Added targets for Qemu and GRUB2 boot, updated README.

README.md

@@ -4,19 +4,27 @@ The main goal of the project is to be multiboot compliant and bootable through
 a bootloader supporting the multiboot standard.
 The architecture in mind now is x86 and it is assumed that the system is in legacy BIOS mode.
 
-## Build
+## Build and install
 
 ### Environment
 
 - Ubuntu 20.04
 - Install dependencies: `sudo apt install g++ binutils libc6-dev-i386 make`
+- Optional dependencies (if you plan to boot the kernel with Qemu): `sudo apt qemu-system-x86`
 
-To build issue command `make mykernel.bin` in `src`.
+### Boot with Qemu 
 
-To install issue `make install` in `src`. This requires sudo privilages
-and will do the build as well.
+Most will prefer this.
 
-The kernel binary by default is installed into `/boot` with `make install`.
+1. To build and install issue command `make install` in `src`.
+2. To boot the kernel with Qemu issue `qemu-system-i386 --kernel mykernel.bin` in `out`.
+
+### Boot on real hardware with GRUB2
+
+This will NOT break your system in any way ;).
+If you want to run it on bare metal, you must have GRUB2 installed.
+
+The kernel binary by default is installed into `/boot` with `make grubinstall`.
 There are multiple ways to add it as an entry, but the easy and dirty way is to add it
 explicitly as a custom binary into the generated GRUB script, which is located at
 `/boot/grub/grub.cfg`.

src/Makefile

@@ -18,6 +18,8 @@ mykernel.bin: linker.ld ${objectfiles}
 	ld ${LD_PARAMS} -T $< -o $@ ${objectfiles}
 
 install: mykernel.bin
-	sudo cp $< /boot/mykernel.bin
 	mv $< ../out
 	mv *.o ../out
+
+grubinstall: mykernel.bin
+	sudo cp $< /boot/mykernel.bin

src/kernel.cpp

@@ -3,6 +3,9 @@ typedef unsigned short USHORT;
 #define HIGH_BYTE 0xFF00
 #define VRAM_ADDRS (USHORT*)0xb8000
 #define MESSAGE (char*)"Kernel main test"
+#define TRUE 1==1
+#define FALSE !TRUE
+#define LANG_C "C"
 
 /* As we do not use glibc, we must write our very basic implementation of print.
  * This implementation only support putting ASCII characters on the screen, with black background and white text.
@@ -14,11 +17,10 @@ typedef unsigned short USHORT;
  * */
 void printf(char* str) 
 { 
- USHORT* vram= VRAM_ADDRS;
+ USHORT* vram = VRAM_ADDRS;
 
  for(int i = 0; str[i] != '\0'; ++i) {
-     USHORT vram_high_byte = (vram[i] & HIGH_BYTE);
-     vram[i] = vram_high_byte | str[i];
+     vram[i] = (USHORT)(vram[i] & HIGH_BYTE) | str[i];
  }
 }
 
@@ -28,7 +30,7 @@ void printf(char* str)
  * to the stack. The multiboot structure can be used for kernel operation, while
  * the multiboot flag can be used to make sure the enviroment is indeed multiboot.
  * */
-extern "C" void kernel_main(void* multiboot_struct, unsigned int multiboot_flag) {
+extern LANG_C void kernel_main(void* multiboot_struct, unsigned int multiboot_flag) {
     printf(MESSAGE);
-    while(1);
+    while(TRUE);
 }