From c1b43683f23f2e7f2b88f9f56859a708d558253d Mon Sep 17 00:00:00 2001
From: ravinperera00 <bravinperera@gmail.com>
Date: Sun, 1 Oct 2023 23:51:31 +0530
Subject: [PATCH] Add Global Descriptor Table

---
 Makefile          |  11 ++++++++
 bin/boot.bin      | Bin 0 -> 512 bytes
 build.sh          |   5 ++++
 src/boot/boot.asm |  62 ++++++++++++++++++++++++++++++++++++++++++++++
 src/kernel.asm    |  17 +++++++++++++
 src/linker.ld     |  26 +++++++++++++++++++
 6 files changed, 121 insertions(+)
 create mode 100644 Makefile
 create mode 100644 bin/boot.bin
 create mode 100755 build.sh
 create mode 100644 src/boot/boot.asm
 create mode 100644 src/kernel.asm
 create mode 100644 src/linker.ld

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..94b2b4b
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,11 @@
+FILES = ./build/kernel.asm.o
+
+all: ./bin/boot.bin $(FILES)
+	dd -f=./bin/boot.bin >> ./bin/os.bin
+	
+./bin/boot.bin: ./src/boot/boot.asm
+	nasm -f bin ./src/boot/boot.asm -o ./bin/boot.bin
+./build/kernel.asm.o: ./src/kernel.asm
+	nasm -f elf -g ./src/kernel.asm -o ./build/kernel.asm.o
+clean:
+	rm -rf ./bin/boot.bin
\ No newline at end of file
diff --git a/bin/boot.bin b/bin/boot.bin
new file mode 100644
index 0000000000000000000000000000000000000000..a00e2c528033ef8b2e0ec10258133d49f8f7ee0e
GIT binary patch
literal 512
zcmaE@G=YH-c%@mx!0>Aa14G}9z5{(1_Au1^{>9HImQus7a3HPu1S7xFfmc~I9B^a)
z{|7Q>oo4{klg=}UGxz`vNZTO*G2lVpi@pnc85k58I^R5*#KZJ#((8Y4y`v0zhCt{l
E0FJ^cjQ{`u

literal 0
HcmV?d00001

diff --git a/build.sh b/build.sh
new file mode 100755
index 0000000..fccb0bd
--- /dev/null
+++ b/build.sh
@@ -0,0 +1,5 @@
+#/bin/bash
+export PREFIX="$HOME/opt/cross"
+export TARGET=i686-elf
+export PATH="$PREFIX/bin:$PATH"
+make all
\ No newline at end of file
diff --git a/src/boot/boot.asm b/src/boot/boot.asm
new file mode 100644
index 0000000..99c0ed0
--- /dev/null
+++ b/src/boot/boot.asm
@@ -0,0 +1,62 @@
+ORG 0x7c00
+BITS 16
+
+CODE_SEG equ gdt_code - gdt_start
+DATA_SEG equ gdt_data - gdt_start
+
+_start:
+    jmp short start
+    nop
+    times 33 db 0
+
+start:
+    jmp 0:step2
+
+step2:
+    cli ; disable interrupts
+    mov ax, 0x00
+    mov ds, ax
+    mov es, ax
+    mov ss, ax
+    mov sp, 0x7c00
+    sti ; enable interrupts
+
+load_protected:
+    cli
+    lgdt[gdt_descriptor]
+    mov eax, cr0
+    or eax, 1
+    mov cr0, eax
+    ;jmp CODE_SEG:load32
+    jmp $
+
+
+;GDT
+gdt_start:
+gdt_null:
+    dd 0x0
+    dd 0x0
+
+gdt_code:
+    dw 0xffff
+    dw 0
+    db 0
+    db 0x9a
+    db 11001111b
+    db 0
+
+gdt_data:
+    dw 0xffff
+    dw 0
+    db 0
+    db 0x92
+    db 11001111b
+    db 0
+gdt_end:
+
+gdt_descriptor:
+    dw gdt_end - gdt_start - 1
+    dd gdt_start
+
+times 510-($-$$) db 0
+dw 0xAA55
\ No newline at end of file
diff --git a/src/kernel.asm b/src/kernel.asm
new file mode 100644
index 0000000..6da6128
--- /dev/null
+++ b/src/kernel.asm
@@ -0,0 +1,17 @@
+BITS 32
+
+load32:
+    mov ax, DATA_SEG
+    mov ds, ax
+    mov es, ax
+    mov fs, ax
+    mov gs, ax
+    mov ss, ax
+    mov ebp, 0x00200000
+    mov esp, ebp
+
+    in al, 0x92
+    or al, 2
+    out 0x92, al
+
+    jmp $
\ No newline at end of file
diff --git a/src/linker.ld b/src/linker.ld
new file mode 100644
index 0000000..c0778ce
--- /dev/null
+++ b/src/linker.ld
@@ -0,0 +1,26 @@
+ENTRY(_start)
+OUTPUT_FORMAT(binary)
+SECTIONS
+{
+    . = 1M;
+    .text :
+    {
+        *(.text)
+    }
+
+    .rodata :
+    {
+        *(.rodata)
+    }
+
+    .data :
+    {
+        *(.data)
+    }
+
+    .bss :
+    {
+        *(COMMON)
+        *(.bss)
+    }
+}
\ No newline at end of file