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]
9 * [--lto-clang] in.map > out.S
10 *
11 * Table compression uses all the unused char codes on the symbols and
12 * maps these to the most used substrings (tokens). For instance, it might
13 * map char code 0xF7 to represent "write_" and then in every symbol where
14 * "write_" appears it can be replaced by 0xF7, saving 5 bytes.
15 * The used codes themselves are also placed in the table so that the
16 * decompresion can work without "special cases".
17 * Applied to kernel symbols, this usually produces a compression ratio
18 * of about 50%.
19 *
20 */
21
22 #include <errno.h>
23 #include <getopt.h>
24 #include <stdbool.h>
25 #include <stdio.h>
26 #include <stdlib.h>
27 #include <string.h>
28 #include <ctype.h>
29 #include <limits.h>
30
31 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0]))
32
33 #define KSYM_NAME_LEN 512
34
35 struct sym_entry {
36 unsigned long long addr;
37 unsigned int len;
38 unsigned int seq;
39 bool percpu_absolute;
40 unsigned char sym[];
41 };
42
43 struct addr_range {
44 const char *start_sym, *end_sym;
45 unsigned long long start, end;
46 };
47
48 static unsigned long long _text;
49 static unsigned long long relative_base;
50 static struct addr_range text_ranges[] = {
51 { "_stext", "_etext" },
52 { "_sinittext", "_einittext" },
53 };
54 #define text_range_text (&text_ranges[0])
55 #define text_range_inittext (&text_ranges[1])
56
57 static struct addr_range percpu_range = {
58 "__per_cpu_start", "__per_cpu_end", -1ULL, 0
59 };
60
61 static struct sym_entry **table;
62 static unsigned int table_size, table_cnt;
63 static int all_symbols;
64 static int absolute_percpu;
65 static int lto_clang;
66
67 static int token_profit[0x10000];
68
69 /* the table that holds the result of the compression */
70 static unsigned char best_table[256][2];
71 static unsigned char best_table_len[256];
72
73
74 static void usage(void)
75 {
76 fprintf(stderr, "Usage: kallsyms [--all-symbols] [--absolute-percpu] "
77 "[--lto-clang] in.map > out.S\n");
78 exit(1);
79 }
80
81 static char *sym_name(const struct sym_entry *s)
82 {
83 return (char *)s->sym + 1;
84 }
85
86 static bool is_ignored_symbol(const char *name, char type)
87 {
88 if (type == 'u' || type == 'n')
89 return true;
90
91 if (toupper(type) == 'A') {
92 /* Keep these useful absolute symbols */
93 if (strcmp(name, "__kernel_syscall_via_break") &&
94 strcmp(name, "__kernel_syscall_via_epc") &&
95 strcmp(name, "__kernel_sigtramp") &&
96 strcmp(name, "__gp"))
97 return true;
98 }
99
100 return false;
101 }
102
103 static void check_symbol_range(const char *sym, unsigned long long addr,
104 struct addr_range *ranges, int entries)
105 {
106 size_t i;
107 struct addr_range *ar;
108
109 for (i = 0; i < entries; ++i) {
110 ar = &ranges[i];
111
112 if (strcmp(sym, ar->start_sym) == 0) {
113 ar->start = addr;
114 return;
115 } else if (strcmp(sym, ar->end_sym) == 0) {
116 ar->end = addr;
117 return;
118 }
119 }
120 }
121
122 static struct sym_entry *read_symbol(FILE *in, char **buf, size_t *buf_len)
123 {
124 char *name, type, *p;
125 unsigned long long addr;
126 size_t len;
127 ssize_t readlen;
128 struct sym_entry *sym;
129
130 errno = 0;
131 readlen = getline(buf, buf_len, in);
132 if (readlen < 0) {
133 if (errno) {
134 perror("read_symbol");
135 exit(EXIT_FAILURE);
136 }
137 return NULL;
138 }
139
140 if ((*buf)[readlen - 1] == '\n')
141 (*buf)[readlen - 1] = 0;
142
143 addr = strtoull(*buf, &p, 16);
