the kernel file.
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section .multiboot
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align 4
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dd MAGIC
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dd FLAGS
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dd CHECKSUM
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; The multiboot standard does not define the value of the stack pointer register
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; (esp) and it is up to the kernel to provide a stack. This allocates room for a
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; small stack by creating a symbol at the bottom of it, then allocating 16384
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; bytes for it, and finally creating a symbol at the top. The stack grows
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; downwards on x86. The stack is in its own section so it can be marked nobits,
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; which means the kernel file is smaller because it does not contain an
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; uninitialized stack. The stack on x86 must be 16-byte aligned according to the
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; System V ABI standard and de-facto extensions. The compiler will assume the
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; stack is properly aligned and failure to align the stack will result in
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; undefined behavior.
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section .bss
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align 16
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stack_bottom:
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resb 16384 ; 16 KiB
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stack_top:
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; The linker script specifies _start as the entry point to the kernel and the
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; bootloader will jump to this position once the kernel has been loaded. It
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; doesn't make sense to return from this function as the bootloader is gone.
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; Declare _start as a function symbol with the given symbol size.
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section .text
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global _start:function (_start.end - _start)
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_start:
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; The bootloader has loaded us into 32-bit protected mode on a x86
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; machine. Interrupts are disabled. Paging is disabled. The processor
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; state is as defined in the multiboot standard. The kernel has full
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; control of the CPU. The kernel can only make use of hardware features
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; and any code it provides as part of itself. There's no printf
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; function, unless the kernel provides its own <stdio.h> header and a
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; printf implementation. There are no security restrictions, no
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; safeguards, no debugging mechanisms, only what the kernel provides
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; itself. It has absolute and complete power over the
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; machine.
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; To set up a stack, we set the esp register to point to the top of our
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; stack (as it grows downwards on x86 systems). This is necessarily done
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; in assembly as languages such as C cannot function without a stack.
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mov esp, stack_top
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; This is a good place to initialize crucial processor state before the
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; high-level kernel is entered. It's best to minimize the early
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; environment where crucial features are offline. Note that the
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; processor is not fully initialized yet: Features such as floating
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; point instructions and instruction set extensions are not initialized
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; yet. The GDT should be loaded here. Paging should be enabled here.
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; C++ features such as global constructors and exceptions will require
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; runtime support to work as well.
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; Enter the high-level kernel. The ABI requires the stack is 16-byte
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; aligned at the time of the call instruction (which afterwards pushes
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; the return pointer of size 4 bytes). The stack was originally 16-byte
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; aligned above and we've since pushed a multiple of 16 bytes to the
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; stack since (pushed 0 bytes so far) and the alignment is thus
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; preserved and the call is well defined.
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; note, that if you are building on Windows, C functions may have "_" prefix in assembly: _kernel_main
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extern kmain
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call kmain
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; If the system has nothing more to do, put the computer into an
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; infinite loop. To do that:
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; 1) Disable interrupts with cli (clear interrupt enable in eflags).
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; They are already disabled by the bootloader, so this is not needed.
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; Mind that you might later enable interrupts and return from
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; kernel_main (which is sort of nonsensical to do).
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; 2) Wait for the next interrupt to arrive with hlt (halt instruction).
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; Since they are disabled, this will lock up the computer.
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; 3) Jump to the hlt instruction if it ever wakes up due to a
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; non-maskable interrupt occurring or due to system management mode.
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cli
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.hang: hlt
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jmp .hang
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.end:
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@ -0,0 +1,109 @@
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/* Declare constants for the multiboot header. */
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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 of above, to prove we are multiboot */
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/*
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Declare a multiboot header that marks the program as a kernel. These are magic
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values that are documented in the multiboot standard. The bootloader will
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search for this signature in the first 8 KiB of the kernel file, aligned at a
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32-bit boundary. The signature is in its own section so the header can be
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forced to be within the first 8 KiB of the kernel file.
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*/
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.section .multiboot
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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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/*
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The multiboot standard does not define the value of the stack pointer register
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(esp) and it is up to the kernel to provide a stack. This allocates room for a
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small stack by creating a symbol at the bottom of it, then allocating 16384
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bytes for it, and finally creating a symbol at the top. The stack grows
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downwards on x86. The stack is in its own section so it can be marked nobits,
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which means the kernel file is smaller because it does not contain an
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uninitialized stack. The stack on x86 must be 16-byte aligned according to the
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System V ABI standard and de-facto extensions. The compiler will assume the
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stack is properly aligned and failure to align the stack will result in
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undefined behavior.
