1 /* Generate assembler source containing symbol information
2 *
3 * Copyright 2002 by Kai Germaschewski
4 *
5 * This software may be used and distributed according to the terms
6 * of the GNU General Public License, incorporated herein by reference.
7 *
8 * Usage: kallsyms [--all-symbols] [--absolute-percpu] in.map > out.S
9 *
10 * Table compression uses all the unused char codes on the symbols and
11 * maps these to the most used substrings (tokens). For instance, it might
12 * map char code 0xF7 to represent "write_" and then in every symbol where
13 * "write_" appears it can be replaced by 0xF7, saving 5 bytes.
14 * The used codes themselves are also placed in the table so that the
15 * decompresion can work without "special cases".
16 * Applied to kernel symbols, this usually produces a compression ratio
17 * of about 50%.
18 *
19 */
20
21 #include <errno.h>
22 #include <getopt.h>
23 #include <stdbool.h>
24 #include <stdio.h>
25 #include <stdlib.h>
26 #include <string.h>
27 #include <ctype.h>
28 #include <limits.h>
29
30 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0]))
31
32 #define KSYM_NAME_LEN 512
33
34 struct sym_entry {
35 unsigned long long addr;
36 unsigned int len;
37 unsigned int seq;
38 bool percpu_absolute;
39 unsigned char sym[];
40 };
41
42 struct addr_range {
43 const char *start_sym, *end_sym;
44 unsigned long long start, end;
45 };
46
47 static unsigned long long _text;
48 static unsigned long long relative_base;
49 static struct addr_range text_ranges[] = {
50 { "_stext", "_etext" },
51 { "_sinittext", "_einittext" },
52 };
53 #define text_range_text (&text_ranges[0])
54 #define text_range_inittext (&text_ranges[1])
55
56 static struct addr_range percpu_range = {
57 "__per_cpu_start", "__per_cpu_end", -1ULL, 0
58 };
59
60 static struct sym_entry **table;
61 static unsigned int table_size, table_cnt;
62 static int all_symbols;
63 static int absolute_percpu;
64
65 static int token_profit[0x10000];
66
67 /* the table that holds the result of the compression */
68 static unsigned char best_table[256][2];
69 static unsigned char best_table_len[256];
70
71
72 static void usage(void)
73 {
74 fprintf(stderr, "Usage: kallsyms [--all-symbols] [--absolute-percpu] in.map > out.S\n");
75 exit(1);
76 }
77
78 static char *sym_name(const struct sym_entry *s)
79 {
80 return (char *)s->sym + 1;
81 }
82
83 static bool is_ignored_symbol(const char *name, char type)
84 {
85 if (type == 'u' || type == 'n')
86 return true;
87
88 if (toupper(type) == 'A') {
89 /* Keep these useful absolute symbols */
90 if (strcmp(name, "__kernel_syscall_via_break") &&
91 strcmp(name, "__kernel_syscall_via_epc") &&
92 strcmp(name, "__kernel_sigtramp") &&
93 strcmp(name, "__gp"))
94 return true;
95 }
96
97 return false;
98 }
99
100 static void check_symbol_range(const char *sym, unsigned long long addr,
101 struct addr_range *ranges, int entries)
102 {
103 size_t i;
104 struct addr_range *ar;
105
106 for (i = 0; i < entries; ++i) {
107 ar = &ranges[i];
108
109 if (strcmp(sym, ar->start_sym) == 0) {
110 ar->start = addr;
111 return;
