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: nm -n vmlinux | scripts/kallsyms [--all-symbols] > symbols.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 <stdio.h>
22 #include <stdlib.h>
23 #include <string.h>
24 #include <ctype.h>
25 #include <limits.h>
26
27 #ifndef ARRAY_SIZE
28 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0]))
29 #endif
30
31 #define KSYM_NAME_LEN 128
32
33 struct sym_entry {
34 unsigned long long addr;
35 unsigned int len;
36 unsigned int start_pos;
37 unsigned char *sym;
38 unsigned int percpu_absolute;
39 };
40
41 struct addr_range {
42 const char *start_sym, *end_sym;
43 unsigned long long start, end;
44 };
45
46 static unsigned long long _text;
47 static unsigned long long relative_base;
48 static struct addr_range text_ranges[] = {
49 { "_stext", "_etext" },
50 { "_sinittext", "_einittext" },
51 };
52 #define text_range_text (&text_ranges[0])
53 #define text_range_inittext (&text_ranges[1])
54
55 static struct addr_range percpu_range = {
56 "__per_cpu_start", "__per_cpu_end", -1ULL, 0
57 };
58
59 static struct sym_entry *table;
60 static unsigned int table_size, table_cnt;
61 static int all_symbols = 0;
62 static int absolute_percpu = 0;
63 static int base_relative = 0;
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
usage(void)72 static void usage(void)
73 {
74 fprintf(stderr, "Usage: kallsyms [--all-symbols] "
75 "[--base-relative] < in.map > out.S\n");
76 exit(1);
77 }
78
79 /*
80 * This ignores the intensely annoying "mapping symbols" found
81 * in ARM ELF files: $a, $t and $d.
82 */
is_arm_mapping_symbol(const char * str)83 static int is_arm_mapping_symbol(const char *str)
84 {
85 return str[0] == '$' && strchr("axtd", str[1])
86 && (str[2] == '\0' || str[2] == '.');
87 }
88
check_symbol_range(const char * sym,unsigned long long addr,struct addr_range * ranges,int entries)89 static int check_symbol_range(const char *sym, unsigned long long addr,
90 struct addr_range *ranges, int entries)
91 {
92 size_t i;
93 struct addr_range *ar;
94
95 for (i = 0; i < entries; ++i) {
96 ar = &ranges[i];
97
98 if (strcmp(sym, ar->start_sym) == 0) {
99 ar->start = addr;
100 return 0;
101 } else if (strcmp(sym, ar->end_sym) == 0) {
102 ar->end = addr;
103 return 0;
104 }
105 }
106
107 return 1;
108 }
109
read_symbol(FILE * in,struct sym_entry * s)110 static int read_symbol(FILE *in, struct sym_entry *s)
111 {
112 char sym[500], stype;
113 int rc;
114
115 rc = fscanf(in, "%llx %c %499s\n", &s->addr, &stype, sym);
116 if (rc != 3) {
117 if (rc != EOF && fgets(sym, 500, in) == NULL)
118 fprintf(stderr, "Read error or end of file.\n");
119 return -1;
120 }
121 if (strlen(sym) >= KSYM_NAME_LEN) {
122 fprintf(stderr, "Symbol %s too long for kallsyms (%zu >= %d).\n"
123 "Please increase KSYM_NAME_LEN both in kernel and kallsyms.c\n",
124 sym, strlen(sym), KSYM_NAME_LEN);
125 return -1;
126 }
127
128 /* Ignore most absolute/undefined (?) symbols. */
129 if (strcmp(sym, "_text") == 0)
130 _text = s->addr;
131 else if (check_symbol_range(sym, s->addr, text_ranges,
132 ARRAY_SIZE(text_ranges)) == 0)
133 /* nothing to do */;
134 else if (toupper(stype) == 'A')
