diff options
Diffstat (limited to 'src/as')
| -rw-r--r-- | src/as/boot.s | 119 | ||||
| -rw-r--r-- | src/as/paging.s | 20 |
2 files changed, 117 insertions, 22 deletions
diff --git a/src/as/boot.s b/src/as/boot.s index f65cc72..adb24b7 100644 --- a/src/as/boot.s +++ b/src/as/boot.s @@ -1,42 +1,125 @@ -.set ALIGN, 1<<0 -.set MEMINFO, 1<<1 -.set FLAGS, ALIGN | MEMINFO -.set MAGIC, 0x1BADB002 -.set CHECKSUM, -(MAGIC + FLAGS) +# Declare constants for the multiboot header. +.set ALIGN, 1<<0 # align loaded modules on page boundaries +.set MEMINFO, 1<<1 # provide memory map +.set FLAGS, ALIGN | MEMINFO # 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 -.section .multiboot +# Declare a multiboot header that marks the program as a kernel. +.section .multiboot.data, "aw" .align 4 .long MAGIC .long FLAGS .long CHECKSUM -.set CODE_SEGMENT, 0x08 -.set DATA_SEGMENT, 0x10 - -.section .bss -.align 16 +# Allocate the initial stack. +.section .bootstrap_stack, "aw", @nobits stack_bottom: -.skip 16384 +.skip 16384 # 16 KiB stack_top: -.section .text +# Preallocate pages used for paging. Don't hard-code addresses and assume they +# are available, as the bootloader might have loaded its multiboot structures or +# modules there. This lets the bootloader know it must avoid the addresses. +.section .bss, "aw", @nobits + .align 4096 +boot_page_directory: + .skip 4096 +boot_page_table1: + .skip 4096 +boot_page_table2: + .skip 4096 +# Further page tables may be required if the kernel grows beyond 3 MiB. + +# The kernel entry point. +.section .multiboot.text, "a" .global _start .type _start, @function _start: + movl $(boot_page_table1 - 0xC0000000), %edi + movl $0, %esi + +1: + jl 2f + cmpl $0x00400000, %esi + jge 3f + + movl %esi, %edx + orl $0x003, %edx + movl %edx, (%edi) + +2: + # Size of page is 4096 bytes. + addl $4096, %esi + # Size of entries in boot_page_table1 is 4 bytes. + addl $4, %edi + # Loop to the next entry if we haven't finished. + loop 1b + +3: + movl $(boot_page_table2 - 0xC0000000), %edi + +4: + jl 5f + cmpl $0x00800000, %esi + jge 6f + + movl %esi, %edx + orl $0x003, %edx + movl %edx, (%edi) + +5: + # Size of page is 4096 bytes. + addl $4096, %esi + # Size of entries in boot_page_table1 is 4 bytes. + addl $4, %edi + # Loop to the next entry if we haven't finished. + loop 4b + +6: + movl $(boot_page_table1 - 0xC0000000 + 0x003), boot_page_directory - 0xC0000000 + 0 * 4 + movl $(boot_page_table2 - 0xC0000000 + 0x003), boot_page_directory - 0xC0000000 + 1 * 4 + movl $(boot_page_table1 - 0xC0000000 + 0x003), boot_page_directory - 0xC0000000 + 768 * 4 + movl $(boot_page_table2 - 0xC0000000 + 0x003), boot_page_directory - 0xC0000000 + 769 * 4 + + # Set cr3 to the address of the boot_page_directory. + movl $(boot_page_directory - 0xC0000000), %ecx + movl %ecx, %cr3 + + # Enable paging and the write-protect bit. + movl %cr0, %ecx + orl $0x80010000, %ecx + movl %ecx, %cr0 + + # Jump to higher half with an absolute jump. + lea 7f, %ecx + jmp *%ecx + +.section .text + +7: + # At this point, paging is fully set up and enabled. + + # Unmap the identity mapping as it is now unnecessary. + movl $0, boot_page_directory + 0 + movl $0, boot_page_directory + 4 + + # Reload crc3 to force a TLB flush so the changes to take effect. + movl %cr3, %ecx + movl %ecx, %cr3 + + movl $stack_top, %esp call init_gdt_table - ljmp $CODE_SEGMENT, $code + ljmp $0x08, $code code: - movw $DATA_SEGMENT, %ax + movw $0x10, %ax movw %ax, %ds movw %ax, %es movw %ax, %fs movw %ax, %gs movw %ax, %ss - movl $stack_top, %esp cli call _init call kernel_main hlt - -.size _start, . - _start diff --git a/src/as/paging.s b/src/as/paging.s index e1cf42a..c3a9a0d 100644 --- a/src/as/paging.s +++ b/src/as/paging.s @@ -1,14 +1,16 @@ +.text + .global loadPageDirectory loadPageDirectory: push %ebp - mov %esp, %ebp - mov 8(%esp), %eax - mov %eax, %cr3 + movl %esp, %ebp + movl 8(%esp), %eax + subl $0xC0000000, %eax + movl %eax, %cr3 mov %ebp, %esp pop %ebp ret -.text .global enablePaging enablePaging: push %ebp @@ -19,3 +21,13 @@ enablePaging: mov %ebp, %esp pop %ebp ret + +.global flushPaging +flushPaging: + push %ebp + mov %esp, %ebp + movl %cr3, %ecx + movl %ecx, %cr3 + mov %ebp, %esp + pop %ebp + ret |