kallsyms.c

  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, "Usage: kallsyms [--all-symbols] in.map > out.S\n");
 71	exit(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(name, "__kernel_syscall_via_break") &&
 87		    strcmp(name, "__kernel_syscall_via_epc") &&
 88		    strcmp(name, "__kernel_sigtramp") &&
 89		    strcmp(name, "__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(sym, ar->start_sym) == 0) {
106			ar->start = addr;
107			return;
108		} else if (strcmp(sym, 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(buf, buf_len, in);
125	if (readlen < 0) {
126		if (errno) {
127			perror("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(*buf, &p, 16);
137
138	if (*buf == p || *p++ != ' ' || !isascii((type = *p++)) || *p++ != ' ') {
139		fprintf(stderr, "line format error\n");
140		exit(EXIT_FAILURE);
141	}
142
143	name = p;
144	len = strlen(name);
145
146	if (len >= KSYM_NAME_LEN) {
147		fprintf(stderr, "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(name, "_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(name, addr, 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(sym_name(sym), 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(s, prefix, strlen(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(name, "__start_") ||
208		    string_starts_with(name, "__stop_"))
209			return 1;
210
211		if (symbol_in_range(s, 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(name, text_range_text->end_sym)) ||
222		    (s->addr == text_range_inittext->end &&
223		     strcmp(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(table[i])) {
238			if (pos != i)
239				table[pos] = table[i];
240			pos++;
241		} else {
242			free(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(in, "r");
256	if (!fp) {
257		perror(in);
258		exit(1);
259	}
260
261	while (!feof(fp)) {
262		sym = read_symbol(fp, &buf, &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(buf);
277	fclose(fp);
278}
279
280static void output_label(const char *label)
281{
282	printf(".globl %s\n", label);
283	printf("\tALGN\n");
284	printf("%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(best_table[c], 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(sym_name(sa), sym_name(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(table, table_cnt, sizeof(table[0]), 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("#include <asm/bitsperlong.h>\n");
347	printf("#if BITS_PER_LONG == 64\n");
348	printf("#define PTR .quad\n");
349	printf("#define ALGN .balign 8\n");
350	printf("#else\n");
351	printf("#define PTR .long\n");
352	printf("#define ALGN .balign 4\n");
353	printf("#endif\n");
354
355	printf("\t.section .rodata, \"a\"\n");
356
357	output_label("kallsyms_num_syms");
358	printf("\t.long\t%u\n", table_cnt);
359	printf("\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("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, "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, "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("\t.byte 0x%02x", table[i]->len);
391			off += table[i]->len + 1;
392		} else {
393			/* "Big" symbols use two bytes. */
394			printf("\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(", 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(table[i]->sym, table[i]->len, buf);
407		strcpy((char *)table[i]->sym, buf);
408		printf("\t/* %s */\n", table[i]->sym);
409	}
410	printf("\n");
411
412	output_label("kallsyms_markers");
413	for (i = 0; i < markers_cnt; i++)
414		printf("\t.long\t%u\n", markers[i]);
415	printf("\n");
416
417	free(markers);
418
419	output_label("kallsyms_token_table");
420	off = 0;
421	for (i = 0; i < 256; i++) {
422		best_idx[i] = off;
423		expand_symbol(best_table[i], best_table_len[i], buf);
424		printf("\t.asciz\t\"%s\"\n", buf);
425		off += strlen(buf) + 1;
426	}
427	printf("\n");
428
429	output_label("kallsyms_token_index");
430	for (i = 0; i < 256; i++)
431		printf("\t.short\t%d\n", best_idx[i]);
432	printf("\n");
433
434	output_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, "kallsyms failure: "
449				"relative symbol value %#llx out of range\n",
450				table[i]->addr);
451			exit(EXIT_FAILURE);
452		}
453		printf("\t.long\t%#x\t/* %s */\n", (int)offset, table[i]->sym);
454	}
455	printf("\n");
456
457	output_label("kallsyms_relative_base");
458	/* Provide proper symbols relocatability by their '_text' relativeness. */
459	if (_text <= relative_base)
460		printf("\tPTR\t_text + %#llx\n", relative_base - _text);
461	else
462		printf("\tPTR\t_text - %#llx\n", _text - relative_base);
463	printf("\n");
464
465	sort_symbols_by_name();
466	output_label("kallsyms_seqs_of_names");
467	for (i = 0; i < table_cnt; i++)
468		printf("\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("\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(table[i]->sym, 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(p1, len, str);
532		if (!p2) continue;
533
534		/* decrease the counts for this symbol's tokens */
535		forget_symbol(table[i]->sym, len);
536
537		size = len;
538
539		do {
540			*p2 = idx;
541			p2++;
542			size -= (p2 - p1);
543			memmove(p2, p2 + 1, size);
544			p1 = p2;
545			len--;
546
547			if (size < 2) break;
548
549			/* find the token on the symbol */
550			p2 = find_token(p1, size, 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(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(best_table[i], 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(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(symbol + 2, "start_", 6))
644		return 1;
645
646	/* __stop_XXXXX */
647	if (!memcmp(symbol + 2, "stop_", 5))
648		return 1;
649
650	/* __end_XXXXX */
651	if (!memcmp(symbol + 2, "end_", 4))
652		return 1;
653
654	/* __XXXXX_start */
655	if (!memcmp(symbol + len - 6, "_start", 6))
656		return 1;
657
658	/* __XXXXX_end */
659	if (!memcmp(symbol + len - 4, "_end", 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(sa);
685	wb = may_be_linker_script_provide_symbol(sb);
686	if (wa != wb)
687		return wa - wb;
688
689	/* sort by the number of prefix underscores */
690	wa = strspn(sym_name(sa), "_");
691	wb = strspn(sym_name(sb), "_");
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(table, table_cnt, sizeof(table[0]), 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			{"all-symbols",     no_argument, &all_symbols,     1},
720			{},
721		};
722
723		int c = getopt_long(argc, argv, "", 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(argv[optind]);
735	shrink_table();
736	sort_symbols();
737	record_relative_base();
738	optimize_token_table();
739	write_src();
740
741	return 0;
742}