135 {
136 /* Keep these useful absolute symbols */
137 if (strcmp(sym, "__kernel_syscall_via_break") &&
138 strcmp(sym, "__kernel_syscall_via_epc") &&
139 strcmp(sym, "__kernel_sigtramp") &&
140 strcmp(sym, "__gp"))
141 return -1;
142
143 }
144 else if (toupper(stype) == 'U' ||
145 is_arm_mapping_symbol(sym))
146 return -1;
147 /* exclude also MIPS ELF local symbols ($L123 instead of .L123) */
148 else if (sym[0] == '$')
149 return -1;
150 /* exclude debugging symbols */
151 else if (stype == 'N' || stype == 'n')
152 return -1;
153 /* exclude s390 kasan local symbols */
154 else if (!strncmp(sym, ".LASANPC", 8))
155 return -1;
156
157 /* include the type field in the symbol name, so that it gets
158 * compressed together */
159 s->len = strlen(sym) + 1;
160 s->sym = malloc(s->len + 1);
161 if (!s->sym) {
162 fprintf(stderr, "kallsyms failure: "
163 "unable to allocate required amount of memory\n");
164 exit(EXIT_FAILURE);
165 }
166 strcpy((char *)s->sym + 1, sym);
167 s->sym[0] = stype;
168
169 s->percpu_absolute = 0;
170
171 /* Record if we've found __per_cpu_start/end. */
172 check_symbol_range(sym, s->addr, &percpu_range, 1);
173
174 return 0;
175 }
176
symbol_in_range(struct sym_entry * s,struct addr_range * ranges,int entries)177 static int symbol_in_range(struct sym_entry *s, struct addr_range *ranges,
178 int entries)
179 {
180 size_t i;
181 struct addr_range *ar;
182
183 for (i = 0; i < entries; ++i) {
184 ar = &ranges[i];
185
186 if (s->addr >= ar->start && s->addr <= ar->end)
187 return 1;
188 }
189
190 return 0;
191 }
192
symbol_valid(struct sym_entry * s)193 static int symbol_valid(struct sym_entry *s)
194 {
195 /* Symbols which vary between passes. Passes 1 and 2 must have
196 * identical symbol lists. The kallsyms_* symbols below are only added
197 * after pass 1, they would be included in pass 2 when --all-symbols is
198 * specified so exclude them to get a stable symbol list.
199 */
200 static char *special_symbols[] = {
201 "kallsyms_addresses",
202 "kallsyms_offsets",
203 "kallsyms_relative_base",
204 "kallsyms_num_syms",
205 "kallsyms_names",
206 "kallsyms_markers",
207 "kallsyms_token_table",
208 "kallsyms_token_index",
209
210 /* Exclude linker generated symbols which vary between passes */
211 "_SDA_BASE_", /* ppc */
212 "_SDA2_BASE_", /* ppc */
213 NULL };
214
215 static char *special_prefixes[] = {
216 "__crc_", /* modversions */
217 "__efistub_", /* arm64 EFI stub namespace */
218 NULL };
219
220 static char *special_suffixes[] = {
221 "_veneer", /* arm */
222 "_from_arm", /* arm */
223 "_from_thumb", /* arm */
224 NULL };
225
226 int i;
227 char *sym_name = (char *)s->sym + 1;
228
229 /* if --all-symbols is not specified, then symbols outside the text
230 * and inittext sections are discarded */
231 if (!all_symbols) {
232 if (symbol_in_range(s, text_ranges,
233 ARRAY_SIZE(text_ranges)) == 0)
234 return 0;
235 /* Corner case. Discard any symbols with the same value as
236 * _etext _einittext; they can move between pass 1 and 2 when
237 * the kallsyms data are added. If these symbols move then
238 * they may get dropped in pass 2, which breaks the kallsyms
239 * rules.
