Hello World!

.gitignore

@@ -1 +1,2 @@
 .envrc
+.ccls-cache

Makefile

@@ -0,0 +1,82 @@
+TARGET=i686
+ARCHDIR=arch/$(TARGET)/
+SOURCEDIR=src/
+BUILDDIR=build/
+
+INCLUDEDIR=$(SOURCEDIR)include/
+
+CFLAGS?=
+ASFLAGS?=
+
+# Define flags for C files
+CFLAGS:=\
+-O2 \
+-std=gnu99 \
+-ffreestanding \
+-Wall -Wextra \
+-Wno-incompatible-pointer-types\
+-I$(INCLUDEDIR) \
+$(CFLAGS)
+
+# Define flags for assembly files
+ASFLAGS:=\
+-I$(SOURCEIDR)$(INCLUDEDIR) \
+-I$(SOURCEDIR)$(ARCHDIR) \
+$(ASFLAGS)
+
+LINKERFLAGS:=\
+-ffreestanding \
+-O2 \
+-nostdlib \
+-lgcc
+
+LIB_OBJS=\
+$(BUILDDIR)$(ARCHDIR)bootstrap.o
+
+KERNEL_OBJS=\
+$(BUILDDIR)kernel/kernel.o
+
+OBJS=$(LIB_OBJS) $(KERNEL_OBJS)
+
+LINKER_PATH=$(SOURCEDIR)$(ARCHDIR)linker.ld
+
+.PHONY: all clean snowstorm.iso debug
+.SUFFIXES: .c .o .s
+
+$(BUILDDIR)%.o : $(SOURCEDIR)%.c
+	i686-elf-gcc -c $< -o $@ $(CFLAGS)
+
+$(BUILDDIR)%.o : $(SOURCEDIR)%.s
+	i686-elf-as $< -o $@ $(ASFLAGS)
+
+all: snowstorm.iso
+
+# Take the kernel file and make a bootable ISO through GRUB
+snowstorm.iso: snowstorm.kernel
+	cp build/snowstorm.kernel build/isodir/boot/snowstorm.kernel
+	grub-mkrescue -o build/snowstorm.iso build/isodir
+
+# link all object files together
+snowstorm.kernel: $(OBJS)
+	i686-elf-gcc -T $(LINKER_PATH) -o build/snowstorm.kernel $(OBJS) $(LINKERFLAGS) 
+	grub-file --is-x86-multiboot build/snowstorm.kernel
+
+debug: CFLAGS += -g -O0
+debug: ASFLAGS += -g
+debug: all
+
+
+clean:
+	rm -f $(OBJS)
+	rm -f build/snowstorm.kernel
+	rm -f build/snowstorm.iso
+	rm -f build/isodir/boot/snowstorm.kernel
+
+run: all
+	qemu-system-i386 -d int -no-reboot -kernel build/snowstorm.kernel
+
+run-debug: debug
+	qemu-system-i386 -d int -no-reboot -S -gdb tcp::9000 build/snowstorm.iso
+
+run-debug-kernel: debug
+	qemu-system-i386 -d int -no-reboot -S -gdb tcp::9000 -kernel build/snowstorm.kernel

build/isodir/boot/grub/grub.cfg

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+menuentry "snowstorm" {
+	multiboot /boot/snowstorm.kernel
+}

src/arch/i686/bootstrap.s

@@ -1 +1,42 @@
+# Declare constants for the multiboot header.
+.set ALIGN,    1<<0             # align loaded modules on page boundaries
+.set MEMINFO,  1<<1             # provide memory map
+.set FLAGS,    ALIGN | MEMINFO  # this is the Multiboot 'flag' field
+.set MAGIC,    0x1BADB002       # 'magic number' lets bootloader find the header
+.set CHECKSUM, -(MAGIC + FLAGS) # checksum of above, to prove we are multiboot
+
+# Declare a multiboot header that marks the program as a kernel.
+.section .multiboot.data, "aw"
+.align 4
+.long MAGIC
+.long FLAGS
+.long CHECKSUM
+
+.section .bss, "aw", @nobits
+.align 16
+stack_bottom:
+.skip (1 << 16) # 64 KiB
+stack_top:
+
+.global boot_page_directory
+ 	.align 4096
+boot_page_directory:
+	.skip 4096
+boot_page_table1:
+    .skip 4096
+
+.section .multiboot.text, "a"
+.global _start
+.type _start, @function
+.extern kernel_main
+_start:
+	mov $stack_top, %esp # The stack grows downwards so it starts at the top
+    # (We kind of need to have a stack to do anything)
+
+    call kernel_main
+
+    # Infinite loop if kernel_main returns, (which it shouldn't do)
+    cli
+1:  hlt
+    jmp 1b
 

src/arch/i686/linker.ld

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+ENTRY(_start)
+
+
+SECTIONS
+{
+    /* Leave 1 Megabyte for GRUB */
+	. = 1M;
+
+    .multiboot.data : 
+    {
+        *(.multiboot.data) /* Take the data from label .multiboot.data from all files and put it in our output file */
+    }
+
+    .multiboot.text : 
+    {
+        *(.multiboot.text) /* Take the data from label .multiboot.data from all files and put it in our output file */
+    }
+
+    .bss : 
+    {
+        *(.bss) /* Take the data from label .multiboot.data from all files and put it in our output file */
+    }
+
+    .data : 
+    {
+        *(.data) /* Take the data from label .multiboot.data from all files and put it in our output file */
+    }
+
+}

src/include/strlib.h

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+static inline int strlen(char *str) {
+    int len = 0;
+    while (str[len] != '\0') {
+        len += 1;
+    }
+    return len;
+}

src/kernel/kernel.c

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+#include <stdbool.h>
+#include <stdint.h>
+#include "strlib.h"
+
+uint16_t* VGA_screen = (uint16_t*)0xB8000;
+char* text = "Hello World!";
+
+void kernel_main() {
+    for (int i = 0; i < strlen(text); i++) {
+        VGA_screen[i] = text[i] | 0x0F00; // 0x0F00: two bytes color, two bytes to combine it with text
+    }
+}