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124 | decky | 1 | \chapter{Boot Loading Process} |
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3 | The startup of HelenOS happens in several steps. |
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4 | Depending on the platform these steps can be either |
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5 | described as \textit{piggybacker loading}: |
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7 | \begin{enumerate} |
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8 | \item Platform boot loader loads the piggybacker image |
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9 | and jumps to its entry point. |
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10 | \item The piggybacker unwraps the kernel image and |
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11 | the images of the initial user space tasks, creates |
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12 | a boot information structure and jumps to the |
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13 | entry point of the kernel. |
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14 | \item The kernel initializes and runs the initial tasks |
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15 | according the boot information structure from the |
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16 | piggybacker. |
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17 | \end{enumerate} |
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18 | |||
19 | If the platform supports a more sophisticated native boot loader, |
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20 | a \textit{multiboot loading} contains following steps: |
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21 | |||
22 | \begin{enumerate} |
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23 | \item Platform boot loader loads the kernel image and initial |
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24 | user space tasks, creates a boot information structure |
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25 | and jumps to the entry point of the kernel. |
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26 | \item The kernel initializes and runs the initial tasks |
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27 | according the boot information structure from the |
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28 | boot loader. |
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29 | \end{enumerate} |
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30 | |||
31 | A third kind of boot loading occurs on platforms with no support |
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32 | of boot loader. It is called \textit{image loading} and is |
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33 | used mostly on simulated architectures. |
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34 | |||
35 | \begin{enumerate} |
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36 | \item The kernel and initial user space images are placed |
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37 | on well-known physical memory locations (usually |
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38 | by a simulator configuration file). The execution |
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39 | starts directly on the kernel entry point. |
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40 | \item The kernel initializes and runs a previously hardwired |
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41 | number of initial user space tasks. |
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42 | \end{enumerate} |
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44 | The following sections describe the particual features of the |
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45 | boot loading process on the supported platforms. |
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46 | |||
47 | \section{IA-32 and AMD64} |
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48 | |||
49 | On both platforms HelenOS depends on a boot loader which |
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50 | supports the Multiboot Specification (i.e. GRUB). The kernel |
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51 | image (usually called \texttt{image.bin}) is loaded by the |
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52 | boot loader just above the 1st megabyte of the physical |
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53 | memory (the exact location is 1081344 bytes). |