bb-bootloader-amd64

A x86_64 Hello World, from bootloader to printf

The main objective is to write a little bootloader abd kernel code that will write on the serial line from x86_64 code.

• stage0 and stage1 are for real mode
• stage2 is for protected mode
• stage3 is for long mode

Usage

A simple make and make boot should do the trick. Make sure to have all the dependencies installed. The printf call is made in a separate win.c file linked with the bootloader.

Paging

This bootloader is using 2-Mbyte page translation for long mode. Please refer to the AMD programmer's manual as it provides a simpler paging documentation than the Intel manual. The virtual address fields are described as follows.

• Bits 63:48 are a sign extension of bit 47 as required for canonical address forms.
• Bits 47:39 index into the 512-entry page-map level-4 table.
• Bits 38:30 index into the 512-entry page-directory-pointer table.
• Bits 29:21 index into the 512-entry page-directory table.
• Bits 20:0 provide the byte offset into the physical page.

The following diagram shows the translation table format used in this bootloader.

This is a must-read

• Intel Architecture Software Developer's Manual Volume 3, section 4.1.2
• Intel Architecture Software Developer's Manual Volume 3, section 4.5.4
• AMD64 Architecture Programmer’s Manual Volume 3, section 5.3