2 * Branch/Call/Jump (BCJ) filter decoders
4 * Authors: Lasse Collin <lasse.collin@tukaani.org>
5 * Igor Pavlov <http://7-zip.org/>
7 * This file has been put into the public domain.
8 * You can do whatever you want with this file.
11 #include "xz_private.h"
14 * The rest of the file is inside this ifdef. It makes things a little more
15 * convenient when building without support for any BCJ filters.
20 /* Type of the BCJ filter being used */
22 BCJ_X86 = 4, /* x86 or x86-64 */
23 BCJ_POWERPC = 5, /* Big endian only */
24 BCJ_IA64 = 6, /* Big or little endian */
25 BCJ_ARM = 7, /* Little endian only */
26 BCJ_ARMTHUMB = 8, /* Little endian only */
27 BCJ_SPARC = 9 /* Big or little endian */
31 * Return value of the next filter in the chain. We need to preserve
32 * this information across calls, because we must not call the next
33 * filter anymore once it has returned XZ_STREAM_END.
37 /* True if we are operating in single-call mode. */
41 * Absolute position relative to the beginning of the uncompressed
42 * data (in a single .xz Block). We care only about the lowest 32
43 * bits so this doesn't need to be uint64_t even with big files.
47 /* x86 filter state */
48 uint32_t x86_prev_mask;
50 /* Temporary space to hold the variables from struct xz_buf */
56 /* Amount of already filtered data in the beginning of buf */
59 /* Total amount of data currently stored in buf */
63 * Buffer to hold a mix of filtered and unfiltered data. This
64 * needs to be big enough to hold Alignment + 2 * Look-ahead:
66 * Type Alignment Look-ahead
80 * This is used to test the most significant byte of a memory address
81 * in an x86 instruction.
83 static inline int bcj_x86_test_msbyte(uint8_t b)
85 return b == 0x00 || b == 0xFF;
88 static size_t bcj_x86(struct xz_dec_bcj *s, uint8_t *buf, size_t size)
90 static const bool mask_to_allowed_status[8]
91 = { true, true, true, false, true, false, false, false };
93 static const uint8_t mask_to_bit_num[8] = { 0, 1, 2, 2, 3, 3, 3, 3 };
96 size_t prev_pos = (size_t)-1;
97 uint32_t prev_mask = s->x86_prev_mask;
107 for (i = 0; i < size; ++i) {
108 if ((buf[i] & 0xFE) != 0xE8)
111 prev_pos = i - prev_pos;
115 prev_mask = (prev_mask << (prev_pos - 1)) & 7;
116 if (prev_mask != 0) {
117 b = buf[i + 4 - mask_to_bit_num[prev_mask]];
118 if (!mask_to_allowed_status[prev_mask]
119 || bcj_x86_test_msbyte(b)) {
121 prev_mask = (prev_mask << 1) | 1;
129 if (bcj_x86_test_msbyte(buf[i + 4])) {
130 src = get_unaligned_le32(buf + i + 1);
132 dest = src - (s->pos + (uint32_t)i + 5);
136 j = mask_to_bit_num[prev_mask] * 8;
137 b = (uint8_t)(dest >> (24 - j));
138 if (!bcj_x86_test_msbyte(b))
141 src = dest ^ (((uint32_t)1 << (32 - j)) - 1);
145 dest |= (uint32_t)0 - (dest & 0x01000000);
146 put_unaligned_le32(dest, buf + i + 1);
149 prev_mask = (prev_mask << 1) | 1;
153 prev_pos = i - prev_pos;
154 s->x86_prev_mask = prev_pos > 3 ? 0 : prev_mask << (prev_pos - 1);
159 #ifdef XZ_DEC_POWERPC
160 static size_t bcj_powerpc(struct xz_dec_bcj *s, uint8_t *buf, size_t size)
165 for (i = 0; i + 4 <= size; i += 4) {
166 instr = get_unaligned_be32(buf + i);
167 if ((instr & 0xFC000003) == 0x48000001) {
169 instr -= s->pos + (uint32_t)i;
172 put_unaligned_be32(instr, buf + i);
181 static size_t bcj_ia64(struct xz_dec_bcj *s, uint8_t *buf, size_t size)
183 static const uint8_t branch_table[32] = {
184 0, 0, 0, 0, 0, 0, 0, 0,
185 0, 0, 0, 0, 0, 0, 0, 0,
186 4, 4, 6, 6, 0, 0, 7, 7,
187 4, 4, 0, 0, 4, 4, 0, 0
191 * The local variables take a little bit stack space, but it's less
192 * than what LZMA2 decoder takes, so it doesn't make sense to reduce
193 * stack usage here without doing that for the LZMA2 decoder too.