144
145 if (*buf == p || *p++ != ' ' || !isascii((type = *p++)) || *p++ != ' ') {
146 fprintf(stderr, "line format error\n");
147 exit(EXIT_FAILURE);
148 }
149
150 name = p;
151 len = strlen(name);
152
153 if (len >= KSYM_NAME_LEN) {
154 fprintf(stderr, "Symbol %s too long for kallsyms (%zu >= %d).\n"
155 "Please increase KSYM_NAME_LEN both in kernel and kallsyms.c\n",
156 name, len, KSYM_NAME_LEN);
157 return NULL;
158 }
159
160 if (strcmp(name, "_text") == 0)
161 _text = addr;
162
163 /* Ignore most absolute/undefined (?) symbols. */
164 if (is_ignored_symbol(name, type))
165 return NULL;
166
167 check_symbol_range(name, addr, text_ranges, ARRAY_SIZE(text_ranges));
168 check_symbol_range(name, addr, &percpu_range, 1);
169
170 /* include the type field in the symbol name, so that it gets
171 * compressed together */
172 len++;
173
174 sym = malloc(sizeof(*sym) + len + 1);
175 if (!sym) {
176 fprintf(stderr, "kallsyms failure: "
177 "unable to allocate required amount of memory\n");
178 exit(EXIT_FAILURE);
179 }
180 sym->addr = addr;
181 sym->len = len;
182 sym->sym[0] = type;
183 strcpy(sym_name(sym), name);
184 sym->percpu_absolute = false;
185
186 return sym;
187 }
188
189 static int symbol_in_range(const struct sym_entry *s,
190 const struct addr_range *ranges, int entries)
191 {
192 size_t i;
193 const struct addr_range *ar;
194
195 for (i = 0; i < entries; ++i) {
196 ar = &ranges[i];
197
198 if (s->addr >= ar->start && s->addr <= ar->end)
199 return 1;
200 }
201
202 return 0;
203 }
204
205 static bool string_starts_with(const char *s, const char *prefix)
206 {
207 return strncmp(s, prefix, strlen(prefix)) == 0;
208 }
209
210 static int symbol_valid(const struct sym_entry *s)
211 {
212 const char *name = sym_name(s);
213
214 /* if --all-symbols is not specified, then symbols outside the text
215 * and inittext sections are discarded */
216 if (!all_symbols) {
217 /*
218 * Symbols starting with __start and __stop are used to denote
219 * section boundaries, and should always be included:
220 */
221 if (string_starts_with(name, "__start_") ||
222 string_starts_with(name, "__stop_"))
223 return 1;
224
225 if (symbol_in_range(s, text_ranges,
226 ARRAY_SIZE(text_ranges)) == 0)
227 return 0;
228 /* Corner case. Discard any symbols with the same value as
229 * _etext _einittext; they can move between pass 1 and 2 when
230 * the kallsyms data are added. If these symbols move then
231 * they may get dropped in pass 2, which breaks the kallsyms
232 * rules.
233 */
234 if ((s->addr == text_range_text->end &&
235 strcmp(name, text_range_text->end_sym)) ||
236 (s->addr == text_range_inittext->end &&
237 strcmp(name, text_range_inittext->end_sym)))
238 return 0;
239 }
240
241 return 1;
242 }
243
244 /* remove all the invalid symbols from the table */
245 static void shrink_table(void)
246 {
247 unsigned int i, pos;
248
249 pos = 0;
250 for (i = 0; i < table_cnt; i++) {
251 if (symbol_valid(table[i])) {
252 if (pos != i)
253 table[pos] = table[i];
254 pos++;
255 } else {
256 free(table[i]);
257 }
258 }
259 table_cnt = pos;
260 }
261
262 static void read_map(const char *in)
263 {
264 FILE *fp;
265 struct sym_entry *sym;
266 char *buf = NULL;
267 size_t buflen = 0;
268
269 fp = fopen(in, "r");
270 if (!fp) {
271 perror(in);
272 exit(1);
273 }
274
275 while (!feof(fp)) {
276 sym = read_symbol(fp, &buf, &buflen);
277 if (!sym)
278 continue;
279
280 sym->seq = table_cnt;
281
282 if (table_cnt >= table_size) {
283 table_size += 10000;
