x86: begin preparations for amd64 support
This is a huge commit, but it mainly just moves some files around and doesn't change their contents much. A lot of stuff works the same on amd64 as it does on i386, so i'm moving the parts that are specific to the latter into separate subdirectories while the rest can be shared with the amd64 codebase.main
parent
4e770a6e58
commit
3fee893f21
GPG Key ID:
EC22E476DC2D3D84
@ -0,0 +1,219 @@
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/* See the end of this file for copyright and license terms. */
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#include <asm/common.h>
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#include <arch/page.h>
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#include <arch/vmparam.h>
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#include <gay/config.h>
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/*
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* Early boot sequence on amd64.
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*
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* This is based on the example code from the OSDev.org wiki:
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* <https://wiki.osdev.org/Higher_Half_x86_Bare_Bones>
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*
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* We basically just turn on paging and map the lower 4 MB (including the VGA
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* console framebuffer) to 0xf0000000 where the kernel image itself is linked
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* to, and then jump to that region and set up the stack. Form there, _boot()
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* takes care of everything.
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*
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* We need to pay special attention to not touch eax and ebx during the entire
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* routine, because those store the multiboot2 magic number and tag table
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* pointer respectively which need to be passed on to _boot(). We can't push
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* them on the stack, because the stack doesn't exist yet.
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*/
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.extern _image_start_phys
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.extern _image_end_phys
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.extern _boot /* main boot routine -- see ./boot.c */
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.extern pd0 /* initial page directory -- see ../mm/page.c */
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.extern pt0 /* first page table -- see ../mm/page.c */
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.section .multiboot.text, "ax", @progbits
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/*
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* referencing symbols from C requires subtracting the relocation offset
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* first because the C code is linked against virtual address space
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*/
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#define phys_addr(c_symbol) (c_symbol - KERN_OFFSET)
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ASM_ENTRY(_setup)
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cli
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/*
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* The kernel image starts at 1 MiB into physical memory.
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* We currently assume the kernel is < 3 MiB
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* and therefore can be mapped within a single page table.
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* As the kernel gets more and more bloated, this might not be the case
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* in the future anymore, so we should ideally add support for multiple
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* page tables soon.
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*/
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mov $phys_addr(pt0), %edi
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xor %esi, %esi
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/*
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* GRUB stores the multiboot tags right after the kernel image (afaik).
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* The previous streategy was to stop the loop after having reached the
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* end of the kernel image (including bss), and keep our fingers crossed
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* that the multiboot tags all fit into the space between the end of the
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* kernel image and the end of that last page so it's still mapped.
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* Now, we just continue mapping until we have reached the last slot in
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* the page table and exit the loop only then (the last slot is for the
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* BIOS character framebuffer, see below).
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*/
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mov $1023, %ecx
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1: cmp $_image_start_phys, %esi
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jl 2f /* don't map pages below the start of the kernel image */
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mov %esi, %edx
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or $0x003, %edx /* set present and rw flags, see below */
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mov %edx, (%edi)
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2: add $PAGE_SIZE, %esi /* advance to next physical page address */
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add $4, %edi /* advance to next pointer in the page table */
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loop 1b
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/*
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* Conveniently, the full VGA character framebuffer fits into one page
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* and even starts at a page aligned address. The physical range
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* 0x000b8000 - 0x000b8fff
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* gets mapped to the virtual address range
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* 0xf03ff000 - 0xf03fffff
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* which is the last page of our 4 MiB page table (index 1023).
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* We also set the Present and RW bits by OR'ing with 0x003.
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*/
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movl $(0x000b8000 | 0x003), (%edi)
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/*
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* We are mapping the lowest 4 MiB of physical memory both to itself and
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* to the relocated region. Thus, the physical address range:
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* 0x00000000 - 0x003fffff
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* becomes available at two virtual address ranges:
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* 0x00000000 - 0x003fffff (identity mapping)
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* 0xf0000000 - 0xf03fffff (highmem mapping)
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*
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* The identity mapping is necessary because when we turn on paging in
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* the next lines, the program counter still refers to physical memory
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* and would thus immediately cause a page fault.
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*
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* The address of pt0 is OR'd with 0x003 (we actually have to add here
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* because of dumb compiler stuff but that doesn't matter because the
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* result is the same) to set the Present and RW flags in the page table
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* entry (the lower 12 bits in page table addresses are always zero
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* because they are page aligned so they are used as flags for the MMU,
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* see ../include/arch/page.h).
