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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] 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#include <xalloc.h>
31
32#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0]))
33
34#define KSYM_NAME_LEN 512
35
36struct sym_entry {
37 unsigned long long addr;
38 unsigned int len;
39 unsigned int seq;
40 unsigned char sym[];
41};
42
43struct addr_range {
44 const char *start_sym, *end_sym;
45 unsigned long long start, end;
46};
47
48static unsigned long long _text;
49static unsigned long long relative_base;
50static 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
57static struct sym_entry **table;
58static unsigned int table_size, table_cnt;
59static int all_symbols;
60
61static int token_profit[0x10000];
62
63/* the table that holds the result of the compression */
64static unsigned char best_table[256][2];
65static unsigned char best_table_len[256];
66
67
68static void usage(void)
69{
70 fprintf(stderr, format: "Usage: kallsyms [--all-symbols] in.map > out.S\n");
71 exit(status: 1);
72}
73
74static char *sym_name(const struct sym_entry *s)
75{
76 return (char *)s->sym + 1;
77}
78
79static bool is_ignored_symbol(const char *name, char type)
80{
81 if (type == 'u' || type == 'n')
82 return true;
83
84 if (toupper(type) == 'A') {
85 /* Keep these useful absolute symbols */
86 if (strcmp(s1: name, s2: "__kernel_syscall_via_break") &&
87 strcmp(s1: name, s2: "__kernel_syscall_via_epc") &&
88 strcmp(s1: name, s2: "__kernel_sigtramp") &&
89 strcmp(s1: name, s2: "__gp"))
90 return true;
91 }
92
93 return false;
94}
95
96static void check_symbol_range(const char *sym, unsigned long long addr,
97 struct addr_range *ranges, int entries)
98{
99 size_t i;
100 struct addr_range *ar;
101
102 for (i = 0; i < entries; ++i) {
103 ar = &ranges[i];
104
105 if (strcmp(s1: sym, s2: ar->start_sym) == 0) {
106 ar->start = addr;
107 return;
108 } else if (strcmp(s1: sym, s2: ar->end_sym) == 0) {
109 ar->end = addr;
110 return;
111 }
112 }
113}
114
115static struct sym_entry *read_symbol(FILE *in, char **buf, size_t *buf_len)
116{
117 char *name, type, *p;
118 unsigned long long addr;
119 size_t len;
120 ssize_t readlen;
121 struct sym_entry *sym;
122
123 errno = 0;
124 readlen = getline(lineptr: buf, n: buf_len, stream: in);
125 if (readlen < 0) {
126 if (errno) {
127 perror(s: "read_symbol");
128 exit(EXIT_FAILURE);
129 }
130 return NULL;
131 }
132
133 if ((*buf)[readlen - 1] == '\n')
134 (*buf)[readlen - 1] = 0;
135
136 addr = strtoull(nptr: *buf, endptr: &p, base: 16);
137
138 if (*buf == p || *p++ != ' ' || !isascii((type = *p++)) || *p++ != ' ') {
139 fprintf(stderr, format: "line format error\n");
140 exit(EXIT_FAILURE);
141 }
142
143 name = p;
144 len = strlen(s: name);
145
146 if (len >= KSYM_NAME_LEN) {
147 fprintf(stderr, format: "Symbol %s too long for kallsyms (%zu >= %d).\n"
148 "Please increase KSYM_NAME_LEN both in kernel and kallsyms.c\n",
149 name, len, KSYM_NAME_LEN);
150 return NULL;
151 }
152
153 if (strcmp(s1: name, s2: "_text") == 0)
154 _text = addr;
155
156 /* Ignore most absolute/undefined (?) symbols. */
157 if (is_ignored_symbol(name, type))
158 return NULL;
159
160 check_symbol_range(sym: name, addr, ranges: text_ranges, ARRAY_SIZE(text_ranges));
161
162 /* include the type field in the symbol name, so that it gets
163 * compressed together */
164 len++;
165
166 sym = xmalloc(sizeof(*sym) + len + 1);
167 sym->addr = addr;
168 sym->len = len;
169 sym->sym[0] = type;
170 strcpy(dest: sym_name(s: sym), src: name);
171
172 return sym;
173}
174
175static int symbol_in_range(const struct sym_entry *s,
176 const struct addr_range *ranges, int entries)
177{
178 size_t i;
179 const struct addr_range *ar;
180
181 for (i = 0; i < entries; ++i) {
182 ar = &ranges[i];
183
184 if (s->addr >= ar->start && s->addr <= ar->end)
185 return 1;
186 }
187
188 return 0;
189}
190
191static bool string_starts_with(const char *s, const char *prefix)
192{
193 return strncmp(s1: s, s2: prefix, n: strlen(s: prefix)) == 0;
194}
195
196static int symbol_valid(const struct sym_entry *s)
197{
198 const char *name = sym_name(s);
199
200 /* if --all-symbols is not specified, then symbols outside the text
201 * and inittext sections are discarded */
202 if (!all_symbols) {
203 /*
204 * Symbols starting with __start and __stop are used to denote
205 * section boundaries, and should always be included:
206 */
207 if (string_starts_with(s: name, prefix: "__start_") ||
208 string_starts_with(s: name, prefix: "__stop_"))
209 return 1;
210
211 if (symbol_in_range(s, ranges: text_ranges,
212 ARRAY_SIZE(text_ranges)) == 0)
213 return 0;
214 /* Corner case. Discard any symbols with the same value as
215 * _etext _einittext; they can move between pass 1 and 2 when
216 * the kallsyms data are added. If these symbols move then
217 * they may get dropped in pass 2, which breaks the kallsyms
218 * rules.
219 */
220 if ((s->addr == text_range_text->end &&
221 strcmp(s1: name, text_range_text->end_sym)) ||
222 (s->addr == text_range_inittext->end &&
223 strcmp(s1: name, text_range_inittext->end_sym)))
224 return 0;
225 }
226
227 return 1;
228}
229
230/* remove all the invalid symbols from the table */
231static void shrink_table(void)
232{
233 unsigned int i, pos;
234
235 pos = 0;
236 for (i = 0; i < table_cnt; i++) {
237 if (symbol_valid(s: table[i])) {
238 if (pos != i)
239 table[pos] = table[i];
240 pos++;
241 } else {
242 free(ptr: table[i]);
243 }
244 }
245 table_cnt = pos;
246}
247
248static void read_map(const char *in)
249{
250 FILE *fp;
251 struct sym_entry *sym;
252 char *buf = NULL;
253 size_t buflen = 0;
254
255 fp = fopen(filename: in, modes: "r");
256 if (!fp) {
257 perror(s: in);
258 exit(status: 1);
259 }
260
261 while (!feof(stream: fp)) {
262 sym = read_symbol(in: fp, buf: &buf, buf_len: &buflen);
263 if (!sym)
264 continue;
265
266 sym->seq = table_cnt;
267
268 if (table_cnt >= table_size) {
269 table_size += 10000;
270 table = xrealloc(table, sizeof(*table) * table_size);
271 }
272
273 table[table_cnt++] = sym;
274 }
275
276 free(ptr: buf);
277 fclose(stream: fp);
278}
279
280static void output_label(const char *label)
281{
282 printf(format: ".globl %s\n", label);
283 printf(format: "\tALGN\n");
284 printf(format: "%s:\n", label);
285}
286
287/* uncompress a compressed symbol. When this function is called, the best table
288 * might still be compressed itself, so the function needs to be recursive */
289static int expand_symbol(const unsigned char *data, int len, char *result)
290{
291 int c, rlen, total=0;
292
293 while (len) {
294 c = *data;
295 /* if the table holds a single char that is the same as the one
296 * we are looking for, then end the search */
297 if (best_table[c][0]==c && best_table_len[c]==1) {
298 *result++ = c;
299 total++;
300 } else {
301 /* if not, recurse and expand */
302 rlen = expand_symbol(data: best_table[c], len: best_table_len[c], result);
303 total += rlen;
304 result += rlen;
305 }
306 data++;
307 len--;
308 }
309 *result=0;
310
311 return total;
312}
313
314static int compare_names(const void *a, const void *b)
315{
316 int ret;
317 const struct sym_entry *sa = *(const struct sym_entry **)a;
318 const struct sym_entry *sb = *(const struct sym_entry **)b;
319
320 ret = strcmp(s1: sym_name(s: sa), s2: sym_name(s: sb));
321 if (!ret) {
322 if (sa->addr > sb->addr)
323 return 1;
324 else if (sa->addr < sb->addr)
325 return -1;
326
327 /* keep old order */
328 return (int)(sa->seq - sb->seq);
329 }
330
331 return ret;
332}
333
334static void sort_symbols_by_name(void)
335{
336 qsort(base: table, nmemb: table_cnt, size: sizeof(table[0]), compar: compare_names);
337}
338
339static void write_src(void)
340{
341 unsigned int i, k, off;
342 unsigned int best_idx[256];
343 unsigned int *markers, markers_cnt;
344 char buf[KSYM_NAME_LEN];
345
346 printf(format: "#include <asm/bitsperlong.h>\n");
347 printf(format: "#if BITS_PER_LONG == 64\n");
348 printf(format: "#define PTR .quad\n");
349 printf(format: "#define ALGN .balign 8\n");
350 printf(format: "#else\n");
351 printf(format: "#define PTR .long\n");
352 printf(format: "#define ALGN .balign 4\n");
353 printf(format: "#endif\n");
354
355 printf(format: "\t.section .rodata, \"a\"\n");
356
357 output_label(label: "kallsyms_num_syms");
358 printf(format: "\t.long\t%u\n", table_cnt);
359 printf(format: "\n");
360
361 /* table of offset markers, that give the offset in the compressed stream
362 * every 256 symbols */
363 markers_cnt = (table_cnt + 255) / 256;
364 markers = xmalloc(sizeof(*markers) * markers_cnt);
365
366 output_label(label: "kallsyms_names");
367 off = 0;
368 for (i = 0; i < table_cnt; i++) {
369 if ((i & 0xFF) == 0)
370 markers[i >> 8] = off;
371 table[i]->seq = i;
372
373 /* There cannot be any symbol of length zero. */
374 if (table[i]->len == 0) {
375 fprintf(stderr, format: "kallsyms failure: "
376 "unexpected zero symbol length\n");
377 exit(EXIT_FAILURE);
378 }
379
380 /* Only lengths that fit in up-to-two-byte ULEB128 are supported. */
381 if (table[i]->len > 0x3FFF) {
382 fprintf(stderr, format: "kallsyms failure: "
383 "unexpected huge symbol length\n");
384 exit(EXIT_FAILURE);
385 }
386
387 /* Encode length with ULEB128. */
388 if (table[i]->len <= 0x7F) {
389 /* Most symbols use a single byte for the length. */
390 printf(format: "\t.byte 0x%02x", table[i]->len);
391 off += table[i]->len + 1;
392 } else {
393 /* "Big" symbols use two bytes. */
394 printf(format: "\t.byte 0x%02x, 0x%02x",
395 (table[i]->len & 0x7F) | 0x80,
396 (table[i]->len >> 7) & 0x7F);
397 off += table[i]->len + 2;
398 }
399 for (k = 0; k < table[i]->len; k++)
400 printf(format: ", 0x%02x", table[i]->sym[k]);
401
402 /*
403 * Now that we wrote out the compressed symbol name, restore the
404 * original name and print it in the comment.
405 */
406 expand_symbol(data: table[i]->sym, len: table[i]->len, result: buf);
407 strcpy(dest: (char *)table[i]->sym, src: buf);
408 printf(format: "\t/* %s */\n", table[i]->sym);
409 }
410 printf(format: "\n");
411
412 output_label(label: "kallsyms_markers");
413 for (i = 0; i < markers_cnt; i++)
414 printf(format: "\t.long\t%u\n", markers[i]);
415 printf(format: "\n");
416
417 free(ptr: markers);
418
419 output_label(label: "kallsyms_token_table");
420 off = 0;
421 for (i = 0; i < 256; i++) {
422 best_idx[i] = off;
423 expand_symbol(data: best_table[i], len: best_table_len[i], result: buf);
424 printf(format: "\t.asciz\t\"%s\"\n", buf);
425 off += strlen(s: buf) + 1;
426 }
427 printf(format: "\n");
428
429 output_label(label: "kallsyms_token_index");
430 for (i = 0; i < 256; i++)
431 printf(format: "\t.short\t%d\n", best_idx[i]);
432 printf(format: "\n");
433
434 output_label(label: "kallsyms_offsets");
435
436 for (i = 0; i < table_cnt; i++) {
437 /*
438 * Use the offset relative to the lowest value
439 * encountered of all relative symbols, and emit
440 * non-relocatable fixed offsets that will be fixed
441 * up at runtime.
442 */
443
444 long long offset;
445
446 offset = table[i]->addr - relative_base;
447 if (offset < 0 || offset > UINT_MAX) {
448 fprintf(stderr, format: "kallsyms failure: "
449 "relative symbol value %#llx out of range\n",
450 table[i]->addr);
451 exit(EXIT_FAILURE);
452 }
453 printf(format: "\t.long\t%#x\t/* %s */\n", (int)offset, table[i]->sym);
454 }
455 printf(format: "\n");
456
457 output_label(label: "kallsyms_relative_base");
458 /* Provide proper symbols relocatability by their '_text' relativeness. */
459 if (_text <= relative_base)
460 printf(format: "\tPTR\t_text + %#llx\n", relative_base - _text);
461 else
462 printf(format: "\tPTR\t_text - %#llx\n", _text - relative_base);
463 printf(format: "\n");
464
465 sort_symbols_by_name();
466 output_label(label: "kallsyms_seqs_of_names");
467 for (i = 0; i < table_cnt; i++)
468 printf(format: "\t.byte 0x%02x, 0x%02x, 0x%02x\t/* %s */\n",
469 (unsigned char)(table[i]->seq >> 16),
470 (unsigned char)(table[i]->seq >> 8),
471 (unsigned char)(table[i]->seq >> 0),
472 table[i]->sym);
473 printf(format: "\n");
474}
475
476
477/* table lookup compression functions */
478
479/* count all the possible tokens in a symbol */
480static void learn_symbol(const unsigned char *symbol, int len)
481{
482 int i;
483
484 for (i = 0; i < len - 1; i++)
485 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++;
486}
487
488/* decrease the count for all the possible tokens in a symbol */
489static void forget_symbol(const unsigned char *symbol, int len)
490{
491 int i;
492
493 for (i = 0; i < len - 1; i++)
494 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--;
495}
496
497/* do the initial token count */
498static void build_initial_token_table(void)
499{
500 unsigned int i;
501
502 for (i = 0; i < table_cnt; i++)
503 learn_symbol(symbol: table[i]->sym, len: table[i]->len);
504}
505
506static unsigned char *find_token(unsigned char *str, int len,
507 const unsigned char *token)
508{
509 int i;
510
511 for (i = 0; i < len - 1; i++) {
512 if (str[i] == token[0] && str[i+1] == token[1])
513 return &str[i];
514 }
515 return NULL;
516}
517
518/* replace a given token in all the valid symbols. Use the sampled symbols
519 * to update the counts */
520static void compress_symbols(const unsigned char *str, int idx)
521{
522 unsigned int i, len, size;
523 unsigned char *p1, *p2;
524
525 for (i = 0; i < table_cnt; i++) {
526
527 len = table[i]->len;
528 p1 = table[i]->sym;
529
530 /* find the token on the symbol */
531 p2 = find_token(str: p1, len, token: str);
532 if (!p2) continue;
533
534 /* decrease the counts for this symbol's tokens */
535 forget_symbol(symbol: table[i]->sym, len);
536
537 size = len;
538
539 do {
540 *p2 = idx;
541 p2++;
542 size -= (p2 - p1);
543 memmove(dest: p2, src: p2 + 1, n: size);
544 p1 = p2;
545 len--;
546
547 if (size < 2) break;
548
549 /* find the token on the symbol */
550 p2 = find_token(str: p1, len: size, token: str);
551
552 } while (p2);
553
554 table[i]->len = len;
555
556 /* increase the counts for this symbol's new tokens */
557 learn_symbol(symbol: table[i]->sym, len);
558 }
559}
560
561/* search the token with the maximum profit */
562static int find_best_token(void)
563{
564 int i, best, bestprofit;
565
566 bestprofit=-10000;
567 best = 0;
568
569 for (i = 0; i < 0x10000; i++) {
570 if (token_profit[i] > bestprofit) {
571 best = i;
572 bestprofit = token_profit[i];
573 }
574 }
575 return best;
576}
577
578/* this is the core of the algorithm: calculate the "best" table */
579static void optimize_result(void)
580{
581 int i, best;
582
583 /* using the '\0' symbol last allows compress_symbols to use standard
584 * fast string functions */
585 for (i = 255; i >= 0; i--) {
586
587 /* if this table slot is empty (it is not used by an actual
