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 addr_range {
40    const char *start_sym, *end_sym;
41    unsigned long long start, end;
42};
43
44static unsigned long long _text;
45static struct addr_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 addr_range percpu_range = {
55    "__per_cpu_start", "__per_cpu_end", -1ULL, 0
56};
57
58static struct sym_entry *table;
59static unsigned int table_size, table_cnt;
60static int all_symbols = 0;
61static int absolute_percpu = 0;
62static char symbol_prefix_char = '\0';
63static unsigned long long kernel_start_addr = 0;
64
65int token_profit[0x10000];
66
67/* the table that holds the result of the compression */
68unsigned char best_table[256][2];
69unsigned char best_table_len[256];
70
71
72static void usage(void)
73{
74    fprintf(stderr, "Usage: kallsyms [--all-symbols] "
75            "[--symbol-prefix=<prefix char>] "
76            "[--page-offset=<CONFIG_PAGE_OFFSET>] "
77            "< in.map > out.S\n");
78    exit(1);
79}
80
81/*
82 * This ignores the intensely annoying "mapping symbols" found
83 * in ARM ELF files: $a, $t and $d.
84 */
85static inline int is_arm_mapping_symbol(const char *str)
86{
87    return str[0] == '$' && strchr("axtd", str[1])
88           && (str[2] == '\0' || str[2] == '.');
89}
90
91static int check_symbol_range(const char *sym, unsigned long long addr,
92                  struct addr_range *ranges, int entries)
93{
94    size_t i;
95    struct addr_range *ar;
96
97    for (i = 0; i < entries; ++i) {
98        ar = &ranges[i];
99
100        if (strcmp(sym, ar->start_sym) == 0) {
101            ar->start = addr;
102            return 0;
103        } else if (strcmp(sym, ar->end_sym) == 0) {
104            ar->end = addr;
105            return 0;
106        }
107    }
108
109    return 1;
110}
111
112static int read_symbol(FILE *in, struct sym_entry *s)
113{
114    char str[500];
115    char *sym, stype;
116    int rc;
117
118    rc = fscanf(in, "%llx %c %499s\n", &s->addr, &stype, str);
119    if (rc != 3) {
120        if (rc != EOF && fgets(str, 500, in) == NULL)
121            fprintf(stderr, "Read error or end of file.\n");
122        return -1;
123    }
124    if (strlen(str) > KSYM_NAME_LEN) {
125        fprintf(stderr, "Symbol %s too long for kallsyms (%zu vs %d).\n"
126                "Please increase KSYM_NAME_LEN both in kernel and kallsyms.c\n",
127            str, strlen(str), KSYM_NAME_LEN);
128        return -1;
129    }
130
131    sym = str;
132    /* skip prefix char */
133    if (symbol_prefix_char && str[0] == symbol_prefix_char)
134        sym++;
135
136    /* Ignore most absolute/undefined (?) symbols. */
137    if (strcmp(sym, "_text") == 0)
138        _text = s->addr;
139    else if (check_symbol_range(sym, s->addr, text_ranges,
140                    ARRAY_SIZE(text_ranges)) == 0)
141        /* nothing to do */;
142    else if (toupper(stype) == 'A')
143    {
144        /* Keep these useful absolute symbols */
145        if (strcmp(sym, "__kernel_syscall_via_break") &&
146            strcmp(sym, "__kernel_syscall_via_epc") &&
147            strcmp(sym, "__kernel_sigtramp") &&
148            strcmp(sym, "__gp"))
149            return -1;
150
151    }
152    else if (toupper(stype) == 'U' ||
153         is_arm_mapping_symbol(sym))
154        return -1;
155    /* exclude also MIPS ELF local symbols ($L123 instead of .L123) */
156    else if (str[0] == '$')
157        return -1;
158    /* exclude debugging symbols */
159    else if (stype == 'N')
160        return -1;
161
162    /* include the type field in the symbol name, so that it gets
163     * compressed together */
164    s->len = strlen(str) + 1;
165    s->sym = malloc(s->len + 1);
166    if (!s->sym) {
167        fprintf(stderr, "kallsyms failure: "
168            "unable to allocate required amount of memory\n");
169        exit(EXIT_FAILURE);
170    }
171    strcpy((char *)s->sym + 1, str);
172    s->sym[0] = stype;
173
174    /* Record if we've found __per_cpu_start/end. */
175    check_symbol_range(sym, s->addr, &percpu_range, 1);
176
177    return 0;
178}
179
180static int symbol_in_range(struct sym_entry *s, struct addr_range *ranges,
181               int entries)
182{
183    size_t i;
184    struct addr_range *ar;
185
186    for (i = 0; i < entries; ++i) {
187        ar = &ranges[i];
188
189        if (s->addr >= ar->start && s->addr <= ar->end)
190            return 1;
191    }
192
193    return 0;
194}
195
196static int symbol_valid(struct sym_entry *s)
197{
198    /* Symbols which vary between passes. Passes 1 and 2 must have
199     * identical symbol lists. The kallsyms_* symbols below are only added
200     * after pass 1, they would be included in pass 2 when --all-symbols is
201     * specified so exclude them to get a stable symbol list.
