Root/scripts/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: 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
32struct sym_entry {
33    unsigned long long addr;
34    unsigned int len;
35    unsigned int start_pos;
36    unsigned char *sym;
37};
38
39struct text_range {
40    const char *stext, *etext;
41    unsigned long long start, end;
42};
43
44static unsigned long long _text;
45static 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
54static struct sym_entry *table;
55static unsigned int table_size, table_cnt;
56static int all_symbols = 0;
57static char symbol_prefix_char = '\0';
58
59int token_profit[0x10000];
60
61/* the table that holds the result of the compression */
62unsigned char best_table[256][2];
63unsigned char best_table_len[256];
64
65
66static 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 $d.
75 */
76static inline int is_arm_mapping_symbol(const char *str)
77{
78    return str[0] == '$' && strchr("atd", str[1])
79           && (str[2] == '\0' || str[2] == '.');
80}
81
82static 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
102static 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
162static 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
177static 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
232static 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
250static 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 */
265static 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
290static 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 */
385static 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 */
394static 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 */
403static 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
419static 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 */
432static 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 */
474static 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 */
491static 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 */
518static 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
534static 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 */
550static 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
584static 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
594static 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
631static void sort_symbols(void)
632{
633    qsort(table, table_cnt, sizeof(struct sym_entry), compare_symbols);
634}
635
636int 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

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