From 2b1b7568b0b2e74dc45a81e14936fd1c2208a542 Mon Sep 17 00:00:00 2001
From: rami <rami.kaldany@pm.me>
Date: Tue, 25 Jun 2024 22:47:21 -0400
Subject: [PATCH] transfer control to C

---
 Makefile                   |  4 ++-
 include/kernel/multiboot.h | 29 +++++++++++++++++
 kernel/init.asm            | 64 +++++++++++++++++++++++++++++++++++---
 kernel/kernel.c            |  8 ++++-
 4 files changed, 99 insertions(+), 6 deletions(-)
 create mode 100644 include/kernel/multiboot.h

diff --git a/Makefile b/Makefile
index 189f709..2e3fb71 100644
--- a/Makefile
+++ b/Makefile
@@ -2,7 +2,9 @@ CC = i686-elf-gcc
 AS = nasm
 
 BUILDDIR := build
-CFLAGS   := -ffreestanding -Wall -Wextra -Werror
+INCLUDEDIR := include
+
+CFLAGS   := -ffreestanding -Wall -Wextra -Werror -I $(INCLUDEDIR)
 LDFLAGS  := -ffreestanding -nostdlib -lgcc -T kernel/kernel.ld
 
 KSRC := $(wildcard kernel/*.asm kernel/*.c)
diff --git a/include/kernel/multiboot.h b/include/kernel/multiboot.h
new file mode 100644
index 0000000..d14b7d2
--- /dev/null
+++ b/include/kernel/multiboot.h
@@ -0,0 +1,29 @@
+#ifndef HAZEL_MULTIBOOT_H_
+#define HAZEL_MULTIBOOT_H_
+
+#include <stdint.h>
+
+typedef struct {
+    uint32_t flags;			//required
+    uint32_t memlower;		//if bit 0 in flags are set
+    uint32_t memupper;		//if bit 0 in flags are set
+    uint32_t bootdevice;		//if bit 1 in flags are set
+    uint32_t commandline;		//if bit 2 in flags are set
+    uint32_t modulecount;		//if bit 3 in flags are set
+    uint32_t moduleaddress;		//if bit 3 in flags are set
+    uint32_t syms[4];		//if bits 4 or 5 in flags are set
+    uint32_t memmaplength;		//if bit 6 in flags is set
+    uint32_t memmapaddress;		//if bit 6 in flags is set
+    uint32_t driveslength;		//if bit 7 in flags is set
+    uint32_t drivesaddress;		//if bit 7 in flags is set
+    uint32_t configtable;		//if bit 8 in flags is set
+    uint32_t apmtable;		//if bit 9 in flags is set
+    uint32_t vbecontrolinfo;	//if bit 10 in flags is set
+    uint32_t vbemodeinfo;		//if bit 11 in flags is set
+    uint32_t vbemode;		// all vbe_* set if bit 12 in flags are set
+    uint32_t vbeinterfaceseg;
+    uint32_t vbeinterfaceoff;
+    uint32_t vbeinterfacelength;
+} multiboot_info_t; 
+
+#endif
diff --git a/kernel/init.asm b/kernel/init.asm
index 44730ca..ee88f16 100644
--- a/kernel/init.asm
+++ b/kernel/init.asm
@@ -9,8 +9,64 @@ dd -(MAGIC + FLAGS)
 section .text
 global _start
 _start:
-   mov byte [0xb8000], 'X'
-   mov byte [0xb8001], 0x0f
+	cli
 
-   cli
-   jmp $
+	; Check if EAX contains this magic value that our bootloader should've set
+	cmp eax, 0x2BADB002
+	jne halt
+
+	; Load GDT
+    lgdt [gdtp]
+	; Offset to kernel data descriptor
+    mov ax, 0x10 
+    mov es, ax
+    mov ds, ax
+    mov fs, ax
+    mov gs, ax
+    mov ss, ax
+	; Offset to kernel code descriptor
+    jmp 0x8:.use_code_seg
+.use_code_seg:
+    mov esp, stack_bottom
+    mov ebp, esp
+    push ebx 
+	and esp, 0xfffffff0
+    extern kernel
+    call kernel
+	cli
+halt:
+	hlt
+	jmp halt
+
+section .data
+; GDT for a flat memory layout
+; We get access to all memory and can utilize paging
+global gdt
+gdt:
+gdt_null:
+    dq 0
+gdt_kern_code:
+    dw 0xffff
+    dw 0x0000
+    db 0x00
+    db 0b10011010
+    db 0b11001111
+    db 0x00
+gdt_kern_data:
+    dw 0xffff
+    dw 0x0000
+    db 0x00
+    db 0b10010010
+    db 0b11001111
+    db 0x00
+gdt_end:
+
+gdtp:
+    dw gdt_end - gdt - 1
+    dd gdt
+
+section .bss
+align 16
+stack_top:
+	resb 16384
+stack_bottom:
diff --git a/kernel/kernel.c b/kernel/kernel.c
index a1e9b0f..b9aaedb 100644
--- a/kernel/kernel.c
+++ b/kernel/kernel.c
@@ -1,4 +1,10 @@
-void kernel() {
+#include <kernel/multiboot.h>
+
+void kernel(multiboot_info_t *info) {
+	char *vmem = (char *)0xb8000;
+	vmem[0] = info->flags; 
+	vmem[1] = 0x0f;
+
     asm volatile ("cli" ::);
     for (;;) {}
 }