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authorXander <xander@icth.xyz>2023-06-28 21:56:30 +0200
committerXander <xander@icth.xyz>2023-06-28 21:56:30 +0200
commit448ecd41edd95b86930b5ac7288f2ea9311d476c (patch)
tree64106ce37ea5c6067835ce747dd650a5e01a4c1e /arch/x86_64/boot
parentfd86b8a4769860f22fc04ce3b80510d809f68d3c (diff)
downloadats-os-448ecd41edd95b86930b5ac7288f2ea9311d476c.tar.xz
ats-os-448ecd41edd95b86930b5ac7288f2ea9311d476c.zip
Reorganizing
Diffstat (limited to 'arch/x86_64/boot')
-rw-r--r--arch/x86_64/boot/README.md5
-rw-r--r--arch/x86_64/boot/boot.asm163
-rw-r--r--arch/x86_64/boot/grub.cfg7
-rw-r--r--arch/x86_64/boot/linker.ld16
-rw-r--r--arch/x86_64/boot/long_mode_init.asm17
-rw-r--r--arch/x86_64/boot/multiboot_header.asm15
6 files changed, 223 insertions, 0 deletions
diff --git a/arch/x86_64/boot/README.md b/arch/x86_64/boot/README.md
new file mode 100644
index 0000000..c7cc505
--- /dev/null
+++ b/arch/x86_64/boot/README.md
@@ -0,0 +1,5 @@
+
+Most of the code in this folder is based on Philipp Oppermann's blog os.
+https://github.com/phil-opp/blog_os
+
+Copyright (c) 2019 Philipp Oppermann
diff --git a/arch/x86_64/boot/boot.asm b/arch/x86_64/boot/boot.asm
new file mode 100644
index 0000000..2e334a8
--- /dev/null
+++ b/arch/x86_64/boot/boot.asm
@@ -0,0 +1,163 @@
+global start
+extern long_mode_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
+
+ ; load the 64-bit GDT
+ lgdt [gdt64.pointer]
+
+ jmp gdt64.code:long_mode_start
+
+ ; print `OK` to screen
+ mov dword [0xb8000], 0x2f4b2f4f
+ 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
+
+; 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
+
+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
+
+section .bss
+align 4096
+p4_table:
+ resb 4096
+p3_table:
+ resb 4096
+p2_table:
+ resb 4096
+stack_bottom:
+ resb 64
+stack_top:
+
+section .rodata
+gdt64:
+ dq 0 ; zero entry
+.code: equ $ - gdt64
+ dq (1<<43) | (1<<44) | (1<<47) | (1<<53) ; code segment
+.pointer:
+ dw $ - gdt64 - 1
+ dq gdt64
diff --git a/arch/x86_64/boot/grub.cfg b/arch/x86_64/boot/grub.cfg
new file mode 100644
index 0000000..7c34c9c
--- /dev/null
+++ b/arch/x86_64/boot/grub.cfg
@@ -0,0 +1,7 @@
+set timeout=0
+set default=0
+
+menuentry "ats-os" {
+ multiboot2 /boot/kernel.bin
+ boot
+}
diff --git a/arch/x86_64/boot/linker.ld b/arch/x86_64/boot/linker.ld
new file mode 100644
index 0000000..5d788f1
--- /dev/null
+++ b/arch/x86_64/boot/linker.ld
@@ -0,0 +1,16 @@
+ENTRY(start)
+
+SECTIONS {
+ . = 1M;
+
+ .boot :
+ {
+ /* ensure that the multiboot header is at the beginning */
+ *(.multiboot_header)
+ }
+
+ .text :
+ {
+ *(.text)
+ }
+}
diff --git a/arch/x86_64/boot/long_mode_init.asm b/arch/x86_64/boot/long_mode_init.asm
new file mode 100644
index 0000000..eab3788
--- /dev/null
+++ b/arch/x86_64/boot/long_mode_init.asm
@@ -0,0 +1,17 @@
+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
+
+ ; print `OKAY` to screen
+ mov rax, 0x2f592f412f4b2f4f
+ mov qword [0xb8000], rax
+ hlt
diff --git a/arch/x86_64/boot/multiboot_header.asm b/arch/x86_64/boot/multiboot_header.asm
new file mode 100644
index 0000000..9a9289c
--- /dev/null
+++ b/arch/x86_64/boot/multiboot_header.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: