diff options
Diffstat (limited to 'boot.s')
| -rw-r--r-- | boot.s | 93 |
1 files changed, 0 insertions, 93 deletions
@@ -1,93 +0,0 @@ -/* - Declare a multiboot header that marks the program as a kernel. - https://www.gnu.org/software/grub/manual/multiboot2/html_node/index.html - - The Multiboot2 header must be contained completely within the first - 32kB of the OS image, and must be 64-bit (8 byte) aligned. -*/ -.set MULTIBOOT_HEADER_MAGIC, 0xe85250d6 # multiboot2 magic number -.set MULTIBOOT_ARCHITECTURE, 0 # protected mode i386 -.set MULTIBOOT_HEADER_TAG_END, 0 - -.section .multiboot -.align 8 -header_start: - .int MULTIBOOT_HEADER_MAGIC - .int MULTIBOOT_ARCHITECTURE - .int header_end - header_start - .int -(MULTIBOOT_HEADER_MAGIC + MULTIBOOT_ARCHITECTURE + (header_end - header_start)) - - # TODO tags go here - - .short MULTIBOOT_HEADER_TAG_END - .short 0 - .int 8 -header_end: - -/* - 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 .stack, "aw", @nobits -.align 16 -stack_bottom: - .skip 16 * 1024 -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. -*/ -.section .text -.global _start -.type _start, @function -_start: - mov $stack_top, %esp # point the stack pointer to the stack - - /* - 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. - */ - - pushl %ebx # push the pointer to the multiboot structure - pushl %eax # push the multiboot magic value - - /* - 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. - */ - call kernel_main - - /* - 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 - -/* -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 |