tor-browser

xz_dec_bcj.c (13905B)

---

/*
* 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 |= (uint64_t)(buf[i + j + byte_pos])
					<< (8 * j);

		norm = instr >> bit_res;

		if (((norm >> 37) & 0x0F) == 0x05
				&& ((norm >> 9) & 0x07) == 0) {
			addr = (norm >> 13) & 0x0FFFFF;
			addr |= ((uint32_t)(norm >> 36) & 1) << 20;
			addr <<= 4;
			addr -= s->pos + (uint32_t)i;
			addr >>= 4;

			norm &= ~((uint64_t)0x8FFFFF << 13);
			norm |= (uint64_t)(addr & 0x0FFFFF) << 13;
			norm |= (uint64_t)(addr & 0x100000)
					<< (36 - 20);

			instr &= (1 << bit_res) - 1;
			instr |= norm << bit_res;

			for (j = 0; j < 6; j++)
				buf[i + j + byte_pos]
					= (uint8_t)(instr >> (8 * j));
		}
	}
}

return i;
}
#endif

#ifdef XZ_DEC_ARM
static size_t bcj_arm(struct xz_dec_bcj *s, uint8_t *buf, size_t size)
{
size_t i;
uint32_t addr;

for (i = 0; i + 4 <= size; i += 4) {
	if (buf[i + 3] == 0xEB) {
		addr = (uint32_t)buf[i] | ((uint32_t)buf[i + 1] << 8)
				| ((uint32_t)buf[i + 2] << 16);
		addr <<= 2;
		addr -= s->pos + (uint32_t)i + 8;
		addr >>= 2;
		buf[i] = (uint8_t)addr;
		buf[i + 1] = (uint8_t)(addr >> 8);
		buf[i + 2] = (uint8_t)(addr >> 16);
	}
}

return i;
}
#endif

#ifdef XZ_DEC_ARMTHUMB
static size_t bcj_armthumb(struct xz_dec_bcj *s, uint8_t *buf, size_t size)
{
size_t i;
uint32_t addr;

for (i = 0; i + 4 <= size; i += 2) {
	if ((buf[i + 1] & 0xF8) == 0xF0
			&& (buf[i + 3] & 0xF8) == 0xF8) {
		addr = (((uint32_t)buf[i + 1] & 0x07) << 19)
				| ((uint32_t)buf[i] << 11)
				| (((uint32_t)buf[i + 3] & 0x07) << 8)
				| (uint32_t)buf[i + 2];
		addr <<= 1;
		addr -= s->pos + (uint32_t)i + 4;
		addr >>= 1;
		buf[i + 1] = (uint8_t)(0xF0 | ((addr >> 19) & 0x07));
		buf[i] = (uint8_t)(addr >> 11);
		buf[i + 3] = (uint8_t)(0xF8 | ((addr >> 8) & 0x07));
		buf[i + 2] = (uint8_t)addr;
		i += 2;
	}
}

return i;
}
#endif

#ifdef XZ_DEC_SPARC
static size_t bcj_sparc(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 >> 22) == 0x100 || (instr >> 22) == 0x1FF) {
		instr <<= 2;
		instr -= s->pos + (uint32_t)i;
		instr >>= 2;
		instr = ((uint32_t)0x40000000 - (instr & 0x400000))
				| 0x40000000 | (instr & 0x3FFFFF);
		put_unaligned_be32(instr, buf + i);
	}
}

return i;
}
#endif

/*
* Apply the selected BCJ filter. Update *pos and s->pos to match the amount
* of data that got filtered.
*
* NOTE: This is implemented as a switch statement to avoid using function
* pointers, which could be problematic in the kernel boot code, which must
* avoid pointers to static data (at least on x86).
*/
static void bcj_apply(struct xz_dec_bcj *s,
	      uint8_t *buf, size_t *pos, size_t size)
{
size_t filtered;

buf += *pos;
size -= *pos;

switch (s->type) {
#ifdef XZ_DEC_X86
case BCJ_X86:
	filtered = bcj_x86(s, buf, size);
	break;
#endif
#ifdef XZ_DEC_POWERPC
case BCJ_POWERPC:
	filtered = bcj_powerpc(s, buf, size);
	break;
#endif
#ifdef XZ_DEC_IA64
case BCJ_IA64:
	filtered = bcj_ia64(s, buf, size);
	break;
#endif
#ifdef XZ_DEC_ARM
case BCJ_ARM:
	filtered = bcj_arm(s, buf, size);
	break;
#endif
#ifdef XZ_DEC_ARMTHUMB
case BCJ_ARMTHUMB:
	filtered = bcj_armthumb(s, buf, size);
	break;
#endif
#ifdef XZ_DEC_SPARC
case BCJ_SPARC:
	filtered = bcj_sparc(s, buf, size);
	break;
#endif
default:
	/* Never reached but silence compiler warnings. */
	filtered = 0;
	break;
}

*pos += filtered;
s->pos += filtered;
}

/*
* Flush pending filtered data from temp to the output buffer.
* Move the remaining mixture of possibly filtered and unfiltered
* data to the beginning of temp.
*/
static void bcj_flush(struct xz_dec_bcj *s, struct xz_buf *b)
{
size_t copy_size;

copy_size = min_t(size_t, s->temp.filtered, b->out_size - b->out_pos);
memcpy(b->out + b->out_pos, s->temp.buf, copy_size);
b->out_pos += copy_size;

s->temp.filtered -= copy_size;
s->temp.size -= copy_size;
memmove(s->temp.buf, s->temp.buf + copy_size, s->temp.size);
}