284 table = realloc(table, sizeof(*table) * table_size);
285 if (!table) {
286 fprintf(stderr, "out of memory\n");
287 fclose(fp);
288 exit (1);
289 }
290 }
291
292 table[table_cnt++] = sym;
293 }
294
295 free(buf);
296 fclose(fp);
297 }
298
299 static void output_label(const char *label)
300 {
301 printf(".globl %s\n", label);
302 printf("\tALGN\n");
303 printf("%s:\n", label);
304 }
305
306 /* Provide proper symbols relocatability by their '_text' relativeness. */
307 static void output_address(unsigned long long addr)
308 {
309 if (_text <= addr)
310 printf("\tPTR\t_text + %#llx\n", addr - _text);
311 else
312 printf("\tPTR\t_text - %#llx\n", _text - addr);
313 }
314
315 /* uncompress a compressed symbol. When this function is called, the best table
316 * might still be compressed itself, so the function needs to be recursive */
317 static int expand_symbol(const unsigned char *data, int len, char *result)
318 {
319 int c, rlen, total=0;
320
321 while (len) {
322 c = *data;
323 /* if the table holds a single char that is the same as the one
324 * we are looking for, then end the search */
325 if (best_table[c][0]==c && best_table_len[c]==1) {
326 *result++ = c;
327 total++;
328 } else {
329 /* if not, recurse and expand */
330 rlen = expand_symbol(best_table[c], best_table_len[c], result);
331 total += rlen;
332 result += rlen;
333 }
334 data++;
335 len--;
336 }
337 *result=0;
338
339 return total;
340 }
341
342 static bool symbol_absolute(const struct sym_entry *s)
343 {
344 return s->percpu_absolute;
345 }
346
347 static void cleanup_symbol_name(char *s)
348 {
349 char *p;
350
351 /*
352 * ASCII[.] = 2e
353 * ASCII[0-9] = 30,39
354 * ASCII[A-Z] = 41,5a
355 * ASCII[_] = 5f
356 * ASCII[a-z] = 61,7a
357 *
358 * As above, replacing the first '.' in ".llvm." with '\0' does not
359 * affect the main sorting, but it helps us with subsorting.
360 */
361 p = strstr(s, ".llvm.");
362 if (p)
363 *p = '\0';
364 }
365
366 static int compare_names(const void *a, const void *b)
367 {
368 int ret;
369 const struct sym_entry *sa = *(const struct sym_entry **)a;
370 const struct sym_entry *sb = *(const struct sym_entry **)b;
371
372 ret = strcmp(sym_name(sa), sym_name(sb));
373 if (!ret) {
374 if (sa->addr > sb->addr)
375 return 1;
376 else if (sa->addr < sb->addr)
377 return -1;
378
379 /* keep old order */
380 return (int)(sa->seq - sb->seq);
381 }
382
383 return ret;
384 }
385
386 static void sort_symbols_by_name(void)
387 {
388 qsort(table, table_cnt, sizeof(table[0]), compare_names);
389 }
390
391 static void write_src(void)
392 {
393 unsigned int i, k, off;
394 unsigned int best_idx[256];
395 unsigned int *markers, markers_cnt;
396 char buf[KSYM_NAME_LEN];
397
398 printf("#include <asm/bitsperlong.h>\n");
399 printf("#if BITS_PER_LONG == 64\n");
400 printf("#define PTR .quad\n");
401 printf("#define ALGN .balign 8\n");
402 printf("#else\n");
403 printf("#define PTR .long\n");
404 printf("#define ALGN .balign 4\n");
405 printf("#endif\n");
406
407 printf("\t.section .rodata, \"a\"\n");
408
409 output_label("kallsyms_num_syms");
410 printf("\t.long\t%u\n", table_cnt);
411 printf("\n");
412
413 /* table of offset markers, that give the offset in the compressed stream
414 * every 256 symbols */
415 markers_cnt = (table_cnt + 255) / 256;
416 markers = malloc(sizeof(*markers) * markers_cnt);
417 if (!markers) {
418 fprintf(stderr, "kallsyms failure: "
419 "unable to allocate required memory\n");
420 exit(EXIT_FAILURE);
