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Merged mcb30-realmode-redesign back to HEAD
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Michael Brown
@@ -15,115 +15,159 @@
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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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* - Modified to be compilable as either 16-bit or 32-bit code.
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* Michael Brown 9 Mar 2005
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*/
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/****************************************************************************
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* This file provides the decompress_block() and decompress_block16()
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* functions which can be called in order to decompress an image
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* compressed with the nrv2b utility in src/util.
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*
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* These functions are designed to be called by the prefix. They are
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* position-independent code.
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*
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* The same basic assembly code is used to compile both
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* decompress_block() and decompress_block16().
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****************************************************************************
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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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#ifdef CODE16
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/****************************************************************************
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* decompress_block16 (real-mode near call, position independent)
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*
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* Parameters (passed via registers):
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* %ds:%si - Pointer to compressed input data
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* %es:%di - Pointer to output buffer
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* Returns:
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* All registers are preserved
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*
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* NOTE: The compressed data size must be in the range [1,65533-%si]
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* and the uncompressed data size must be in the range [1,65536-%di]
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* (where %si and %di are the input values for those registers). Note
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* particularly that the lower limit is 1, not 0, and that the upper
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* limit on the input (compressed) data really is 65533, since the
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* algorithm may read up to three bytes beyond the end of the input
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* data, since it reads dwords.
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*
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* Although splitting up the data into (almost) 64kB chunks for
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* compression is awkward and worsens the compression ratio, it has
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* little to no practical effect since our image size is currently
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* <64kB for all single drivers. Having a decompression routine that
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* can run in real-mode avoids the need to duplicate RM-to-PM
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* transition code from librm (or have part of librm kept
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* uncompressed, which is itself awkward) and means that we don't need
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* to set up the PM stack until we hit the setup routine itself.
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****************************************************************************
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*/
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#define REG(x) x
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.code16
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.globl decompress_block16
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decompress_block16:
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.globl decompress
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decompress:
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/* Save the initial register values */
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#else /* CODE16 */
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/****************************************************************************
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* decompress_block (32-bit protected-mode near call, position independent)
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*
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* Parameters (passed via registers):
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* %ds:%esi - Pointer to compressed input data
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* %es:%edi - Pointer to output buffer
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* Returns:
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* All registers are preserved
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****************************************************************************
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*/
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#define REG(x) e ## x
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.code32
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.globl decompress_block
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decompress_block:
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#endif /* CODE16 */
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#define xAX REG(ax)
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#define xCX REG(cx)
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#define xBP REG(bp)
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#define xSI REG(si)
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#define xDI REG(di)
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/* Save registers */
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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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/* Do the decompression */
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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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xor %xBP, %xBP
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dec %xBP /* 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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call getbit32
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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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xor %xAX, %xAX
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inc %xAX /* 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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call getbit1
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adc %xAX, %xAX /* m_off = m_off*2 + getbit() */
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call getbit1
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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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sub $3, %xAX
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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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shl $8, %xAX
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movb (%xSI), %al /* m_off = (m_off - 3)*256 + src[ilen++] */
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inc %xSI
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not %xAX
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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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mov %xAX, %xBP /* 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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xor %xCX, %xCX
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call getbit1
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adc %xCX, %xCX /* m_len = getbit() */
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call getbit1
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adc %xCX, %xCX /* 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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inc %xCX /* 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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call getbit1
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adc %xCX, %xCX /* m_len = m_len*2 + getbit() */
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call getbit1
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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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inc %xCX
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inc %xCX /* 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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cmp $-0xd00, %xBP
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adc $1, %xCX /* m_len = m_len + 1 + (last_m_off > 0xd00) */
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push %xSI
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lea (%xBP,%xDI), %xSI /* 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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es movsb /* dst[olen++] = *m_pos++ while(m_len > 0) */
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pop %xSI
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jmp decompr_loop_n2b
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getbit1:
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addl %ebx, %ebx
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jnz 1f
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getbit32:
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movl (%xSI), %ebx
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sub $-4, %xSI /* sets carry flag */
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adcl %ebx, %ebx
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1:
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ret
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decompr_end_n2b:
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/* Restore the initial register values */
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/* Restore registers and return */
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popal
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ret
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