diff options
Diffstat (limited to 'arch/x86_64/src/boot/boot.s')
| -rw-r--r-- | arch/x86_64/src/boot/boot.s | 368 |
1 files changed, 0 insertions, 368 deletions
diff --git a/arch/x86_64/src/boot/boot.s b/arch/x86_64/src/boot/boot.s deleted file mode 100644 index 7932045..0000000 --- a/arch/x86_64/src/boot/boot.s +++ /dev/null @@ -1,368 +0,0 @@ -.extern _end_physical -.extern _init -.extern kernel_main - - -/** - * Uninitialized data for the bootstrapping process. - */ -.section .boot_bss, "aw", @nobits - -/** - * Reserve some space for the Multiboot 2 information pointer. - */ -.global multiboot_information_pointer -multiboot_information_pointer: .skip 4 - -/** - * Align page maps to 4 KiB or the assembler code, will cause crashes when attempting to enable paging. - */ -.align 4096 - -/** - * Reserve space for the page maps we are going to use during startup. - * - * Note: We are going to use large pages to make the initial mapping code - * simpler. - * - * We need: - * - A single PML 4 (since we will only use 4-level paging) - * - 1 PML 3 - * - 1 PML 2 - */ - -.global page_map_level_4 -page_map_level_4: .skip 512 * 8 - -.global page_map_level_3 -page_map_level_3: .skip 512 * 8 - -.global page_map_level_2 -page_map_level_2: .skip 512 * 8 - -/** - * Stack space for the bootstrapping process. - * - * Note: We are going to reserve 1 MiB for now. If/when the kernel requires - * more space to run, it will have to relocate the stack. - */ -.section .boot_stack, "aw", @nobits -.align 16 - -stack_bottom: .skip 1 << 20 -stack_top: - -/** - * Constants for the bootstrapping process. - */ -.section .boot_rodata, "a", @progbits - -/** - * A valid Global Descriptor Table is still required in long mode. However, we - * only need a single entry for the "code segment", so we will setup a single - * segment table below. - * - * Bit 43: "E" in the access byte => mark the segment as executable. - * Bit 44: "S" in the access byte => mark the segment as code or data. - * Bit 47: "P" in the access byte => mark the segment as being present. - * Bit 53: "L" in the flags byte => mark the segment as being for long mode - */ - -global_descriptor_table: .quad 0 -global_descriptor_table_code = . - global_descriptor_table -.quad (1<<43) | (1<<44) | (1<<47) | (1<<53) - -/** - * We also need a pointer that we can load into the GDTR. - * - * The pointer consists of a word describing the size of the table minus 1 and - * the pointer to the actual table. - */ -global_descriptor_table_pointer: -.word . - global_descriptor_table - 1 -.quad global_descriptor_table - -/** - * We are going to print some messages in case we panic during boot, so we are - * going to store them here as well - */ -.global message_prefix_panic -message_prefix_panic: -.string "TeachOS Panic: " -message_not_loaded_by_multiboot2: -.string "The operating system was not loaded by a Multiboot 2 loader." -message_cpuid_instruction_no_supported: -.string "The 'cpuid' instruction is not supported on this platform." -mesage_long_mode_not_supported: -.string "Long mode is not supported by this platform." - -/** - * Mutable data for the bootstrapping process. - */ -.section .boot_data, "aw", @progbits - -/** - * We need a pointer to our current position in the VGA text buffer. - */ -.global vga_buffer_pointer -vga_buffer_pointer: .long 0xb8000 - -/** - * Code for the bootstrapping process. - */ -.section .boot_text, "ax", @progbits -.align 16 -.code32 - -.global halt -halt: -1: - hlt - jmp 1b - -/** - * Print a given panic message and then halt the machine. - * - * Parameters: - * - [stack - 0] message: the message to print - */ -_panic: - push %ebp - mov %esp, %ebp - - push message_prefix_panic - push $0x4f - call _print - add $8, %esp - - push 8(%ebp) - push 0x4f - call _print - add $8, %esp - - call halt - -/** - * Print a message via the VGA buffer. - * - * Parameters: - * - [stack - 4] message: the message to print - * - [stack - 0] color: the color of the message - */ -_print: - push %ebp - mov %esp, %ebp - - push %ebx - push %esi - mov 8(%ebp), %eax - mov 12(%ebp), %ebx - mov $0, %ecx - mov (vga_buffer_pointer), %esi - -.Lprint_loop: - mov (%ebx, %ecx), %dl - test %dl, %dl - je .Lupdate_vga_buffer_address - mov %dl, (%esi, %ecx, 2) - mov %al, 1(%esi, %ecx, 2) - inc %ecx - jmp .Lprint_loop - -.Lupdate_vga_buffer_address: - shl $1, %ecx - add %ecx, (vga_buffer_pointer) - -.Lprint_end: - pop %esi - pop %ebx - mov %ebp, %esp - pop %ebp - ret - -/** - * This is our entry point after being loaded by the bootloader. - * - * Having this in assembly makes it easier for us to keep things together. - */ -.global _start -_start: - mov $stack_top, %esp - mov %esp, %ebp - - call assert_loaded_by_multiboot2_loader - call assert_cpuid_instruction_is_supported - call assert_cpu_supports_long_mode - call prepare_page_maps - call enable_paging - call enable_sse - - lgdt (global_descriptor_table_pointer) - jmp $global_descriptor_table_code, $_transition_to_long_mode - - call halt - -/** - * Assert that the CPU supports going into long mode. - */ -assert_cpu_supports_long_mode: - mov $0x80000000, %eax - cpuid - cmp $0x80000001, %eax - jb .Llong_mode_assertion_failed - - mov $0x80000001, %eax - cpuid - test $(1 << 29), %edx - jz .Llong_mode_assertion_failed - ret -.Llong_mode_assertion_failed: - push $mesage_long_mode_not_supported - call _panic - -/** - * Assert that the CPU supports the CPUID instruction. - * - * The primary way to check for support of the instruction is to flip the ID - * bin in EFLAGS and then check if this changed was accepted. If so, the CPU - * supports the CPUID instruction, otherwise it most-likely doesn't. - */ -assert_cpuid_instruction_is_supported: - pushfl - pop %eax - mov %eax, %ecx - - xor $(1 << 21), %eax /* Flip the ID bit */ - push %eax /* Move the new bitset on the stack for loading */ - popfl /* Load the flags with ID set back into EFLAGS */ - pushfl /* Copy the flags back onto the stack */ - pop %eax /* Load the flags for further checking */ - - push %ecx - popfl - - cmp %ecx, %eax - je .Lcpuid_assertion_fail - ret -.Lcpuid_assertion_fail: - push $message_cpuid_instruction_no_supported - call _panic - -/** - * Assert that we were loaded by a Multiboot 2 compliant bootloader. - * - * This assertion will panic the system if the magic signature was not found. - * If we were loaded my an appropriate bootloader, this function also saves - * the provided MBI pointer to `multiboot_information_pointer`. - */ -assert_loaded_by_multiboot2_loader: - cmp $0x36d76289, %eax /* Check if we received the - expected magic */ - jne .Lmultiboot2_assertion_fail /* Panic otherwise */ - mov %ebx, multiboot_information_pointer /* Store the MBI pointer */ - ret -.Lmultiboot2_assertion_fail: - push $message_not_loaded_by_multiboot2 - call _panic - -/** - * Enable paging. - * - * Note: This routine expects for there to be a valid set of page maps already - * set up for use. - */ -enable_paging: - mov $page_map_level_4, %eax - mov %eax, %cr3 - - /* Enable Physical Address Extension */ - mov %cr4, %eax - or $(1 << 5), %eax - mov %eax, %cr4 - - /* Enable long mode support */ - mov $0xC0000080, %ecx - rdmsr - or $(1 << 8), %eax - wrmsr - - /* Enable paging */ - mov %cr0, %eax - or $(1 << 31), %eax - mov %eax, %cr0 - - ret - -/** - * Enable use of SSE instructions. - */ -enable_sse: - mov %cr0, %eax - and $0xfffffffb, %eax - or $0x00000002, %eax - mov %eax, %cr0 - - mov %cr4, %eax - or $(3 << 9), %eax - mov %eax, %cr4 - - ret - -/** - * Prepare the page maps. - * - * We map all physical memory we were loaded in plus one additional page. The - * mapping is done in terms of huge pages (2 MiB per page) to save on required - * page map entries. - */ -prepare_page_maps: - /* Map the P4 table recursively */ - mov $page_map_level_4, %eax - or $0b11, %eax /* Write present + writable flags into eax register */ - mov %eax, (page_map_level_4 + 511 * 8) - - /* Add an entry to the PML4, pointing to the PML3 */ - mov $page_map_level_3, %eax - or $0x3, %eax - mov %eax, (page_map_level_4 + ((0x0000000000100000 >> 39) & 0x1ff) * 8) - - /* Add an entry to the PML3, pointing to the PML2 */ - mov $page_map_level_2, %eax - or $0x3, %eax - mov %eax, (page_map_level_3 + ((0x0000000000100000 >> 30) & 0x1ff) * 8) - - xor %ecx, %ecx - - mov $_end_linear, %esi - shr $21, %esi - add $2, %esi - -.Lmap_pages: - mov $(1 << 21), %eax - mul %ecx - or $((1 << 0) | (1 << 1) | (1 << 7)), %eax - mov %eax, page_map_level_2(,%ecx,8) - - inc %ecx - cmp %esi, %ecx - jne .Lmap_pages - - ret - -.section .boot_text, "ax", @progbits -.code64 - -_transition_to_long_mode: - xor %rax, %rax - mov %rax, %ss - mov %rax, %ds - mov %rax, %es - mov %rax, %fs - mov %rax, %gs - - movl $0xb8000, (vga_buffer_pointer) - - call _init - - call kernel_main - call halt |