202     */
203    static char *special_symbols[] = {
204        "kallsyms_addresses",
205        "kallsyms_num_syms",
206        "kallsyms_names",
207        "kallsyms_markers",
208        "kallsyms_token_table",
209        "kallsyms_token_index",
210
211    /* Exclude linker generated symbols which vary between passes */
212        "_SDA_BASE_", /* ppc */
213        "_SDA2_BASE_", /* ppc */
214        NULL };
215    int i;
216    int offset = 1;
217
218    if (s->addr < kernel_start_addr)
219        return 0;
220
221    /* skip prefix char */
222    if (symbol_prefix_char && *(s->sym + 1) == symbol_prefix_char)
223        offset++;
224
225    /* if --all-symbols is not specified, then symbols outside the text
226     * and inittext sections are discarded */
227    if (!all_symbols) {
228        if (symbol_in_range(s, text_ranges,
229                    ARRAY_SIZE(text_ranges)) == 0)
230            return 0;
231        /* Corner case. Discard any symbols with the same value as
232         * _etext _einittext; they can move between pass 1 and 2 when
233         * the kallsyms data are added. If these symbols move then
234         * they may get dropped in pass 2, which breaks the kallsyms
235         * rules.
236         */
237        if ((s->addr == text_range_text->end &&
238                strcmp((char *)s->sym + offset,
239                       text_range_text->end_sym)) ||
240            (s->addr == text_range_inittext->end &&
241                strcmp((char *)s->sym + offset,
242                       text_range_inittext->end_sym)))
243            return 0;
244    }
245
246    /* Exclude symbols which vary between passes. */
247    if (strstr((char *)s->sym + offset, "_compiled."))
248        return 0;
249
250    for (i = 0; special_symbols[i]; i++)
251        if( strcmp((char *)s->sym + offset, special_symbols[i]) == 0 )
252            return 0;
253
254    return 1;
255}
256
257static void read_map(FILE *in)
258{
259    while (!feof(in)) {
260        if (table_cnt >= table_size) {
261            table_size += 10000;
262            table = realloc(table, sizeof(*table) * table_size);
263            if (!table) {
264                fprintf(stderr, "out of memory\n");
265                exit (1);
266            }
267        }
268        if (read_symbol(in, &table[table_cnt]) == 0) {
269            table[table_cnt].start_pos = table_cnt;
270            table_cnt++;
271        }
272    }
273}
274
275static void output_label(char *label)
276{
277    if (symbol_prefix_char)
278        printf(".globl %c%s\n", symbol_prefix_char, label);
279    else
280        printf(".globl %s\n", label);
281    printf("\tALGN\n");
282    if (symbol_prefix_char)
283        printf("%c%s:\n", symbol_prefix_char, label);
284    else
285        printf("%s:\n", label);
286}
287
288/* uncompress a compressed symbol. When this function is called, the best table
289 * might still be compressed itself, so the function needs to be recursive */
290static int expand_symbol(unsigned char *data, int len, char *result)
291{
292    int c, rlen, total=0;
293
294    while (len) {
295        c = *data;
296        /* if the table holds a single char that is the same as the one
297         * we are looking for, then end the search */
298        if (best_table[c][0]==c && best_table_len[c]==1) {
299            *result++ = c;
300            total++;
301        } else {
302            /* if not, recurse and expand */
303            rlen = expand_symbol(best_table[c], best_table_len[c], result);
304            total += rlen;
305            result += rlen;
306        }
307        data++;
308        len--;
309    }
310    *result=0;
311
312    return total;
313}
314
315static int symbol_absolute(struct sym_entry *s)
316{