240 */
241 if ((s->addr == text_range_text->end &&
242 strcmp(sym_name,
243 text_range_text->end_sym)) ||
244 (s->addr == text_range_inittext->end &&
245 strcmp(sym_name,
246 text_range_inittext->end_sym)))
247 return 0;
248 }
249
250 /* Exclude symbols which vary between passes. */
251 for (i = 0; special_symbols[i]; i++)
252 if (strcmp(sym_name, special_symbols[i]) == 0)
253 return 0;
254
255 for (i = 0; special_prefixes[i]; i++) {
256 int l = strlen(special_prefixes[i]);
257
258 if (l <= strlen(sym_name) &&
259 strncmp(sym_name, special_prefixes[i], l) == 0)
260 return 0;
261 }
262
263 for (i = 0; special_suffixes[i]; i++) {
264 int l = strlen(sym_name) - strlen(special_suffixes[i]);
265
266 if (l >= 0 && strcmp(sym_name + l, special_suffixes[i]) == 0)
267 return 0;
268 }
269
270 return 1;
271 }
272
read_map(FILE * in)273 static void read_map(FILE *in)
274 {
275 while (!feof(in)) {
276 if (table_cnt >= table_size) {
277 table_size += 10000;
278 table = realloc(table, sizeof(*table) * table_size);
279 if (!table) {
280 fprintf(stderr, "out of memory\n");
281 exit (1);
282 }
283 }
284 if (read_symbol(in, &table[table_cnt]) == 0) {
285 table[table_cnt].start_pos = table_cnt;
286 table_cnt++;
287 }
288 }
289 }
290
output_label(char * label)291 static void output_label(char *label)
292 {
293 printf(".globl %s\n", label);
294 printf("\tALGN\n");
295 printf("%s:\n", label);
296 }
297
298 /* uncompress a compressed symbol. When this function is called, the best table
299 * might still be compressed itself, so the function needs to be recursive */
expand_symbol(unsigned char * data,int len,char * result)300 static int expand_symbol(unsigned char *data, int len, char *result)
301 {
302 int c, rlen, total=0;
303
304 while (len) {
305 c = *data;
306 /* if the table holds a single char that is the same as the one
307 * we are looking for, then end the search */
308 if (best_table[c][0]==c && best_table_len[c]==1) {
309 *result++ = c;
310 total++;
311 } else {
312 /* if not, recurse and expand */
313 rlen = expand_symbol(best_table[c], best_table_len[c], result);
314 total += rlen;
315 result += rlen;
316 }
317 data++;
318 len--;
319 }
320 *result=0;
321
322 return total;
323 }
324
symbol_absolute(struct sym_entry * s)325 static int symbol_absolute(struct sym_entry *s)
326 {
327 return s->percpu_absolute;
328 }
329
write_src(void)330 static void write_src(void)
331 {
332 unsigned int i, k, off;
333 unsigned int best_idx[256];
334 unsigned int *markers;
335 char buf[KSYM_NAME_LEN];
336
337 printf("#include <asm/bitsperlong.h>\n");
338 printf("#if BITS_PER_LONG == 64\n");
339 printf("#define PTR .quad\n");
340 printf("#define ALGN .balign 8\n");
341 printf("#else\n");
342 printf("#define PTR .long\n");
343 printf("#define ALGN .balign 4\n");
344 printf("#endif\n");
345
346 printf("\t.section .rodata, \"a\"\n");
347
348 /* Provide proper symbols relocatability by their relativeness
349 * to a fixed anchor point in the runtime image, either '_text'
350 * for absolute address tables, in which case the linker will
351 * emit the final addresses at build time. Otherwise, use the
352 * offset relative to the lowest value encountered of all relative
353 * symbols, and emit non-relocatable fixed offsets that will be fixed
354 * up at runtime.
355 *
356 * The symbol names cannot be used to construct normal symbol
357 * references as the list of symbols contains symbols that are
358 * declared static and are private to their .o files. This prevents
359 * .tmp_kallsyms.o or any other object from referencing them.