/*
* The BCJ filter functions are primitive in sense that they process the
* data in chunks of 1-16 bytes. To hide this issue, this function does
* some buffering.
*/
XZ_EXTERN enum xz_ret xz_dec_bcj_run(struct xz_dec_bcj *s,
			     struct xz_dec_lzma2 *lzma2,
			     struct xz_buf *b)
{
size_t out_start;

/*
 * Flush pending already filtered data to the output buffer. Return
 * immediatelly if we couldn't flush everything, or if the next
 * filter in the chain had already returned XZ_STREAM_END.
 */
if (s->temp.filtered > 0) {
	bcj_flush(s, b);
	if (s->temp.filtered > 0)
		return XZ_OK;

	if (s->ret == XZ_STREAM_END)
		return XZ_STREAM_END;
}

/*
 * If we have more output space than what is currently pending in
 * temp, copy the unfiltered data from temp to the output buffer
 * and try to fill the output buffer by decoding more data from the
 * next filter in the chain. Apply the BCJ filter on the new data
 * in the output buffer. If everything cannot be filtered, copy it
 * to temp and rewind the output buffer position accordingly.
 *
 * This needs to be always run when temp.size == 0 to handle a special
 * case where the output buffer is full and the next filter has no
 * more output coming but hasn't returned XZ_STREAM_END yet.
 */
if (s->temp.size < b->out_size - b->out_pos || s->temp.size == 0) {
	out_start = b->out_pos;
	memcpy(b->out + b->out_pos, s->temp.buf, s->temp.size);
	b->out_pos += s->temp.size;

	s->ret = xz_dec_lzma2_run(lzma2, b);
	if (s->ret != XZ_STREAM_END
			&& (s->ret != XZ_OK || s->single_call))
		return s->ret;

	bcj_apply(s, b->out, &out_start, b->out_pos);

	/*
	 * As an exception, if the next filter returned XZ_STREAM_END,
	 * we can do that too, since the last few bytes that remain
	 * unfiltered are meant to remain unfiltered.
	 */
	if (s->ret == XZ_STREAM_END)
		return XZ_STREAM_END;

	s->temp.size = b->out_pos - out_start;
	b->out_pos -= s->temp.size;
	memcpy(s->temp.buf, b->out + b->out_pos, s->temp.size);

	/*
	 * If there wasn't enough input to the next filter to fill
	 * the output buffer with unfiltered data, there's no point
	 * to try decoding more data to temp.
	 */
	if (b->out_pos + s->temp.size < b->out_size)
		return XZ_OK;
}

/*
 * We have unfiltered data in temp. If the output buffer isn't full
 * yet, try to fill the temp buffer by decoding more data from the
 * next filter. Apply the BCJ filter on temp. Then we hopefully can
 * fill the actual output buffer by copying filtered data from temp.
 * A mix of filtered and unfiltered data may be left in temp; it will
 * be taken care on the next call to this function.
 */
if (b->out_pos < b->out_size) {
	/* Make b->out{,_pos,_size} temporarily point to s->temp. */
	s->out = b->out;
	s->out_pos = b->out_pos;
	s->out_size = b->out_size;
	b->out = s->temp.buf;
	b->out_pos = s->temp.size;
	b->out_size = sizeof(s->temp.buf);

	s->ret = xz_dec_lzma2_run(lzma2, b);

	s->temp.size = b->out_pos;
	b->out = s->out;
	b->out_pos = s->out_pos;
	b->out_size = s->out_size;

	if (s->ret != XZ_OK && s->ret != XZ_STREAM_END)
		return s->ret;

	bcj_apply(s, s->temp.buf, &s->temp.filtered, s->temp.size);

	/*
	 * If the next filter returned XZ_STREAM_END, we mark that
	 * everything is filtered, since the last unfiltered bytes
	 * of the stream are meant to be left as is.
	 */
	if (s->ret == XZ_STREAM_END)
		s->temp.filtered = s->temp.size;

	bcj_flush(s, b);
	if (s->temp.filtered > 0)
		return XZ_OK;
}

return s->ret;
}

XZ_EXTERN struct xz_dec_bcj *xz_dec_bcj_create(bool single_call)
{
struct xz_dec_bcj *s = kmalloc(sizeof(*s), GFP_KERNEL);
if (s != NULL)
	s->single_call = single_call;

return s;
}

XZ_EXTERN enum xz_ret xz_dec_bcj_reset(struct xz_dec_bcj *s, uint8_t id)
{
switch (id) {
#ifdef XZ_DEC_X86
case BCJ_X86:
#endif
#ifdef XZ_DEC_POWERPC
case BCJ_POWERPC:
#endif
#ifdef XZ_DEC_IA64
case BCJ_IA64:
#endif
#ifdef XZ_DEC_ARM
case BCJ_ARM:
#endif
#ifdef XZ_DEC_ARMTHUMB
case BCJ_ARMTHUMB:
#endif
#ifdef XZ_DEC_SPARC
case BCJ_SPARC:
#endif
	break;

default:
	/* Unsupported Filter ID */
	return XZ_OPTIONS_ERROR;
}

s->type = id;
s->ret = XZ_OK;
s->pos = 0;
s->x86_prev_mask = 0;
s->temp.filtered = 0;
s->temp.size = 0;

return XZ_OK;
}

#endif