xref: /openbmc/linux/scripts/kallsyms.c (revision d5cb9783536a41df9f9cba5b0a1d78047ed787f7)
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  * ChangeLog:
11  *
12  * (25/Aug/2004) Paulo Marques <pmarques@grupopie.com>
13  *      Changed the compression method from stem compression to "table lookup"
14  *      compression
15  *
16  *      Table compression uses all the unused char codes on the symbols and
17  *  maps these to the most used substrings (tokens). For instance, it might
18  *  map char code 0xF7 to represent "write_" and then in every symbol where
19  *  "write_" appears it can be replaced by 0xF7, saving 5 bytes.
20  *      The used codes themselves are also placed in the table so that the
21  *  decompresion can work without "special cases".
22  *      Applied to kernel symbols, this usually produces a compression ratio
23  *  of about 50%.
24  *
25  */
26 
27 #define _GNU_SOURCE
28 
29 #include <stdio.h>
30 #include <stdlib.h>
31 #include <string.h>
32 #include <ctype.h>
33 
34 #define KSYM_NAME_LEN		127
35 
36 
37 struct sym_entry {
38 	unsigned long long addr;
39 	unsigned int len;
40 	unsigned char *sym;
41 };
42 
43 
44 static struct sym_entry *table;
45 static unsigned int table_size, table_cnt;
46 static unsigned long long _stext, _etext, _sinittext, _einittext, _sextratext, _eextratext;
47 static int all_symbols = 0;
48 static char symbol_prefix_char = '\0';
49 
50 int token_profit[0x10000];
51 
52 /* the table that holds the result of the compression */
53 unsigned char best_table[256][2];
54 unsigned char best_table_len[256];
55 
56 
57 static void usage(void)
58 {
59 	fprintf(stderr, "Usage: kallsyms [--all-symbols] [--symbol-prefix=<prefix char>] < in.map > out.S\n");
60 	exit(1);
61 }
62 
63 /*
64  * This ignores the intensely annoying "mapping symbols" found
65  * in ARM ELF files: $a, $t and $d.
66  */
67 static inline int is_arm_mapping_symbol(const char *str)
68 {
69 	return str[0] == '$' && strchr("atd", str[1])
70 	       && (str[2] == '\0' || str[2] == '.');
71 }
72 
73 static int read_symbol(FILE *in, struct sym_entry *s)
74 {
75 	char str[500];
76 	char *sym, stype;
77 	int rc;
78 
79 	rc = fscanf(in, "%llx %c %499s\n", &s->addr, &stype, str);
80 	if (rc != 3) {
81 		if (rc != EOF) {
82 			/* skip line */
83 			fgets(str, 500, in);
84 		}
85 		return -1;
86 	}
87 
88 	sym = str;
89 	/* skip prefix char */
90 	if (symbol_prefix_char && str[0] == symbol_prefix_char)
91 		sym++;
92 
93 	/* Ignore most absolute/undefined (?) symbols. */
94 	if (strcmp(sym, "_stext") == 0)
95 		_stext = s->addr;
96 	else if (strcmp(sym, "_etext") == 0)
97 		_etext = s->addr;
98 	else if (strcmp(sym, "_sinittext") == 0)
99 		_sinittext = s->addr;
100 	else if (strcmp(sym, "_einittext") == 0)
101 		_einittext = s->addr;
102 	else if (strcmp(sym, "_sextratext") == 0)
103 		_sextratext = s->addr;
104 	else if (strcmp(sym, "_eextratext") == 0)
105 		_eextratext = s->addr;
106 	else if (toupper(stype) == 'A')
107 	{
108 		/* Keep these useful absolute symbols */
109 		if (strcmp(sym, "__kernel_syscall_via_break") &&
110 		    strcmp(sym, "__kernel_syscall_via_epc") &&
111 		    strcmp(sym, "__kernel_sigtramp") &&
112 		    strcmp(sym, "__gp"))
113 			return -1;
114 
115 	}
116 	else if (toupper(stype) == 'U' ||
117 		 is_arm_mapping_symbol(sym))
118 		return -1;
119 	/* exclude also MIPS ELF local symbols ($L123 instead of .L123) */
120 	else if (str[0] == '$')
121 		return -1;
122 
123 	/* include the type field in the symbol name, so that it gets
124 	 * compressed together */
125 	s->len = strlen(str) + 1;
126 	s->sym = malloc(s->len + 1);
127 	strcpy((char *)s->sym + 1, str);
128 	s->sym[0] = stype;
129 
130 	return 0;
131 }
132 
133 static int symbol_valid(struct sym_entry *s)
134 {
135 	/* Symbols which vary between passes.  Passes 1 and 2 must have
136 	 * identical symbol lists.  The kallsyms_* symbols below are only added
137 	 * after pass 1, they would be included in pass 2 when --all-symbols is
138 	 * specified so exclude them to get a stable symbol list.