360 */
361 if (!base_relative)
362 output_label("kallsyms_addresses");
363 else
364 output_label("kallsyms_offsets");
365
366 for (i = 0; i < table_cnt; i++) {
367 if (base_relative) {
368 long long offset;
369 int overflow;
370
371 if (!absolute_percpu) {
372 offset = table[i].addr - relative_base;
373 overflow = (offset < 0 || offset > UINT_MAX);
374 } else if (symbol_absolute(&table[i])) {
375 offset = table[i].addr;
376 overflow = (offset < 0 || offset > INT_MAX);
377 } else {
378 offset = relative_base - table[i].addr - 1;
379 overflow = (offset < INT_MIN || offset >= 0);
380 }
381 if (overflow) {
382 fprintf(stderr, "kallsyms failure: "
383 "%s symbol value %#llx out of range in relative mode\n",
384 symbol_absolute(&table[i]) ? "absolute" : "relative",
385 table[i].addr);
386 exit(EXIT_FAILURE);
387 }
388 printf("\t.long\t%#x\n", (int)offset);
389 } else if (!symbol_absolute(&table[i])) {
390 if (_text <= table[i].addr)
391 printf("\tPTR\t_text + %#llx\n",
392 table[i].addr - _text);
393 else
394 printf("\tPTR\t_text - %#llx\n",
395 _text - table[i].addr);
396 } else {
397 printf("\tPTR\t%#llx\n", table[i].addr);
398 }
399 }
400 printf("\n");
401
402 if (base_relative) {
403 output_label("kallsyms_relative_base");
404 printf("\tPTR\t_text - %#llx\n", _text - relative_base);
405 printf("\n");
406 }
407
408 output_label("kallsyms_num_syms");
409 printf("\t.long\t%u\n", table_cnt);
410 printf("\n");
411
412 /* table of offset markers, that give the offset in the compressed stream
413 * every 256 symbols */
414 markers = malloc(sizeof(unsigned int) * ((table_cnt + 255) / 256));
415 if (!markers) {
416 fprintf(stderr, "kallsyms failure: "
417 "unable to allocate required memory\n");
418 exit(EXIT_FAILURE);
419 }
420
421 output_label("kallsyms_names");
422 off = 0;
423 for (i = 0; i < table_cnt; i++) {
424 if ((i & 0xFF) == 0)
425 markers[i >> 8] = off;
426
427 printf("\t.byte 0x%02x", table[i].len);
428 for (k = 0; k < table[i].len; k++)
429 printf(", 0x%02x", table[i].sym[k]);
430 printf("\n");
431
432 off += table[i].len + 1;
433 }
434 printf("\n");
435
436 output_label("kallsyms_markers");
437 for (i = 0; i < ((table_cnt + 255) >> 8); i++)
438 printf("\t.long\t%u\n", markers[i]);
439 printf("\n");
440
441 free(markers);
442
443 output_label("kallsyms_token_table");
444 off = 0;
445 for (i = 0; i < 256; i++) {
446 best_idx[i] = off;
447 expand_symbol(best_table[i], best_table_len[i], buf);
448 printf("\t.asciz\t\"%s\"\n", buf);
449 off += strlen(buf) + 1;
450 }
451 printf("\n");
452
453 output_label("kallsyms_token_index");
454 for (i = 0; i < 256; i++)
455 printf("\t.short\t%d\n", best_idx[i]);
456 printf("\n");
457 }
458
459
460 /* table lookup compression functions */
461
462 /* count all the possible tokens in a symbol */
learn_symbol(unsigned char * symbol,int len)463 static void learn_symbol(unsigned char *symbol, int len)
464 {
465 int i;
466
467 for (i = 0; i < len - 1; i++)
468 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++;
469 }
470
471 /* decrease the count for all the possible tokens in a symbol */
forget_symbol(unsigned char * symbol,int len)472 static void forget_symbol(unsigned char *symbol, int len)
473 {
474 int i;
475
476 for (i = 0; i < len - 1; i++)
477 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--;
478 }
479
480 /* remove all the invalid symbols from the table and do the initial token count */
build_initial_tok_table(void)481 static void build_initial_tok_table(void)
482 {
483 unsigned int i, pos;
484
