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 <stdbool.h>
22 #include <stdio.h>
23 #include <stdlib.h>
24 #include <string.h>
25 #include <ctype.h>
26 #include <limits.h>
27
28 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0]))
29
30 #define KSYM_NAME_LEN 128
31
32 struct sym_entry {
33 unsigned long long addr;
34 unsigned int len;
35 unsigned int start_pos;
36 unsigned int percpu_absolute;
37 unsigned char sym[];
38 };
39
40 struct addr_range {
41 const char *start_sym, *end_sym;
42 unsigned long long start, end;
43 };
44
45 static unsigned long long _text;
46 static unsigned long long relative_base;
47 static struct addr_range text_ranges[] = {
48 { "_stext", "_etext" },
49 { "_sinittext", "_einittext" },
50 };
51 #define text_range_text (&text_ranges[0])
52 #define text_range_inittext (&text_ranges[1])
53
54 static struct addr_range percpu_range = {
55 "__per_cpu_start", "__per_cpu_end", -1ULL, 0
56 };
57
58 static struct sym_entry **table;
59 static unsigned int table_size, table_cnt;
60 static int all_symbols;
61 static int absolute_percpu;
62 static int base_relative;
63
64 static int token_profit[0x10000];
65
66 /* the table that holds the result of the compression */
67 static unsigned char best_table[256][2];
68 static unsigned char best_table_len[256];
69
70
usage(void)71 static void usage(void)
72 {
73 fprintf(stderr, "Usage: kallsyms [--all-symbols] "
74 "[--base-relative] < in.map > out.S\n");
75 exit(1);
76 }
77
sym_name(const struct sym_entry * s)78 static char *sym_name(const struct sym_entry *s)
79 {
80 return (char *)s->sym + 1;
81 }
82
is_ignored_symbol(const char * name,char type)83 static bool is_ignored_symbol(const char *name, char type)
84 {
85 /* Symbol names that exactly match to the following are ignored.*/
86 static const char * const ignored_symbols[] = {
87 /*
88 * Symbols which vary between passes. Passes 1 and 2 must have
89 * identical symbol lists. The kallsyms_* symbols below are
90 * only added after pass 1, they would be included in pass 2
91 * when --all-symbols is specified so exclude them to get a
92 * stable symbol list.
93 */
94 "kallsyms_addresses",
95 "kallsyms_offsets",
96 "kallsyms_relative_base",
97 "kallsyms_num_syms",
98 "kallsyms_names",
99 "kallsyms_markers",
100 "kallsyms_token_table",
101 "kallsyms_token_index",
102 /* Exclude linker generated symbols which vary between passes */
103 "_SDA_BASE_", /* ppc */
104 "_SDA2_BASE_", /* ppc */
105 NULL
106 };
107
108 /* Symbol names that begin with the following are ignored.*/
109 static const char * const ignored_prefixes[] = {
110 "$", /* local symbols for ARM, MIPS, etc. */
111 ".LASANPC", /* s390 kasan local symbols */
112 "__crc_", /* modversions */
113 "__efistub_", /* arm64 EFI stub namespace */
114 "__kvm_nvhe_", /* arm64 non-VHE KVM namespace */
115 NULL
116 };
117
118 /* Symbol names that end with the following are ignored.*/
119 static const char * const ignored_suffixes[] = {
120 "_from_arm", /* arm */
121 "_from_thumb", /* arm */
122 "_veneer", /* arm */
123 NULL
124 };
125
126 /* Symbol names that contain the following are ignored.*/
127 static const char * const ignored_matches[] = {
128 ".long_branch.", /* ppc stub */
129 ".plt_branch.", /* ppc stub */
130 NULL
131 };
132
133 const char * const *p;
134
135 for (p = ignored_symbols; *p; p++)
136 if (!strcmp(name, *p))
137 return true;
138
139 for (p = ignored_prefixes; *p; p++)
140 if (!strncmp(name, *p, strlen(*p)))
141 return true;
142
143 for (p = ignored_suffixes; *p; p++) {
144 int l = strlen(name) - strlen(*p);
145
