pc

The x86_64 pc implementation uses GRUB as the bootloader.

Config file

ARCH  = x86_64
BOARD = pc
 
# This is only useful when QEMU is used.
CONFIG_SEMIHOSTING = 1

Boot options

The GRUB configuration offers two choices: the normal mode and the kernel mode. The normal (or "default") mode will load the /bin/init program in user mode ("ring 3"). The kernel mode will load the kshell instead and will stay in kernel mode (as its name implies).

It is possible to change the command line by passing the CMDLINE variable to make (or add it to your config file):

$ make clean run-debug CMDLINE="/bin/init foo bar"

Note: It is also possible to set KERNEL_CMDLINE, which is passed to the kernel when it boots in kernel mode.

Early boot sequence

The BIOS loads the bootloader (GRUB) from the ISO
The bootloader reads the kernel executable and finds the multiboot header (placed at the beginning of the .text section)
The bootloader loads the kernel sections into memory (the .text section is loaded at 0x100000)
The bootloader jumps to the entry point (start)
Various checks are performed to make sure we can continue the boot process
The page tables and paging are configured and enabled
A 64-bit Global Descriptor Table is loaded
A Task State Segment is loaded
All the data segment registers are reloaded
The C kmain() function is called
Eventually, the kernel switches to user mode and calls /bin/init by default

See the x86_64 architecture page for memory management/layout details shared with other boards.