462 lines
12 KiB
Go
462 lines
12 KiB
Go
/*
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* Branch/Call/Jump (BCJ) filter decoders
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*
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* Authors: Lasse Collin <lasse.collin@tukaani.org>
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* Igor Pavlov <http://7-zip.org/>
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*
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* Translation to Go: Michael Cross <https://github.com/xi2>
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*
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* This file has been put into the public domain.
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* You can do whatever you want with this file.
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*/
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package xz
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/* from linux/lib/xz/xz_dec_bcj.c *************************************/
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type xzDecBCJ struct {
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/* Type of the BCJ filter being used */
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typ xzFilterID
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/*
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* Return value of the next filter in the chain. We need to preserve
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* this information across calls, because we must not call the next
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* filter anymore once it has returned xzStreamEnd
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*/
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ret xzRet
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/*
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* Absolute position relative to the beginning of the uncompressed
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* data (in a single .xz Block).
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*/
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pos int
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/* x86 filter state */
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x86PrevMask uint32
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/* Temporary space to hold the variables from xzBuf */
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out []byte
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outPos int
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temp struct {
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/* Amount of already filtered data in the beginning of buf */
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filtered int
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/*
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* Buffer to hold a mix of filtered and unfiltered data. This
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* needs to be big enough to hold Alignment + 2 * Look-ahead:
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*
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* Type Alignment Look-ahead
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* x86 1 4
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* PowerPC 4 0
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* IA-64 16 0
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* ARM 4 0
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* ARM-Thumb 2 2
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* SPARC 4 0
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*/
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buf []byte // slice buf will be backed by bufArray
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bufArray [16]byte
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}
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}
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/*
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* This is used to test the most significant byte of a memory address
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* in an x86 instruction.
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*/
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func bcjX86TestMSByte(b byte) bool {
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return b == 0x00 || b == 0xff
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}
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func bcjX86Filter(s *xzDecBCJ, buf []byte) int {
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var maskToAllowedStatus = []bool{
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true, true, true, false, true, false, false, false,
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}
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var maskToBitNum = []byte{0, 1, 2, 2, 3, 3, 3, 3}
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var i int
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var prevPos int = -1
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var prevMask uint32 = s.x86PrevMask
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var src uint32
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var dest uint32
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var j uint32
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var b byte
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if len(buf) <= 4 {
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return 0
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}
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for i = 0; i < len(buf)-4; i++ {
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if buf[i]&0xfe != 0xe8 {
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continue
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}
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prevPos = i - prevPos
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if prevPos > 3 {
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prevMask = 0
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} else {
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prevMask = (prevMask << (uint(prevPos) - 1)) & 7
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if prevMask != 0 {
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b = buf[i+4-int(maskToBitNum[prevMask])]
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if !maskToAllowedStatus[prevMask] || bcjX86TestMSByte(b) {
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prevPos = i
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prevMask = prevMask<<1 | 1
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continue
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}
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}
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}
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prevPos = i
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if bcjX86TestMSByte(buf[i+4]) {
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src = getLE32(buf[i+1:])
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for {
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dest = src - uint32(s.pos+i+5)
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if prevMask == 0 {
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break
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}
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j = uint32(maskToBitNum[prevMask]) * 8
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b = byte(dest >> (24 - j))
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if !bcjX86TestMSByte(b) {
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break
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}
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src = dest ^ (1<<(32-j) - 1)
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}
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dest &= 0x01FFFFFF
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dest |= 0 - dest&0x01000000
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putLE32(dest, buf[i+1:])
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i += 4
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} else {
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prevMask = prevMask<<1 | 1
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}
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}
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prevPos = i - prevPos
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if prevPos > 3 {
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s.x86PrevMask = 0
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} else {
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s.x86PrevMask = prevMask << (uint(prevPos) - 1)
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}
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return i
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}
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func bcjPowerPCFilter(s *xzDecBCJ, buf []byte) int {
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var i int
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var instr uint32
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for i = 0; i+4 <= len(buf); i += 4 {
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instr = getBE32(buf[i:])
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if instr&0xFC000003 == 0x48000001 {
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instr &= 0x03FFFFFC
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instr -= uint32(s.pos + i)
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instr &= 0x03FFFFFC
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instr |= 0x48000001
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putBE32(instr, buf[i:])
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}
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}
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return i
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}
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var bcjIA64BranchTable = [...]byte{
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0, 0, 0, 0, 0, 0, 0, 0,
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0, 0, 0, 0, 0, 0, 0, 0,
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4, 4, 6, 6, 0, 0, 7, 7,
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4, 4, 0, 0, 4, 4, 0, 0,
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}
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func bcjIA64Filter(s *xzDecBCJ, buf []byte) int {
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var branchTable = bcjIA64BranchTable[:]
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/*
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* The local variables take a little bit stack space, but it's less
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* than what LZMA2 decoder takes, so it doesn't make sense to reduce
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* stack usage here without doing that for the LZMA2 decoder too.
