130 lines
3.0 KiB
ArmAsm
130 lines
3.0 KiB
ArmAsm
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/*
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* Copyright (C) 1996-2002 Markus Franz Xaver Johannes Oberhumer
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*
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* This file is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of
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* the License, or (at your option) any later version.
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*
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* Originally this code was part of ucl the data compression library
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* for upx the ``Ultimate Packer of eXecutables''.
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*
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* - Converted to gas assembly, and refitted to work with etherboot.
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* Eric Biederman 20 Aug 2002
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*
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* - Structure modified to be a subroutine call rather than an
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* executable prefix.
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* Michael Brown 30 Mar 2004
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*/
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.text
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.arch i386
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.section ".prefix", "ax", @progbits
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.code32
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.globl decompress
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decompress:
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/* Save the initial register values */
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pushal
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/*
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* See where I am running, and compute %ebp
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* %ebp holds delta between physical and virtual addresses.
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*/
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call 1f
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1: popl %ebp
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subl $1b, %ebp
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/* "compressed" and "decompress_to" defined by linker script */
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/* move compressed image up to temporary area before decompressing */
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std
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movl $_compressed_size, %ecx
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leal _compressed+4-1(%ebp, %ecx), %esi
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leal _compressed_copy-1(%ebp, %ecx), %edi
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rep movsb
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/* Setup to run the decompressor */
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cld
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leal _compressed_copy(%ebp), %esi
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leal decompress_to(%ebp), %edi
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movl $-1, %ebp /* last_m_off = -1 */
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jmp dcl1_n2b
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/* ------------- DECOMPRESSION -------------
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Input:
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%esi - source
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%edi - dest
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%ebp - -1
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cld
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Output:
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%eax - 0
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%ecx - 0
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*/
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.macro getbit bits
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.if \bits == 1
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addl %ebx, %ebx
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jnz 1f
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.endif
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movl (%esi), %ebx
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subl $-4, %esi /* sets carry flag */
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adcl %ebx, %ebx
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1:
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.endm
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decompr_literals_n2b:
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movsb
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decompr_loop_n2b:
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addl %ebx, %ebx
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jnz dcl2_n2b
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dcl1_n2b:
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getbit 32
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dcl2_n2b:
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jc decompr_literals_n2b
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xorl %eax, %eax
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incl %eax /* m_off = 1 */
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loop1_n2b:
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getbit 1
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adcl %eax, %eax /* m_off = m_off*2 + getbit() */
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getbit 1
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jnc loop1_n2b /* while(!getbit()) */
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xorl %ecx, %ecx
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subl $3, %eax
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jb decompr_ebpeax_n2b /* if (m_off == 2) goto decompr_ebpeax_n2b ? */
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shll $8, %eax
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movb (%esi), %al /* m_off = (m_off - 3)*256 + src[ilen++] */
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incl %esi
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xorl $-1, %eax
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jz decompr_end_n2b /* if (m_off == 0xffffffff) goto decomp_end_n2b */
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movl %eax, %ebp /* last_m_off = m_off ?*/
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decompr_ebpeax_n2b:
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getbit 1
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adcl %ecx, %ecx /* m_len = getbit() */
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getbit 1
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adcl %ecx, %ecx /* m_len = m_len*2 + getbit()) */
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jnz decompr_got_mlen_n2b /* if (m_len == 0) goto decompr_got_mlen_n2b */
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incl %ecx /* m_len++ */
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loop2_n2b:
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getbit 1
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adcl %ecx, %ecx /* m_len = m_len*2 + getbit() */
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getbit 1
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jnc loop2_n2b /* while(!getbit()) */
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incl %ecx
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incl %ecx /* m_len += 2 */
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decompr_got_mlen_n2b:
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cmpl $-0xd00, %ebp
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adcl $1, %ecx /* m_len = m_len + 1 + (last_m_off > 0xd00) */
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pushl %esi
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leal (%edi,%ebp), %esi /* m_pos = dst + olen + -m_off */
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rep
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movsb /* dst[olen++] = *m_pos++ while(m_len > 0) */
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popl %esi
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jmp decompr_loop_n2b
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decompr_end_n2b:
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/* Restore the initial register values */
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popal
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ret
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