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https://github.com/veracrypt/VeraCrypt
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MBR Bootloader: dynamically determine boot loader memory segment instead of hardcoded values (proposed by neos6464 at https://sourceforge.net/p/veracrypt/tickets/240/)
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@ -43,23 +43,24 @@ main:
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call print
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skip_loader_name_msg:
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; Determine boot loader segment
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mov ax, TC_BOOT_LOADER_SEGMENT
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; Determine boot loader segment
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mov ax, word ptr [ds:413h] ;available kB from BIOS
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sub ax, TC_BOOT_MEMORY_REQUIRED ;minus TC_BOOT_MEMORY_REQUIRED
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jc mem_toolow
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and ax, 0FFE0h ;32K align
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shl ax, 6 ;convert kB to segment addr (*1024/16)
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cmp ax, 8000h
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jb mem_toolow ;we can't load below 8000h
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cmp ax, TC_BOOT_LOADER_SEGMENT
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jbe memory_ok ;don't load above TC_BOOT_LOADER_SEGMENT (9000h)
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mov ax, TC_BOOT_LOADER_SEGMENT
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jmp memory_ok
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; Check available memory
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cmp word ptr [ds:413h], TC_BOOT_LOADER_SEGMENT / 1024 * 16 + TC_BOOT_MEMORY_REQUIRED
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jge memory_ok
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mov ax, TC_BOOT_LOADER_SEGMENT_LOW
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cmp word ptr [ds:413h], TC_BOOT_LOADER_SEGMENT_LOW / 1024 * 16 + TC_BOOT_MEMORY_REQUIRED
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jge memory_ok
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; Insufficient memory
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mov ax, TC_BOOT_LOADER_LOWMEM_SEGMENT
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mem_toolow:
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mov ax, TC_BOOT_LOADER_LOWMEM_SEGMENT
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memory_ok:
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mov es, ax
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mov es, ax
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; Clear BSS section
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xor al, al
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