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*/
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.section .bss
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.align 16
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stack_bottom:
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.skip 16384 # 16 KiB
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stack_top:
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/*
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The linker script specifies _start as the entry point to the kernel and the
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bootloader will jump to this position once the kernel has been loaded. It
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doesn't make sense to return from this function as the bootloader is gone.
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*/
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.section .text
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.global _start
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.type _start, @function
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_start:
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/*
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The bootloader has loaded us into 32-bit protected mode on a x86
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machine. Interrupts are disabled. Paging is disabled. The processor
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state is as defined in the multiboot standard. The kernel has full
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control of the CPU. The kernel can only make use of hardware features
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and any code it provides as part of itself. There's no printf
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function, unless the kernel provides its own <stdio.h> header and a
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printf implementation. There are no security restrictions, no
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safeguards, no debugging mechanisms, only what the kernel provides
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itself. It has absolute and complete power over the
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machine.
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*/
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/*
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To set up a stack, we set the esp register to point to the top of our
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stack (as it grows downwards on x86 systems). This is necessarily done
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in assembly as languages such as C cannot function without a stack.
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*/
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mov $stack_top, %esp
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/*
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This is a good place to initialize crucial processor state before the
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high-level kernel is entered. It's best to minimize the early
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environment where crucial features are offline. Note that the
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processor is not fully initialized yet: Features such as floating
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point instructions and instruction set extensions are not initialized
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yet. The GDT should be loaded here. Paging should be enabled here.
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C++ features such as global constructors and exceptions will require
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runtime support to work as well.
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*/
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/*
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Enter the high-level kernel. The ABI requires the stack is 16-byte
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aligned at the time of the call instruction (which afterwards pushes
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the return pointer of size 4 bytes). The stack was originally 16-byte
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aligned above and we've since pushed a multiple of 16 bytes to the
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stack since (pushed 0 bytes so far) and the alignment is thus
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preserved and the call is well defined.
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*/
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call kmain
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/*
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If the system has nothing more to do, put the computer into an
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infinite loop. To do that:
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1) Disable interrupts with cli (clear interrupt enable in eflags).
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They are already disabled by the bootloader, so this is not needed.
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Mind that you might later enable interrupts and return from
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kernel_main (which is sort of nonsensical to do).
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2) Wait for the next interrupt to arrive with hlt (halt instruction).
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Since they are disabled, this will lock up the computer.
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3) Jump to the hlt instruction if it ever wakes up due to a
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non-maskable interrupt occurring or due to system management mode.
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*/
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cli
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1: hlt
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jmp 1b
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/*
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Set the size of the _start symbol to the current location '.' minus its start.
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This is useful when debugging or when you implement call tracing.
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*/
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.size _start, . - _start
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37
linker.ld
37
linker.ld
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@ -1,26 +1,43 @@
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ENTRY(boot)
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OUTPUT_FORMAT("binary")
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SECTIONS {
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. = 0x7c00;
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.text :
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/* The bootloader will look at this image and start execution at the symbol
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designated as the entry point. */
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ENTRY(_start)
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/* Tell where the various sections of the object files will be put in the final
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kernel image. */
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SECTIONS
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{
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/* Begin putting sections at 1 MiB, a conventional place for kernels to be
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loaded at by the bootloader. */
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. = 1M;
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/* First put the multiboot header, as it is required to be put very early
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early in the image or the bootloader won't recognize the file format.