139 	 */
140 	static char *special_symbols[] = {
141 		"kallsyms_addresses",
142 		"kallsyms_num_syms",
143 		"kallsyms_names",
144 		"kallsyms_markers",
145 		"kallsyms_token_table",
146 		"kallsyms_token_index",
147 
148 	/* Exclude linker generated symbols which vary between passes */
149 		"_SDA_BASE_",		/* ppc */
150 		"_SDA2_BASE_",		/* ppc */
151 		NULL };
152 	int i;
153 	int offset = 1;
154 
155 	/* skip prefix char */
156 	if (symbol_prefix_char && *(s->sym + 1) == symbol_prefix_char)
157 		offset++;
158 
159 	/* if --all-symbols is not specified, then symbols outside the text
160 	 * and inittext sections are discarded */
161 	if (!all_symbols) {
162 		if ((s->addr < _stext || s->addr > _etext)
163 		    && (s->addr < _sinittext || s->addr > _einittext)
164 		    && (s->addr < _sextratext || s->addr > _eextratext))
165 			return 0;
166 		/* Corner case.  Discard any symbols with the same value as
167 		 * _etext _einittext or _eextratext; they can move between pass
168 		 * 1 and 2 when the kallsyms data are added.  If these symbols
169 		 * move then they may get dropped in pass 2, which breaks the
170 		 * kallsyms rules.
171 		 */
172 		if ((s->addr == _etext && strcmp((char*)s->sym + offset, "_etext")) ||
173 		    (s->addr == _einittext && strcmp((char*)s->sym + offset, "_einittext")) ||
174 		    (s->addr == _eextratext && strcmp((char*)s->sym + offset, "_eextratext")))
175 			return 0;
176 	}
177 
178 	/* Exclude symbols which vary between passes. */
179 	if (strstr((char *)s->sym + offset, "_compiled."))
180 		return 0;
181 
182 	for (i = 0; special_symbols[i]; i++)
183 		if( strcmp((char *)s->sym + offset, special_symbols[i]) == 0 )
184 			return 0;
185 
186 	return 1;
187 }
188 
189 static void read_map(FILE *in)
190 {
191 	while (!feof(in)) {
192 		if (table_cnt >= table_size) {
193 			table_size += 10000;
194 			table = realloc(table, sizeof(*table) * table_size);
195 			if (!table) {
196 				fprintf(stderr, "out of memory\n");
197 				exit (1);
198 			}
199 		}
200 		if (read_symbol(in, &table[table_cnt]) == 0)
201 			table_cnt++;
202 	}
203 }
204 
205 static void output_label(char *label)
206 {
207 	if (symbol_prefix_char)
208 		printf(".globl %c%s\n", symbol_prefix_char, label);
209 	else
210 		printf(".globl %s\n", label);
211 	printf("\tALGN\n");
212 	if (symbol_prefix_char)
213 		printf("%c%s:\n", symbol_prefix_char, label);
214 	else
215 		printf("%s:\n", label);
216 }
217 
218 /* uncompress a compressed symbol. When this function is called, the best table
219  * might still be compressed itself, so the function needs to be recursive */
220 static int expand_symbol(unsigned char *data, int len, char *result)
221 {
222 	int c, rlen, total=0;
223 
224 	while (len) {
225 		c = *data;
226 		/* if the table holds a single char that is the same as the one
227 		 * we are looking for, then end the search */
228 		if (best_table[c][0]==c && best_table_len[c]==1) {
229 			*result++ = c;
230 			total++;
231 		} else {
232 			/* if not, recurse and expand */
233 			rlen = expand_symbol(best_table[c], best_table_len[c], result);
234 			total += rlen;
235 			result += rlen;
236 		}
237 		data++;
238 		len--;
239 	}
240 	*result=0;
241 
242 	return total;
243 }
244 