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*
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* The offset added to pd0 is the page table number multiplied with the
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* size of a page directory entry (4 bytes). The page table number can
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* be calculated by dividing the number of the first page it maps
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* through the total number of entries in the page directory.
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*/
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movl $(phys_addr(pt0) + 0x003), phys_addr(pd0) + (( 0x00000000 / PAGE_SIZE) / 1024) * 4
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movl $(phys_addr(pt0) + 0x003), phys_addr(pd0) + ((KERN_OFFSET / PAGE_SIZE) / 1024) * 4
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/*
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* The last entry in the page directory points to itself.
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* This has the effect of mapping all page tables in the page directory to
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* 0xffc00000 - 0xffffefff
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* and the page directory itself to
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* 0xfffff000 - 0xffffffff
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* because the page directory is being interpreted as a page table.
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* This allows us to manipulate the table while we are in virtual memory.
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*/
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movl $(phys_addr(pd0) + 0x003), phys_addr(pd0) + 1023 * 4 /* 0xffc00000 */
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/* set the Page Size Extensions bit in cr4 */
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mov %cr4, %ecx
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or $0x00000010, %ecx
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mov %ecx, %cr4
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/* put the (physical) address of pd0 into cr3 so it will be used */
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mov $phys_addr(pd0), %ecx
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mov %ecx, %cr3
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/* set the paging and write-protect bit in cr0 */
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mov %cr0, %ecx
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or $0x80010000, %ecx
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mov %ecx, %cr0
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/*
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* Alright, we are in virtual address space! But %eip still points to
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* low memory (making use of the identity mapping), so we are going to
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* do an absolute jump to the mapped kernel code somewhere at 0xf01*****.
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*/
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lea _setup_highmem, %ecx
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jmp *%ecx
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/*
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* this is just because you can't span functions across multiple sections,
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* the actual code flow makes a jump from low (.multiboot.text section)
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* to high memory (.text section).
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*/
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ASM_END(_setup)
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.text
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.extern x86_replace_gdt
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.extern x86_load_idt
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ASM_ENTRY(_setup_highmem)
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/*
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* Now that we've completely transitioned to high memory, we can remove
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* the identity mapping because we don't need it anymore.
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*/
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movl $0, pd0 + 0 * 4
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/* bonk the TLB by reloading cr3 to apply the updated page table */
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mov %cr3, %ecx
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mov %ecx, %cr3
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/* set up the initial stack frame */
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mov $stack_top, %ebp
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mov %ebp, %esp
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/* reset EFLAGS */
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pushl $0
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popf
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/* these are set by GRUB, see the comment at the beginning of _start */
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/* parameter 2 for _boot() is header address */
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push %ebx
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/* parameter 1 for _boot() is MB2_BOOTLOADER_MAGIC */
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push %eax
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/*
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* but before we call _boot(), we replace the GDT provided by GRUB
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* with our own (arch/mm/segment.S) and load the IDT (arch/sys/idt.S).
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*/
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call x86_replace_gdt
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call _boot
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/* this should never(TM) be reached */
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cli
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3: hlt
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jmp 3b
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ASM_END(_setup_highmem)
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.section .bootstrap_stack, "aw", @nobits
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stack_bottom:
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.skip 16384 /* 16 KiB for the stack should be plenty for now */
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stack_top:
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/*
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* This file is part of GayBSD.
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* Copyright (c) 2021 fef <owo@fef.moe>.
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*
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* GayBSD is nonviolent software: you may only use, redistribute, and/or
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* modify it under the terms of the Cooperative Nonviolent Public License
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* (CNPL) as found in the LICENSE file in the source code root directory
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* or at <https://git.pixie.town/thufie/npl-builder>; either version 7
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* of the license, or (at your option) any later version.
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*
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* GayBSD comes with ABSOLUTELY NO WARRANTY, to the extent
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* permitted by applicable law. See the CNPL for details.
