2022-04-25 19:16:07 +00:00
|
|
|
|
/* Declare constants for the multiboot header */
|
|
|
|
|
.set ALIGN, 1<<0 /* align loaded modules on page boundaries */
|
|
|
|
|
.set MEMINFO, 1<<1 /* provide memory map */
|
|
|
|
|
.set VIDEO, 1<<2 /* enable graphics framebuffer */
|
|
|
|
|
.set FLAGS, ALIGN | MEMINFO | VIDEO /* 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 */
|
|
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
These are not used, but are needed for padding since we enable video and we
|
|
|
|
|
are interested in the graphics field of the multiboot header.
|
|
|
|
|
*/
|
|
|
|
|
.set HEADER_ADDR, 0x0
|
|
|
|
|
.set LOAD_ADDR, 0x0
|
|
|
|
|
.set LOAD_END_ADDR, 0x0
|
|
|
|
|
.set BSS_END_ADDR, 0x0
|
|
|
|
|
.set ENTRY_ADDR, 0x0
|
|
|
|
|
|
|
|
|
|
/* Graphics field of the multiboot header */
|
|
|
|
|
.set MODE_TYPE, 0x0 /* Contains ‘0’ for linear graphics mode or ‘1’ for EGA-standard text mode */
|
|
|
|
|
.set WIDTH, 0x0 /* Contains the number of the columns */
|
|
|
|
|
.set HEIGHT, 0x0 /* Contains the number of the lines */
|
|
|
|
|
.set DEPTH, 0x0 /* Contains the number of bits per pixel in a graphics mode, and zero in a text mode */
|
|
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
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
|
2022-05-02 14:26:07 +00:00
|
|
|
|
.code32
|
2022-04-25 19:16:07 +00:00
|
|
|
|
.align 4
|
|
|
|
|
.long MAGIC
|
|
|
|
|
.long FLAGS
|
|
|
|
|
.long CHECKSUM
|
|
|
|
|
.long HEADER_ADDR
|
|
|
|
|
.long LOAD_ADDR
|
|
|
|
|
.long LOAD_END_ADDR
|
|
|
|
|
.long BSS_END_ADDR
|
|
|
|
|
.long ENTRY_ADDR
|
|
|
|
|
.long MODE_TYPE
|
|
|
|
|
.long WIDTH
|
|
|
|
|
.long HEIGHT
|
|
|
|
|
.long DEPTH
|
|
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
The multiboot header layout is as follows:
|
|
|
|
|
Offset Type Field Name Note
|
|
|
|
|
0 u32 magic required
|
|
|
|
|
4 u32 flags required
|
|
|
|
|
8 u32 checksum required
|
|
|
|
|
12 u32 header_addr if flags[16] is set
|
|
|
|
|
16 u32 load_addr if flags[16] is set
|
|
|
|
|
20 u32 load_end_addr if flags[16] is set
|
|
|
|
|
24 u32 bss_end_addr if flags[16] is set
|
|
|
|
|
28 u32 entry_addr if flags[16] is set
|
|
|
|
|
32 u32 mode_type if flags[2] is set
|
|
|
|
|
36 u32 width if flags[2] is set
|
|
|
|
|
40 u32 height if flags[2] is set
|
|
|
|
|
44 u32 depth if flags[2] is set
|
|
|
|
|
*/
|
|
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
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, the 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 no 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.
|
|
|
|
|
*/
|
2022-05-02 14:26:07 +00:00
|
|
|
|
|
|
|
|
|
/* 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
|
|
|
|
|
|
2022-04-25 19:16:07 +00:00
|
|
|
|
.section .bss
|
2022-05-02 14:26:07 +00:00
|
|
|
|
/* 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
|
2022-04-25 19:16:07 +00:00
|
|
|
|
stack_bottom:
|
2022-05-02 14:26:07 +00:00
|
|
|
|
.skip 4096 * 4
|
2022-04-25 19:16:07 +00:00
|
|
|
|
stack_top:
|
|
|
|
|
|
2022-05-02 14:26:07 +00:00
|
|
|
|
.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
|
|
|
|
|
|
2022-04-25 19:16:07 +00:00
|
|
|
|
/*
|
|
|
|
|
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
|
2022-05-02 14:26:07 +00:00
|
|
|
|
.code32
|
2022-04-25 19:16:07 +00:00
|
|
|
|
.global _start
|
2022-05-02 14:26:07 +00:00
|
|
|
|
.extern long_mode_start
|
2022-04-25 19:16:07 +00:00
|
|
|
|
.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
|
|
|
|
|
safeguard, no debugging mechanisms, only what the kernel provides
|
|
|
|
|
itself. It has absolute and comlete power over the machine.
|
|
|
|
|
*/
|
|
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
To set up a stack, we set the esp register to point to the top of the
|
|
|
|
|
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 pushed a multiple of 16 bytes to the stack
|
|
|
|
|
since (pushed 0 bytes so far), so the alignment has thus been
|
|
|
|
|
preserved and the call is well defined.
|
|
|
|
|
*/
|
2022-05-02 14:26:07 +00:00
|
|
|
|
call setup_page_tables
|
|
|
|
|
call setup_framebuffer_page_tables
|
|
|
|
|
call enable_paging
|
|
|
|
|
|
|
|
|
|
lgdt (gdt64_pointer)
|
|
|
|
|
ljmp $gdt64_code_segment, $long_mode_start
|
2022-04-25 19:16:07 +00:00
|
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
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
|
2022-05-02 14:26:07 +00:00
|
|
|
|
|
|
|
|
|
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
|