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\chapter{Boot Loading Process}
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The startup of HelenOS happens in several steps.
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Depending on the platform these steps can be either
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described as \textit{piggybacker loading}:
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\begin{enumerate}
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 \item Platform boot loader loads the piggybacker image
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       and jumps to its entry point.
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 \item The piggybacker unwraps the kernel image and
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       the images of the initial user space tasks, creates
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       a boot information structure and jumps to the
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       entry point of the kernel.
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 \item The kernel initializes and runs the initial tasks
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       according the boot information structure from the
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       piggybacker.
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\end{enumerate}
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If the platform supports a more sophisticated native boot loader,
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a \textit{multiboot loading} contains following steps:
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\begin{enumerate}
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 \item Platform boot loader loads the kernel image and initial
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       user space tasks, creates a boot information structure
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       and jumps to the entry point of the kernel.
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 \item The kernel initializes and runs the initial tasks
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       according the boot information structure from the
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       boot loader.
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\end{enumerate}
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A third kind of boot loading occurs on platforms with no support
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of boot loader. It is called \textit{image loading} and is
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used mostly on simulated architectures.
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\begin{enumerate}
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 \item The kernel and initial user space images are placed
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       on well-known physical memory locations (usually
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       by a simulator configuration file). The execution
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       starts directly on the kernel entry point.
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 \item The kernel initializes and runs a previously hardwired
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       number of initial user space tasks.
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\end{enumerate}
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The following sections describe the particual features of the
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boot loading process on the supported platforms.
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\section{IA-32 and AMD64}
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On both platforms HelenOS depends on a boot loader which
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supports the Multiboot Specification (i.e. GRUB). The kernel
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image (usually called \texttt{image.bin}) is loaded by the
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boot loader just above the 1st megabyte of the physical
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memory (the exact location is 1081344 bytes).