40 lines
1.7 KiB
Markdown
40 lines
1.7 KiB
Markdown
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# Legacy Loader
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The legacy loader only is another code path which, in the end, merges together
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with the UEFI - code path again. It has no special purpose except of that one.
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## Order of Working
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The Nightloader's Stage 0 - Loader searchs for its partition which has the
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type `0x9d` in the MBR (Master Boot Record).
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It initializes a GDT (Global Descriptor Table) for going into 32-bit - mode,
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making it possible to use more of the RAM. This is particularily useful for
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loading the whole partition of the Stage 2 into RAM without having problems
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with the memory limitations of the 16-bit real mode (which has 20-bit addresses).
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Following that, it loads the 256MB of the NightLoader-partition into memory
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at address 0x8000, or 32768 in decimal. If the partition has another size than
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256MB, the Nightloader - Stage 0 will fail to load it.
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If the partition isn't formatted correctly, the boot process will fail.
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The Stage 0 - loader tries to find the path `/night/starter.bin` in its
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partition and starts that executable code, which it loads to address 0x8000,
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at its first byte.
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Now, the Starter is working. Aforementioned executable code has one purpose:
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load the ELF-executable of the actual Stage 2 - loader and start a function
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inside of it which is named `main`. If such function does not exist, it should
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display a debug-message which basically tells that the user needs a *very*
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skilled technician right about *yesterday*.
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## Current State
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The Nightloader:
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- can find its own partition in the Master Boot Record
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- writes an error message onto the screen if it couldn't find its own partition
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- does not go into 32-bit mode
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- only loads 8 sectors (4096 bytes) of the Stage 2 - partition into the RAM
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