485 pos = 0;
486 for (i = 0; i < table_cnt; i++) {
487 if ( symbol_valid(&table[i]) ) {
488 if (pos != i)
489 table[pos] = table[i];
490 learn_symbol(table[pos].sym, table[pos].len);
491 pos++;
492 }
493 }
494 table_cnt = pos;
495 }
496
find_token(unsigned char * str,int len,unsigned char * token)497 static void *find_token(unsigned char *str, int len, unsigned char *token)
498 {
499 int i;
500
501 for (i = 0; i < len - 1; i++) {
502 if (str[i] == token[0] && str[i+1] == token[1])
503 return &str[i];
504 }
505 return NULL;
506 }
507
508 /* replace a given token in all the valid symbols. Use the sampled symbols
509 * to update the counts */
compress_symbols(unsigned char * str,int idx)510 static void compress_symbols(unsigned char *str, int idx)
511 {
512 unsigned int i, len, size;
513 unsigned char *p1, *p2;
514
515 for (i = 0; i < table_cnt; i++) {
516
517 len = table[i].len;
518 p1 = table[i].sym;
519
520 /* find the token on the symbol */
521 p2 = find_token(p1, len, str);
522 if (!p2) continue;
523
524 /* decrease the counts for this symbol's tokens */
525 forget_symbol(table[i].sym, len);
526
527 size = len;
528
529 do {
530 *p2 = idx;
531 p2++;
532 size -= (p2 - p1);
533 memmove(p2, p2 + 1, size);
534 p1 = p2;
535 len--;
536
537 if (size < 2) break;
538
539 /* find the token on the symbol */
540 p2 = find_token(p1, size, str);
541
542 } while (p2);
543
544 table[i].len = len;
545
546 /* increase the counts for this symbol's new tokens */
547 learn_symbol(table[i].sym, len);
548 }
549 }
550
551 /* search the token with the maximum profit */
find_best_token(void)552 static int find_best_token(void)
553 {
554 int i, best, bestprofit;
555
556 bestprofit=-10000;
557 best = 0;
558
559 for (i = 0; i < 0x10000; i++) {
560 if (token_profit[i] > bestprofit) {
561 best = i;
562 bestprofit = token_profit[i];
563 }
564 }
565 return best;
566 }
567
568 /* this is the core of the algorithm: calculate the "best" table */
optimize_result(void)569 static void optimize_result(void)
570 {
571 int i, best;
572
573 /* using the '\0' symbol last allows compress_symbols to use standard
574 * fast string functions */
575 for (i = 255; i >= 0; i--) {
576
577 /* if this table slot is empty (it is not used by an actual
578 * original char code */
579 if (!best_table_len[i]) {
580
581 /* find the token with the best profit value */
582 best = find_best_token();
583 if (token_profit[best] == 0)
584 break;
585
586 /* place it in the "best" table */
587 best_table_len[i] = 2;
588 best_table[i][0] = best & 0xFF;
589 best_table[i][1] = (best >> 8) & 0xFF;
590
591 /* replace this token in all the valid symbols */
592 compress_symbols(best_table[i], i);
593 }
594 }
595 }
596
597 /* start by placing the symbols that are actually used on the table */
insert_real_symbols_in_table(void)598 static void insert_real_symbols_in_table(void)
599 {
600 unsigned int i, j, c;
601
602 for (i = 0; i < table_cnt; i++) {
603 for (j = 0; j < table[i].len; j++) {
604 c = table[i].sym[j];
605 best_table[c][0]=c;
606 best_table_len[c]=1;
607 }
608 }
609 }
610
optimize_token_table(void)611 static void optimize_token_table(void)
612 {
613 build_initial_tok_table();
614
615 insert_real_symbols_in_table();
616
617 /* When valid symbol is not registered, exit to error */
618 if (!table_cnt) {
619 fprintf(stderr, "No valid symbol.\n");
620 exit(1);
621 }
622
623 optimize_result();
624 }
625
626 /* guess for "linker script provide" symbol */