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*/
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/* Loop counters */
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var i int
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var j int
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/* Instruction slot (0, 1, or 2) in the 128-bit instruction word */
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var slot uint32
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/* Bitwise offset of the instruction indicated by slot */
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var bitPos uint32
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/* bit_pos split into byte and bit parts */
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var bytePos uint32
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var bitRes uint32
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/* Address part of an instruction */
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var addr uint32
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/* Mask used to detect which instructions to convert */
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var mask uint32
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/* 41-bit instruction stored somewhere in the lowest 48 bits */
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var instr uint64
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/* Instruction normalized with bit_res for easier manipulation */
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var norm uint64
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for i = 0; i+16 <= len(buf); i += 16 {
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mask = uint32(branchTable[buf[i]&0x1f])
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for slot, bitPos = 0, 5; slot < 3; slot, bitPos = slot+1, bitPos+41 {
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if (mask>>slot)&1 == 0 {
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continue
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}
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bytePos = bitPos >> 3
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bitRes = bitPos & 7
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instr = 0
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for j = 0; j < 6; j++ {
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instr |= uint64(buf[i+j+int(bytePos)]) << (8 * uint(j))
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}
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norm = instr >> bitRes
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if (norm>>37)&0x0f == 0x05 && (norm>>9)&0x07 == 0 {
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addr = uint32((norm >> 13) & 0x0fffff)
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addr |= (uint32(norm>>36) & 1) << 20
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addr <<= 4
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addr -= uint32(s.pos + i)
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addr >>= 4
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norm &= ^(uint64(0x8fffff) << 13)
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norm |= uint64(addr&0x0fffff) << 13
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norm |= uint64(addr&0x100000) << (36 - 20)
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instr &= 1<<bitRes - 1
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instr |= norm << bitRes
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for j = 0; j < 6; j++ {
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buf[i+j+int(bytePos)] = byte(instr >> (8 * uint(j)))
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}
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}
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}
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}
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return i
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}
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func bcjARMFilter(s *xzDecBCJ, buf []byte) int {
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var i int
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var addr uint32
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for i = 0; i+4 <= len(buf); i += 4 {
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if buf[i+3] == 0xeb {
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addr = uint32(buf[i]) | uint32(buf[i+1])<<8 |
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uint32(buf[i+2])<<16
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addr <<= 2
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addr -= uint32(s.pos + i + 8)
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addr >>= 2
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buf[i] = byte(addr)
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buf[i+1] = byte(addr >> 8)
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buf[i+2] = byte(addr >> 16)
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}
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}
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return i
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}
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func bcjARMThumbFilter(s *xzDecBCJ, buf []byte) int {
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var i int
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var addr uint32
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for i = 0; i+4 <= len(buf); i += 2 {
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if buf[i+1]&0xf8 == 0xf0 && buf[i+3]&0xf8 == 0xf8 {
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addr = uint32(buf[i+1]&0x07)<<19 |
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uint32(buf[i])<<11 |
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uint32(buf[i+3]&0x07)<<8 |
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uint32(buf[i+2])
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addr <<= 1
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addr -= uint32(s.pos + i + 4)
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addr >>= 1
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buf[i+1] = byte(0xf0 | (addr>>19)&0x07)
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buf[i] = byte(addr >> 11)
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buf[i+3] = byte(0xf8 | (addr>>8)&0x07)
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buf[i+2] = byte(addr)
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i += 2
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}
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}
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return i
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}
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func bcjSPARCFilter(s *xzDecBCJ, buf []byte) int {
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var i int
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var instr uint32
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for i = 0; i+4 <= len(buf); i += 4 {
