From 24d85843aca047943c3bde7f891a5a43ad78e2d9 Mon Sep 17 00:00:00 2001
From: notsomeidiot123 <kiminosei321@gmail.com>
Date: Wed, 2 Oct 2024 17:38:15 -0400
Subject: [PATCH] relocating file during load to allow for use of more memory

---
 linker.ld             | 35 ++++++++++++++++++++++
 makefile              | 15 ++++++++--
 src/bootloader/main.s | 69 ++++++++++++++++++++++++++++++++-----------
 src/kernel/entry.s    | 10 +++++++
 src/kernel/kmain.c    |  3 ++
 5 files changed, 112 insertions(+), 20 deletions(-)
 create mode 100644 linker.ld
 create mode 100644 src/kernel/entry.s
 create mode 100644 src/kernel/kmain.c

diff --git a/linker.ld b/linker.ld
new file mode 100644
index 0000000..9873a11
--- /dev/null
+++ b/linker.ld
@@ -0,0 +1,35 @@
+ENTRY(_start)
+/* OUTPUT_FORMAT(elf32-i386) */
+OUTPUT_FORMAT(binary)
+OUTPUT(kernel.elf)
+SEARCH_DIR(bin/kernel)
+SECTIONS{
+    . = 0xc0000000;
+    .text : AT(ADDR(.text) - 0xc0000000){
+        _code = .;
+        *(.text)
+        *(.rodata)
+        . = ALIGN(4096);
+    }
+    .data : AT(ADDR(.data) - 0xc0000000){
+        _data = .;
+        *(.data)
+    }
+    .eh_frame : AT(ADDR(.eh_frame) - 0xc0000000){
+        _eh_frame = .;
+        *(.eh_frame)
+        . = ALIGN(4096);
+    }
+    
+    .bss : AT(ADDR(.bss) - 0xc0000000){
+        _bss = .;
+        *(.bss)
+        *(.COMMON)
+        . = ALIGN(4096);
+    }
+    _end = .;
+    /DISCARD/ : 
+    {
+        *(.comment)
+    }
+}
\ No newline at end of file
diff --git a/makefile b/makefile
index 2c759d7..dbf5110 100644
--- a/makefile
+++ b/makefile
@@ -1,11 +1,14 @@
 CC := gcc
 AS := nasm
+CFLAGS := -c -mno-sse -mno-sse2 -mno-red-zone -ffreestanding -fno-pie -fno-stack-protector -mno-mmx
 BL_ASFLAGS := -f bin
+SRCS := $(wildcard src/kernel/*.c)
+OBJS := $(patsubst src/kernel/%.c, bin/kernel/%.o, $(SRCS))
 
-all: bootloader tools
+all: bootloader tools kernel
 	cp bin/bootloader.bin image.bin
 	qemu-img resize -f raw image.bin 512M
-	./diskwrite -v kernel.elf -o image.bin 
+	./diskwrite -v kernel.elf -o image.bin
 	qemu-system-i386 -hda image.bin --no-reboot --no-shutdown -m 32m -smp 2 -serial mon:stdio
 	
 tools:
@@ -13,6 +16,14 @@ tools:
 
 bootloader:
 	$(AS) src/bootloader/main.s $(BL_ASFLAGS) -o bin/bootloader.bin
+
+kernel: $(OBJS)
+	nasm src/kernel/entry.s -o bin/kernel/entry.o -f elf32
+	ld -T linker.ld bin/kernel/entry.o -melf_i386
+
+%.o: $(SRCS)
+	$(CC) $(CFLAGS) $< -o $@
+
 init:
 	@mkdir mount
 	@mkdir bin
diff --git a/src/bootloader/main.s b/src/bootloader/main.s
index 57f77a5..d6d04a6 100644
--- a/src/bootloader/main.s
+++ b/src/bootloader/main.s
@@ -202,7 +202,7 @@ load_part2:
         push 0
         pop ds
         mov si, DAP
-        ; jmp $
+        
         int 0x13
         jc load_fail
         jmp part_2
@@ -305,7 +305,7 @@ part_2:
     mov edi, kernel_file
     call open_file
     mov esi, eax
-    mov edi, file_buffer
+    mov edi, 0x10000
     call read_file
     jc load_fail
     
@@ -449,9 +449,8 @@ read_file:
     xor edx, edx
     mov eax, esi
     mov cl, [fat_bpb.sectors_per_cluster]
-    ; jmp $
     mul ecx; eax  = offset from file table
-    ; jmp $
+
     push eax
     xor eax, eax
     xor ecx, ecx
@@ -471,11 +470,13 @@ read_file:
     xor ecx, ecx
     mov cl, [fat_bpb.sectors_per_cluster]
     mov [DAP.read_count], cx
-    push edi
-    shr edi, 16
-    mov [DAP.segment], di
-    pop edi
-    mov [DAP.offset], di
+    ; push edi
+    ; shr edi, 16
+    ; mov [DAP.segment], di
+    ; pop edi
+    ; mov [DAP.offset], di
+    mov word [DAP.segment], 0
+    mov word [DAP.offset], file_buffer
     
     mov ah, 0x42
     mov dl, [data.boot_disc]
@@ -483,11 +484,7 @@ read_file:
     int 0x13
     jc .exit_err
     
-    ; debug
-    pop esi
-    call read_fat
-    cmp eax, 0xffffffff
-    je .exit_success
+    
     ; debug
     xor eax, eax
     mov al, [fat_bpb.sectors_per_cluster]
@@ -496,6 +493,17 @@ read_file:
     mov cx, [fat_bpb.bytes_per_sector]
     mul ecx
     
+    mov esi, file_buffer
+    mov ebx, eax
+    call mmove
+    
+    pop esi
+    call read_fat
+    
+    cmp eax, 0xffffffff
+    je .exit_success
+    
+    
     add edi, eax
     jmp read_file
     
@@ -517,19 +525,19 @@ read_fat:
     shr esi, 12
     cmp esi, [loaded_fat_block]
     mov eax, [loaded_fat_block]
-    ; jmp $
+    
     je .read
     
     call cache_file_table
     ; mov eax, [loaded_fat_block]
     ; mov esi, [file_table + 0x4 * 3]
-    ; jmp $
+    
     .read:
         pop esi
         and esi, 0xfff
-        ; jmp $
+        
         mov eax, [esi * 0x4 + file_table]
-        ; jmp $
+        
         ret
 cache_file_table:
     ;args: 
@@ -569,6 +577,30 @@ cache_file_table:
     pop edx
     ret
     jmp $
+
+mmove:
+    ;esi = src
+    ;edi = dest
+    ;ebx = count
+    push eax
+    push ecx
+    
+    ; debug
+    xor ecx, ecx
+    .mlp:
+        cmp ecx, ebx
+        jge .ret
+        mov al, [ds:esi + ecx]
+        mov [ds:edi + ecx], al
+        inc ecx
+        jmp .mlp
+    .ret:
+    ; debug
+        pop ecx
+        pop eax
+        
+        ret
+
 load_elf:
     ;parse elf and relocate each section to it's appropriate location
 ;kernel info
@@ -588,6 +620,7 @@ k_info:
     ;.type:  db 0
 kernel_file: db "kernel", 0x0, 0x0, "elf"
 loaded_fat_block: dd 0
+kload_paddr: dd 0x10000
 file_buffer EQU 0xa000
 root_dir EQU 0x1000
 file_table EQU 0xf000
diff --git a/src/kernel/entry.s b/src/kernel/entry.s
new file mode 100644
index 0000000..119afb7
--- /dev/null
+++ b/src/kernel/entry.s
@@ -0,0 +1,10 @@
+bits 16
+
+global _start
+
+_start:
+    mov ebx, 0xb8000
+    mov word [ds:ebx], 0x0f41
+    cli
+    hlt
+    jmp $
\ No newline at end of file
diff --git a/src/kernel/kmain.c b/src/kernel/kmain.c
new file mode 100644
index 0000000..a4c8922
--- /dev/null
+++ b/src/kernel/kmain.c
@@ -0,0 +1,3 @@
+void kmain(){
+    return;
+}
\ No newline at end of file