146 if (l >= 0 && !strcmp(name + l, *p))
147 return true;
148 }
149
150 for (p = ignored_matches; *p; p++) {
151 if (strstr(name, *p))
152 return true;
153 }
154
155 if (type == 'U' || type == 'u')
156 return true;
157 /* exclude debugging symbols */
158 if (type == 'N' || type == 'n')
159 return true;
160
161 if (toupper(type) == 'A') {
162 /* Keep these useful absolute symbols */
163 if (strcmp(name, "__kernel_syscall_via_break") &&
164 strcmp(name, "__kernel_syscall_via_epc") &&
165 strcmp(name, "__kernel_sigtramp") &&
166 strcmp(name, "__gp"))
167 return true;
168 }
169
170 return false;
171 }
172
check_symbol_range(const char * sym,unsigned long long addr,struct addr_range * ranges,int entries)173 static void check_symbol_range(const char *sym, unsigned long long addr,
174 struct addr_range *ranges, int entries)
175 {
176 size_t i;
177 struct addr_range *ar;
178
179 for (i = 0; i < entries; ++i) {
180 ar = &ranges[i];
181
182 if (strcmp(sym, ar->start_sym) == 0) {
183 ar->start = addr;
184 return;
185 } else if (strcmp(sym, ar->end_sym) == 0) {
186 ar->end = addr;
187 return;
188 }
189 }
190 }
191
read_symbol(FILE * in)192 static struct sym_entry *read_symbol(FILE *in)
193 {
194 char name[500], type;
195 unsigned long long addr;
196 unsigned int len;
197 struct sym_entry *sym;
198 int rc;
199
200 rc = fscanf(in, "%llx %c %499s\n", &addr, &type, name);
201 if (rc != 3) {
202 if (rc != EOF && fgets(name, 500, in) == NULL)
203 fprintf(stderr, "Read error or end of file.\n");
204 return NULL;
205 }
206 if (strlen(name) >= KSYM_NAME_LEN) {
207 fprintf(stderr, "Symbol %s too long for kallsyms (%zu >= %d).\n"
208 "Please increase KSYM_NAME_LEN both in kernel and kallsyms.c\n",
209 name, strlen(name), KSYM_NAME_LEN);
210 return NULL;
211 }
212
213 if (strcmp(name, "_text") == 0)
214 _text = addr;
215
216 /* Ignore most absolute/undefined (?) symbols. */
217 if (is_ignored_symbol(name, type))
218 return NULL;
219
220 check_symbol_range(name, addr, text_ranges, ARRAY_SIZE(text_ranges));
221 check_symbol_range(name, addr, &percpu_range, 1);
222
223 /* include the type field in the symbol name, so that it gets
224 * compressed together */
225
226 len = strlen(name) + 1;
227
228 sym = malloc(sizeof(*sym) + len + 1);
229 if (!sym) {
230 fprintf(stderr, "kallsyms failure: "
231 "unable to allocate required amount of memory\n");
232 exit(EXIT_FAILURE);
233 }
234 sym->addr = addr;
235 sym->len = len;
236 sym->sym[0] = type;
237 strcpy(sym_name(sym), name);
238 sym->percpu_absolute = 0;
239
240 return sym;
241 }
242
symbol_in_range(const struct sym_entry * s,const struct addr_range * ranges,int entries)243 static int symbol_in_range(const struct sym_entry *s,
244 const struct addr_range *ranges, int entries)
245 {
246 size_t i;
247 const struct addr_range *ar;
248
249 for (i = 0; i < entries; ++i) {
250 ar = &ranges[i];
251
252 if (s->addr >= ar->start && s->addr <= ar->end)
253 return 1;
254 }
255
256 return 0;
257 }
258
symbol_valid(const struct sym_entry * s)259 static int symbol_valid(const struct sym_entry *s)
260 {
261 const char *name = sym_name(s);
262
263 /* if --all-symbols is not specified, then symbols outside the text
264 * and inittext sections are discarded */
265 if (!all_symbols) {
266 if (symbol_in_range(s, text_ranges,
267 ARRAY_SIZE(text_ranges)) == 0)
268 return 0;
269 /* Corner case. Discard any symbols with the same value as
270 * _etext _einittext; they can move between pass 1 and 2 when
271 * the kallsyms data are added. If these symbols move then
272 * they may get dropped in pass 2, which breaks the kallsyms
273 * rules.
274 */
275 if ((s->addr == text_range_text->end &&
276 strcmp(name, text_range_text->end_sym)) ||
277 (s->addr == text_range_inittext->end &&
278 strcmp(name, text_range_inittext->end_sym)))
279 return 0;
280 }
281
282 return 1;
283 }
284
285 /* remove all the invalid symbols from the table */
shrink_table(void)286 static void shrink_table(void)
287 {
288 unsigned int i, pos;
289
290 pos = 0;
291 for (i = 0; i < table_cnt; i++) {
292 if (symbol_valid(table[i])) {
293 if (pos != i)
294 table[pos] = table[i];
295 pos++;
296 } else {
297 free(table[i]);
298 }
299 }
300 table_cnt = pos;
301
302 /* When valid symbol is not registered, exit to error */
303 if (!table_cnt) {
304 fprintf(stderr, "No valid symbol.\n");
305 exit(1);
306 }
307 }
308
read_map(FILE * in)309 static void read_map(FILE *in)
310 {
311 struct sym_entry *sym;
312
313 while (!feof(in)) {
314 sym = read_symbol(in);
315 if (!sym)
316 continue;
317
318 sym->start_pos = table_cnt;
319
320 if (table_cnt >= table_size) {
321 table_size += 10000;
322 table = realloc(table, sizeof(*table) * table_size);
323 if (!table) {
324 fprintf(stderr, "out of memory\n");
325 exit (1);
326 }
327 }
328
329 table[table_cnt++] = sym;
330 }
331 }
332
output_label(const char * label)333 static void output_label(const char *label)
334 {
335 printf(".globl %s\n", label);
336 printf("\tALGN\n");
337 printf("%s:\n", label);
338 }
339
340 /* Provide proper symbols relocatability by their '_text' relativeness. */
output_address(unsigned long long addr)341 static void output_address(unsigned long long addr)
342 {
343 if (_text <= addr)
344 printf("\tPTR\t_text + %#llx\n", addr - _text);
345 else
346 printf("\tPTR\t_text - %#llx\n", _text - addr);
347 }
348
349 /* uncompress a compressed symbol. When this function is called, the best table
350 * might still be compressed itself, so the function needs to be recursive */
expand_symbol(const unsigned char * data,int len,char * result)351 static int expand_symbol(const unsigned char *data, int len, char *result)
352 {
353 int c, rlen, total=0;
354
355 while (len) {
356 c = *data;
357 /* if the table holds a single char that is the same as the one
358 * we are looking for, then end the search */
359 if (best_table[c][0]==c && best_table_len[c]==1) {
360 *result++ = c;
361 total++;
362 } else {
363 /* if not, recurse and expand */
364 rlen = expand_symbol(best_table[c], best_table_len[c], result);
365 total += rlen;
366 result += rlen;
367 }
368 data++;
369 len--;
370 }
371 *result=0;
372
373 return total;
374 }
375
symbol_absolute(const struct sym_entry * s)376 static int symbol_absolute(const struct sym_entry *s)
377 {
378 return s->percpu_absolute;
379 }
380
write_src(void)381 static void write_src(void)
382 {
383 unsigned int i, k, off;
384 unsigned int best_idx[256];
385 unsigned int *markers;
386 char buf[KSYM_NAME_LEN];
387
388 printf("#include <asm/bitsperlong.h>\n");
389 printf("#if BITS_PER_LONG == 64\n");
390 printf("#define PTR .quad\n");
391 printf("#define ALGN .balign 8\n");
392 printf("#else\n");
393 printf("#define PTR .long\n");
394 printf("#define ALGN .balign 4\n");
395 printf("#endif\n");
396
397 printf("\t.section .rodata, \"a\"\n");
398
399 if (!base_relative)
400 output_label("kallsyms_addresses");
401 else
402 output_label("kallsyms_offsets");
403
404 for (i = 0; i < table_cnt; i++) {
405 if (base_relative) {
406 /*
407 * Use the offset relative to the lowest value
408 * encountered of all relative symbols, and emit
409 * non-relocatable fixed offsets that will be fixed
410 * up at runtime.
411 */
412
413 long long offset;
414 int overflow;
415
416 if (!absolute_percpu) {
417 offset = table[i]->addr - relative_base;
418 overflow = (offset < 0 || offset > UINT_MAX);
419 } else if (symbol_absolute(table[i])) {
420 offset = table[i]->addr;
421 overflow = (offset < 0 || offset > INT_MAX);
422 } else {
423 offset = relative_base - table[i]->addr - 1;
424 overflow = (offset < INT_MIN || offset >= 0);
425 }
426 if (overflow) {
427 fprintf(stderr, "kallsyms failure: "
428 "%s symbol value %#llx out of range in relative mode\n",
429 symbol_absolute(table[i]) ? "absolute" : "relative",
430 table[i]->addr);
431 exit(EXIT_FAILURE);
432 }
433 printf("\t.long\t%#x\n", (int)offset);
434 } else if (!symbol_absolute(table[i])) {
435 output_address(table[i]->addr);
436 } else {
437 printf("\tPTR\t%#llx\n", table[i]->addr);
438 }
439 }
440 printf("\n");
441
442 if (base_relative) {
443 output_label("kallsyms_relative_base");
444 output_address(relative_base);
445 printf("\n");
446 }
447
448 output_label("kallsyms_num_syms");
449 printf("\t.long\t%u\n", table_cnt);
450 printf("\n");
451
452 /* table of offset markers, that give the offset in the compressed stream
453 * every 256 symbols */
454 markers = malloc(sizeof(unsigned int) * ((table_cnt + 255) / 256));
455 if (!markers) {
456 fprintf(stderr, "kallsyms failure: "
457 "unable to allocate required memory\n");
458 exit(EXIT_FAILURE);
459 }
460
461 output_label("kallsyms_names");
462 off = 0;
463 for (i = 0; i < table_cnt; i++) {
464 if ((i & 0xFF) == 0)
465 markers[i >> 8] = off;
466
467 printf("\t.byte 0x%02x", table[i]->len);
468 for (k = 0; k < table[i]->len; k++)
469 printf(", 0x%02x", table[i]->sym[k]);
470 printf("\n");
471
472 off += table[i]->len + 1;
473 }
474 printf("\n");
475
476 output_label("kallsyms_markers");
477 for (i = 0; i < ((table_cnt + 255) >> 8); i++)
478 printf("\t.long\t%u\n", markers[i]);
479 printf("\n");
480
481 free(markers);
482
483 output_label("kallsyms_token_table");
484 off = 0;
485 for (i = 0; i < 256; i++) {
486 best_idx[i] = off;
487 expand_symbol(best_table[i], best_table_len[i], buf);
488 printf("\t.asciz\t\"%s\"\n", buf);
489 off += strlen(buf) + 1;
490 }
491 printf("\n");
492
493 output_label("kallsyms_token_index");
494 for (i = 0; i < 256; i++)
495 printf("\t.short\t%d\n", best_idx[i]);
496 printf("\n");
497 }
498
499
500 /* table lookup compression functions */
501
502 /* count all the possible tokens in a symbol */
learn_symbol(const unsigned char * symbol,int len)503 static void learn_symbol(const unsigned char *symbol, int len)
504 {
505 int i;
506
507 for (i = 0; i < len - 1; i++)
508 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++;
509 }
510
511 /* decrease the count for all the possible tokens in a symbol */
forget_symbol(const unsigned char * symbol,int len)512 static void forget_symbol(const unsigned char *symbol, int len)
513 {
514 int i;
515
516 for (i = 0; i < len - 1; i++)
517 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--;
518 }
519
520 /* do the initial token count */
build_initial_tok_table(void)521 static void build_initial_tok_table(void)
522 {
523 unsigned int i;
524
525 for (i = 0; i < table_cnt; i++)
526 learn_symbol(table[i]->sym, table[i]->len);
527 }
528
find_token(unsigned char * str,int len,const unsigned char * token)529 static unsigned char *find_token(unsigned char *str, int len,
530 const unsigned char *token)
531 {
532 int i;
533
534 for (i = 0; i < len - 1; i++) {
535 if (str[i] == token[0] && str[i+1] == token[1])
536 return &str[i];
537 }
538 return NULL;
539 }
540
541 /* replace a given token in all the valid symbols. Use the sampled symbols
542 * to update the counts */
compress_symbols(const unsigned char * str,int idx)543 static void compress_symbols(const unsigned char *str, int idx)
544 {
545 unsigned int i, len, size;
546 unsigned char *p1, *p2;
547
548 for (i = 0; i < table_cnt; i++) {
549
550 len = table[i]->len;
551 p1 = table[i]->sym;
552
553 /* find the token on the symbol */
554 p2 = find_token(p1, len, str);
555 if (!p2) continue;
556
557 /* decrease the counts for this symbol's tokens */
558 forget_symbol(table[i]->sym, len);
559
560 size = len;
561
562 do {
563 *p2 = idx;
564 p2++;
565 size -= (p2 - p1);
566 memmove(p2, p2 + 1, size);
567 p1 = p2;
568 len--;
569
570 if (size < 2) break;
571
572 /* find the token on the symbol */
573 p2 = find_token(p1, size, str);
574
575 } while (p2);
576
577 table[i]->len = len;
578
579 /* increase the counts for this symbol's new tokens */
580 learn_symbol(table[i]->sym, len);
581 }
582 }
583
584 /* search the token with the maximum profit */
find_best_token(void)585 static int find_best_token(void)
586 {
587 int i, best, bestprofit;
588
589 bestprofit=-10000;
590 best = 0;
591
592 for (i = 0; i < 0x10000; i++) {
593 if (token_profit[i] > bestprofit) {
594 best = i;
595 bestprofit = token_profit[i];
596 }
597 }
598 return best;
599 }
600
601 /* this is the core of the algorithm: calculate the "best" table */
optimize_result(void)602 static void optimize_result(void)
603 {
604 int i, best;
605
606 /* using the '\0' symbol last allows compress_symbols to use standard
607 * fast string functions */
608 for (i = 255; i >= 0; i--) {
609
610 /* if this table slot is empty (it is not used by an actual
611 * original char code */
612 if (!best_table_len[i]) {
613
614 /* find the token with the best profit value */
615 best = find_best_token();
616 if (token_profit[best] == 0)
617 break;
618
619 /* place it in the "best" table */
620 best_table_len[i] = 2;
621 best_table[i][0] = best & 0xFF;
622 best_table[i][1] = (best >> 8) & 0xFF;
623
624 /* replace this token in all the valid symbols */
625 compress_symbols(best_table[i], i);
626 }
627 }
628 }
629
630 /* start by placing the symbols that are actually used on the table */
insert_real_symbols_in_table(void)631 static void insert_real_symbols_in_table(void)
632 {
633 unsigned int i, j, c;
634
635 for (i = 0; i < table_cnt; i++) {
636 for (j = 0; j < table[i]->len; j++) {
637 c = table[i]->sym[j];
638 best_table[c][0]=c;
639 best_table_len[c]=1;
640 }
641 }
642 }
643
optimize_token_table(void)644 static void optimize_token_table(void)
645 {
646 build_initial_tok_table();
647
648 insert_real_symbols_in_table();
649
650 optimize_result();
651 }
652
653 /* guess for "linker script provide" symbol */
may_be_linker_script_provide_symbol(const struct sym_entry * se)654 static int may_be_linker_script_provide_symbol(const struct sym_entry *se)
655 {