112 } else if (strcmp(sym, ar->end_sym) == 0) {
113 ar->end = addr;
114 return;
115 }
116 }
117 }
118
119 static struct sym_entry *read_symbol(FILE *in, char **buf, size_t *buf_len)
120 {
121 char *name, type, *p;
122 unsigned long long addr;
123 size_t len;
124 ssize_t readlen;
125 struct sym_entry *sym;
126
127 errno = 0;
128 readlen = getline(buf, buf_len, in);
129 if (readlen < 0) {
130 if (errno) {
131 perror("read_symbol");
132 exit(EXIT_FAILURE);
133 }
134 return NULL;
135 }
136
137 if ((*buf)[readlen - 1] == '\n')
138 (*buf)[readlen - 1] = 0;
139
140 addr = strtoull(*buf, &p, 16);
141
142 if (*buf == p || *p++ != ' ' || !isascii((type = *p++)) || *p++ != ' ') {
143 fprintf(stderr, "line format error\n");
144 exit(EXIT_FAILURE);
145 }
146
147 name = p;
148 len = strlen(name);
149
150 if (len >= KSYM_NAME_LEN) {
151 fprintf(stderr, "Symbol %s too long for kallsyms (%zu >= %d).\n"
152 "Please increase KSYM_NAME_LEN both in kernel and kallsyms.c\n",
153 name, len, KSYM_NAME_LEN);
154 return NULL;
155 }
156
157 if (strcmp(name, "_text") == 0)
158 _text = addr;
159
160 /* Ignore most absolute/undefined (?) symbols. */
161 if (is_ignored_symbol(name, type))
162 return NULL;
163
164 check_symbol_range(name, addr, text_ranges, ARRAY_SIZE(text_ranges));
165 check_symbol_range(name, addr, &percpu_range, 1);
166
167 /* include the type field in the symbol name, so that it gets
168 * compressed together */
169 len++;
170
171 sym = malloc(sizeof(*sym) + len + 1);
172 if (!sym) {
173 fprintf(stderr, "kallsyms failure: "
174 "unable to allocate required amount of memory\n");
175 exit(EXIT_FAILURE);
176 }
177 sym->addr = addr;
178 sym->len = len;
179 sym->sym[0] = type;
180 strcpy(sym_name(sym), name);
181 sym->percpu_absolute = false;
182
183 return sym;
184 }
185
186 static int symbol_in_range(const struct sym_entry *s,
187 const struct addr_range *ranges, int entries)
188 {
189 size_t i;
190 const struct addr_range *ar;
191
192 for (i = 0; i < entries; ++i) {
193 ar = &ranges[i];
194
195 if (s->addr >= ar->start && s->addr <= ar->end)
196 return 1;
197 }
198
199 return 0;
200 }
201
202 static bool string_starts_with(const char *s, const char *prefix)
203 {
204 return strncmp(s, prefix, strlen(prefix)) == 0;
205 }
206
207 static int symbol_valid(const struct sym_entry *s)
208 {
209 const char *name = sym_name(s);
210
211 /* if --all-symbols is not specified, then symbols outside the text
212 * and inittext sections are discarded */
213 if (!all_symbols) {
214 /*
215 * Symbols starting with __start and __stop are used to denote
216 * section boundaries, and should always be included:
217 */
218 if (string_starts_with(name, "__start_") ||
219 string_starts_with(name, "__stop_"))
220 return 1;
221
222 if (symbol_in_range(s, text_ranges,
223 ARRAY_SIZE(text_ranges)) == 0)
224 return 0;
225 /* Corner case. Discard any symbols with the same value as
226 * _etext _einittext; they can move between pass 1 and 2 when
227 * the kallsyms data are added. If these symbols move then
228 * they may get dropped in pass 2, which breaks the kallsyms
229 * rules.