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instr = getBE32(buf[i:])
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if instr>>22 == 0x100 || instr>>22 == 0x1ff {
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instr <<= 2
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instr -= uint32(s.pos + i)
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instr >>= 2
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instr = (0x40000000 - instr&0x400000) |
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0x40000000 | (instr & 0x3FFFFF)
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putBE32(instr, buf[i:])
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}
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}
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return i
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}
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/*
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* Apply the selected BCJ filter. Update *pos and s.pos to match the amount
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* of data that got filtered.
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*/
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func bcjApply(s *xzDecBCJ, buf []byte, pos *int) {
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var filtered int
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buf = buf[*pos:]
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switch s.typ {
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case idBCJX86:
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filtered = bcjX86Filter(s, buf)
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case idBCJPowerPC:
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filtered = bcjPowerPCFilter(s, buf)
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case idBCJIA64:
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filtered = bcjIA64Filter(s, buf)
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case idBCJARM:
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filtered = bcjARMFilter(s, buf)
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case idBCJARMThumb:
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filtered = bcjARMThumbFilter(s, buf)
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case idBCJSPARC:
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filtered = bcjSPARCFilter(s, buf)
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default:
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/* Never reached */
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}
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*pos += filtered
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s.pos += filtered
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}
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/*
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* Flush pending filtered data from temp to the output buffer.
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* Move the remaining mixture of possibly filtered and unfiltered
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* data to the beginning of temp.
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*/
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func bcjFlush(s *xzDecBCJ, b *xzBuf) {
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var copySize int
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copySize = len(b.out) - b.outPos
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if copySize > s.temp.filtered {
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copySize = s.temp.filtered
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}
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copy(b.out[b.outPos:], s.temp.buf[:copySize])
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b.outPos += copySize
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s.temp.filtered -= copySize
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copy(s.temp.buf, s.temp.buf[copySize:])
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s.temp.buf = s.temp.buf[:len(s.temp.buf)-copySize]
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}
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/*
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* Decode raw stream which has a BCJ filter as the first filter.
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*
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* The BCJ filter functions are primitive in sense that they process the
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* data in chunks of 1-16 bytes. To hide this issue, this function does
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* some buffering.
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*/
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func xzDecBCJRun(s *xzDecBCJ, b *xzBuf, chain func(*xzBuf) xzRet) xzRet {
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var outStart int
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/*
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* Flush pending already filtered data to the output buffer. Return
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* immediately if we couldn't flush everything, or if the next
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* filter in the chain had already returned xzStreamEnd.
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*/
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if s.temp.filtered > 0 {
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bcjFlush(s, b)
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if s.temp.filtered > 0 {
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return xzOK
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}
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if s.ret == xzStreamEnd {
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return xzStreamEnd
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}
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}
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/*
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* If we have more output space than what is currently pending in
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* temp, copy the unfiltered data from temp to the output buffer
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* and try to fill the output buffer by decoding more data from the
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* next filter in the chain. Apply the BCJ filter on the new data
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* in the output buffer. If everything cannot be filtered, copy it
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* to temp and rewind the output buffer position accordingly.
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*
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* This needs to be always run when len(temp.buf) == 0 to handle a special
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* case where the output buffer is full and the next filter has no
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* more output coming but hasn't returned xzStreamEnd yet.
