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/*
* Branch/Call/Jump (BCJ) filter decoders
*
* Authors: Lasse Collin <lasse.collin@tukaani.org>
* Igor Pavlov <http://7-zip.org/>
*
* This file has been put into the public domain.
* You can do whatever you want with this file.
*/
#include "xz_private.h"
/*
* The rest of the file is inside this ifdef. It makes things a little more
* convenient when building without support for any BCJ filters.
*/
#ifdef XZ_DEC_BCJ
struct xz_dec_bcj {
/* Type of the BCJ filter being used */
enum {
BCJ_X86 = 4, /* x86 or x86-64 */
BCJ_POWERPC = 5, /* Big endian only */
BCJ_IA64 = 6, /* Big or little endian */
BCJ_ARM = 7, /* Little endian only */
BCJ_ARMTHUMB = 8, /* Little endian only */
BCJ_SPARC = 9 /* Big or little endian */
} type;
/*
* Return value of the next filter in the chain. We need to preserve
* this information across calls, because we must not call the next
* filter anymore once it has returned XZ_STREAM_END.
*/
enum xz_ret ret;
/* True if we are operating in single-call mode. */
bool single_call;
/*
* Absolute position relative to the beginning of the uncompressed
* data (in a single .xz Block). We care only about the lowest 32
* bits so this doesn't need to be uint64_t even with big files.
*/
uint32_t pos;
/* x86 filter state */
uint32_t x86_prev_mask;
/* Temporary space to hold the variables from struct xz_buf */
uint8_t *out;
size_t out_pos;
size_t out_size;
struct {
/* Amount of already filtered data in the beginning of buf */
size_t filtered;
/* Total amount of data currently stored in buf */
size_t size;
/*
* Buffer to hold a mix of filtered and unfiltered data. This
* needs to be big enough to hold Alignment + 2 * Look-ahead:
*
* Type Alignment Look-ahead
* x86 1 4
* PowerPC 4 0
* IA-64 16 0
* ARM 4 0
* ARM-Thumb 2 2
* SPARC 4 0
*/
uint8_t buf[16];
} temp;
};
#ifdef XZ_DEC_X86
/*
* This is used to test the most significant byte of a memory address
* in an x86 instruction.
*/
static inline int bcj_x86_test_msbyte(uint8_t b)
{
return b == 0x00 || b == 0xFF;
}
static size_t bcj_x86(struct xz_dec_bcj *s, uint8_t *buf, size_t size)
{
static const bool mask_to_allowed_status[8]
= { true, true, true, false, true, false, false, false };
static const uint8_t mask_to_bit_num[8] = { 0, 1, 2, 2, 3, 3, 3, 3 };
size_t i;
size_t prev_pos = (size_t)-1;
uint32_t prev_mask = s->x86_prev_mask;
uint32_t src;
uint32_t dest;
uint32_t j;
uint8_t b;
if (size <= 4)
return 0;
size -= 4;
for (i = 0; i < size; ++i) {
if ((buf[i] & 0xFE) != 0xE8)
continue;
prev_pos = i - prev_pos;
if (prev_pos > 3) {
prev_mask = 0;
} else {
prev_mask = (prev_mask << (prev_pos - 1)) & 7;
if (prev_mask != 0) {
b = buf[i + 4 - mask_to_bit_num[prev_mask]];
if (!mask_to_allowed_status[prev_mask]
|| bcj_x86_test_msbyte(b)) {
prev_pos = i;
prev_mask = (prev_mask << 1) | 1;
continue;
}
}
}
prev_pos = i;
if (bcj_x86_test_msbyte(buf[i + 4])) {
src = get_unaligned_le32(buf + i + 1);
while (true) {
dest = src - (s->pos + (uint32_t)i + 5);
if (prev_mask == 0)
break;
j = mask_to_bit_num[prev_mask] * 8;
b = (uint8_t)(dest >> (24 - j));
if (!bcj_x86_test_msbyte(b))
break;
src = dest ^ (((uint32_t)1 << (32 - j)) - 1);
}
dest &= 0x01FFFFFF;
dest |= (uint32_t)0 - (dest & 0x01000000);
put_unaligned_le32(dest, buf + i + 1);
i += 4;
} else {
prev_mask = (prev_mask << 1) | 1;
}
}
prev_pos = i - prev_pos;
s->x86_prev_mask = prev_pos > 3 ? 0 : prev_mask << (prev_pos - 1);
return i;
}
#endif
#ifdef XZ_DEC_POWERPC
static size_t bcj_powerpc(struct xz_dec_bcj *s, uint8_t *buf, size_t size)
{
size_t i;
uint32_t instr;
for (i = 0; i + 4 <= size; i += 4) {
instr = get_unaligned_be32(buf + i);
if ((instr & 0xFC000003) == 0x48000001) {
instr &= 0x03FFFFFC;
instr -= s->pos + (uint32_t)i;
instr &= 0x03FFFFFC;
instr |= 0x48000001;
put_unaligned_be32(instr, buf + i);
}
}
return i;
}
#endif
#ifdef XZ_DEC_IA64
static size_t bcj_ia64(struct xz_dec_bcj *s, uint8_t *buf, size_t size)
{
static const uint8_t branch_table[32] = {
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
4, 4, 6, 6, 0, 0, 7, 7,
4, 4, 0, 0, 4, 4, 0, 0
};
/*
* The local variables take a little bit stack space, but it's less
* than what LZMA2 decoder takes, so it doesn't make sense to reduce
* stack usage here without doing that for the LZMA2 decoder too.
*/
/* Loop counters */
size_t i;
size_t j;
/* Instruction slot (0, 1, or 2) in the 128-bit instruction word */
uint32_t slot;
/* Bitwise offset of the instruction indicated by slot */
uint32_t bit_pos;
/* bit_pos split into byte and bit parts */
uint32_t byte_pos;
uint32_t bit_res;
/* Address part of an instruction */
uint32_t addr;
/* Mask used to detect which instructions to convert */
uint32_t mask;
/* 41-bit instruction stored somewhere in the lowest 48 bits */
uint64_t instr;
/* Instruction normalized with bit_res for easier manipulation */
uint64_t norm;
for (i = 0; i + 16 <= size; i += 16) {
mask = branch_table[buf[i] & 0x1F];
for (slot = 0, bit_pos = 5; slot < 3; ++slot, bit_pos += 41) {
if (((mask >> slot) & 1) == 0)
continue;
byte_pos = bit_pos >> 3;
bit_res = bit_pos & 7;
instr = 0;
for (j = 0; j < 6; ++j)
instr |=
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