421 }
422
423 output_label("kallsyms_names");
424 off = 0;
425 for (i = 0; i < table_cnt; i++) {
426 if ((i & 0xFF) == 0)
427 markers[i >> 8] = off;
428 table[i]->seq = i;
429
430 /* There cannot be any symbol of length zero. */
431 if (table[i]->len == 0) {
432 fprintf(stderr, "kallsyms failure: "
433 "unexpected zero symbol length\n");
434 exit(EXIT_FAILURE);
435 }
436
437 /* Only lengths that fit in up-to-two-byte ULEB128 are supported. */
438 if (table[i]->len > 0x3FFF) {
439 fprintf(stderr, "kallsyms failure: "
440 "unexpected huge symbol length\n");
441 exit(EXIT_FAILURE);
442 }
443
444 /* Encode length with ULEB128. */
445 if (table[i]->len <= 0x7F) {
446 /* Most symbols use a single byte for the length. */
447 printf("\t.byte 0x%02x", table[i]->len);
448 off += table[i]->len + 1;
449 } else {
450 /* "Big" symbols use two bytes. */
451 printf("\t.byte 0x%02x, 0x%02x",
452 (table[i]->len & 0x7F) | 0x80,
453 (table[i]->len >> 7) & 0x7F);
454 off += table[i]->len + 2;
455 }
456 for (k = 0; k < table[i]->len; k++)
457 printf(", 0x%02x", table[i]->sym[k]);
458
459 /*
460 * Now that we wrote out the compressed symbol name, restore the
461 * original name and print it in the comment.
462 */
463 expand_symbol(table[i]->sym, table[i]->len, buf);
464 strcpy((char *)table[i]->sym, buf);
465 printf("\t/* %s */\n", table[i]->sym);
466 }
467 printf("\n");
468
469 output_label("kallsyms_markers");
470 for (i = 0; i < markers_cnt; i++)
471 printf("\t.long\t%u\n", markers[i]);
472 printf("\n");
473
474 free(markers);
475
476 output_label("kallsyms_token_table");
477 off = 0;
478 for (i = 0; i < 256; i++) {
479 best_idx[i] = off;
480 expand_symbol(best_table[i], best_table_len[i], buf);
481 printf("\t.asciz\t\"%s\"\n", buf);
482 off += strlen(buf) + 1;
483 }
484 printf("\n");
485
486 output_label("kallsyms_token_index");
487 for (i = 0; i < 256; i++)
488 printf("\t.short\t%d\n", best_idx[i]);
489 printf("\n");
490
491 output_label("kallsyms_offsets");
492
493 for (i = 0; i < table_cnt; i++) {
494 /*
495 * Use the offset relative to the lowest value
496 * encountered of all relative symbols, and emit
497 * non-relocatable fixed offsets that will be fixed
498 * up at runtime.
499 */
500
501 long long offset;
502 int overflow;
503
504 if (!absolute_percpu) {
505 offset = table[i]->addr - relative_base;
506 overflow = (offset < 0 || offset > UINT_MAX);
507 } else if (symbol_absolute(table[i])) {
508 offset = table[i]->addr;
509 overflow = (offset < 0 || offset > INT_MAX);
510 } else {
511 offset = relative_base - table[i]->addr - 1;
512 overflow = (offset < INT_MIN || offset >= 0);
513 }
514 if (overflow) {
515 fprintf(stderr, "kallsyms failure: "
516 "%s symbol value %#llx out of range in relative mode\n",
517 symbol_absolute(table[i]) ? "absolute" : "relative",
518 table[i]->addr);
519 exit(EXIT_FAILURE);
520 }
521 printf("\t.long\t%#x\t/* %s */\n", (int)offset, table[i]->sym);
522 }
523 printf("\n");
524
525 output_label("kallsyms_relative_base");
526 output_address(relative_base);
527 printf("\n");
528
529 if (lto_clang)
530 for (i = 0; i < table_cnt; i++)
531 cleanup_symbol_name((char *)table[i]->sym);
532
533 sort_symbols_by_name();
534 output_label("kallsyms_seqs_of_names");
535 for (i = 0; i < table_cnt; i++)
536 printf("\t.byte 0x%02x, 0x%02x, 0x%02x\t/* %s */\n",
537 (unsigned char)(table[i]->seq >> 16),
538 (unsigned char)(table[i]->seq >> 8),
539 (unsigned char)(table[i]->seq >> 0),
540 table[i]->sym);
541 printf("\n");
542 }
543
544
545 /* table lookup compression functions */
546
547 /* count all the possible tokens in a symbol */
548 static void learn_symbol(const unsigned char *symbol, int len)
549 {
550 int i;
551
552 for (i = 0; i < len - 1; i++)
553 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++;
554 }
555
556 /* decrease the count for all the possible tokens in a symbol */
557 static void forget_symbol(const unsigned char *symbol, int len)
558 {
559 int i;
560
561 for (i = 0; i < len - 1; i++)
562 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--;
563 }
564
565 /* do the initial token count */
566 static void build_initial_token_table(void)
567 {
568 unsigned int i;
569
570 for (i = 0; i < table_cnt; i++)
571 learn_symbol(table[i]->sym, table[i]->len);
572 }
573
574 static unsigned char *find_token(unsigned char *str, int len,
575 const unsigned char *token)
576 {
577 int i;
578
579 for (i = 0; i < len - 1; i++) {
580 if (str[i] == token[0] && str[i+1] == token[1])
581 return &str[i];
582 }
583 return NULL;
584 }
585
586 /* replace a given token in all the valid symbols. Use the sampled symbols
587 * to update the counts */
588 static void compress_symbols(const unsigned char *str, int idx)
589 {
590 unsigned int i, len, size;
591 unsigned char *p1, *p2;
592
593 for (i = 0; i < table_cnt; i++) {
594
595 len = table[i]->len;
596 p1 = table[i]->sym;
597
598 /* find the token on the symbol */
599 p2 = find_token(p1, len, str);
600 if (!p2) continue;
601
602 /* decrease the counts for this symbol's tokens */
603 forget_symbol(table[i]->sym, len);
604
605 size = len;
606
607 do {
608 *p2 = idx;
609 p2++;
610 size -= (p2 - p1);
611 memmove(p2, p2 + 1, size);
612 p1 = p2;
613 len--;
614
615 if (size < 2) break;
616
617 /* find the token on the symbol */
618 p2 = find_token(p1, size, str);
619
620 } while (p2);
621
622 table[i]->len = len;
623
624 /* increase the counts for this symbol's new tokens */
625 learn_symbol(table[i]->sym, len);
626 }
627 }
628
629 /* search the token with the maximum profit */
630 static int find_best_token(void)
631 {
632 int i, best, bestprofit;
633
634 bestprofit=-10000;
635 best = 0;
636
637 for (i = 0; i < 0x10000; i++) {
638 if (token_profit[i] > bestprofit) {
639 best = i;
640 bestprofit = token_profit[i];
641 }
642 }
643 return best;
644 }
645
646 /* this is the core of the algorithm: calculate the "best" table */
647 static void optimize_result(void)
648 {
649 int i, best;
650
651 /* using the '\0' symbol last allows compress_symbols to use standard
652 * fast string functions */
653 for (i = 255; i >= 0; i--) {
654
655 /* if this table slot is empty (it is not used by an actual
656 * original char code */
657 if (!best_table_len[i]) {
658
659 /* find the token with the best profit value */
660 best = find_best_token();
661 if (token_profit[best] == 0)
662 break;
663
664 /* place it in the "best" table */
665 best_table_len[i] = 2;
666 best_table[i][0] = best & 0xFF;
667 best_table[i][1] = (best >> 8) & 0xFF;
668
669 /* replace this token in all the valid symbols */
670 compress_symbols(best_table[i], i);
671 }
672 }
673 }
674
675 /* start by placing the symbols that are actually used on the table */
676 static void insert_real_symbols_in_table(void)
677 {
678 unsigned int i, j, c;
679
680 for (i = 0; i < table_cnt; i++) {
681 for (j = 0; j < table[i]->len; j++) {
682 c = table[i]->sym[j];
683 best_table[c][0]=c;
684 best_table_len[c]=1;
685 }
686 }
687 }
688
689 static void optimize_token_table(void)
690 {
691 build_initial_token_table();
692
693 insert_real_symbols_in_table();
694
695 optimize_result();
696 }
697
698 /* guess for "linker script provide" symbol */
699 static int may_be_linker_script_provide_symbol(const struct sym_entry *se)
700 {
701 const char *symbol = sym_name(se);
702 int len = se->len - 1;
703
704 if (len < 8)
705 return 0;
706
707 if (symbol[0] != '_' || symbol[1] != '_')
708 return 0;
709
710 /* __start_XXXXX */
711 if (!memcmp(symbol + 2, "start_", 6))
712 return 1;
713
714 /* __stop_XXXXX */
715 if (!memcmp(symbol + 2, "stop_", 5))
716 return 1;
717
718 /* __end_XXXXX */
719 if (!memcmp(symbol + 2, "end_", 4))
720 return 1;
721
722 /* __XXXXX_start */
723 if (!memcmp(symbol + len - 6, "_start", 6))
724 return 1;
725
726 /* __XXXXX_end */
727 if (!memcmp(symbol + len - 4, "_end", 4))
728 return 1;
729
730 return 0;
731 }
732
733 static int compare_symbols(const void *a, const void *b)
734 {
735 const struct sym_entry *sa = *(const struct sym_entry **)a;
736 const struct sym_entry *sb = *(const struct sym_entry **)b;
737 int wa, wb;
738
739 /* sort by address first */
740 if (sa->addr > sb->addr)
741 return 1;
742 if (sa->addr < sb->addr)
743 return -1;
744
745 /* sort by "weakness" type */
746 wa = (sa->sym[0] == 'w') || (sa->sym[0] == 'W');
747 wb = (sb->sym[0] == 'w') || (sb->sym[0] == 'W');
748 if (wa != wb)
749 return wa - wb;
750
751 /* sort by "linker script provide" type */
752 wa = may_be_linker_script_provide_symbol(sa);
753 wb = may_be_linker_script_provide_symbol(sb);
754 if (wa != wb)
755 return wa - wb;
756
757 /* sort by the number of prefix underscores */
758 wa = strspn(sym_name(sa), "_");
759 wb = strspn(sym_name(sb), "_");
760 if (wa != wb)
761 return wa - wb;
762
763 /* sort by initial order, so that other symbols are left undisturbed */
764 return sa->seq - sb->seq;
765 }
766
767 static void sort_symbols(void)
768 {
769 qsort(table, table_cnt, sizeof(table[0]), compare_symbols);
770 }
771
772 static void make_percpus_absolute(void)
773 {
774 unsigned int i;
775
776 for (i = 0; i < table_cnt; i++)
777 if (symbol_in_range(table[i], &percpu_range, 1)) {
778 /*
779 * Keep the 'A' override for percpu symbols to
780 * ensure consistent behavior compared to older
781 * versions of this tool.
782 */
783 table[i]->sym[0] = 'A';
784 table[i]->percpu_absolute = true;
785 }
786 }
787
788 /* find the minimum non-absolute symbol address */
789 static void record_relative_base(void)
790 {
791 unsigned int i;
792
793 for (i = 0; i < table_cnt; i++)
794 if (!symbol_absolute(table[i])) {
795 /*
796 * The table is sorted by address.
797 * Take the first non-absolute symbol value.
798 */
799 relative_base = table[i]->addr;
800 return;
801 }
802 }
803
804 int main(int argc, char **argv)
805 {
806 while (1) {
807 static const struct option long_options[] = {
808 {"all-symbols", no_argument, &all_symbols, 1},
809 {"absolute-percpu", no_argument, &absolute_percpu, 1},
810 {"lto-clang", no_argument, <o_clang, 1},
811 {},
812 };
813
814 int c = getopt_long(argc, argv, "", long_options, NULL);
815
816 if (c == -1)
817 break;
818 if (c != 0)
819 usage();
820 }
821
822 if (optind >= argc)
823 usage();
824
825 read_map(argv[optind]);
826 shrink_table();
827 if (absolute_percpu)
828 make_percpus_absolute();
829 sort_symbols();
830 record_relative_base();
831 optimize_token_table();
832 write_src();
833
834 return 0;
835 }
836
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.