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Make kernel multiboot compatible

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This commit is contained in:
Mathieu Maret 2018-07-20 16:41:32 +02:00
parent 2c251fa51c
commit c1afe927cb
5 changed files with 228 additions and 173 deletions
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4
Makefile
View File

@ -17,7 +17,7 @@ cobj=$(csrc:%.c=%.o)
deps = $(csrc:%.c=%.d)
kernel:$(asmobj) $(cobj) linker.ld
$(CXX) $(LDFLAGS) $(cobj) $(asmobj) -o $@ -T linker.ld
$(CC) -m32 -ffreestanding -nostdlib $(cobj) $(asmobj) -o $@ -T linker.ld
fd.img: kernel
dd if=/dev/zero of=$@ bs=512 count=2880
@ -33,7 +33,7 @@ core/irq_handler.o:core/irq_handler.c
$(AS) $(ASFLAGS) -o $@ $<
test:kernel
qemu-system-x86_64 -fda $<
qemu-system-x86_64 -kernel $<
clean:
$(RM) kernel $(asmobj) $(cobj) $(deps)

90
boot.asm Normal file
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@ -0,0 +1,90 @@
; Declare constants for the multiboot header.
MBALIGN equ 1 << 0 ; align loaded modules on page boundaries
MEMINFO equ 1 << 1 ; provide memory map
FLAGS equ MBALIGN | MEMINFO ; this is the Multiboot 'flag' field
MAGIC equ 0x1BADB002 ; 'magic number' lets bootloader find the header
CHECKSUM equ -(MAGIC + FLAGS) ; checksum of above, to prove we are multiboot
; Declare a multiboot header that marks the program as a kernel. These are magic
; values that are documented in the multiboot standard. The bootloader will
; search for this signature in the first 8 KiB of the kernel file, aligned at a
; 32-bit boundary. The signature is in its own section so the header can be
; forced to be within the first 8 KiB of the kernel file.
section .multiboot
align 4
dd MAGIC
dd FLAGS
dd CHECKSUM
; The multiboot standard does not define the value of the stack pointer register
; (esp) and it is up to the kernel to provide a stack. This allocates room for a
; small stack by creating a symbol at the bottom of it, then allocating 16384
; bytes for it, and finally creating a symbol at the top. The stack grows
; downwards on x86. The stack is in its own section so it can be marked nobits,
; which means the kernel file is smaller because it does not contain an
; uninitialized stack. The stack on x86 must be 16-byte aligned according to the
; 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.
section .bss
align 16
stack_bottom:
resb 16384 ; 16 KiB
stack_top:
; 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.
; Declare _start as a function symbol with the given symbol size.
section .text
global _start:function (_start.end - _start)
_start:
; The bootloader has loaded us into 32-bit protected mode on a x86
; machine. Interrupts are disabled. Paging is disabled. The processor
; state is as defined in the multiboot standard. The kernel has full
; control of the CPU. The kernel can only make use of hardware features
; and any code it provides as part of itself. There's no printf
; function, unless the kernel provides its own <stdio.h> header and a
; printf implementation. There are no security restrictions, no
; safeguards, no debugging mechanisms, only what the kernel provides
; itself. It has absolute and complete power over the
; machine.
; To set up a stack, we set the esp register to point to the top of our
; stack (as it grows downwards on x86 systems). This is necessarily done
; in assembly as languages such as C cannot function without a stack.
mov esp, stack_top
; This is a good place to initialize crucial processor state before the
; high-level kernel is entered. It's best to minimize the early
; environment where crucial features are offline. Note that the
; processor is not fully initialized yet: Features such as floating
; point instructions and instruction set extensions are not initialized
; yet. The GDT should be loaded here. Paging should be enabled here.
; C++ features such as global constructors and exceptions will require
; runtime support to work as well.
; Enter the high-level kernel. The ABI requires the stack is 16-byte
; aligned at the time of the call instruction (which afterwards pushes
; the return pointer of size 4 bytes). The stack was originally 16-byte
; aligned above and we've since pushed a multiple of 16 bytes to the
; stack since (pushed 0 bytes so far) and the alignment is thus
; preserved and the call is well defined.
; note, that if you are building on Windows, C functions may have "_" prefix in assembly: _kernel_main
extern kmain
call kmain
; If the system has nothing more to do, put the computer into an
; infinite loop. To do that:
; 1) Disable interrupts with cli (clear interrupt enable in eflags).
; They are already disabled by the bootloader, so this is not needed.
; Mind that you might later enable interrupts and return from
; kernel_main (which is sort of nonsensical to do).
; 2) Wait for the next interrupt to arrive with hlt (halt instruction).
; Since they are disabled, this will lock up the computer.
; 3) Jump to the hlt instruction if it ever wakes up due to a
; non-maskable interrupt occurring or due to system management mode.
cli
.hang: hlt
jmp .hang
.end:

109
boot.s Normal file
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@ -0,0 +1,109 @@
/* Declare constants for the multiboot header. */
.set ALIGN, 1<<0 /* align loaded modules on page boundaries */
.set MEMINFO, 1<<1 /* provide memory map */
.set FLAGS, ALIGN | MEMINFO /* this is the Multiboot 'flag' field */
.set MAGIC, 0x1BADB002 /* 'magic number' lets bootloader find the header */
.set CHECKSUM, -(MAGIC + FLAGS) /* checksum of above, to prove we are multiboot */
/*
Declare a multiboot header that marks the program as a kernel. These are magic
values that are documented in the multiboot standard. The bootloader will
search for this signature in the first 8 KiB of the kernel file, aligned at a
32-bit boundary. The signature is in its own section so the header can be
forced to be within the first 8 KiB of the kernel file.
*/
.section .multiboot
.align 4
.long MAGIC
.long FLAGS
.long CHECKSUM
/*
The multiboot standard does not define the value of the stack pointer register
(esp) and it is up to the kernel to provide a stack. This allocates room for a
small stack by creating a symbol at the bottom of it, then allocating 16384
bytes for it, and finally creating a symbol at the top. The stack grows
downwards on x86. The stack is in its own section so it can be marked nobits,
which means the kernel file is smaller because it does not contain an
uninitialized stack. The stack on x86 must be 16-byte aligned according to the
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.
*/
.section .bss
.align 16
stack_bottom:
.skip 16384 # 16 KiB
stack_top:
/*
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
.global _start
.type _start, @function
_start:
/*
The bootloader has loaded us into 32-bit protected mode on a x86
machine. Interrupts are disabled. Paging is disabled. The processor
state is as defined in the multiboot standard. The kernel has full
control of the CPU. The kernel can only make use of hardware features
and any code it provides as part of itself. There's no printf
function, unless the kernel provides its own <stdio.h> header and a
printf implementation. There are no security restrictions, no
safeguards, no debugging mechanisms, only what the kernel provides
itself. It has absolute and complete power over the
machine.
*/
/*
To set up a stack, we set the esp register to point to the top of our
stack (as it grows downwards on x86 systems). This is necessarily done
in assembly as languages such as C cannot function without a stack.
*/
mov $stack_top, %esp
/*
This is a good place to initialize crucial processor state before the
high-level kernel is entered. It's best to minimize the early
environment where crucial features are offline. Note that the
processor is not fully initialized yet: Features such as floating
point instructions and instruction set extensions are not initialized
yet. The GDT should be loaded here. Paging should be enabled here.
C++ features such as global constructors and exceptions will require
runtime support to work as well.
*/
/*
Enter the high-level kernel. The ABI requires the stack is 16-byte
aligned at the time of the call instruction (which afterwards pushes
the return pointer of size 4 bytes). The stack was originally 16-byte
aligned above and we've since pushed a multiple of 16 bytes to the
stack since (pushed 0 bytes so far) and the alignment is thus
preserved and the call is well defined.
*/
call kmain
/*
If the system has nothing more to do, put the computer into an
infinite loop. To do that:
1) Disable interrupts with cli (clear interrupt enable in eflags).
They are already disabled by the bootloader, so this is not needed.
Mind that you might later enable interrupts and return from
kernel_main (which is sort of nonsensical to do).
2) Wait for the next interrupt to arrive with hlt (halt instruction).
Since they are disabled, this will lock up the computer.
3) Jump to the hlt instruction if it ever wakes up due to a
non-maskable interrupt occurring or due to system management mode.
*/
cli
1: hlt
jmp 1b
/*
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

37
linker.ld
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@ -1,26 +1,43 @@
ENTRY(boot)
OUTPUT_FORMAT("binary")
SECTIONS {
. = 0x7c00;
.text :
/* The bootloader will look at this image and start execution at the symbol
designated as the entry point. */
ENTRY(_start)
/* Tell where the various sections of the object files will be put in the final
kernel image. */
SECTIONS
{
/* Begin putting sections at 1 MiB, a conventional place for kernels to be
loaded at by the bootloader. */
. = 1M;
/* First put the multiboot header, as it is required to be put very early
early in the image or the bootloader won't recognize the file format.
Next we'll put the .text section. */
.text BLOCK(4K) : ALIGN(4K)
{
*(.boot)
*(.multiboot)
*(.text)
}
.rodata :
/* Read-only data. */
.rodata BLOCK(4K) : ALIGN(4K)
{
*(.rodata)
}
.data :
/* Read-write data (initialized) */
.data BLOCK(4K) : ALIGN(4K)
{
*(.data)
}
.bss :
/* Read-write data (uninitialized) and stack */
.bss BLOCK(4K) : ALIGN(4K)
{
*(COMMON)
*(.bss)
}
}
/* The compiler may produce other sections, by default it will put them in
a segment with the same name. Simply add stuff here as needed. */
}