317    return toupper(s->sym[0]) == 'A';
318}
319
320static void write_src(void)
321{
322    unsigned int i, k, off;
323    unsigned int best_idx[256];
324    unsigned int *markers;
325    char buf[KSYM_NAME_LEN];
326
327    printf("#include <asm/types.h>\n");
328    printf("#if BITS_PER_LONG == 64\n");
329    printf("#define PTR .quad\n");
330    printf("#define ALGN .align 8\n");
331    printf("#else\n");
332    printf("#define PTR .long\n");
333    printf("#define ALGN .align 4\n");
334    printf("#endif\n");
335
336    printf("\t.section .rodata, \"a\"\n");
337
338    /* Provide proper symbols relocatability by their '_text'
339     * relativeness. The symbol names cannot be used to construct
340     * normal symbol references as the list of symbols contains
341     * symbols that are declared static and are private to their
342     * .o files. This prevents .tmp_kallsyms.o or any other
343     * object from referencing them.
344     */
345    output_label("kallsyms_addresses");
346    for (i = 0; i < table_cnt; i++) {
347        if (!symbol_absolute(&table[i])) {
348            if (_text <= table[i].addr)
349                printf("\tPTR\t_text + %#llx\n",
350                    table[i].addr - _text);
351            else
352                printf("\tPTR\t_text - %#llx\n",
353                    _text - table[i].addr);
354        } else {
355            printf("\tPTR\t%#llx\n", table[i].addr);
356        }
357    }
358    printf("\n");
359
360    output_label("kallsyms_num_syms");
361    printf("\tPTR\t%d\n", table_cnt);
362    printf("\n");
363
364    /* table of offset markers, that give the offset in the compressed stream
365     * every 256 symbols */
366    markers = malloc(sizeof(unsigned int) * ((table_cnt + 255) / 256));
367    if (!markers) {
368        fprintf(stderr, "kallsyms failure: "
369            "unable to allocate required memory\n");
370        exit(EXIT_FAILURE);
371    }
372
373    output_label("kallsyms_names");
374    off = 0;
375    for (i = 0; i < table_cnt; i++) {
376        if ((i & 0xFF) == 0)
377            markers[i >> 8] = off;
378
379        printf("\t.byte 0x%02x", table[i].len);
380        for (k = 0; k < table[i].len; k++)
381            printf(", 0x%02x", table[i].sym[k]);
382        printf("\n");
383
384        off += table[i].len + 1;
385    }
386    printf("\n");
387
388    output_label("kallsyms_markers");
389    for (i = 0; i < ((table_cnt + 255) >> 8); i++)
390        printf("\tPTR\t%d\n", markers[i]);
391    printf("\n");
392
393    free(markers);
394
395    output_label("kallsyms_token_table");
396    off = 0;
397    for (i = 0; i < 256; i++) {
398        best_idx[i] = off;
399        expand_symbol(best_table[i], best_table_len[i], buf);
400        printf("\t.asciz\t\"%s\"\n", buf);
401        off += strlen(buf) + 1;
402    }
403    printf("\n");
404
405    output_label("kallsyms_token_index");
406    for (i = 0; i < 256; i++)
407        printf("\t.short\t%d\n", best_idx[i]);
408    printf("\n");
409}
410
411
412/* table lookup compression functions */
413
414/* count all the possible tokens in a symbol */
415static void learn_symbol(unsigned char *symbol, int len)
416{
417    int i;
418
419    for (i = 0; i < len - 1; i++)
420        token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++;
421}
422
423/* decrease the count for all the possible tokens in a symbol */
424static void forget_symbol(unsigned char *symbol, int len)
425{
426    int i;
427
428    for (i = 0; i < len - 1; i++)
429        token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--;
430}
431
432/* remove all the invalid symbols from the table and do the initial token count */
433static void build_initial_tok_table(void)
434{
435    unsigned int i, pos;
436
437    pos = 0;
438    for (i = 0; i < table_cnt; i++) {
439        if ( symbol_valid(&table[i]) ) {
440            if (pos != i)
441                table[pos] = table[i];
442            learn_symbol(table[pos].sym, table[pos].len);
443            pos++;
444        }
445    }
446    table_cnt = pos;
447}
448
449static void *find_token(unsigned char *str, int len, unsigned char *token)
450{
451    int i;
452
453    for (i = 0; i < len - 1; i++) {
454        if (str[i] == token[0] && str[i+1] == token[1])
455            return &str[i];
456    }
457    return NULL;
458}
459
460/* replace a given token in all the valid symbols. Use the sampled symbols
461 * to update the counts */
462static void compress_symbols(unsigned char *str, int idx)
463{
464    unsigned int i, len, size;
465    unsigned char *p1, *p2;
466
467    for (i = 0; i < table_cnt; i++) {
468
469        len = table[i].len;
470        p1 = table[i].sym;
471
472        /* find the token on the symbol */
473        p2 = find_token(p1, len, str);
474        if (!p2) continue;
475
476        /* decrease the counts for this symbol's tokens */
477        forget_symbol(table[i].sym, len);
478
479        size = len;
480
481        do {
482            *p2 = idx;
483            p2++;
484            size -= (p2 - p1);
485            memmove(p2, p2 + 1, size);
486            p1 = p2;
487            len--;
488
489            if (size < 2) break;
490
491            /* find the token on the symbol */
492            p2 = find_token(p1, size, str);
493
494        } while (p2);
495
496        table[i].len = len;
497
498        /* increase the counts for this symbol's new tokens */
499        learn_symbol(table[i].sym, len);
500    }
501}
502
503/* search the token with the maximum profit */
504static int find_best_token(void)
505{
506    int i, best, bestprofit;
507
508    bestprofit=-10000;
509    best = 0;
510
511    for (i = 0; i < 0x10000; i++) {
512        if (token_profit[i] > bestprofit) {
513            best = i;
514            bestprofit = token_profit[i];
515        }
516    }
517    return best;
518}
519
520/* this is the core of the algorithm: calculate the "best" table */
521static void optimize_result(void)
522{
523    int i, best;
524
525    /* using the '\0' symbol last allows compress_symbols to use standard
526     * fast string functions */
527    for (i = 255; i >= 0; i--) {
528
529        /* if this table slot is empty (it is not used by an actual
530         * original char code */
531        if (!best_table_len[i]) {
532
533            /* find the token with the breates profit value */
534            best = find_best_token();
535            if (token_profit[best] == 0)
536                break;
537
538            /* place it in the "best" table */
539            best_table_len[i] = 2;
540            best_table[i][0] = best & 0xFF;
541            best_table[i][1] = (best >> 8) & 0xFF;
542
543            /* replace this token in all the valid symbols */
544            compress_symbols(best_table[i], i);
545        }
546    }
547}
548
549/* start by placing the symbols that are actually used on the table */
550static void insert_real_symbols_in_table(void)
551{
552    unsigned int i, j, c;
553
554    memset(best_table, 0, sizeof(best_table));
555    memset(best_table_len, 0, sizeof(best_table_len));
556
557    for (i = 0; i < table_cnt; i++) {
558        for (j = 0; j < table[i].len; j++) {
559            c = table[i].sym[j];
560            best_table[c][0]=c;
561            best_table_len[c]=1;
562        }
563    }
564}
565
566static void optimize_token_table(void)
567{
568    build_initial_tok_table();
569
570    insert_real_symbols_in_table();
571
572    /* When valid symbol is not registered, exit to error */
573    if (!table_cnt) {