230 */
231 if ((s->addr == text_range_text->end &&
232 strcmp(name, text_range_text->end_sym)) ||
233 (s->addr == text_range_inittext->end &&
234 strcmp(name, text_range_inittext->end_sym)))
235 return 0;
236 }
237
238 return 1;
239 }
240
241 /* remove all the invalid symbols from the table */
242 static void shrink_table(void)
243 {
244 unsigned int i, pos;
245
246 pos = 0;
247 for (i = 0; i < table_cnt; i++) {
248 if (symbol_valid(table[i])) {
249 if (pos != i)
250 table[pos] = table[i];
251 pos++;
252 } else {
253 free(table[i]);
254 }
255 }
256 table_cnt = pos;
257 }
258
259 static void read_map(const char *in)
260 {
261 FILE *fp;
262 struct sym_entry *sym;
263 char *buf = NULL;
264 size_t buflen = 0;
265
266 fp = fopen(in, "r");
267 if (!fp) {
268 perror(in);
269 exit(1);
270 }
271
272 while (!feof(fp)) {
273 sym = read_symbol(fp, &buf, &buflen);
274 if (!sym)
275 continue;
276
277 sym->seq = table_cnt;
278
279 if (table_cnt >= table_size) {
280 table_size += 10000;
281 table = realloc(table, sizeof(*table) * table_size);
282 if (!table) {
283 fprintf(stderr, "out of memory\n");
284 fclose(fp);
285 exit (1);
286 }
287 }
288
289 table[table_cnt++] = sym;
290 }
291
292 free(buf);
293 fclose(fp);
294 }
295
296 static void output_label(const char *label)
297 {
298 printf(".globl %s\n", label);
299 printf("\tALGN\n");
300 printf("%s:\n", label);
301 }
302
303 /* Provide proper symbols relocatability by their '_text' relativeness. */
304 static void output_address(unsigned long long addr)
305 {
306 if (_text <= addr)
307 printf("\tPTR\t_text + %#llx\n", addr - _text);
308 else
309 printf("\tPTR\t_text - %#llx\n", _text - addr);
310 }
311
312 /* uncompress a compressed symbol. When this function is called, the best table
313 * might still be compressed itself, so the function needs to be recursive */
314 static int expand_symbol(const unsigned char *data, int len, char *result)
315 {
316 int c, rlen, total=0;
317
318 while (len) {
319 c = *data;
320 /* if the table holds a single char that is the same as the one
321 * we are looking for, then end the search */
322 if (best_table[c][0]==c && best_table_len[c]==1) {
323 *result++ = c;
324 total++;
325 } else {
326 /* if not, recurse and expand */
327 rlen = expand_symbol(best_table[c], best_table_len[c], result);
328 total += rlen;
329 result += rlen;
330 }
331 data++;
332 len--;
333 }
334 *result=0;
335
336 return total;
337 }
338
339 static bool symbol_absolute(const struct sym_entry *s)
340 {
341 return s->percpu_absolute;
342 }
343
344 static int compare_names(const void *a, const void *b)
345 {
346 int ret;
347 const struct sym_entry *sa = *(const struct sym_entry **)a;
348 const struct sym_entry *sb = *(const struct sym_entry **)b;
349
350 ret = strcmp(sym_name(sa), sym_name(sb));
351 if (!ret) {
352 if (sa->addr > sb->addr)
353 return 1;
354 else if (sa->addr < sb->addr)
355 return -1;
356
357 /* keep old order */
358 return (int)(sa->seq - sb->seq);
359 }
360
361 return ret;
362 }
363
364 static void sort_symbols_by_name(void)
365 {
366 qsort(table, table_cnt, sizeof(table[0]), compare_names);
367 }
368
369 static void write_src(void)
370 {
371 unsigned int i, k, off;
372 unsigned int best_idx[256];
373 unsigned int *markers, markers_cnt;
374 char buf[KSYM_NAME_LEN];
375
376 printf("#include <asm/bitsperlong.h>\n");
377 printf("#if BITS_PER_LONG == 64\n");
378 printf("#define PTR .quad\n");
379 printf("#define ALGN .balign 8\n");
380 printf("#else\n");
381 printf("#define PTR .long\n");
382 printf("#define ALGN .balign 4\n");
383 printf("#endif\n");
384
385 printf("\t.section .rodata, \"a\"\n");
386
387 output_label("kallsyms_num_syms");
388 printf("\t.long\t%u\n", table_cnt);
389 printf("\n");
390
391 /* table of offset markers, that give the offset in the compressed stream
392 * every 256 symbols */
393 markers_cnt = (table_cnt + 255) / 256;
394 markers = malloc(sizeof(*markers) * markers_cnt);
395 if (!markers) {
396 fprintf(stderr, "kallsyms failure: "
397 "unable to allocate required memory\n");
398 exit(EXIT_FAILURE);
399 }
400
401 output_label("kallsyms_names");
402 off = 0;
403 for (i = 0; i < table_cnt; i++) {
404 if ((i & 0xFF) == 0)
405 markers[i >> 8] = off;
406 table[i]->seq = i;
407
408 /* There cannot be any symbol of length zero. */
409 if (table[i]->len == 0) {
410 fprintf(stderr, "kallsyms failure: "
411 "unexpected zero symbol length\n");
412 exit(EXIT_FAILURE);
413 }
414
415 /* Only lengths that fit in up-to-two-byte ULEB128 are supported. */
416 if (table[i]->len > 0x3FFF) {
417 fprintf(stderr, "kallsyms failure: "
418 "unexpected huge symbol length\n");
419 exit(EXIT_FAILURE);
420 }
421
422 /* Encode length with ULEB128. */
423 if (table[i]->len <= 0x7F) {
424 /* Most symbols use a single byte for the length. */
425 printf("\t.byte 0x%02x", table[i]->len);
426 off += table[i]->len + 1;
427 } else {
428 /* "Big" symbols use two bytes. */
429 printf("\t.byte 0x%02x, 0x%02x",
430 (table[i]->len & 0x7F) | 0x80,
431 (table[i]->len >> 7) & 0x7F);
432 off += table[i]->len + 2;
433 }
434 for (k = 0; k < table[i]->len; k++)
435 printf(", 0x%02x", table[i]->sym[k]);
436
437 /*
438 * Now that we wrote out the compressed symbol name, restore the
439 * original name and print it in the comment.
440 */
441 expand_symbol(table[i]->sym, table[i]->len, buf);
442 strcpy((char *)table[i]->sym, buf);
443 printf("\t/* %s */\n", table[i]->sym);
444 }
445 printf("\n");
446
447 output_label("kallsyms_markers");
448 for (i = 0; i < markers_cnt; i++)
449 printf("\t.long\t%u\n", markers[i]);
450 printf("\n");
451
452 free(markers);
453
454 output_label("kallsyms_token_table");
455 off = 0;
456 for (i = 0; i < 256; i++) {
457 best_idx[i] = off;
458 expand_symbol(best_table[i], best_table_len[i], buf);
459 printf("\t.asciz\t\"%s\"\n", buf);
460 off += strlen(buf) + 1;
461 }
462 printf("\n");
463
464 output_label("kallsyms_token_index");
465 for (i = 0; i < 256; i++)
466 printf("\t.short\t%d\n", best_idx[i]);
467 printf("\n");
468
469 output_label("kallsyms_offsets");
470
471 for (i = 0; i < table_cnt; i++) {
472 /*
473 * Use the offset relative to the lowest value
474 * encountered of all relative symbols, and emit
475 * non-relocatable fixed offsets that will be fixed
476 * up at runtime.
477 */
478
479 long long offset;
480 int overflow;
481
482 if (!absolute_percpu) {
483 offset = table[i]->addr - relative_base;
484 overflow = (offset < 0 || offset > UINT_MAX);
485 } else if (symbol_absolute(table[i])) {
486 offset = table[i]->addr;
487 overflow = (offset < 0 || offset > INT_MAX);
488 } else {
489 offset = relative_base - table[i]->addr - 1;
490 overflow = (offset < INT_MIN || offset >= 0);
491 }
492 if (overflow) {
493 fprintf(stderr, "kallsyms failure: "
494 "%s symbol value %#llx out of range in relative mode\n",
495 symbol_absolute(table[i]) ? "absolute" : "relative",
496 table[i]->addr);
497 exit(EXIT_FAILURE);
498 }
499 printf("\t.long\t%#x\t/* %s */\n", (int)offset, table[i]->sym);
500 }
501 printf("\n");
502
503 output_label("kallsyms_relative_base");
504 output_address(relative_base);
505 printf("\n");
506
507 sort_symbols_by_name();
508 output_label("kallsyms_seqs_of_names");
509 for (i = 0; i < table_cnt; i++)
510 printf("\t.byte 0x%02x, 0x%02x, 0x%02x\t/* %s */\n",
511 (unsigned char)(table[i]->seq >> 16),
512 (unsigned char)(table[i]->seq >> 8),
513 (unsigned char)(table[i]->seq >> 0),
514 table[i]->sym);
515 printf("\n");
516 }
517
518
519 /* table lookup compression functions */
520
521 /* count all the possible tokens in a symbol */
522 static void learn_symbol(const unsigned char *symbol, int len)
523 {
524 int i;
525
526 for (i = 0; i < len - 1; i++)
527 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++;
528 }
529
530 /* decrease the count for all the possible tokens in a symbol */
531 static void forget_symbol(const unsigned char *symbol, int len)
532 {
533 int i;
534
535 for (i = 0; i < len - 1; i++)
536 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--;
537 }
538
539 /* do the initial token count */
540 static void build_initial_token_table(void)
541 {
542 unsigned int i;
543
544 for (i = 0; i < table_cnt; i++)
545 learn_symbol(table[i]->sym, table[i]->len);
546 }
547
548 static unsigned char *find_token(unsigned char *str, int len,
549 const unsigned char *token)
550 {
551 int i;
552
553 for (i = 0; i < len - 1; i++) {
554 if (str[i] == token[0] && str[i+1] == token[1])
555 return &str[i];
556 }
557 return NULL;
558 }
559
560 /* replace a given token in all the valid symbols. Use the sampled symbols
561 * to update the counts */
562 static void compress_symbols(const unsigned char *str, int idx)
563 {
564 unsigned int i, len, size;
565 unsigned char *p1, *p2;
566
567 for (i = 0; i < table_cnt; i++) {
568
569 len = table[i]->len;
570 p1 = table[i]->sym;
571
572 /* find the token on the symbol */
573 p2 = find_token(p1, len, str);
574 if (!p2) continue;
575
576 /* decrease the counts for this symbol's tokens */
577 forget_symbol(table[i]->sym, len);
578
579 size = len;
580
581 do {
582 *p2 = idx;
583 p2++;
584 size -= (p2 - p1);
585 memmove(p2, p2 + 1, size);
586 p1 = p2;
587 len--;
588
589 if (size < 2) break;
590
591 /* find the token on the symbol */
592 p2 = find_token(p1, size, str);
593
594 } while (p2);
595
596 table[i]->len = len;
597
598 /* increase the counts for this symbol's new tokens */
599 learn_symbol(table[i]->sym, len);
600 }
601 }
602
603 /* search the token with the maximum profit */
604 static int find_best_token(void)
605 {
606 int i, best, bestprofit;
607
608 bestprofit=-10000;
609 best = 0;
610
611 for (i = 0; i < 0x10000; i++) {
612 if (token_profit[i] > bestprofit) {
613 best = i;
614 bestprofit = token_profit[i];
615 }
616 }
617 return best;
618 }
619
620 /* this is the core of the algorithm: calculate the "best" table */
621 static void optimize_result(void)
622 {
623 int i, best;
624
625 /* using the '\0' symbol last allows compress_symbols to use standard
626 * fast string functions */
627 for (i = 255; i >= 0; i--) {
628
629 /* if this table slot is empty (it is not used by an actual
630 * original char code */
631 if (!best_table_len[i]) {
632
633 /* find the token with the best profit value */
634 best = find_best_token();
635 if (token_profit[best] == 0)
636 break;
637
638 /* place it in the "best" table */
639 best_table_len[i] = 2;
640 best_table[i][0] = best & 0xFF;
641 best_table[i][1] = (best >> 8) & 0xFF;
642
643 /* replace this token in all the valid symbols */
644 compress_symbols(best_table[i], i);
645 }
646 }
647 }
648
649 /* start by placing the symbols that are actually used on the table */
650 static void insert_real_symbols_in_table(void)
651 {
652 unsigned int i, j, c;
653
654 for (i = 0; i < table_cnt; i++) {
655 for (j = 0; j < table[i]->len; j++) {
656 c = table[i]->sym[j];
657 best_table[c][0]=c;
658 best_table_len[c]=1;
659 }
660 }
661 }
662
663 static void optimize_token_table(void)
664 {
665 build_initial_token_table();
666
667 insert_real_symbols_in_table();
668
669 optimize_result();
670 }
671
672 /* guess for "linker script provide" symbol */
673 static int may_be_linker_script_provide_symbol(const struct sym_entry *se)
674 {
675 const char *symbol = sym_name(se);
676 int len = se->len - 1;
677
678 if (len < 8)
679 return 0;
680
681 if (symbol[0] != '_' || symbol[1] != '_')
682 return 0;
683
684 /* __start_XXXXX */
685 if (!memcmp(symbol + 2, "start_", 6))
686 return 1;
687
688 /* __stop_XXXXX */
689 if (!memcmp(symbol + 2, "stop_", 5))
690 return 1;
691
692 /* __end_XXXXX */
693 if (!memcmp(symbol + 2, "end_", 4))
694 return 1;
695
696 /* __XXXXX_start */
697 if (!memcmp(symbol + len - 6, "_start", 6))
698 return 1;
699
700 /* __XXXXX_end */
701 if (!memcmp(symbol + len - 4, "_end", 4))
702 return 1;
703
704 return 0;
705 }
706
707 static int compare_symbols(const void *a, const void *b)
708 {
709 const struct sym_entry *sa = *(const struct sym_entry **)a;
710 const struct sym_entry *sb = *(const struct sym_entry **)b;
711 int wa, wb;
712
713 /* sort by address first */
714 if (sa->addr > sb->addr)
715 return 1;
716 if (sa->addr < sb->addr)
717 return -1;
718
719 /* sort by "weakness" type */
720 wa = (sa->sym[0] == 'w') || (sa->sym[0] == 'W');
721 wb = (sb->sym[0] == 'w') || (sb->sym[0] == 'W');
722 if (wa != wb)
723 return wa - wb;
724
725 /* sort by "linker script provide" type */
726 wa = may_be_linker_script_provide_symbol(sa);
727 wb = may_be_linker_script_provide_symbol(sb);
728 if (wa != wb)
729 return wa - wb;
730
731 /* sort by the number of prefix underscores */
732 wa = strspn(sym_name(sa), "_");
733 wb = strspn(sym_name(sb), "_");
734 if (wa != wb)
735 return wa - wb;
736
737 /* sort by initial order, so that other symbols are left undisturbed */
738 return sa->seq - sb->seq;
739 }
740
741 static void sort_symbols(void)
742 {
743 qsort(table, table_cnt, sizeof(table[0]), compare_symbols);
744 }
745
746 static void make_percpus_absolute(void)
747 {
748 unsigned int i;
749
750 for (i = 0; i < table_cnt; i++)
751 if (symbol_in_range(table[i], &percpu_range, 1)) {
752 /*
753 * Keep the 'A' override for percpu symbols to
754 * ensure consistent behavior compared to older
755 * versions of this tool.
756 */
757 table[i]->sym[0] = 'A';
758 table[i]->percpu_absolute = true;
759 }
760 }
761
762 /* find the minimum non-absolute symbol address */
763 static void record_relative_base(void)
764 {
765 unsigned int i;
766
767 for (i = 0; i < table_cnt; i++)
768 if (!symbol_absolute(table[i])) {
769 /*
770 * The table is sorted by address.
771 * Take the first non-absolute symbol value.
772 */
773 relative_base = table[i]->addr;
774 return;
775 }
776 }
777
778 int main(int argc, char **argv)
779 {
780 while (1) {
781 static const struct option long_options[] = {
782 {"all-symbols", no_argument, &all_symbols, 1},
783 {"absolute-percpu", no_argument, &absolute_percpu, 1},
784 {},
785 };
786
787 int c = getopt_long(argc, argv, "", long_options, NULL);
788
789 if (c == -1)
790 break;
791 if (c != 0)
792 usage();
793 }
794
795 if (optind >= argc)
796 usage();
797
798 read_map(argv[optind]);
799 shrink_table();
800 if (absolute_percpu)
801 make_percpus_absolute();
802 sort_symbols();
803 record_relative_base();
804 optimize_token_table();
805 write_src();
806
807 return 0;
808 }
809
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