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*/
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@ -0,0 +1,33 @@
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/* See the end of this file for copyright and license terms. */
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#pragma once
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#define _ARCH_VMPARAM_H_
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#ifdef __x86_64__
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#include <amd64/vmparam.h>
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#else
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#include <i386/vmparam.h>
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#endif
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#define USER_START ((void *)USER_OFFSET)
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#define USER_END (USER_START + USER_LENGTH)
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#define DMAP_START ((void *)DMAP_OFFSET)
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#define DMAP_END (DMAP_START + DMAP_LENGTH)
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#define KERN_START ((void *)KERN_OFFSET)
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#define KERN_END (KERN_START + KERN_LENGTH)
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/*
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* This file is part of GayBSD.
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* Copyright (c) 2021 fef <owo@fef.moe>.
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*
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* GayBSD is nonviolent software: you may only use, redistribute, and/or
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* modify it under the terms of the Cooperative Nonviolent Public License
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* (CNPL) as found in the LICENSE file in the source code root directory
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* or at <https://git.pixie.town/thufie/npl-builder>; either version 7
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* of the license, or (at your option) any later version.
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*
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* GayBSD comes with ABSOLUTELY NO WARRANTY, to the extent
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* permitted by applicable law. See the CNPL for details.
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*/
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@ -0,0 +1,93 @@
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/* See the end of this file for copyright and license terms. */
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#pragma once
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#ifndef _ARCH_PAGE_H_
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#error "This file is not meant to be included directly, use <arch/page.h>"
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#endif
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/** @brief Binary logarithm of `HUGEPAGE_SIZE`. */
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#define HUGEPAGE_SHIFT 22
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#ifndef _ASM_SOURCE
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#include <gay/cdefs.h>
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#include <gay/types.h>
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struct x86_page_table_entry {
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unsigned present:1; /**< Page Fault on access if 0 */
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unsigned rw:1; /**< Page Fault on write if 0 */
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unsigned user:1; /**< Page Fault on user mode access if 0 */
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unsigned write_through:1; /**< Enable write-through caching */
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unsigned cache_disabled:1; /**< Disable caching in TLB */
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unsigned accessed:1; /**< 1 if page has been accessed */
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unsigned dirty:1; /**< 1 if page has been written to */
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unsigned _reserved0:1;
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unsigned global:1; /**< Don't update the TLB on table swap if 1 */
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unsigned _reserved1:3;
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uintptr_t shifted_address:20; /**< Aligned pointer to the physical page */
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} __packed;
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struct x86_page_table {
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struct x86_page_table_entry entries[1024];
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} __aligned(PAGE_SIZE);
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/**
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* @brief Currently active page table at position `index` in the page directory.
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* The last entry in the page directory is mapped to itself, therefore being
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* interpreted by the MMU as a page table. This has the effect that the last
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* page table, i.e. the page directory again, maps the entire page directory
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* structure so it can be manipulated while paging is active. See the comment
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* at the beginning of `arch/x86/mm/page.c` for a more detailed explanation.
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*
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* @param index Table index in the page directory
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*/
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#define X86_CURRENT_PT(index) ( &((struct x86_page_table *)X86_PD_OFFSET)[index] )
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struct x86_page_directory_entry {
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unsigned present:1; /**< Page Fault on access if 0 */
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unsigned rw:1; /**< Page Fault on write if 0 */
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unsigned user:1; /**< Page Fault on user mode access if 0 */
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unsigned write_through:1; /**< Enable write-through caching */
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unsigned cache_disabled:1; /**< Disable caching in TLB */
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unsigned accessed:1; /**< 1 if page has been accessed */
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unsigned _reserved0:1;
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unsigned huge:1; /**< 0 = 4K, 1 = 4M */
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unsigned _reserved1:1;
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unsigned _ignored2:3;
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uintptr_t shifted_address:20; /**< Aligned pointer to `struct x86_page_table` */
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} __packed;
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struct x86_page_directory {
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struct x86_page_directory_entry entries[1024];
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} __aligned(PAGE_SIZE);
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/**
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* @brief Currently active page directory.
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* The last entry in the page directory is mapped to itself, therefore being
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* interpreted by the MMU as a page table. See the comment at the start of
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* `arch/x86/mm/page.c` for a more detailed explanation.
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*/
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#define X86_CURRENT_PD ((struct x86_page_directory *)X86_CURRENT_PT(1023))
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/**
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* @brief Arch dependent virtual memory information data structure (x86 version).
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* Outside of `/arch/x86`, this is treated as a completely obfuscated type,
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* and only pointers to it are stored and passed around.
