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\chapter{Boot Loading Process}

\chapter{Boot Loading Process}

The startup of HelenOS happens in several steps.

The startup of HelenOS happens in several steps.

Depending on the platform these steps can be either

Depending on the platform these steps can be either

described as \textit{piggybacker loading}:

described as \textit{piggybacker loading}:

\begin{enumerate}

\begin{enumerate}

 \item Platform boot loader loads the piggybacker image

 \item Platform boot loader loads the piggybacker image

       and jumps to its entry point.

       and jumps to its entry point.

 \item The piggybacker unwraps the kernel image and

 \item The piggybacker unwraps the kernel image and

       the images of the initial user space tasks, creates

       the images of the initial user space tasks, creates

       a boot information structure and jumps to the

       a boot information structure and jumps to the

       entry point of the kernel.

       entry point of the kernel.

 \item The kernel initializes and runs the initial tasks

 \item The kernel initializes and runs the initial tasks

       according the boot information structure from the

       according the boot information structure from the

       piggybacker.

       piggybacker.

\end{enumerate}

\end{enumerate}

If the platform supports a more sophisticated native boot loader,

If the platform supports a more sophisticated native boot loader,

a \textit{multiboot loading} contains following steps:

a \textit{multiboot loading} contains following steps:

\begin{enumerate}

\begin{enumerate}

 \item Platform boot loader loads the kernel image and initial

 \item Platform boot loader loads the kernel image and initial

       user space tasks, creates a boot information structure

       user space tasks, creates a boot information structure

       and jumps to the entry point of the kernel.

       and jumps to the entry point of the kernel.

 \item The kernel initializes and runs the initial tasks

 \item The kernel initializes and runs the initial tasks

       according the boot information structure from the

       according the boot information structure from the

       boot loader.

       boot loader.

\end{enumerate}

\end{enumerate}

A third kind of boot loading occurs on platforms with no support

A third kind of boot loading occurs on platforms with no support

of boot loader. It is called \textit{image loading} and is

of boot loader. It is called \textit{image loading} and is

used mostly on simulated architectures.

used mostly on simulated architectures.

\begin{enumerate}

\begin{enumerate}

 \item The kernel and initial user space images are placed

 \item The kernel and initial user space images are placed

       on well-known physical memory locations (usually

       on well-known physical memory locations (usually

       by a simulator configuration file). The execution

       by a simulator configuration file). The execution

       starts directly on the kernel entry point.

       starts directly on the kernel entry point.

 \item The kernel initializes and runs a previously hardwired

 \item The kernel initializes and runs a previously hardwired

       number of initial user space tasks.

       number of initial user space tasks.

\end{enumerate}

\end{enumerate}

The following sections describe the particual features of the

The following sections describe the particual features of the

\section{IA-32 and AMD64}

\section{IA-32 and AMD64}

On both platforms HelenOS depends on a boot loader which

On both platforms HelenOS depends on a boot loader which

supports the Multiboot Specification (i.e. GRUB). The kernel

supports the Multiboot Specification (i.e. GRUB). The kernel

image (usually called \texttt{image.bin}) is loaded by the

image (usually called \texttt{image.bin}) is loaded by the

boot loader just above the 1st megabyte of the physical

boot loader just above the 1st megabyte of the physical

memory (the exact location is 1081344 bytes). Modules loaded by