xref: /openbmc/linux/scripts/kallsyms.c (revision 9d56dd3b083a3bec56e9da35ce07baca81030b03)
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 
59 int token_profit[0x10000];
60 
61 /* the table that holds the result of the compression */
62 unsigned char best_table[256][2];
63 unsigned char best_table_len[256];
64 
65 
66 static void usage(void)
67 {
68 	fprintf(stderr, "Usage: kallsyms [--all-symbols] [--symbol-prefix=<prefix char>] < in.map > out.S\n");
69 	exit(1);
70 }
71 
72 /*
73  * This ignores the intensely annoying "mapping symbols" found
74  * in ARM ELF files: $a, $t and $d.
75  */
76 static inline int is_arm_mapping_symbol(const char *str)
77 {
78 	return str[0] == '$' && strchr("atd", str[1])
79 	       && (str[2] == '\0' || str[2] == '.');
80 }
81 
82 static int read_symbol_tr(const char *sym, unsigned long long addr)
83 {
84 	size_t i;
85 	struct text_range *tr;
86 
87 	for (i = 0; i < ARRAY_SIZE(text_ranges); ++i) {
88 		tr = &text_ranges[i];
89 
90 		if (strcmp(sym, tr->stext) == 0) {
91 			tr->start = addr;
92 			return 0;
93 		} else if (strcmp(sym, tr->etext) == 0) {
94 			tr->end = addr;
95 			return 0;
96 		}
97 	}
98 
99 	return 1;
100 }
101 
102 static int read_symbol(FILE *in, struct sym_entry *s)
103 {
104 	char str[500];
105 	char *sym, stype;
106 	int rc;
107 
108 	rc = fscanf(in, "%llx %c %499s\n", &s->addr, &stype, str);
109 	if (rc != 3) {
110 		if (rc != EOF) {
111 			/* skip line */
112 			fgets(str, 500, in);
113 		}
114 		return -1;
115 	}
116 
117 	sym = str;
118 	/* skip prefix char */
119 	if (symbol_prefix_char && str[0] == symbol_prefix_char)
120 		sym++;
121 
122 	/* Ignore most absolute/undefined (?) symbols. */
123 	if (strcmp(sym, "_text") == 0)
124 		_text = s->addr;
125 	else if (read_symbol_tr(sym, s->addr) == 0)
126 		/* nothing to do */;
127 	else if (toupper(stype) == 'A')
128 	{
129 		/* Keep these useful absolute symbols */
130 		if (strcmp(sym, "__kernel_syscall_via_break") &&
131 		    strcmp(sym, "__kernel_syscall_via_epc") &&
132 		    strcmp(sym, "__kernel_sigtramp") &&
133 		    strcmp(sym, "__gp"))
134 			return -1;
135 
136 	}
137 	else if (toupper(stype) == 'U' ||
138 		 is_arm_mapping_symbol(sym))
139 		return -1;
140 	/* exclude also MIPS ELF local symbols ($L123 instead of .L123) */
141 	else if (str[0] == '$')
142 		return -1;
143 	/* exclude debugging symbols */
144 	else if (stype == 'N')
145 		return -1;
146 
147 	/* include the type field in the symbol name, so that it gets
148 	 * compressed together */
149 	s->len = strlen(str) + 1;
150 	s->sym = malloc(s->len + 1);
151 	if (!s->sym) {
152 		fprintf(stderr, "kallsyms failure: "
153 			"unable to allocate required amount of memory\n");
154 		exit(EXIT_FAILURE);
155 	}
156 	strcpy((char *)s->sym + 1, str);
157 	s->sym[0] = stype;
158 
159 	return 0;
160 }
161 
162 static int symbol_valid_tr(struct sym_entry *s)
163 {
164 	size_t i;
165 	struct text_range *tr;
166 
167 	for (i = 0; i < ARRAY_SIZE(text_ranges); ++i) {
168 		tr = &text_ranges[i];
169 
170 		if (s->addr >= tr->start && s->addr <= tr->end)
171 			return 1;
172 	}
173 
174 	return 0;
175 }
176 
177 static int symbol_valid(struct sym_entry *s)
178 {
179 	/* Symbols which vary between passes.  Passes 1 and 2 must have
180 	 * identical symbol lists.  The kallsyms_* symbols below are only added
181 	 * after pass 1, they would be included in pass 2 when --all-symbols is
182 	 * specified so exclude them to get a stable symbol list.