656 const char *symbol = sym_name(se);
657 int len = se->len - 1;
658
659 if (len < 8)
660 return 0;
661
662 if (symbol[0] != '_' || symbol[1] != '_')
663 return 0;
664
665 /* __start_XXXXX */
666 if (!memcmp(symbol + 2, "start_", 6))
667 return 1;
668
669 /* __stop_XXXXX */
670 if (!memcmp(symbol + 2, "stop_", 5))
671 return 1;
672
673 /* __end_XXXXX */
674 if (!memcmp(symbol + 2, "end_", 4))
675 return 1;
676
677 /* __XXXXX_start */
678 if (!memcmp(symbol + len - 6, "_start", 6))
679 return 1;
680
681 /* __XXXXX_end */
682 if (!memcmp(symbol + len - 4, "_end", 4))
683 return 1;
684
685 return 0;
686 }
687
compare_symbols(const void * a,const void * b)688 static int compare_symbols(const void *a, const void *b)
689 {
690 const struct sym_entry *sa = *(const struct sym_entry **)a;
691 const struct sym_entry *sb = *(const struct sym_entry **)b;
692 int wa, wb;
693
694 /* sort by address first */
695 if (sa->addr > sb->addr)
696 return 1;
697 if (sa->addr < sb->addr)
698 return -1;
699
700 /* sort by "weakness" type */
701 wa = (sa->sym[0] == 'w') || (sa->sym[0] == 'W');
702 wb = (sb->sym[0] == 'w') || (sb->sym[0] == 'W');
703 if (wa != wb)
704 return wa - wb;
705
706 /* sort by "linker script provide" type */
707 wa = may_be_linker_script_provide_symbol(sa);
708 wb = may_be_linker_script_provide_symbol(sb);
709 if (wa != wb)
710 return wa - wb;
711
712 /* sort by the number of prefix underscores */
713 wa = strspn(sym_name(sa), "_");
714 wb = strspn(sym_name(sb), "_");
715 if (wa != wb)
716 return wa - wb;
717
718 /* sort by initial order, so that other symbols are left undisturbed */
719 return sa->start_pos - sb->start_pos;
720 }
721
sort_symbols(void)722 static void sort_symbols(void)
723 {
724 qsort(table, table_cnt, sizeof(table[0]), compare_symbols);
725 }
726
make_percpus_absolute(void)727 static void make_percpus_absolute(void)
728 {
729 unsigned int i;
730
731 for (i = 0; i < table_cnt; i++)
732 if (symbol_in_range(table[i], &percpu_range, 1)) {
733 /*
734 * Keep the 'A' override for percpu symbols to
735 * ensure consistent behavior compared to older
736 * versions of this tool.
737 */
738 table[i]->sym[0] = 'A';
739 table[i]->percpu_absolute = 1;
740 }
741 }
742
743 /* find the minimum non-absolute symbol address */
record_relative_base(void)744 static void record_relative_base(void)
745 {
746 unsigned int i;
747
748 for (i = 0; i < table_cnt; i++)
749 if (!symbol_absolute(table[i])) {
750 /*
751 * The table is sorted by address.
752 * Take the first non-absolute symbol value.
753 */
754 relative_base = table[i]->addr;
755 return;
756 }
757 }
758
main(int argc,char ** argv)759 int main(int argc, char **argv)
760 {
761 if (argc >= 2) {
762 int i;
763 for (i = 1; i < argc; i++) {
764 if(strcmp(argv[i], "--all-symbols") == 0)
765 all_symbols = 1;
766 else if (strcmp(argv[i], "--absolute-percpu") == 0)
767 absolute_percpu = 1;
768 else if (strcmp(argv[i], "--base-relative") == 0)
769 base_relative = 1;
770 else
771 usage();
772 }
773 } else if (argc != 1)
774 usage();
775
776 read_map(stdin);
777 shrink_table();
778 if (absolute_percpu)
779 make_percpus_absolute();
780 sort_symbols();
781 if (base_relative)
782 record_relative_base();
783 optimize_token_table();
784 write_src();
785
786 return 0;
787 }
788