200 /* Instruction slot (0, 1, or 2) in the 128-bit instruction word */
203 /* Bitwise offset of the instruction indicated by slot */
206 /* bit_pos split into byte and bit parts */
210 /* Address part of an instruction */
213 /* Mask used to detect which instructions to convert */
216 /* 41-bit instruction stored somewhere in the lowest 48 bits */
219 /* Instruction normalized with bit_res for easier manipulation */
222 for (i = 0; i + 16 <= size; i += 16) {
223 mask = branch_table[buf[i] & 0x1F];
224 for (slot = 0, bit_pos = 5; slot < 3; ++slot, bit_pos += 41) {
225 if (((mask >> slot) & 1) == 0)
228 byte_pos = bit_pos >> 3;
229 bit_res = bit_pos & 7;
231 for (j = 0; j < 6; ++j)
232 instr |= (uint64_t)(buf[i + j + byte_pos])
235 norm = instr >> bit_res;
237 if (((norm >> 37) & 0x0F) == 0x05
238 && ((norm >> 9) & 0x07) == 0) {
239 addr = (norm >> 13) & 0x0FFFFF;
240 addr |= ((uint32_t)(norm >> 36) & 1) << 20;
242 addr -= s->pos + (uint32_t)i;
245 norm &= ~((uint64_t)0x8FFFFF << 13);
246 norm |= (uint64_t)(addr & 0x0FFFFF) << 13;
247 norm |= (uint64_t)(addr & 0x100000)
250 instr &= (1 << bit_res) - 1;
251 instr |= norm << bit_res;
253 for (j = 0; j < 6; j++)
254 buf[i + j + byte_pos]
255 = (uint8_t)(instr >> (8 * j));
265 static size_t bcj_arm(struct xz_dec_bcj *s, uint8_t *buf, size_t size)
270 for (i = 0; i + 4 <= size; i += 4) {
271 if (buf[i + 3] == 0xEB) {
272 addr = (uint32_t)buf[i] | ((uint32_t)buf[i + 1] << 8)
273 | ((uint32_t)buf[i + 2] << 16);
275 addr -= s->pos + (uint32_t)i + 8;
277 buf[i] = (uint8_t)addr;
278 buf[i + 1] = (uint8_t)(addr >> 8);
279 buf[i + 2] = (uint8_t)(addr >> 16);
287 #ifdef XZ_DEC_ARMTHUMB
288 static size_t bcj_armthumb(struct xz_dec_bcj *s, uint8_t *buf, size_t size)
293 for (i = 0; i + 4 <= size; i += 2) {
294 if ((buf[i + 1] & 0xF8) == 0xF0
295 && (buf[i + 3] & 0xF8) == 0xF8) {
296 addr = (((uint32_t)buf[i + 1] & 0x07) << 19)
297 | ((uint32_t)buf[i] << 11)
298 | (((uint32_t)buf[i + 3] & 0x07) << 8)
299 | (uint32_t)buf[i + 2];
301 addr -= s->pos + (uint32_t)i + 4;
303 buf[i + 1] = (uint8_t)(0xF0 | ((addr >> 19) & 0x07));
304 buf[i] = (uint8_t)(addr >> 11);
305 buf[i + 3] = (uint8_t)(0xF8 | ((addr >> 8) & 0x07));
306 buf[i + 2] = (uint8_t)addr;
316 static size_t bcj_sparc(struct xz_dec_bcj *s, uint8_t *buf, size_t size)
321 for (i = 0; i + 4 <= size; i += 4) {
322 instr = get_unaligned_be32(buf + i);
323 if ((instr >> 22) == 0x100 || (instr >> 22) == 0x1FF) {
325 instr -= s->pos + (uint32_t)i;
327 instr = ((uint32_t)0x40000000 - (instr & 0x400000))
328 | 0x40000000 | (instr & 0x3FFFFF);
329 put_unaligned_be32(instr, buf + i);
338 * Apply the selected BCJ filter. Update *pos and s->pos to match the amount
339 * of data that got filtered.
341 * NOTE: This is implemented as a switch statement to avoid using function
342 * pointers, which could be problematic in the kernel boot code, which must
343 * avoid pointers to static data (at least on x86).
345 static void bcj_apply(struct xz_dec_bcj *s,
346 uint8_t *buf, size_t *pos, size_t size)
356 filtered = bcj_x86(s, buf, size);
359 #ifdef XZ_DEC_POWERPC
361 filtered = bcj_powerpc(s, buf, size);
366 filtered = bcj_ia64(s, buf, size);
371 filtered = bcj_arm(s, buf, size);
374 #ifdef XZ_DEC_ARMTHUMB
376 filtered = bcj_armthumb(s, buf, size);
381 filtered = bcj_sparc(s, buf, size);
385 /* Never reached but silence compiler warnings. */
395 * Flush pending filtered data from temp to the output buffer.
396 * Move the remaining mixture of possibly filtered and unfiltered
397 * data to the beginning of temp.
399 static void bcj_flush(struct xz_dec_bcj *s, struct xz_buf *b)
403 copy_size = min_t(size_t, s->temp.filtered, b->out_size - b->out_pos);
404 memcpy(b->out + b->out_pos, s->temp.buf, copy_size);
405 b->out_pos += copy_size;
407 s->temp.filtered -= copy_size;
408 s->temp.size -= copy_size;
409 memmove(s->temp.buf, s->temp.buf + copy_size, s->temp.size);
413 * The BCJ filter functions are primitive in sense that they process the
414 * data in chunks of 1-16 bytes. To hide this issue, this function does
417 XZ_EXTERN enum xz_ret xz_dec_bcj_run(struct xz_dec_bcj *s,
418 struct xz_dec_lzma2 *lzma2,
424 * Flush pending already filtered data to the output buffer. Return
425 * immediatelly if we couldn't flush everything, or if the next
426 * filter in the chain had already returned XZ_STREAM_END.
428 if (s->temp.filtered > 0) {
430 if (s->temp.filtered > 0)
433 if (s->ret == XZ_STREAM_END)
434 return XZ_STREAM_END;
438 * If we have more output space than what is currently pending in
439 * temp, copy the unfiltered data from temp to the output buffer
440 * and try to fill the output buffer by decoding more data from the
441 * next filter in the chain. Apply the BCJ filter on the new data
442 * in the output buffer. If everything cannot be filtered, copy it
443 * to temp and rewind the output buffer position accordingly.
445 if (s->temp.size < b->out_size - b->out_pos) {
446 out_start = b->out_pos;
447 memcpy(b->out + b->out_pos, s->temp.buf, s->temp.size);
448 b->out_pos += s->temp.size;
450 s->ret = xz_dec_lzma2_run(lzma2, b);
451 if (s->ret != XZ_STREAM_END
452 && (s->ret != XZ_OK || s->single_call))
455 bcj_apply(s, b->out, &out_start, b->out_pos);
458 * As an exception, if the next filter returned XZ_STREAM_END,
459 * we can do that too, since the last few bytes that remain
460 * unfiltered are meant to remain unfiltered.
462 if (s->ret == XZ_STREAM_END)
463 return XZ_STREAM_END;
465 s->temp.size = b->out_pos - out_start;
466 b->out_pos -= s->temp.size;
467 memcpy(s->temp.buf, b->out + b->out_pos, s->temp.size);
471 * If we have unfiltered data in temp, try to fill by decoding more
472 * data from the next filter. Apply the BCJ filter on temp. Then we
473 * hopefully can fill the actual output buffer by copying filtered
474 * data from temp. A mix of filtered and unfiltered data may be left
475 * in temp; it will be taken care on the next call to this function.
477 if (s->temp.size > 0) {
478 /* Make b->out{,_pos,_size} temporarily point to s->temp. */
480 s->out_pos = b->out_pos;
481 s->out_size = b->out_size;
482 b->out = s->temp.buf;
483 b->out_pos = s->temp.size;
484 b->out_size = sizeof(s->temp.buf);
486 s->ret = xz_dec_lzma2_run(lzma2, b);
488 s->temp.size = b->out_pos;
490 b->out_pos = s->out_pos;
491 b->out_size = s->out_size;
493 if (s->ret != XZ_OK && s->ret != XZ_STREAM_END)
496 bcj_apply(s, s->temp.buf, &s->temp.filtered, s->temp.size);
499 * If the next filter returned XZ_STREAM_END, we mark that
500 * everything is filtered, since the last unfiltered bytes
501 * of the stream are meant to be left as is.
503 if (s->ret == XZ_STREAM_END)
504 s->temp.filtered = s->temp.size;
507 if (s->temp.filtered > 0)
514 XZ_EXTERN struct xz_dec_bcj *xz_dec_bcj_create(bool single_call)
516 struct xz_dec_bcj *s = kmalloc(sizeof(*s), GFP_KERNEL);
518 s->single_call = single_call;
523 XZ_EXTERN enum xz_ret xz_dec_bcj_reset(struct xz_dec_bcj *s, uint8_t id)
529 #ifdef XZ_DEC_POWERPC
538 #ifdef XZ_DEC_ARMTHUMB
547 /* Unsupported Filter ID */
548 return XZ_OPTIONS_ERROR;
554 s->x86_prev_mask = 0;
555 s->temp.filtered = 0;