183 	 */
184 	static char *special_symbols[] = {
185 		"kallsyms_addresses",
186 		"kallsyms_num_syms",
187 		"kallsyms_names",
188 		"kallsyms_markers",
189 		"kallsyms_token_table",
190 		"kallsyms_token_index",
191 
192 	/* Exclude linker generated symbols which vary between passes */
193 		"_SDA_BASE_",		/* ppc */
194 		"_SDA2_BASE_",		/* ppc */
195 		NULL };
196 	int i;
197 	int offset = 1;
198 
199 	/* skip prefix char */
200 	if (symbol_prefix_char && *(s->sym + 1) == symbol_prefix_char)
201 		offset++;
202 
203 	/* if --all-symbols is not specified, then symbols outside the text
204 	 * and inittext sections are discarded */
205 	if (!all_symbols) {
206 		if (symbol_valid_tr(s) == 0)
207 			return 0;
208 		/* Corner case.  Discard any symbols with the same value as
209 		 * _etext _einittext; they can move between pass 1 and 2 when
210 		 * the kallsyms data are added.  If these symbols move then
211 		 * they may get dropped in pass 2, which breaks the kallsyms
212 		 * rules.
213 		 */
214 		if ((s->addr == text_range_text->end &&
215 				strcmp((char *)s->sym + offset, text_range_text->etext)) ||
216 		    (s->addr == text_range_inittext->end &&
217 				strcmp((char *)s->sym + offset, text_range_inittext->etext)))
218 			return 0;
219 	}
220 
221 	/* Exclude symbols which vary between passes. */
222 	if (strstr((char *)s->sym + offset, "_compiled."))
223 		return 0;
224 
225 	for (i = 0; special_symbols[i]; i++)
226 		if( strcmp((char *)s->sym + offset, special_symbols[i]) == 0 )
227 			return 0;
228 
229 	return 1;
230 }
231 
232 static void read_map(FILE *in)
233 {
234 	while (!feof(in)) {
235 		if (table_cnt >= table_size) {
236 			table_size += 10000;
237 			table = realloc(table, sizeof(*table) * table_size);
238 			if (!table) {
239 				fprintf(stderr, "out of memory\n");
240 				exit (1);
241 			}
242 		}
243 		if (read_symbol(in, &table[table_cnt]) == 0) {
244 			table[table_cnt].start_pos = table_cnt;
245 			table_cnt++;
246 		}
247 	}
248 }
249 
250 static void output_label(char *label)
251 {
252 	if (symbol_prefix_char)
253 		printf(".globl %c%s\n", symbol_prefix_char, label);
254 	else
255 		printf(".globl %s\n", label);
256 	printf("\tALGN\n");
257 	if (symbol_prefix_char)
258 		printf("%c%s:\n", symbol_prefix_char, label);
259 	else
260 		printf("%s:\n", label);
261 }
262 
263 /* uncompress a compressed symbol. When this function is called, the best table
264  * might still be compressed itself, so the function needs to be recursive */
265 static int expand_symbol(unsigned char *data, int len, char *result)
266 {
267 	int c, rlen, total=0;
268 
269 	while (len) {
270 		c = *data;
271 		/* if the table holds a single char that is the same as the one
272 		 * we are looking for, then end the search */
273 		if (best_table[c][0]==c && best_table_len[c]==1) {
274 			*result++ = c;
275 			total++;
276 		} else {
277 			/* if not, recurse and expand */
278 			rlen = expand_symbol(best_table[c], best_table_len[c], result);
279 			total += rlen;
280 			result += rlen;
281 		}
282 		data++;
283 		len--;
284 	}
285 	*result=0;
286 
287 	return total;
288 }
289 
290 static void write_src(void)
291 {
292 	unsigned int i, k, off;
293 	unsigned int best_idx[256];
294 	unsigned int *markers;
295 	char buf[KSYM_NAME_LEN];
296 
297 	printf("#include <asm/types.h>\n");
298 	printf("#if BITS_PER_LONG == 64\n");
299 	printf("#define PTR .quad\n");
300 	printf("#define ALGN .align 8\n");
301 	printf("#else\n");
302 	printf("#define PTR .long\n");
303 	printf("#define ALGN .align 4\n");
304 	printf("#endif\n");
305 
306 	printf("\t.section .rodata, \"a\"\n");
307 
308 	/* Provide proper symbols relocatability by their '_text'
309 	 * relativeness.  The symbol names cannot be used to construct
310 	 * normal symbol references as the list of symbols contains
311 	 * symbols that are declared static and are private to their
312 	 * .o files.  This prevents .tmp_kallsyms.o or any other
313 	 * object from referencing them.