245 static void write_src(void)
246 {
247 	unsigned int i, k, off;
248 	unsigned int best_idx[256];
249 	unsigned int *markers;
250 	char buf[KSYM_NAME_LEN+1];
251 
252 	printf("#include <asm/types.h>\n");
253 	printf("#if BITS_PER_LONG == 64\n");
254 	printf("#define PTR .quad\n");
255 	printf("#define ALGN .align 8\n");
256 	printf("#else\n");
257 	printf("#define PTR .long\n");
258 	printf("#define ALGN .align 4\n");
259 	printf("#endif\n");
260 
261 	printf(".data\n");
262 
263 	output_label("kallsyms_addresses");
264 	for (i = 0; i < table_cnt; i++) {
265 		printf("\tPTR\t%#llx\n", table[i].addr);
266 	}
267 	printf("\n");
268 
269 	output_label("kallsyms_num_syms");
270 	printf("\tPTR\t%d\n", table_cnt);
271 	printf("\n");
272 
273 	/* table of offset markers, that give the offset in the compressed stream
274 	 * every 256 symbols */
275 	markers = (unsigned int *) malloc(sizeof(unsigned int) * ((table_cnt + 255) / 256));
276 
277 	output_label("kallsyms_names");
278 	off = 0;
279 	for (i = 0; i < table_cnt; i++) {
280 		if ((i & 0xFF) == 0)
281 			markers[i >> 8] = off;
282 
283 		printf("\t.byte 0x%02x", table[i].len);
284 		for (k = 0; k < table[i].len; k++)
285 			printf(", 0x%02x", table[i].sym[k]);
286 		printf("\n");
287 
288 		off += table[i].len + 1;
289 	}
290 	printf("\n");
291 
292 	output_label("kallsyms_markers");
293 	for (i = 0; i < ((table_cnt + 255) >> 8); i++)
294 		printf("\tPTR\t%d\n", markers[i]);
295 	printf("\n");
296 
297 	free(markers);
298 
299 	output_label("kallsyms_token_table");
300 	off = 0;
301 	for (i = 0; i < 256; i++) {
302 		best_idx[i] = off;
303 		expand_symbol(best_table[i], best_table_len[i], buf);
304 		printf("\t.asciz\t\"%s\"\n", buf);
305 		off += strlen(buf) + 1;
306 	}
307 	printf("\n");
308 
309 	output_label("kallsyms_token_index");
310 	for (i = 0; i < 256; i++)
311 		printf("\t.short\t%d\n", best_idx[i]);
312 	printf("\n");
313 }
314 
315 
316 /* table lookup compression functions */
317 
318 /* count all the possible tokens in a symbol */
319 static void learn_symbol(unsigned char *symbol, int len)
320 {
321 	int i;
322 
323 	for (i = 0; i < len - 1; i++)
324 		token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++;
325 }
326 
327 /* decrease the count for all the possible tokens in a symbol */
328 static void forget_symbol(unsigned char *symbol, int len)
329 {
330 	int i;
331 
332 	for (i = 0; i < len - 1; i++)
333 		token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--;
334 }
335 
336 /* remove all the invalid symbols from the table and do the initial token count */
337 static void build_initial_tok_table(void)
338 {
339 	unsigned int i, pos;
340 
341 	pos = 0;
342 	for (i = 0; i < table_cnt; i++) {
343 		if ( symbol_valid(&table[i]) ) {
344 			if (pos != i)
345 				table[pos] = table[i];
346 			learn_symbol(table[pos].sym, table[pos].len);
347 			pos++;
348 		}
349 	}
350 	table_cnt = pos;
351 }
352 
353 /* replace a given token in all the valid symbols. Use the sampled symbols
354  * to update the counts */
355 static void compress_symbols(unsigned char *str, int idx)
356 {
357 	unsigned int i, len, size;
358 	unsigned char *p1, *p2;
359 
360 	for (i = 0; i < table_cnt; i++) {
361 
362 		len = table[i].len;