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*/
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typedef struct x86_page_directory vm_info_t;
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#endif /* not _ASM_SOURCE */
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/*
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* This file is part of GayBSD.
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* Copyright (c) 2021 fef <owo@fef.moe>.
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*
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* GayBSD is nonviolent software: you may only use, redistribute, and/or
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* modify it under the terms of the Cooperative Nonviolent Public License
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* (CNPL) as found in the LICENSE file in the source code root directory
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* or at <https://git.pixie.town/thufie/npl-builder>; either version 7
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* of the license, or (at your option) any later version.
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*
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* GayBSD comes with ABSOLUTELY NO WARRANTY, to the extent
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* permitted by applicable law. See the CNPL for details.
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*/
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@ -0,0 +1,37 @@
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/* See the end of this file for copyright and license terms. */
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#pragma once
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#ifndef _ARCH_VMPARAM_H_
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#error "This file is not meant to be included directly, use <arch/vmparam.h>"
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#endif
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/** @brief Userland memory region */
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#define USER_OFFSET 0x00000000
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#define USER_LENGTH 0x80000000
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/** @brief Direct (contiguous) mapping of physical memory, also used as heap */
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#define DMAP_OFFSET 0x80000000
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/* this gives us ~ 1.7 GB of effectively usable RAM for *everything*, much wow */
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#define DMAP_LENGTH 0x70000000
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/** @brief Kernel image (code + data) */
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#define KERN_OFFSET 0xf0000000
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#define KERN_LENGTH 0x0f000000
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/** @brief Recursive Page Directory map */
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#define X86_PD_OFFSET 0xffc00000
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#define X86_PD_LENGTH 0x00400000
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/*
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* This file is part of GayBSD.
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* Copyright (c) 2021 fef <owo@fef.moe>.
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*
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* GayBSD is nonviolent software: you may only use, redistribute, and/or
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* modify it under the terms of the Cooperative Nonviolent Public License
|
||||
* (CNPL) as found in the LICENSE file in the source code root directory
|
||||
* or at <https://git.pixie.town/thufie/npl-builder>; either version 7
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||||
* of the license, or (at your option) any later version.
|
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*
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* GayBSD comes with ABSOLUTELY NO WARRANTY, to the extent
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* permitted by applicable law. See the CNPL for details.
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*/
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@ -0,0 +1,22 @@
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# See the end of this file for copyright and license terms.
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target_sources(gay_arch PRIVATE
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atom.S
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idt.S
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irq.S
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port.S
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switch.S
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trap.S
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)
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# This file is part of GayBSD.
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# Copyright (c) 2021 fef <owo@fef.moe>.
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#
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# GayBSD is nonviolent software: you may only use, redistribute, and/or
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# modify it under the terms of the Cooperative Nonviolent Public License
|
||||
# (CNPL) as found in the LICENSE file in the source code root directory
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# or at <https://git.pixie.town/thufie/npl-builder>; either version 7
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# of the license, or (at your option) any later version.
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#
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# GayBSD comes with ABSOLUTELY NO WARRANTY, to the extent
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# permitted by applicable law. See the CNPL for details.
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@ -0,0 +1,21 @@
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# Virtual Memory Layout on i386
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GayBSD's virtual memory map is loosely based on the one from FreeBSD.
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The size specifiers here are powers of two (1 KB = 1024 B).
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start address | offset | end address | size | description
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:-------------:|-----------:|:-----------:|-----------:|:-----------------------
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`00000000` | +0 | `7fffffff` | 2 GB | userland area
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`80000000` | -2 GB | `efffffff` | ~ 1.8 GB | linear physical memory
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`f0000000` | ~ -262 MB | `ffbfffff` | ~ 258 MB | kernel image
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`ffc00000` | ~ -12.2 MB | `ffffffff` | ~ 12.2 MB | recursive page table
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The linear physical memory is a direct mapping of physical RAM, which is
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required because `kmalloc()` needs to be able to allocate *physically*
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contiguous memory for DMA transfers.
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It is also used as the heap area.
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Unfortunately, because i don't have the resources to maintain it, the maximum
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supported memory size on i386 is around 1.8 GB.
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This is due to the required direct mapping and would require a fair bit of work
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to get fixed, and 32-bit support is likely to be dropped in the near future.
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