314 	 */
315 	output_label("kallsyms_addresses");
316 	for (i = 0; i < table_cnt; i++) {
317 		if (toupper(table[i].sym[0]) != 'A') {
318 			if (_text <= table[i].addr)
319 				printf("\tPTR\t_text + %#llx\n",
320 					table[i].addr - _text);
321 			else
322 				printf("\tPTR\t_text - %#llx\n",
323 					_text - table[i].addr);
324 		} else {
325 			printf("\tPTR\t%#llx\n", table[i].addr);
326 		}
327 	}
328 	printf("\n");
329 
330 	output_label("kallsyms_num_syms");
331 	printf("\tPTR\t%d\n", table_cnt);
332 	printf("\n");
333 
334 	/* table of offset markers, that give the offset in the compressed stream
335 	 * every 256 symbols */
336 	markers = malloc(sizeof(unsigned int) * ((table_cnt + 255) / 256));
337 	if (!markers) {
338 		fprintf(stderr, "kallsyms failure: "
339 			"unable to allocate required memory\n");
340 		exit(EXIT_FAILURE);
341 	}
342 
343 	output_label("kallsyms_names");
344 	off = 0;
345 	for (i = 0; i < table_cnt; i++) {
346 		if ((i & 0xFF) == 0)
347 			markers[i >> 8] = off;
348 
349 		printf("\t.byte 0x%02x", table[i].len);
350 		for (k = 0; k < table[i].len; k++)
351 			printf(", 0x%02x", table[i].sym[k]);
352 		printf("\n");
353 
354 		off += table[i].len + 1;
355 	}
356 	printf("\n");
357 
358 	output_label("kallsyms_markers");
359 	for (i = 0; i < ((table_cnt + 255) >> 8); i++)
360 		printf("\tPTR\t%d\n", markers[i]);
361 	printf("\n");
362 
363 	free(markers);
364 
365 	output_label("kallsyms_token_table");
366 	off = 0;
367 	for (i = 0; i < 256; i++) {
368 		best_idx[i] = off;
369 		expand_symbol(best_table[i], best_table_len[i], buf);
370 		printf("\t.asciz\t\"%s\"\n", buf);
371 		off += strlen(buf) + 1;
372 	}
373 	printf("\n");
374 
375 	output_label("kallsyms_token_index");
376 	for (i = 0; i < 256; i++)
377 		printf("\t.short\t%d\n", best_idx[i]);
378 	printf("\n");
379 }
380 
381 
382 /* table lookup compression functions */
383 
384 /* count all the possible tokens in a symbol */
385 static void learn_symbol(unsigned char *symbol, int len)
386 {
387 	int i;
388 
389 	for (i = 0; i < len - 1; i++)
390 		token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++;
391 }
392 
393 /* decrease the count for all the possible tokens in a symbol */
394 static void forget_symbol(unsigned char *symbol, int len)
395 {
396 	int i;
397 
398 	for (i = 0; i < len - 1; i++)
399 		token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--;
400 }
401 
402 /* remove all the invalid symbols from the table and do the initial token count */
403 static void build_initial_tok_table(void)
404 {
405 	unsigned int i, pos;
406 
407 	pos = 0;
408 	for (i = 0; i < table_cnt; i++) {
409 		if ( symbol_valid(&table[i]) ) {
410 			if (pos != i)
411 				table[pos] = table[i];
412 			learn_symbol(table[pos].sym, table[pos].len);
413 			pos++;
414 		}
415 	}
416 	table_cnt = pos;
417 }
418 
419 static void *find_token(unsigned char *str, int len, unsigned char *token)
420 {
421 	int i;
422 
423 	for (i = 0; i < len - 1; i++) {
424 		if (str[i] == token[0] && str[i+1] == token[1])
425 			return &str[i];
426 	}
427 	return NULL;
428 }
429 
430 /* replace a given token in all the valid symbols. Use the sampled symbols
431  * to update the counts */
432 static void compress_symbols(unsigned char *str, int idx)
433 {
434 	unsigned int i, len, size;
435 	unsigned char *p1, *p2;
436 
437 	for (i = 0; i < table_cnt; i++) {
438 
439 		len = table[i].len;
440 		p1 = table[i].sym;
441 
442 		/* find the token on the symbol */
443 		p2 = find_token(p1, len, str);
444 		if (!p2) continue;
445 
446 		/* decrease the counts for this symbol's tokens */
447 		forget_symbol(table[i].sym, len);
448 
449 		size = len;
450 
451 		do {
452 			*p2 = idx;
453 			p2++;
454 			size -= (p2 - p1);
455 			memmove(p2, p2 + 1, size);
456 			p1 = p2;
457 			len--;
458 
459 			if (size < 2) break;
460 
461 			/* find the token on the symbol */
462 			p2 = find_token(p1, size, str);
463 
464 		} while (p2);
465 
466 		table[i].len = len;
467 
468 		/* increase the counts for this symbol's new tokens */
469 		learn_symbol(table[i].sym, len);
470 	}
471 }
472 
473 /* search the token with the maximum profit */
474 static int find_best_token(void)
475 {
476 	int i, best, bestprofit;
477 
478 	bestprofit=-10000;
479 	best = 0;
480 
481 	for (i = 0; i < 0x10000; i++) {
482 		if (token_profit[i] > bestprofit) {
483 			best = i;
484 			bestprofit = token_profit[i];
485 		}
486 	}
487 	return best;
488 }
489 
490 /* this is the core of the algorithm: calculate the "best" table */
491 static void optimize_result(void)
492 {
493 	int i, best;
494 
495 	/* using the '\0' symbol last allows compress_symbols to use standard
496 	 * fast string functions */
497 	for (i = 255; i >= 0; i--) {
498 
499 		/* if this table slot is empty (it is not used by an actual
500 		 * original char code */
501 		if (!best_table_len[i]) {
502 
503 			/* find the token with the breates profit value */
504 			best = find_best_token();
505 
506 			/* place it in the "best" table */
507 			best_table_len[i] = 2;
508 			best_table[i][0] = best & 0xFF;
509 			best_table[i][1] = (best >> 8) & 0xFF;
510 
511 			/* replace this token in all the valid symbols */
512 			compress_symbols(best_table[i], i);
513 		}
514 	}
515 }
516 
517 /* start by placing the symbols that are actually used on the table */
518 static void insert_real_symbols_in_table(void)
519 {
520 	unsigned int i, j, c;
521 
522 	memset(best_table, 0, sizeof(best_table));
523 	memset(best_table_len, 0, sizeof(best_table_len));
524 
525 	for (i = 0; i < table_cnt; i++) {
526 		for (j = 0; j < table[i].len; j++) {
527 			c = table[i].sym[j];
528 			best_table[c][0]=c;
529 			best_table_len[c]=1;
530 		}
531 	}
532 }
533 
534 static void optimize_token_table(void)
535 {
536 	build_initial_tok_table();
537 
538 	insert_real_symbols_in_table();
539 
540 	/* When valid symbol is not registered, exit to error */
