From 8285981871dabf7cf972c5832eb3f676b8c9a663 Mon Sep 17 00:00:00 2001 From: Erin Date: Sat, 3 Jun 2017 12:59:19 -0500 Subject: [PATCH] '''small''' asm multiboot2 stub (switches to long mode) --- src/arch/x86_64/boot.asm | 172 ++++++++++++++++++++++++++++++++++++++++++ src/arch/x86_64/grub.cfg | 7 ++ src/arch/x86_64/linker.ld | 15 ++++ src/arch/x86_64/long.asm | 20 +++++ src/arch/x86_64/multiboot.asm | 16 ++++ 5 files changed, 230 insertions(+) create mode 100644 src/arch/x86_64/boot.asm create mode 100644 src/arch/x86_64/grub.cfg create mode 100644 src/arch/x86_64/linker.ld create mode 100644 src/arch/x86_64/long.asm create mode 100644 src/arch/x86_64/multiboot.asm diff --git a/src/arch/x86_64/boot.asm b/src/arch/x86_64/boot.asm new file mode 100644 index 0000000..bef3778 --- /dev/null +++ b/src/arch/x86_64/boot.asm @@ -0,0 +1,172 @@ +global start +extern long_start + +section .text +bits 32 +start: + ; point the esp register to the top of our stack + ; (the stack grows downwards) + mov esp, stack_top + + call check_multiboot + call check_cpuid + call check_long_mode + + call setup_ptables + call enable_paging + + ; load the 64-bit gdt + lgdt [gdt64.pointer] + jmp gdt64.code:long_start + + ; print OK + ; mov dword [0xb8000], 0x2f4b2f4f + + hlt ; halt + +; Checks that we were actually loaded by a Multiboot-compatible system +check_multiboot: + cmp eax, 0x36d76289 + jne .no_multiboot + ret +.no_multiboot: + mov al, "m" + jmp error + +; Checks that we have a CPUID-enabled processor +check_cpuid: + ; Check if CPUID is supported by attempting to flip the ID bit (bit 21) in + ; the FLAGS register. If we can flip it, CPUID is available. + + ; Copy FLAGS in to EAX via stack + pushfd + pop eax + + ; Copy to ECX as well for comparing later on + mov ecx, eax + + ; Flip the ID bit + xor eax, 1 << 21 + + ; Copy EAX to FLAGS via the stack + push eax + popfd + + ; Copy FLAGS back to EAX (with the flipped bit if CPUID is supported) + pushfd + pop eax + + ; Restore FLAGS from the old version stored in ECX (i.e. flipping the ID bit + ; back if it was ever flipped). + push ecx + popfd + + ; Compare EAX and ECX. If they are equal then that means the bit wasn't + ; flipped, and CPUID isn't supported. + xor eax, ecx + jz .no_cpuid + ret +.no_cpuid: + mov al, "c" + jmp error + +; Checks if long mode is supported +check_long_mode: + ; test if extended processor info in available + mov eax, 0x80000000 ; implicit argument for cpuid + cpuid ; get highest supported argument + cmp eax, 0x80000001 ; it needs to be at least 0x80000001 + jb .no_long_mode ; if it's less, the CPU is too old for long mode + + ; use extended info to test if long mode is available + mov eax, 0x80000001 ; argument for extended processor info + cpuid ; returns various feature bits in ecx and edx + test edx, 1 << 29 ; test if the LM-bit is set in the D-register + jz .no_long_mode ; If it's not set, there is no long mode + ret +.no_long_mode: + mov al, "2" + jmp error + +setup_ptables: + ; p4[0] -> p3 + mov eax, p3_table + or eax, 0b11 ; present + writable + mov [p4_table], eax + + ; p3[0] -> p2 + mov eax, p2_table + or eax, 0b1 ; present + writable + mov [p3_table], eax + + ; map each p2 entry to a 2mib hugepage + mov ecx, 0 +.map_p2: + ; p2[ecx] -> huge_page{@2MiB*ecx} + mov eax, 0x200000 ; 2MiB + mul ecx ; start address + or eax, 0b10000011 ; present + writable + huge + mov [p2_table + ecx*8], eax ; map ecx-th entry + + inc ecx ; increase counter + cmp ecx, 512 ; whole table is mapped if ecx == 512 + jne .map_p2 ; else map the next entry + + ret + +enable_paging: + ; load P4 to cr3 register (cpu uses this to access the P4 table) + mov eax, p4_table + mov cr3, eax + + ; enable PAE-flag in cr4 (Physical Address Extension) + mov eax, cr4 + or eax, 1 << 5 + mov cr4, eax + + ; set the long mode bit in the EFER MSR (model specific register) + mov ecx, 0xC0000080 + rdmsr + or eax, 1 << 8 + wrmsr + + ; enable paging in the cr0 register + mov eax, cr0 + or eax, 1 << 31 + mov cr0, eax + + ret + +; Print `ERR: ` + error code to screen and then HLTs +; lovingly ripped off from Phil Oppermann's os.phil-opp.com +; parameter: error code (ascii) in al +error: + mov dword [0xb8000], 0x4f524f45 + mov dword [0xb8004], 0x4f3a4f52 + mov dword [0xb8008], 0x4f204f20 + mov byte [0xb800a], al + hlt + +;;; Smol stack (64 bytes) just to make stuff work atm +section .bss +align 4096 +p4_table: + resb 4096 +p3_table: + resb 4096 +p2_table: + resb 4096 +p1_table: + resb 4096 +stack_bottom: + resb 64 +stack_top: + +section .rodata +gdt64: + dq 0 ; zero entry +.code: equ $ - gdt64 ; new + dq (1<<43) | (1<<44) | (1<<47) | (1<<53) ; code segment +.pointer: + dw $ - gdt64 - 1 + dq gdt64 \ No newline at end of file diff --git a/src/arch/x86_64/grub.cfg b/src/arch/x86_64/grub.cfg new file mode 100644 index 0000000..e63b4c4 --- /dev/null +++ b/src/arch/x86_64/grub.cfg @@ -0,0 +1,7 @@ +set timeout=0 +set default=0 + +menuentry "vgaflag" { + multiboot2 /boot/kernel.bin + boot +} \ No newline at end of file diff --git a/src/arch/x86_64/linker.ld b/src/arch/x86_64/linker.ld new file mode 100644 index 0000000..60e920c --- /dev/null +++ b/src/arch/x86_64/linker.ld @@ -0,0 +1,15 @@ +ENTRY(start) + +SECTIONS { + . = 1M; /* load the kernel at 1MiB above 0x0 */ + + .boot : { + /* ensure the multiboot header is at the start of the binary */ + KEEP(*(.multiboot_header)) + } + + .text : { + /* Kernel code */ + *(.text) + } +} \ No newline at end of file diff --git a/src/arch/x86_64/long.asm b/src/arch/x86_64/long.asm new file mode 100644 index 0000000..3c03974 --- /dev/null +++ b/src/arch/x86_64/long.asm @@ -0,0 +1,20 @@ +global long_start + +section .text +bits 64 +long_start: + ; load 0 into all data segment registers + mov ax, 0 + mov ss, ax + mov ds, ax + mov es, ax + mov fs, ax + mov gs, ax + + extern kernel_main + call kernel_main + + ; print `OKAY` to screen + mov rax, 0x2f592f412f4b2f4f + mov qword [0xb8000], rax + hlt diff --git a/src/arch/x86_64/multiboot.asm b/src/arch/x86_64/multiboot.asm new file mode 100644 index 0000000..191aab8 --- /dev/null +++ b/src/arch/x86_64/multiboot.asm @@ -0,0 +1,16 @@ +section .multiboot_header +align 4 +header_start: + dd 0xe85250d6 ; magic number + dd 0 ; architecture 0 (protected mode i386) + dd header_end-header_start ; header length + ; checksum + dd 0x100000000 - (0xe85250d6 + 0 + (header_end - header_start)) + + ; ... multiboot tags? ... + + ; end tag + dw 0 ; type + dw 0 ; flags + dd 8 ; size +header_end: