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TOMOYO Linux Cross Reference
Linux/scripts/kallsyms.c

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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: 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 
 26 #ifndef ARRAY_SIZE
 27 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0]))
 28 #endif
 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 char *sym;
 37 };
 38 
 39 struct text_range {
 40         const char *stext, *etext;
 41         unsigned long long start, end;
 42 };
 43 
 44 static unsigned long long _text;
 45 static struct text_range text_ranges[] = {
 46         { "_stext",     "_etext"     },
 47         { "_sinittext", "_einittext" },
 48         { "_stext_l1",  "_etext_l1"  }, /* Blackfin on-chip L1 inst SRAM */
 49         { "_stext_l2",  "_etext_l2"  }, /* Blackfin on-chip L2 SRAM */
 50 };
 51 #define text_range_text     (&text_ranges[0])
 52 #define text_range_inittext (&text_ranges[1])
 53 
 54 static struct sym_entry *table;
 55 static unsigned int table_size, table_cnt;
 56 static int all_symbols = 0;
 57 static char symbol_prefix_char = '\0';
 58 static unsigned long long kernel_start_addr = 0;
 59 
 60 int token_profit[0x10000];
 61 
 62 /* the table that holds the result of the compression */
 63 unsigned char best_table[256][2];
 64 unsigned char best_table_len[256];
 65 
 66 
 67 static void usage(void)
 68 {
 69         fprintf(stderr, "Usage: kallsyms [--all-symbols] "
 70                         "[--symbol-prefix=<prefix char>] "
 71                         "[--page-offset=<CONFIG_PAGE_OFFSET>] "
 72                         "< in.map > out.S\n");
 73         exit(1);
 74 }
 75 
 76 /*
 77  * This ignores the intensely annoying "mapping symbols" found
 78  * in ARM ELF files: $a, $t and $d.
 79  */
 80 static inline int is_arm_mapping_symbol(const char *str)
 81 {
 82         return str[0] == '$' && strchr("atd", str[1])
 83                && (str[2] == '\0' || str[2] == '.');
 84 }
 85 
 86 static int read_symbol_tr(const char *sym, unsigned long long addr)
 87 {
 88         size_t i;
 89         struct text_range *tr;
 90 
 91         for (i = 0; i < ARRAY_SIZE(text_ranges); ++i) {
 92                 tr = &text_ranges[i];
 93 
 94                 if (strcmp(sym, tr->stext) == 0) {
 95                         tr->start = addr;
 96                         return 0;
 97                 } else if (strcmp(sym, tr->etext) == 0) {
 98                         tr->end = addr;
 99                         return 0;
100                 }
101         }
102 
103         return 1;
104 }
105 
106 static int read_symbol(FILE *in, struct sym_entry *s)
107 {
108         char str[500];
109         char *sym, stype;
110         int rc;
111 
112         rc = fscanf(in, "%llx %c %499s\n", &s->addr, &stype, str);
113         if (rc != 3) {
114                 if (rc != EOF && fgets(str, 500, in) == NULL)
115                         fprintf(stderr, "Read error or end of file.\n");
116                 return -1;
117         }
118 
119         sym = str;
120         /* skip prefix char */
121         if (symbol_prefix_char && str[0] == symbol_prefix_char)
122                 sym++;
123 
124         /* Ignore most absolute/undefined (?) symbols. */
125         if (strcmp(sym, "_text") == 0)
126                 _text = s->addr;
127         else if (read_symbol_tr(sym, s->addr) == 0)
128                 /* nothing to do */;
129         else if (toupper(stype) == 'A')
130         {
131                 /* Keep these useful absolute symbols */
132                 if (strcmp(sym, "__kernel_syscall_via_break") &&
133                     strcmp(sym, "__kernel_syscall_via_epc") &&
134                     strcmp(sym, "__kernel_sigtramp") &&
135                     strcmp(sym, "__gp"))
136                         return -1;
137 
138         }
139         else if (toupper(stype) == 'U' ||
140                  is_arm_mapping_symbol(sym))
141                 return -1;
142         /* exclude also MIPS ELF local symbols ($L123 instead of .L123) */
143         else if (str[0] == '$')
144                 return -1;
145         /* exclude debugging symbols */
146         else if (stype == 'N')
147                 return -1;
148 
149         /* include the type field in the symbol name, so that it gets
150          * compressed together */
151         s->len = strlen(str) + 1;
152         s->sym = malloc(s->len + 1);
153         if (!s->sym) {
154                 fprintf(stderr, "kallsyms failure: "
155                         "unable to allocate required amount of memory\n");
156                 exit(EXIT_FAILURE);
157         }
158         strcpy((char *)s->sym + 1, str);
159         s->sym[0] = stype;
160 
161         return 0;
162 }
163 
164 static int symbol_valid_tr(struct sym_entry *s)
165 {
166         size_t i;
167         struct text_range *tr;
168 
169         for (i = 0; i < ARRAY_SIZE(text_ranges); ++i) {
170                 tr = &text_ranges[i];
171 
172                 if (s->addr >= tr->start && s->addr <= tr->end)
173                         return 1;
174         }
175 
176         return 0;
177 }
178 
179 static int symbol_valid(struct sym_entry *s)
180 {
181         /* Symbols which vary between passes.  Passes 1 and 2 must have
182          * identical symbol lists.  The kallsyms_* symbols below are only added
183          * after pass 1, they would be included in pass 2 when --all-symbols is
184          * specified so exclude them to get a stable symbol list.
185          */
186         static char *special_symbols[] = {
187                 "kallsyms_addresses",
188                 "kallsyms_num_syms",
189                 "kallsyms_names",
190                 "kallsyms_markers",
191                 "kallsyms_token_table",
192                 "kallsyms_token_index",
193 
194         /* Exclude linker generated symbols which vary between passes */
195                 "_SDA_BASE_",           /* ppc */
196                 "_SDA2_BASE_",          /* ppc */
197                 NULL };
198         int i;
199         int offset = 1;
200 
201         if (s->addr < kernel_start_addr)
202                 return 0;
203 
204         /* skip prefix char */
205         if (symbol_prefix_char && *(s->sym + 1) == symbol_prefix_char)
206                 offset++;
207 
208         /* if --all-symbols is not specified, then symbols outside the text
209          * and inittext sections are discarded */
210         if (!all_symbols) {
211                 if (symbol_valid_tr(s) == 0)
212                         return 0;
213                 /* Corner case.  Discard any symbols with the same value as
214                  * _etext _einittext; they can move between pass 1 and 2 when
215                  * the kallsyms data are added.  If these symbols move then
216                  * they may get dropped in pass 2, which breaks the kallsyms
217                  * rules.
218                  */
219                 if ((s->addr == text_range_text->end &&
220                                 strcmp((char *)s->sym + offset, text_range_text->etext)) ||
221                     (s->addr == text_range_inittext->end &&
222                                 strcmp((char *)s->sym + offset, text_range_inittext->etext)))
223                         return 0;
224         }
225 
226         /* Exclude symbols which vary between passes. */
227         if (strstr((char *)s->sym + offset, "_compiled."))
228                 return 0;
229 
230         for (i = 0; special_symbols[i]; i++)
231                 if( strcmp((char *)s->sym + offset, special_symbols[i]) == 0 )
232                         return 0;
233 
234         return 1;
235 }
236 
237 static void read_map(FILE *in)
238 {
239         while (!feof(in)) {
240                 if (table_cnt >= table_size) {
241                         table_size += 10000;
242                         table = realloc(table, sizeof(*table) * table_size);
243                         if (!table) {
244                                 fprintf(stderr, "out of memory\n");
245                                 exit (1);
246                         }
247                 }
248                 if (read_symbol(in, &table[table_cnt]) == 0) {
249                         table[table_cnt].start_pos = table_cnt;
250                         table_cnt++;
251                 }
252         }
253 }
254 
255 static void output_label(char *label)
256 {
257         if (symbol_prefix_char)
258                 printf(".globl %c%s\n", symbol_prefix_char, label);
259         else
260                 printf(".globl %s\n", label);
261         printf("\tALGN\n");
262         if (symbol_prefix_char)
263                 printf("%c%s:\n", symbol_prefix_char, label);
264         else
265                 printf("%s:\n", label);
266 }
267 
268 /* uncompress a compressed symbol. When this function is called, the best table
269  * might still be compressed itself, so the function needs to be recursive */
270 static int expand_symbol(unsigned char *data, int len, char *result)
271 {
272         int c, rlen, total=0;
273 
274         while (len) {
275                 c = *data;
276                 /* if the table holds a single char that is the same as the one
277                  * we are looking for, then end the search */
278                 if (best_table[c][0]==c && best_table_len[c]==1) {
279                         *result++ = c;
280                         total++;
281                 } else {
282                         /* if not, recurse and expand */
283                         rlen = expand_symbol(best_table[c], best_table_len[c], result);
284                         total += rlen;
285                         result += rlen;
286                 }
287                 data++;
288                 len--;
289         }
290         *result=0;
291 
292         return total;
293 }
294 
295 static void write_src(void)
296 {
297         unsigned int i, k, off;
298         unsigned int best_idx[256];
299         unsigned int *markers;
300         char buf[KSYM_NAME_LEN];
301 
302         printf("#include <asm/types.h>\n");
303         printf("#if BITS_PER_LONG == 64\n");
304         printf("#define PTR .quad\n");
305         printf("#define ALGN .align 8\n");
306         printf("#else\n");
307         printf("#define PTR .long\n");
308         printf("#define ALGN .align 4\n");
309         printf("#endif\n");
310 
311         printf("\t.section .rodata, \"a\"\n");
312 
313         /* Provide proper symbols relocatability by their '_text'
314          * relativeness.  The symbol names cannot be used to construct
315          * normal symbol references as the list of symbols contains
316          * symbols that are declared static and are private to their
317          * .o files.  This prevents .tmp_kallsyms.o or any other
318          * object from referencing them.
319          */
320         output_label("kallsyms_addresses");
321         for (i = 0; i < table_cnt; i++) {
322                 if (toupper(table[i].sym[0]) != 'A') {
323                         if (_text <= table[i].addr)
324                                 printf("\tPTR\t_text + %#llx\n",
325                                         table[i].addr - _text);
326                         else
327                                 printf("\tPTR\t_text - %#llx\n",
328                                         _text - table[i].addr);
329                 } else {
330                         printf("\tPTR\t%#llx\n", table[i].addr);
331                 }
332         }
333         printf("\n");
334 
335         output_label("kallsyms_num_syms");
336         printf("\tPTR\t%d\n", table_cnt);
337         printf("\n");
338 
339         /* table of offset markers, that give the offset in the compressed stream
340          * every 256 symbols */
341         markers = malloc(sizeof(unsigned int) * ((table_cnt + 255) / 256));
342         if (!markers) {
343                 fprintf(stderr, "kallsyms failure: "
344                         "unable to allocate required memory\n");
345                 exit(EXIT_FAILURE);
346         }
347 
348         output_label("kallsyms_names");
349         off = 0;
350         for (i = 0; i < table_cnt; i++) {
351                 if ((i & 0xFF) == 0)
352                         markers[i >> 8] = off;
353 
354                 printf("\t.byte 0x%02x", table[i].len);
355                 for (k = 0; k < table[i].len; k++)
356                         printf(", 0x%02x", table[i].sym[k]);
357                 printf("\n");
358 
359                 off += table[i].len + 1;
360         }
361         printf("\n");
362 
363         output_label("kallsyms_markers");
364         for (i = 0; i < ((table_cnt + 255) >> 8); i++)
365                 printf("\tPTR\t%d\n", markers[i]);
366         printf("\n");
367 
368         free(markers);
369 
370         output_label("kallsyms_token_table");
371         off = 0;
372         for (i = 0; i < 256; i++) {
373                 best_idx[i] = off;
374                 expand_symbol(best_table[i], best_table_len[i], buf);
375                 printf("\t.asciz\t\"%s\"\n", buf);
376                 off += strlen(buf) + 1;
377         }
378         printf("\n");
379 
380         output_label("kallsyms_token_index");
381         for (i = 0; i < 256; i++)
382                 printf("\t.short\t%d\n", best_idx[i]);
383         printf("\n");
384 }
385 
386 
387 /* table lookup compression functions */
388 
389 /* count all the possible tokens in a symbol */
390 static void learn_symbol(unsigned char *symbol, int len)
391 {
392         int i;
393 
394         for (i = 0; i < len - 1; i++)
395                 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++;
396 }
397 
398 /* decrease the count for all the possible tokens in a symbol */
399 static void forget_symbol(unsigned char *symbol, int len)
400 {
401         int i;
402 
403         for (i = 0; i < len - 1; i++)
404                 token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--;
405 }
406 
407 /* remove all the invalid symbols from the table and do the initial token count */
408 static void build_initial_tok_table(void)
409 {
410         unsigned int i, pos;
411 
412         pos = 0;
413         for (i = 0; i < table_cnt; i++) {
414                 if ( symbol_valid(&table[i]) ) {
415                         if (pos != i)
416                                 table[pos] = table[i];
417                         learn_symbol(table[pos].sym, table[pos].len);
418                         pos++;
419                 }
420         }
421         table_cnt = pos;
422 }
423 
424 static void *find_token(unsigned char *str, int len, unsigned char *token)
425 {
426         int i;
427 
428         for (i = 0; i < len - 1; i++) {
429                 if (str[i] == token[0] && str[i+1] == token[1])
430                         return &str[i];
431         }
432         return NULL;
433 }
434 
435 /* replace a given token in all the valid symbols. Use the sampled symbols
436  * to update the counts */
437 static void compress_symbols(unsigned char *str, int idx)
438 {
439         unsigned int i, len, size;
440         unsigned char *p1, *p2;
441 
442         for (i = 0; i < table_cnt; i++) {
443 
444                 len = table[i].len;
445                 p1 = table[i].sym;
446 
447                 /* find the token on the symbol */
448                 p2 = find_token(p1, len, str);
449                 if (!p2) continue;
450 
451                 /* decrease the counts for this symbol's tokens */
452                 forget_symbol(table[i].sym, len);
453 
454                 size = len;
455 
456                 do {
457                         *p2 = idx;
458                         p2++;
459                         size -= (p2 - p1);
460                         memmove(p2, p2 + 1, size);
461                         p1 = p2;
462                         len--;
463 
464                         if (size < 2) break;
465 
466                         /* find the token on the symbol */
467                         p2 = find_token(p1, size, str);
468 
469                 } while (p2);
470 
471                 table[i].len = len;
472 
473                 /* increase the counts for this symbol's new tokens */
474                 learn_symbol(table[i].sym, len);
475         }
476 }
477 
478 /* search the token with the maximum profit */
479 static int find_best_token(void)
480 {
481         int i, best, bestprofit;
482 
483         bestprofit=-10000;
484         best = 0;
485 
486         for (i = 0; i < 0x10000; i++) {
487                 if (token_profit[i] > bestprofit) {
488                         best = i;
489                         bestprofit = token_profit[i];
490                 }
491         }
492         return best;
493 }
494 
495 /* this is the core of the algorithm: calculate the "best" table */
496 static void optimize_result(void)
497 {
498         int i, best;
499 
500         /* using the '\0' symbol last allows compress_symbols to use standard
501          * fast string functions */
502         for (i = 255; i >= 0; i--) {
503 
504                 /* if this table slot is empty (it is not used by an actual
505                  * original char code */
506                 if (!best_table_len[i]) {
507 
508                         /* find the token with the breates profit value */
509                         best = find_best_token();
510                         if (token_profit[best] == 0)
511                                 break;
512 
513                         /* place it in the "best" table */
514                         best_table_len[i] = 2;
515                         best_table[i][0] = best & 0xFF;