541 	if (!table_cnt) {
542 		fprintf(stderr, "No valid symbol.\n");
543 		exit(1);
544 	}
545 
546 	optimize_result();
547 }
548 
549 /* guess for "linker script provide" symbol */
550 static int may_be_linker_script_provide_symbol(const struct sym_entry *se)
551 {
552 	const char *symbol = (char *)se->sym + 1;
553 	int len = se->len - 1;
554 
555 	if (len < 8)
556 		return 0;
557 
558 	if (symbol[0] != '_' || symbol[1] != '_')
559 		return 0;
560 
561 	/* __start_XXXXX */
562 	if (!memcmp(symbol + 2, "start_", 6))
563 		return 1;
564 
565 	/* __stop_XXXXX */
566 	if (!memcmp(symbol + 2, "stop_", 5))
567 		return 1;
568 
569 	/* __end_XXXXX */
570 	if (!memcmp(symbol + 2, "end_", 4))
571 		return 1;
572 
573 	/* __XXXXX_start */
574 	if (!memcmp(symbol + len - 6, "_start", 6))
575 		return 1;
576 
577 	/* __XXXXX_end */
578 	if (!memcmp(symbol + len - 4, "_end", 4))
579 		return 1;
580 
581 	return 0;
582 }
583 
584 static int prefix_underscores_count(const char *str)
585 {
586 	const char *tail = str;
587 
588 	while (*tail == '_')
589 		tail++;
590 
591 	return tail - str;
592 }
593 
594 static int compare_symbols(const void *a, const void *b)
595 {
596 	const struct sym_entry *sa;
597 	const struct sym_entry *sb;
598 	int wa, wb;
599 
600 	sa = a;
601 	sb = b;
602 
603 	/* sort by address first */
604 	if (sa->addr > sb->addr)
605 		return 1;
606 	if (sa->addr < sb->addr)
607 		return -1;
608 
609 	/* sort by "weakness" type */
610 	wa = (sa->sym[0] == 'w') || (sa->sym[0] == 'W');
611 	wb = (sb->sym[0] == 'w') || (sb->sym[0] == 'W');
612 	if (wa != wb)
613 		return wa - wb;
614 
615 	/* sort by "linker script provide" type */
616 	wa = may_be_linker_script_provide_symbol(sa);
617 	wb = may_be_linker_script_provide_symbol(sb);
618 	if (wa != wb)
619 		return wa - wb;
620 
621 	/* sort by the number of prefix underscores */
622 	wa = prefix_underscores_count((const char *)sa->sym + 1);
623 	wb = prefix_underscores_count((const char *)sb->sym + 1);
624 	if (wa != wb)
625 		return wa - wb;
626 
627 	/* sort by initial order, so that other symbols are left undisturbed */
628 	return sa->start_pos - sb->start_pos;
629 }
630 
631 static void sort_symbols(void)
632 {
633 	qsort(table, table_cnt, sizeof(struct sym_entry), compare_symbols);
634 }
635 
636 int main(int argc, char **argv)
637 {
638 	if (argc >= 2) {
639 		int i;
640 		for (i = 1; i < argc; i++) {
641 			if(strcmp(argv[i], "--all-symbols") == 0)
642 				all_symbols = 1;
643 			else if (strncmp(argv[i], "--symbol-prefix=", 16) == 0) {
644 				char *p = &argv[i][16];
645 				/* skip quote */
646 				if ((*p == '"' && *(p+2) == '"') || (*p == '\'' && *(p+2) == '\''))
647 					p++;
648 				symbol_prefix_char = *p;
649 			} else
650 				usage();
651 		}
652 	} else if (argc != 1)
653 		usage();
654 
655 	read_map(stdin);
656 	sort_symbols();
657 	optimize_token_table();
658 	write_src();
659 
660 	return 0;
661 }
662