9c3ead9386
removes external dependency on tinf by replacing the compression algorithm with a simpler, faster, smaller and more auditable fixed-width LZ77 encoding purpose-tailored to x86 code mixed with data. before: decompressor.bin 2,492 bytes (tinf dependency) with .text 0x875 and .rodata 0x13c bytes each. after: decompressor.bin consists only of .text, 0xe6-byte decompressor; 90.8% reduction in decompressor volume. the dependency on gzip during compile-time is replaced by host/limlzpack.c, a Lempel-Ziv encoder in 275 SLoC that uses a suffix array matchfinder (prefix-doubling in mathcal O(n log^2 n) and Storer-Szymanski backwards parse. the fixed-width formats packets as [F][LLLL][MMM], favouring a literal-skewed distribution with F switching between one-byte and two-byte offsets (favouring recent statistics). integrity checking is done via crc32 with the polynomial 0xEDB88320, reflected. the effective loss in compression ratio by using a tremendously simpler and less packed with edge cases algorithm causes a compression ratio hit well below 1KB, factoring in the stub sizes. also adds new machinery for host cc detection per review.
61 lines
950 B
NASM
61 lines
950 B
NASM
org 0x7c00
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bits 16
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start:
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cli
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cld
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jmp 0x0000:.initialise_cs
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.initialise_cs:
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xor ax, ax
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mov ds, ax
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mov es, ax
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mov ss, ax
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mov sp, 0x7c00
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lgdt [gdt]
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mov eax, cr0
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bts ax, 0
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mov cr0, eax
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jmp 0x08:.mode32
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bits 32
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.mode32:
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mov eax, 0x10
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mov ds, ax
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mov es, ax
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mov fs, ax
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mov gs, ax
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mov ss, ax
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push 0x1
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and edx, 0xff
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push edx
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push stage2.size
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push (stage2 - decompressor) + 0x70000
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mov esi, decompressor
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mov edi, 0x70000
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mov ecx, stage2.fullsize
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rep movsb
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call 0x70000
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; Includes
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%include '../gdt.asm'
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; ********************* Stage 2 *********************
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decompressor:
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%strcat DECOMPRESSOR_PATH BUILDDIR, '/decompressor-build/decompressor.bin'
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incbin DECOMPRESSOR_PATH
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align 16
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stage2:
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%strcat STAGE2_PATH BUILDDIR, '/common-bios/stage2.bin.limlz'
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incbin STAGE2_PATH
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.size: equ $ - stage2
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.fullsize: equ $ - decompressor
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