588 * original char code */
589 if (!best_table_len[i]) {
590
591 /* find the token with the best profit value */
592 best = find_best_token();
593 if (token_profit[best] == 0)
594 break;
595
596 /* place it in the "best" table */
597 best_table_len[i] = 2;
598 best_table[i][0] = best & 0xFF;
599 best_table[i][1] = (best >> 8) & 0xFF;
600
601 /* replace this token in all the valid symbols */
602 compress_symbols(str: best_table[i], idx: i);
603 }
604 }
605}
606
607/* start by placing the symbols that are actually used on the table */
608static void insert_real_symbols_in_table(void)
609{
610 unsigned int i, j, c;
611
612 for (i = 0; i < table_cnt; i++) {
613 for (j = 0; j < table[i]->len; j++) {
614 c = table[i]->sym[j];
615 best_table[c][0]=c;
616 best_table_len[c]=1;
617 }
618 }
619}
620
621static void optimize_token_table(void)
622{
623 build_initial_token_table();
624
625 insert_real_symbols_in_table();
626
627 optimize_result();
628}
629
630/* guess for "linker script provide" symbol */
631static int may_be_linker_script_provide_symbol(const struct sym_entry *se)
632{
633 const char *symbol = sym_name(s: se);
634 int len = se->len - 1;
635
636 if (len < 8)
637 return 0;
638
639 if (symbol[0] != '_' || symbol[1] != '_')
640 return 0;
641
642 /* __start_XXXXX */
643 if (!memcmp(s1: symbol + 2, s2: "start_", n: 6))
644 return 1;
645
646 /* __stop_XXXXX */
647 if (!memcmp(s1: symbol + 2, s2: "stop_", n: 5))
648 return 1;
649
650 /* __end_XXXXX */
651 if (!memcmp(s1: symbol + 2, s2: "end_", n: 4))
652 return 1;
653
654 /* __XXXXX_start */
655 if (!memcmp(s1: symbol + len - 6, s2: "_start", n: 6))
656 return 1;
657
658 /* __XXXXX_end */
659 if (!memcmp(s1: symbol + len - 4, s2: "_end", n: 4))
660 return 1;
661
662 return 0;
663}
664
665static int compare_symbols(const void *a, const void *b)
666{
667 const struct sym_entry *sa = *(const struct sym_entry **)a;
668 const struct sym_entry *sb = *(const struct sym_entry **)b;
669 int wa, wb;
670
671 /* sort by address first */
672 if (sa->addr > sb->addr)
673 return 1;
674 if (sa->addr < sb->addr)
675 return -1;
676
677 /* sort by "weakness" type */
678 wa = (sa->sym[0] == 'w') || (sa->sym[0] == 'W');
679 wb = (sb->sym[0] == 'w') || (sb->sym[0] == 'W');
680 if (wa != wb)
681 return wa - wb;
682
683 /* sort by "linker script provide" type */
684 wa = may_be_linker_script_provide_symbol(se: sa);
685 wb = may_be_linker_script_provide_symbol(se: sb);
686 if (wa != wb)
687 return wa - wb;
688
689 /* sort by the number of prefix underscores */
690 wa = strspn(s: sym_name(s: sa), accept: "_");
691 wb = strspn(s: sym_name(s: sb), accept: "_");
692 if (wa != wb)
693 return wa - wb;
694
695 /* sort by initial order, so that other symbols are left undisturbed */
696 return sa->seq - sb->seq;
697}
698
699static void sort_symbols(void)
700{
701 qsort(base: table, nmemb: table_cnt, size: sizeof(table[0]), compar: compare_symbols);
702}
703
704/* find the minimum non-absolute symbol address */
705static void record_relative_base(void)
706{
707 /*
708 * The table is sorted by address.
709 * Take the first symbol value.
710 */
711 if (table_cnt)
712 relative_base = table[0]->addr;
713}
714
715int main(int argc, char **argv)
716{
717 while (1) {
718 static const struct option long_options[] = {
719 {.name: "all-symbols", no_argument, .flag: &all_symbols, .val: 1},
720 {},
721 };
722
723 int c = getopt_long(argc: argc, argv: argv, shortopts: "", longopts: long_options, NULL);
724
725 if (c == -1)
726 break;
727 if (c != 0)
728 usage();
729 }
730
731 if (optind >= argc)
732 usage();
733
734 read_map(in: argv[optind]);
735 shrink_table();
736 sort_symbols();
737 record_relative_base();
738 optimize_token_table();
739 write_src();
740
741 return 0;
742}
743

source code of linux/scripts/kallsyms.c