diff options
Diffstat (limited to 'kernel/boot/init/boot.s')
| -rw-r--r-- | kernel/boot/init/boot.s | 144 |
1 files changed, 72 insertions, 72 deletions
diff --git a/kernel/boot/init/boot.s b/kernel/boot/init/boot.s index 001e254..c9c6dd5 100644 --- a/kernel/boot/init/boot.s +++ b/kernel/boot/init/boot.s @@ -1,20 +1,20 @@ /* -* CMOS -* Copyright (C) 2024 Raghuram Subramani <raghus2247@gmail.com> -* -* This program is free software: you can redistribute it and/or modify -* it under the terms of the GNU General Public License as published by -* the Free Software Foundation, either version 3 of the License, or -* (at your option) any later version. -* -* This program is distributed in the hope that it will be useful, -* but WITHOUT ANY WARRANTY; without even the implied warranty of -* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the -* GNU General Public License for more details. -* -* You should have received a copy of the GNU General Public License -* along with this program. If not, see <http://www.gnu.org/licenses/>. -*/ + * CMOS + * Copyright (C) 2024 Raghuram Subramani <raghus2247@gmail.com> + * + * This program is free software: you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation, either version 3 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program. If not, see <http://www.gnu.org/licenses/>. + */ /* Adapted from https://wiki.osdev.org/Bare_Bones */ @@ -65,70 +65,70 @@ stack_top: .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. - */ + /* + 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. - */ - movl $stack_top, %esp + /* + 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. + */ + movl $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. - */ + /* + 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. + */ - /* TODO: Initialize global descriptor table */ + /* TODO: Initialize global descriptor table */ - /* Call the global constructors. */ - call _init + /* Call the global constructors. */ + call _init - /* - 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 + /* + 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 - jmp quit + /* + 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 + jmp quit quit: - hlt - jmp quit + hlt + jmp quit /* Set the size of the _start symbol to the current location '.' minus its start. |