161
mbr.asm
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@ -1,161 +0,0 @@
section .boot
bits 16
global boot
boot:
jmp main
display_enable:
push bp
mov bp, sp
mov ah, 0h ; 00h Set Video Mode
mov al, 07h ; Txt, monochrome, 80x25
int 10h
mov sp, bp
pop bp
ret
print:
push bp
mov bp, sp
mov si, [bp + 4]; put first function arg in si. sp is stask pointer
.loop:
lodsb ; load si content into al then inc si
cmp al, 0;
je .end
mov ah, 0eh
mov bx, 0
int 10h
jmp .loop
.end:
mov sp, bp
pop bp
ret
println:
push bp
mov bp, sp
push word [bp + 4]
call print
add sp, 2
mov ah, 03h ; read cursor position
int 10h ; row number in dh. Col in dl
inc dh ; goto next line
mov dl, 0
mov ah, 02h ; Set Cursor Position
int 10h
mov sp, bp
pop bp
ret
hello db 'Booting matOs', 0
main:
sti ; enable virtual interupts
mov [disk],dl ; save disk used to boot by bios
call display_enable
push hello
call println
add sp, 2
; Switch in 32bits Protected mode
; Activate A20 http://wiki.osdev.org/A20_Line to be able to access more than 1Mb memory
mov ah, 0h
mov ax, 0x2401
int 0x15
; Change video mode to display VGA
mov ax, 0x3
int 0x10
; http://www.ctyme.com/intr/rb-0607.htm
; Bios read first 512 bytes, read next disk sector
mov ah, 0x2 ;read sectors
mov al, 15 ;sectors to read
mov ch, 0 ;cylinder idx
mov dh, 0 ;head idx
mov cl, 2 ;sector idx
mov dl, [disk] ;disk idx
mov bx, copy_target;target pointer
int 0x13
cli ; disable interruption when setting GDT
; switch in 32 bits
lgdt [gdt_pointer] ; switch in 32bits here
mov eax, cr0
or eax,0x1; set the protected mode bit on special CPU reg cr0
mov cr0, eax
jmp CODE_SEG:boot2 ; In protected mode we need to add the segment selector
; GDT table desciption could be found http://wiki.osdev.org/Global_Descriptor_Table
; here we define the 3 64bits segment needed: null segment, code segment and data segment
gdt_start: ;null segment
dq 0x0
gdt_code: ;code segment
dw 0xFFFF ; limit [0:15]
dw 0x0 ; base [0:15]
db 0x0 ; base [16:23]
db 10011010b ; access byte: Present(1)| Priv(2) 0 ->kernel 3->userspace | 1 | Executable(1) | Direction/Conformity (1) | RW(1) | Accessed(1)
db 11001111b ; Granularity(1) | Size (1) 0-> 16bit mode 1->32protected mode | 0 | 0 | Limit [16:19]
db 0x0 ; base [24:31]
gdt_data:
dw 0xFFFF
dw 0x0
db 0x0
db 10010010b
db 11001111b
db 0x0
gdt_end:
gdt_pointer:
dw gdt_end - gdt_start
dd gdt_start
disk:
db 0x0
CODE_SEG equ gdt_code - gdt_start
DATA_SEG equ gdt_data - gdt_start
times 510 - ($-$$) db 0
dw 0xaa55
copy_target:
bits 32
boot2:
mov ax, DATA_SEG ; set all segments to point to DATA_SEG https://en.wikipedia.org/wiki/X86_memory_segmentation
mov ds, ax ; Data segment
mov es, ax ; Extra Segment (for string operation)
mov fs, ax ; No Specific use
mov gs, ax ; No Specific use
mov ss, ax ; stack segment
mov esi,hello32
mov ebx,0xb8000 ; Cannot use BIOS anymore, use VGA Text buffer instead
.loop32:
lodsb
or al,al
jz halt
or eax,0x0100 ; blue bg
mov word [ebx], ax
add ebx,2
jmp .loop32
halt:
mov esp,kernel_stack_top
extern kmain
call kmain
cli
hlt
hello32: db "Hello 32 bits world!",0
section .bss
align 4
kernel_stack_bottom: equ $
resb 16384 ; 16 KB
kernel_stack_top: