mirror of
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4fa82854dd
- bl stage 1: move gdt+pm setup to stage 2 (avoids mode switching) - bl stage 2: at entry query e820 table from bios, then setup gdt+pm - kernel/memmap: pad map entry to 24 bytes, as exported by bl - kernel/memmap: map copy (gbowne1) - Makefile: facilitate placing the memory map at a known location - Update bl docs
28 lines
743 B
Markdown
28 lines
743 B
Markdown
# ClassicOS 2-stage bootloader
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Bootloader documentation for ClassicOS
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## Disk image organization:
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```
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[ 512 B ] [ 2048 B ] [ Unspecified ]
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Stage 1 Stage 2 Kernel
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```
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## Stage 1 (`stage1.asm`)
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- Queries CHS parameters from BIOS
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- Loads the second stage bootloader (2048 B) to `0x7c00`
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- Enables A20
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- Jumps to stage2
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## Stage 2 (`stage2.asm, stage2_load.c`)
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- Read and store E820 memory map from BIOS
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- Sets up a GDT with descriptor entries for code and data both covering the whole 32-bit address space
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- Set CR0.PE (enable protected mode)
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- Set up segment registers
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- Load the kernel ELF header
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- Parse the program headers, and load all `PT_LOAD` segments from disk
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- Jump to the kernel entry
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