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*/
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if len(s.temp.buf) < len(b.out)-b.outPos || len(s.temp.buf) == 0 {
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outStart = b.outPos
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copy(b.out[b.outPos:], s.temp.buf)
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b.outPos += len(s.temp.buf)
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s.ret = chain(b)
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if s.ret != xzStreamEnd && s.ret != xzOK {
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return s.ret
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}
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bcjApply(s, b.out[:b.outPos], &outStart)
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/*
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* As an exception, if the next filter returned xzStreamEnd,
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* we can do that too, since the last few bytes that remain
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* unfiltered are meant to remain unfiltered.
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*/
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if s.ret == xzStreamEnd {
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return xzStreamEnd
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}
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s.temp.buf = s.temp.bufArray[:b.outPos-outStart]
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b.outPos -= len(s.temp.buf)
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copy(s.temp.buf, b.out[b.outPos:])
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/*
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* If there wasn't enough input to the next filter to fill
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* the output buffer with unfiltered data, there's no point
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* to try decoding more data to temp.
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*/
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if b.outPos+len(s.temp.buf) < len(b.out) {
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return xzOK
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}
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}
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/*
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* We have unfiltered data in temp. If the output buffer isn't full
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* yet, try to fill the temp buffer by decoding more data from the
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* next filter. Apply the BCJ filter on temp. Then we hopefully can
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* fill the actual output buffer by copying filtered data from temp.
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* A mix of filtered and unfiltered data may be left in temp; it will
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* be taken care on the next call to this function.
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*/
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if b.outPos < len(b.out) {
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/* Make b.out temporarily point to s.temp. */
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s.out = b.out
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s.outPos = b.outPos
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b.out = s.temp.bufArray[:]
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b.outPos = len(s.temp.buf)
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s.ret = chain(b)
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s.temp.buf = s.temp.bufArray[:b.outPos]
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b.out = s.out
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b.outPos = s.outPos
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if s.ret != xzOK && s.ret != xzStreamEnd {
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return s.ret
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}
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bcjApply(s, s.temp.buf, &s.temp.filtered)
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/*
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* If the next filter returned xzStreamEnd, we mark that
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* everything is filtered, since the last unfiltered bytes
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* of the stream are meant to be left as is.
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*/
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if s.ret == xzStreamEnd {
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s.temp.filtered = len(s.temp.buf)
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}
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bcjFlush(s, b)
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if s.temp.filtered > 0 {
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return xzOK
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}
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}
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return s.ret
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}
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/*
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* Allocate memory for BCJ decoders. xzDecBCJReset must be used before
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* calling xzDecBCJRun.
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*/
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func xzDecBCJCreate() *xzDecBCJ {
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return new(xzDecBCJ)
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}
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/*
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* Decode the Filter ID of a BCJ filter and check the start offset is
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* valid. Returns xzOK if the given Filter ID and offset is
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* supported. Otherwise xzOptionsError is returned.
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*/
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func xzDecBCJReset(s *xzDecBCJ, id xzFilterID, offset int) xzRet {
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switch id {
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case idBCJX86:
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case idBCJPowerPC:
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case idBCJIA64:
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case idBCJARM:
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case idBCJARMThumb:
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case idBCJSPARC:
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default:
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/* Unsupported Filter ID */
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return xzOptionsError
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}
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// check offset is a multiple of alignment
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switch id {
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case idBCJPowerPC, idBCJARM, idBCJSPARC:
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if offset%4 != 0 {
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return xzOptionsError
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}
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case idBCJIA64:
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if offset%16 != 0 {
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return xzOptionsError
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}
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case idBCJARMThumb:
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if offset%2 != 0 {
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return xzOptionsError
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}
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}
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s.typ = id
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s.ret = xzOK
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s.pos = offset
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s.x86PrevMask = 0
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s.temp.filtered = 0
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s.temp.buf = nil
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return xzOK
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}
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