574        fprintf(stderr, "No valid symbol.\n");
575        exit(1);
576    }
577
578    optimize_result();
579}
580
581/* guess for "linker script provide" symbol */
582static int may_be_linker_script_provide_symbol(const struct sym_entry *se)
583{
584    const char *symbol = (char *)se->sym + 1;
585    int len = se->len - 1;
586
587    if (len < 8)
588        return 0;
589
590    if (symbol[0] != '_' || symbol[1] != '_')
591        return 0;
592
593    /* __start_XXXXX */
594    if (!memcmp(symbol + 2, "start_", 6))
595        return 1;
596
597    /* __stop_XXXXX */
598    if (!memcmp(symbol + 2, "stop_", 5))
599        return 1;
600
601    /* __end_XXXXX */
602    if (!memcmp(symbol + 2, "end_", 4))
603        return 1;
604
605    /* __XXXXX_start */
606    if (!memcmp(symbol + len - 6, "_start", 6))
607        return 1;
608
609    /* __XXXXX_end */
610    if (!memcmp(symbol + len - 4, "_end", 4))
611        return 1;
612
613    return 0;
614}
615
616static int prefix_underscores_count(const char *str)
617{
618    const char *tail = str;
619
620    while (*tail == '_')
621        tail++;
622
623    return tail - str;
624}
625
626static int compare_symbols(const void *a, const void *b)
627{
628    const struct sym_entry *sa;
629    const struct sym_entry *sb;
630    int wa, wb;
631
632    sa = a;
633    sb = b;
634
635    /* sort by address first */
636    if (sa->addr > sb->addr)
637        return 1;
638    if (sa->addr < sb->addr)
639        return -1;
640
641    /* sort by "weakness" type */
642    wa = (sa->sym[0] == 'w') || (sa->sym[0] == 'W');
643    wb = (sb->sym[0] == 'w') || (sb->sym[0] == 'W');
644    if (wa != wb)
645        return wa - wb;
646
647    /* sort by "linker script provide" type */
648    wa = may_be_linker_script_provide_symbol(sa);
649    wb = may_be_linker_script_provide_symbol(sb);
650    if (wa != wb)
651        return wa - wb;
652
653    /* sort by the number of prefix underscores */
654    wa = prefix_underscores_count((const char *)sa->sym + 1);
655    wb = prefix_underscores_count((const char *)sb->sym + 1);
656    if (wa != wb)
657        return wa - wb;
658
659    /* sort by initial order, so that other symbols are left undisturbed */
660    return sa->start_pos - sb->start_pos;
661}
662
663static void sort_symbols(void)
664{
665    qsort(table, table_cnt, sizeof(struct sym_entry), compare_symbols);
666}
667
668static void make_percpus_absolute(void)
669{
670    unsigned int i;
671
672    for (i = 0; i < table_cnt; i++)
673        if (symbol_in_range(&table[i], &percpu_range, 1))
674            table[i].sym[0] = 'A';
675}
676
677int main(int argc, char **argv)
678{
679    if (argc >= 2) {
680        int i;
681        for (i = 1; i < argc; i++) {
682            if(strcmp(argv[i], "--all-symbols") == 0)
683                all_symbols = 1;
684            else if (strcmp(argv[i], "--absolute-percpu") == 0)
685                absolute_percpu = 1;
686            else if (strncmp(argv[i], "--symbol-prefix=", 16) == 0) {
687                char *p = &argv[i][16];
688                /* skip quote */
689                if ((*p == '"' && *(p+2) == '"') || (*p == '\'' && *(p+2) == '\''))
690                    p++;
691                symbol_prefix_char = *p;
692            } else if (strncmp(argv[i], "--page-offset=", 14) == 0) {
693                const char *p = &argv[i][14];
694                kernel_start_addr = strtoull(p, NULL, 16);
695            } else
696                usage();
697        }
698    } else if (argc != 1)
699        usage();
700
701    read_map(stdin);
702    if (absolute_percpu)
703        make_percpus_absolute();
704    sort_symbols();
705    optimize_token_table();
706    write_src();
707
708    return 0;
709}
710

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