363 		p1 = table[i].sym;
364 
365 		/* find the token on the symbol */
366 		p2 = memmem(p1, len, str, 2);
367 		if (!p2) continue;
368 
369 		/* decrease the counts for this symbol's tokens */
370 		forget_symbol(table[i].sym, len);
371 
372 		size = len;
373 
374 		do {
375 			*p2 = idx;
376 			p2++;
377 			size -= (p2 - p1);
378 			memmove(p2, p2 + 1, size);
379 			p1 = p2;
380 			len--;
381 
382 			if (size < 2) break;
383 
384 			/* find the token on the symbol */
385 			p2 = memmem(p1, size, str, 2);
386 
387 		} while (p2);
388 
389 		table[i].len = len;
390 
391 		/* increase the counts for this symbol's new tokens */
392 		learn_symbol(table[i].sym, len);
393 	}
394 }
395 
396 /* search the token with the maximum profit */
397 static int find_best_token(void)
398 {
399 	int i, best, bestprofit;
400 
401 	bestprofit=-10000;
402 	best = 0;
403 
404 	for (i = 0; i < 0x10000; i++) {
405 		if (token_profit[i] > bestprofit) {
406 			best = i;
407 			bestprofit = token_profit[i];
408 		}
409 	}
410 	return best;
411 }
412 
413 /* this is the core of the algorithm: calculate the "best" table */
414 static void optimize_result(void)
415 {
416 	int i, best;
417 
418 	/* using the '\0' symbol last allows compress_symbols to use standard
419 	 * fast string functions */
420 	for (i = 255; i >= 0; i--) {
421 
422 		/* if this table slot is empty (it is not used by an actual
423 		 * original char code */
424 		if (!best_table_len[i]) {
425 
426 			/* find the token with the breates profit value */
427 			best = find_best_token();
428 
429 			/* place it in the "best" table */
430 			best_table_len[i] = 2;
431 			best_table[i][0] = best & 0xFF;
432 			best_table[i][1] = (best >> 8) & 0xFF;
433 
434 			/* replace this token in all the valid symbols */
435 			compress_symbols(best_table[i], i);
436 		}
437 	}
438 }
439 
440 /* start by placing the symbols that are actually used on the table */
441 static void insert_real_symbols_in_table(void)
442 {
443 	unsigned int i, j, c;
444 
445 	memset(best_table, 0, sizeof(best_table));
446 	memset(best_table_len, 0, sizeof(best_table_len));
447 
448 	for (i = 0; i < table_cnt; i++) {
449 		for (j = 0; j < table[i].len; j++) {
450 			c = table[i].sym[j];
451 			best_table[c][0]=c;
452 			best_table_len[c]=1;
453 		}
454 	}
455 }
456 
457 static void optimize_token_table(void)
458 {
459 	build_initial_tok_table();
460 
461 	insert_real_symbols_in_table();
462 
463 	/* When valid symbol is not registered, exit to error */
464 	if (!table_cnt) {
465 		fprintf(stderr, "No valid symbol.\n");
466 		exit(1);
467 	}
468 
469 	optimize_result();
470 }
471 
472 
473 int main(int argc, char **argv)
474 {
475 	if (argc >= 2) {
476 		int i;
477 		for (i = 1; i < argc; i++) {
478 			if(strcmp(argv[i], "--all-symbols") == 0)
479 				all_symbols = 1;
480 			else if (strncmp(argv[i], "--symbol-prefix=", 16) == 0) {
481 				char *p = &argv[i][16];
482 				/* skip quote */
483 				if ((*p == '"' && *(p+2) == '"') || (*p == '\'' && *(p+2) == '\''))
484 					p++;
485 				symbol_prefix_char = *p;
486 			} else
487 				usage();
488 		}
489 	} else if (argc != 1)
490 		usage();
491 
492 	read_map(stdin);
493 	optimize_token_table();
494 	write_src();
495 
496 	return 0;
497 }
498