516                         best_table[i][1] = (best >> 8) & 0xFF;
517 
518                         /* replace this token in all the valid symbols */
519                         compress_symbols(best_table[i], i);
520                 }
521         }
522 }
523 
524 /* start by placing the symbols that are actually used on the table */
525 static void insert_real_symbols_in_table(void)
526 {
527         unsigned int i, j, c;
528 
529         memset(best_table, 0, sizeof(best_table));
530         memset(best_table_len, 0, sizeof(best_table_len));
531 
532         for (i = 0; i < table_cnt; i++) {
533                 for (j = 0; j < table[i].len; j++) {
534                         c = table[i].sym[j];
535                         best_table[c][0]=c;
536                         best_table_len[c]=1;
537                 }
538         }
539 }
540 
541 static void optimize_token_table(void)
542 {
543         build_initial_tok_table();
544 
545         insert_real_symbols_in_table();
546 
547         /* When valid symbol is not registered, exit to error */
548         if (!table_cnt) {
549                 fprintf(stderr, "No valid symbol.\n");
550                 exit(1);
551         }
552 
553         optimize_result();
554 }
555 
556 /* guess for "linker script provide" symbol */
557 static int may_be_linker_script_provide_symbol(const struct sym_entry *se)
558 {
559         const char *symbol = (char *)se->sym + 1;
560         int len = se->len - 1;
561 
562         if (len < 8)
563                 return 0;
564 
565         if (symbol[0] != '_' || symbol[1] != '_')
566                 return 0;
567 
568         /* __start_XXXXX */
569         if (!memcmp(symbol + 2, "start_", 6))
570                 return 1;
571 
572         /* __stop_XXXXX */
573         if (!memcmp(symbol + 2, "stop_", 5))
574                 return 1;
575 
576         /* __end_XXXXX */
577         if (!memcmp(symbol + 2, "end_", 4))
578                 return 1;
579 
580         /* __XXXXX_start */
581         if (!memcmp(symbol + len - 6, "_start", 6))
582                 return 1;
583 
584         /* __XXXXX_end */
585         if (!memcmp(symbol + len - 4, "_end", 4))
586                 return 1;
587 
588         return 0;
589 }
590 
591 static int prefix_underscores_count(const char *str)
592 {
593         const char *tail = str;
594 
595         while (*tail == '_')
596                 tail++;
597 
598         return tail - str;
599 }
600 
601 static int compare_symbols(const void *a, const void *b)
602 {
603         const struct sym_entry *sa;
604         const struct sym_entry *sb;
605         int wa, wb;
606 
607         sa = a;
608         sb = b;
609 
610         /* sort by address first */
611         if (sa->addr > sb->addr)
612                 return 1;
613         if (sa->addr < sb->addr)
614                 return -1;
615 
616         /* sort by "weakness" type */
617         wa = (sa->sym[0] == 'w') || (sa->sym[0] == 'W');
618         wb = (sb->sym[0] == 'w') || (sb->sym[0] == 'W');
619         if (wa != wb)
620                 return wa - wb;
621 
622         /* sort by "linker script provide" type */
623         wa = may_be_linker_script_provide_symbol(sa);
624         wb = may_be_linker_script_provide_symbol(sb);
625         if (wa != wb)
626                 return wa - wb;
627 
628         /* sort by the number of prefix underscores */
629         wa = prefix_underscores_count((const char *)sa->sym + 1);
630         wb = prefix_underscores_count((const char *)sb->sym + 1);
631         if (wa != wb)
632                 return wa - wb;
633 
634         /* sort by initial order, so that other symbols are left undisturbed */
635         return sa->start_pos - sb->start_pos;
636 }
637 
638 static void sort_symbols(void)
639 {
640         qsort(table, table_cnt, sizeof(struct sym_entry), compare_symbols);
641 }
642 
643 int main(int argc, char **argv)
644 {
645         if (argc >= 2) {
646                 int i;
647                 for (i = 1; i < argc; i++) {
648                         if(strcmp(argv[i], "--all-symbols") == 0)
649                                 all_symbols = 1;
650                         else if (strncmp(argv[i], "--symbol-prefix=", 16) == 0) {
651                                 char *p = &argv[i][16];
652                                 /* skip quote */
653                                 if ((*p == '"' && *(p+2) == '"') || (*p == '\'' && *(p+2) == '\''))
654                                         p++;
655                                 symbol_prefix_char = *p;
656                         } else if (strncmp(argv[i], "--page-offset=", 14) == 0) {
657                                 const char *p = &argv[i][14];
658                                 kernel_start_addr = strtoull(p, NULL, 16);
659                         } else
660                                 usage();
661                 }
662         } else if (argc != 1)
663                 usage();
664 
665         read_map(stdin);
666         sort_symbols();
667         optimize_token_table();
668         write_src();
669 
670         return 0;
671 }
672 

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