Creating a 64-bit kernel: Difference between revisions

 

=== kernel.c ===

void kernel_main(void)

{

/* What goes here is up to you */

}

 

== Compiling ==

Linking will be done later...

 

x86_64-elf-gcc -ffreestanding -mcmodel=large -mno-red-zone -mno-mmx -mno-sse -mno-sse2 -c foo.c -o foo.o

 

The -mcmodel=large argument enables us to run the kernel at any 64-bit virtual memory address we want. In fact, using the 'large' code model is discouraged due to its inefficiency, but it can be fine as a start. Check the [[System V ABI|SysV AMD64 ABI]] document for extra details.

You can link the kernel like this:

 

 

'''Note''': Obviously there is no bootstrap assembly yet, which is the hard part of starting out, and you can't link without it.

Note that, although nasm will not complain about this, Microsoft link will. It complains about address relocations, due to the memory model settings (/LARGEADDRESSAWARE, which is required for /DRIVER).

As such, you need a method of generating the correct 32 bit code, while fooling link into generating a 64 bit relocation. Here is a macro for you:

;Encode 32 bit moves without the ADDR32 issue

%macro mov_abs32 2

;mov_abs32 eax, (gdtr-KADDR_OFFSET)

;lgdt [eax]

 

== Possible Problems ==

[[Category:Tutorials|Creating a 64-bit kernel]]

[[Category:X86-64|Creating a 64-bit kernel]]