may_be_linker_script_provide_symbol(const struct sym_entry * se)627 static int may_be_linker_script_provide_symbol(const struct sym_entry *se)
628 {
629 const char *symbol = (char *)se->sym + 1;
630 int len = se->len - 1;
631
632 if (len < 8)
633 return 0;
634
635 if (symbol[0] != '_' || symbol[1] != '_')
636 return 0;
637
638 /* __start_XXXXX */
639 if (!memcmp(symbol + 2, "start_", 6))
640 return 1;
641
642 /* __stop_XXXXX */
643 if (!memcmp(symbol + 2, "stop_", 5))
644 return 1;
645
646 /* __end_XXXXX */
647 if (!memcmp(symbol + 2, "end_", 4))
648 return 1;
649
650 /* __XXXXX_start */
651 if (!memcmp(symbol + len - 6, "_start", 6))
652 return 1;
653
654 /* __XXXXX_end */
655 if (!memcmp(symbol + len - 4, "_end", 4))
656 return 1;
657
658 return 0;
659 }
660
prefix_underscores_count(const char * str)661 static int prefix_underscores_count(const char *str)
662 {
663 const char *tail = str;
664
665 while (*tail == '_')
666 tail++;
667
668 return tail - str;
669 }
670
compare_symbols(const void * a,const void * b)671 static int compare_symbols(const void *a, const void *b)
672 {
673 const struct sym_entry *sa;
674 const struct sym_entry *sb;
675 int wa, wb;
676
677 sa = a;
678 sb = b;
679
680 /* sort by address first */
681 if (sa->addr > sb->addr)
682 return 1;
683 if (sa->addr < sb->addr)
684 return -1;
685
686 /* sort by "weakness" type */
687 wa = (sa->sym[0] == 'w') || (sa->sym[0] == 'W');
688 wb = (sb->sym[0] == 'w') || (sb->sym[0] == 'W');
689 if (wa != wb)
690 return wa - wb;
691
692 /* sort by "linker script provide" type */
693 wa = may_be_linker_script_provide_symbol(sa);
694 wb = may_be_linker_script_provide_symbol(sb);
695 if (wa != wb)
696 return wa - wb;
697
698 /* sort by the number of prefix underscores */
699 wa = prefix_underscores_count((const char *)sa->sym + 1);
700 wb = prefix_underscores_count((const char *)sb->sym + 1);
701 if (wa != wb)
702 return wa - wb;
703
704 /* sort by initial order, so that other symbols are left undisturbed */
705 return sa->start_pos - sb->start_pos;
706 }
707
sort_symbols(void)708 static void sort_symbols(void)
709 {
710 qsort(table, table_cnt, sizeof(struct sym_entry), compare_symbols);
711 }
712
make_percpus_absolute(void)713 static void make_percpus_absolute(void)
714 {
715 unsigned int i;
716
717 for (i = 0; i < table_cnt; i++)
718 if (symbol_in_range(&table[i], &percpu_range, 1)) {
719 /*
720 * Keep the 'A' override for percpu symbols to
721 * ensure consistent behavior compared to older
722 * versions of this tool.
723 */
724 table[i].sym[0] = 'A';
725 table[i].percpu_absolute = 1;
726 }
727 }
728
729 /* find the minimum non-absolute symbol address */
record_relative_base(void)730 static void record_relative_base(void)
731 {
732 unsigned int i;
733
734 relative_base = -1ULL;
735 for (i = 0; i < table_cnt; i++)
736 if (!symbol_absolute(&table[i]) &&
737 table[i].addr < relative_base)
738 relative_base = table[i].addr;
739 }
740
main(int argc,char ** argv)741 int main(int argc, char **argv)
742 {
743 if (argc >= 2) {
744 int i;
745 for (i = 1; i < argc; i++) {
746 if(strcmp(argv[i], "--all-symbols") == 0)
747 all_symbols = 1;
748 else if (strcmp(argv[i], "--absolute-percpu") == 0)
749 absolute_percpu = 1;
750 else if (strcmp(argv[i], "--base-relative") == 0)
751 base_relative = 1;
752 else
753 usage();
754 }
755 } else if (argc != 1)
756 usage();
757
758 read_map(stdin);
759 if (absolute_percpu)
760 make_percpus_absolute();
761 if (base_relative)
762 record_relative_base();
763 sort_symbols();
764 optimize_token_table();
765 write_src();
766
767 return 0;
768 }
769