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Next we'll put the .text section. */
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.text BLOCK(4K) : ALIGN(4K)
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{
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*(.boot)
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*(.multiboot)
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*(.text)
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}
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.rodata :
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/* Read-only data. */
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.rodata BLOCK(4K) : ALIGN(4K)
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{
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*(.rodata)
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}
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.data :
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/* Read-write data (initialized) */
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.data BLOCK(4K) : ALIGN(4K)
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{
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*(.data)
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}
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.bss :
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/* Read-write data (uninitialized) and stack */
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.bss BLOCK(4K) : ALIGN(4K)
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{
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*(COMMON)
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*(.bss)
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}
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}
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/* The compiler may produce other sections, by default it will put them in
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a segment with the same name. Simply add stuff here as needed. */
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}
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161
mbr.asm
161
mbr.asm
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@ -1,161 +0,0 @@
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section .boot
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bits 16
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global boot
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boot:
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jmp main
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display_enable:
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push bp
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mov bp, sp
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mov ah, 0h ; 00h Set Video Mode
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mov al, 07h ; Txt, monochrome, 80x25
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int 10h
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mov sp, bp
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pop bp
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ret
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print:
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push bp
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mov bp, sp
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mov si, [bp + 4]; put first function arg in si. sp is stask pointer
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.loop:
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lodsb ; load si content into al then inc si
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cmp al, 0;
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je .end
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mov ah, 0eh
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mov bx, 0
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int 10h
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jmp .loop
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.end:
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mov sp, bp
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pop bp
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ret
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println:
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push bp
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mov bp, sp
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push word [bp + 4]
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call print
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add sp, 2
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mov ah, 03h ; read cursor position
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int 10h ; row number in dh. Col in dl
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inc dh ; goto next line
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mov dl, 0
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mov ah, 02h ; Set Cursor Position
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int 10h
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mov sp, bp
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pop bp
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ret
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hello db 'Booting matOs', 0
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main:
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sti ; enable virtual interupts
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mov [disk],dl ; save disk used to boot by bios
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call display_enable
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push hello
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call println
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add sp, 2
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; Switch in 32bits Protected mode
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; Activate A20 http://wiki.osdev.org/A20_Line to be able to access more than 1Mb memory
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mov ah, 0h
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mov ax, 0x2401
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int 0x15
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; Change video mode to display VGA
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mov ax, 0x3
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int 0x10
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; http://www.ctyme.com/intr/rb-0607.htm
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; Bios read first 512 bytes, read next disk sector
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mov ah, 0x2 ;read sectors
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mov al, 15 ;sectors to read
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mov ch, 0 ;cylinder idx
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mov dh, 0 ;head idx
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mov cl, 2 ;sector idx
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mov dl, [disk] ;disk idx
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mov bx, copy_target;target pointer
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int 0x13
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cli ; disable interruption when setting GDT
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; switch in 32 bits
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lgdt [gdt_pointer] ; switch in 32bits here
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mov eax, cr0
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or eax,0x1; set the protected mode bit on special CPU reg cr0
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mov cr0, eax
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jmp CODE_SEG:boot2 ; In protected mode we need to add the segment selector
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; GDT table desciption could be found http://wiki.osdev.org/Global_Descriptor_Table
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; here we define the 3 64bits segment needed: null segment, code segment and data segment
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gdt_start: ;null segment
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dq 0x0
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gdt_code: ;code segment
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dw 0xFFFF ; limit [0:15]
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dw 0x0 ; base [0:15]
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db 0x0 ; base [16:23]
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db 10011010b ; access byte: Present(1)| Priv(2) 0 ->kernel 3->userspace | 1 | Executable(1) | Direction/Conformity (1) | RW(1) | Accessed(1)
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db 11001111b ; Granularity(1) | Size (1) 0-> 16bit mode 1->32protected mode | 0 | 0 | Limit [16:19]
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db 0x0 ; base [24:31]
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gdt_data:
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dw 0xFFFF
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dw 0x0
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db 0x0
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db 10010010b
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db 11001111b
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db 0x0
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gdt_end:
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gdt_pointer:
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dw gdt_end - gdt_start
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dd gdt_start
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disk:
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db 0x0
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CODE_SEG equ gdt_code - gdt_start
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DATA_SEG equ gdt_data - gdt_start
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times 510 - ($-$$) db 0
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dw 0xaa55
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copy_target:
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bits 32
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boot2:
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mov ax, DATA_SEG ; set all segments to point to DATA_SEG https://en.wikipedia.org/wiki/X86_memory_segmentation
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mov ds, ax ; Data segment
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mov es, ax ; Extra Segment (for string operation)
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mov fs, ax ; No Specific use
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mov gs, ax ; No Specific use
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mov ss, ax ; stack segment
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mov esi,hello32
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mov ebx,0xb8000 ; Cannot use BIOS anymore, use VGA Text buffer instead
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.loop32:
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lodsb
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or al,al
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jz halt
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or eax,0x0100 ; blue bg
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mov word [ebx], ax
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add ebx,2
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jmp .loop32
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halt:
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mov esp,kernel_stack_top
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extern kmain
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call kmain
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cli
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hlt
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hello32: db "Hello 32 bits world!",0
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section .bss
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align 4
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kernel_stack_bottom: equ $
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resb 16384 ; 16 KB
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kernel_stack_top:
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