feat(grub): add multi-boot support and long mode swap

Signed-off-by: Julien CLEMENT <julien.clement@epita.fr>

.cargo/config.toml

@@ -4,6 +4,3 @@ target = "x86_64-julios.json"
 [unstable]
 build-std-features = ["compiler-builtins-mem"]
 build-std = ["core", "compiler_builtins"]
-
-[target.'cfg(target_os = "none")']
-runner = "bootimage runner"

.gitignore

@@ -1 +1,5 @@
 /target
+iso
+*.iso
+*.o
+julios

Cargo.lock

@@ -2,15 +2,6 @@
 # It is not intended for manual editing.
 version = 3
 
-[[package]]
-name = "bootloader"
-version = "0.9.19"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b7c452074efc3c0bfb241fb7bc87df04741c7c85e926f6a07c05f8fbd6008240"
-
 [[package]]
 name = "julios"
 version = "0.1.0"
-dependencies = [
- "bootloader",
-]

Cargo.toml

@@ -5,5 +5,5 @@ edition = "2018"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
-[dependencies]
-bootloader = "0.9.8"
+[lib]
+crate-type = ["staticlib"]

Makefile

@@ -0,0 +1,39 @@
+KERNEL = julios
+ISO = julios.iso
+INSTALL_ROOT = iso
+ABS_INSTALL = $(abspath $(INSTALL_ROOT))
+
+LINKER_SCRIPT = src/linker.ld
+BOOT_OBJS = src/multiboot.o src/boot.o
+LIB_JULIOS = target/x86_64-julios/debug/libjulios.a
+
+GRUB_CFG = grub/grub.cfg
+
+all: $(ISO)
+
+$(ISO): install
+	./tools/create-iso.sh $@ $(INSTALL_ROOT)
+
+install: $(KERNEL) $(GRUB_CFG)
+	mkdir -p $(ABS_INSTALL)
+	mkdir -p $(ABS_INSTALL)/boot/grub
+	cp $(KERNEL) $(ABS_INSTALL)/boot
+	cp grub/grub.cfg $(ABS_INSTALL)/boot/grub
+
+$(KERNEL): $(LIB_JULIOS) $(LINKER_SCRIPT) $(BOOT_OBJS)
+	ld -n -T $(LINKER_SCRIPT) -o $(KERNEL) $(BOOT_OBJS) $(LIB_JULIOS)
+
+$(LIB_JULIOS):
+	cargo build
+
+
+%.o: %.asm
+	nasm -f elf64 $^ -o $@
+
+clean:
+	$(RM) $(BOOT_OBJS)
+	$(RM) $(KERNEL)
+	$(RM) julios.iso
+	$(RM) -r iso
+
+.PHONY: $(INSTALL_ROOT) install clean all

grub/grub.cfg

@@ -0,0 +1,4 @@
+menuentry "julios" {
+    multiboot2 /boot/julios
+    boot
+}

src/boot.asm

@@ -0,0 +1,190 @@
+section .rodata
+gdt64:
+    dq 0
+.code: equ $ - gdt64
+    dq (1<<43) | (1<<44) | (1<<47) | (1<<53)
+
+.pointer:
+    dw $ - gdt64 - 1
+    dq gdt64
+
+
+global _start
+section .text
+bits 32
+
+_start:
+    mov esp, stack_top
+
+    call check_multiboot
+    call check_cpuid
+    call check_long_mode
+
+    call set_up_page_tables
+    call enable_paging
+
+    lgdt [gdt64.pointer]
+    jmp gdt64.code:long_mode_start
+
+set_up_page_tables:
+    ; map first P4 entry to P3 table
+    mov eax, p3_table
+    or eax, 0b11 ; present + writable
+    mov [p4_table], eax
+
+    ; map first P3 entry to P2 table
+    mov eax, p2_table
+    or eax, 0b11 ; present + writable
+    mov [p3_table], eax
+
+    ; map each P2 entry to a huge 2MiB page
+    mov ecx, 0         ; counter variable
+
+.map_p2_table:
+    ; map ecx-th P2 entry to a huge page that starts at address 2MiB*ecx
+    mov eax, 0x200000  ; 2MiB
+    mul ecx            ; start address of ecx-th page
+    or eax, 0b10000011 ; present + writable + huge
+    mov [p2_table + ecx * 8], eax ; map ecx-th entry
+
+    inc ecx            ; increase counter
+    cmp ecx, 512       ; if counter == 512, the whole P2 table is mapped
+    jne .map_p2_table  ; 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
+
+
+
+; Prints `ERR: ` and the given error code to screen and hangs.
+; parameter: error code (in ascii) in al
+error:
+    mov dword [0xb8000], 0x4f524f45
+    mov dword [0xb8004], 0x4f3a4f52
+    mov dword [0xb8008], 0x4f204f20
+    mov byte  [0xb800a], al
+    hlt
+
+
+check_multiboot:
+    cmp eax, 0x36d76289
+    jne .no_multiboot
+    ret
+.no_multiboot:
+    mov al, "0"
+    jmp error
+
+
+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.
+    cmp eax, ecx
+    je .no_cpuid
+    ret
+.no_cpuid:
+    mov al, "1"
+    jmp error
+
+
+
+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
+
+
+section .bss
+align 4096
+p4_table:
+    resb 4096
+p3_table:
+    resb 4096
+p2_table:
+    resb 4096
+
+stack_bottom:
+    resb 64
+stack_top:
+
+
+global long_mode_start
+section .text
+bits 64
+
+long_mode_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 julios_main
+    call julios_main
+
+    mov rax, 0x2f592f412f4b2f4f
+    mov qword [0xb8000], rax
+.loop:
+    jmp .loop

src/lib.rs

@@ -10,7 +10,7 @@ fn panic(_info: &core::panic::PanicInfo) -> !
 static HELLO: &[u8] = b"Welcome to the JuliOS";
 
 #[no_mangle]
-pub extern "C" fn _start() -> !
+pub extern "C" fn julios_main() -> !
 {
     let vga_buffer: *mut u8 = 0xb8000 as *mut u8;
 

src/linker.ld

@@ -0,0 +1,16 @@
+ENTRY(_start)
+
+SECTIONS {
+    . = 1M;
+
+    .boot :
+    {
+        /* ensure that the multiboot header is at the beginning */
+        *(.multiboot_header)
+    }
+
+    .text :
+    {
+        *(.text)
+    }
+}

src/multiboot.asm

@@ -0,0 +1,15 @@
+section .multiboot_header
+header_start:
+    dd 0xe85250d6                ; magic number (multiboot 2)
+    dd 0                         ; architecture 0 (protected mode i386)
+    dd header_end - header_start ; header length
+    ; checksum
+    dd 0x100000000 - (0xe85250d6 + 0 + (header_end - header_start))
+
+    ; insert optional multiboot tags here
+
+    ; required end tag
+    dw 0    ; type
+    dw 0    ; flags
+    dd 8    ; size
+header_end:

tools/create-iso.sh

@@ -0,0 +1,8 @@
+#!/bin/sh
+
+iso_filename=$1
+base_dir=$2
+
+unset MFLAGS MAKEFLAGS
+
+grub-mkrescue -o $iso_filename $base_dir