diff options
Diffstat (limited to 'arch/x86/boot/multiboot/multiboot.s')
| -rw-r--r-- | arch/x86/boot/multiboot/multiboot.s | 113 |
1 files changed, 0 insertions, 113 deletions
diff --git a/arch/x86/boot/multiboot/multiboot.s b/arch/x86/boot/multiboot/multiboot.s deleted file mode 100644 index e6e8c21..0000000 --- a/arch/x86/boot/multiboot/multiboot.s +++ /dev/null @@ -1,113 +0,0 @@ -# https://www.gnu.org/software/grub/manual/multiboot/multiboot.html - -.include "bare_multiboot.h" # the file is auto-generated - -/* -Declare constants for the multiboot header. -*/ -.set FLAGS, MULTIBOOT_PAGE_ALIGN | MULTIBOOT_MEMORY_INFO # this is the Multiboot 'flag' field -.set CHECKSUM, -(MULTIBOOT_HEADER_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 MULTIBOOT_HEADER_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 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. - */ - 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 -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 |