root/scripts/kallsyms.c

DEFINITIONS

1. usage
2. is_arm_mapping_symbol
3. check_symbol_range
4. read_symbol
5. symbol_in_range
6. symbol_valid
7. read_map
8. output_label
9. expand_symbol
10. symbol_absolute
11. write_src
12. learn_symbol
13. forget_symbol
14. build_initial_tok_table
15. find_token
16. compress_symbols
17. find_best_token
18. optimize_result
19. insert_real_symbols_in_table
20. optimize_token_table
21. may_be_linker_script_provide_symbol
22. prefix_underscores_count
23. compare_symbols
24. sort_symbols
25. make_percpus_absolute
26. main

/* Generate assembler source containing symbol information
 *
 * Copyright 2002       by Kai Germaschewski
 *
 * This software may be used and distributed according to the terms
 * of the GNU General Public License, incorporated herein by reference.
 *
 * Usage: nm -n vmlinux | scripts/kallsyms [--all-symbols] > symbols.S
 *
 *      Table compression uses all the unused char codes on the symbols and
 *  maps these to the most used substrings (tokens). For instance, it might
 *  map char code 0xF7 to represent "write_" and then in every symbol where
 *  "write_" appears it can be replaced by 0xF7, saving 5 bytes.
 *      The used codes themselves are also placed in the table so that the
 *  decompresion can work without "special cases".
 *      Applied to kernel symbols, this usually produces a compression ratio
 *  of about 50%.
 *
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

#ifndef ARRAY_SIZE
#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0]))
#endif

#define KSYM_NAME_LEN           128

struct sym_entry {
        unsigned long long addr;
        unsigned int len;
        unsigned int start_pos;
        unsigned char *sym;
};

struct addr_range {
        const char *start_sym, *end_sym;
        unsigned long long start, end;
};

static unsigned long long _text;
static struct addr_range text_ranges[] = {
        { "_stext",     "_etext"     },
        { "_sinittext", "_einittext" },
        { "_stext_l1",  "_etext_l1"  }, /* Blackfin on-chip L1 inst SRAM */
        { "_stext_l2",  "_etext_l2"  }, /* Blackfin on-chip L2 SRAM */
};
#define text_range_text     (&text_ranges[0])
#define text_range_inittext (&text_ranges[1])

static struct addr_range percpu_range = {
        "__per_cpu_start", "__per_cpu_end", -1ULL, 0
};

static struct sym_entry *table;
static unsigned int table_size, table_cnt;
static int all_symbols = 0;
static int absolute_percpu = 0;
static char symbol_prefix_char = '\0';
static unsigned long long kernel_start_addr = 0;

int token_profit[0x10000];

/* the table that holds the result of the compression */
unsigned char best_table[256][2];
unsigned char best_table_len[256];


static void usage(void)
{
        fprintf(stderr, "Usage: kallsyms [--all-symbols] "
                        "[--symbol-prefix=<prefix char>] "
                        "[--page-offset=<CONFIG_PAGE_OFFSET>] "
                        "< in.map > out.S\n");
        exit(1);
}

/*
 * This ignores the intensely annoying "mapping symbols" found
 * in ARM ELF files: $a, $t and $d.
 */
static inline int is_arm_mapping_symbol(const char *str)
{
        return str[0] == '$' && strchr("axtd", str[1])
               && (str[2] == '\0' || str[2] == '.');
}

static int check_symbol_range(const char *sym, unsigned long long addr,
                              struct addr_range *ranges, int entries)
{
        size_t i;
        struct addr_range *ar;

        for (i = 0; i < entries; ++i) {
                ar = &ranges[i];

                if (strcmp(sym, ar->start_sym) == 0) {
                        ar->start = addr;
                        return 0;
                } else if (strcmp(sym, ar->end_sym) == 0) {
                        ar->end = addr;
                        return 0;
                }
        }

        return 1;
}

static int read_symbol(FILE *in, struct sym_entry *s)
{
        char str[500];
        char *sym, stype;
        int rc;

        rc = fscanf(in, "%llx %c %499s\n", &s->addr, &stype, str);
        if (rc != 3) {
                if (rc != EOF && fgets(str, 500, in) == NULL)
                        fprintf(stderr, "Read error or end of file.\n");
                return -1;
        }
        if (strlen(str) > KSYM_NAME_LEN) {
                fprintf(stderr, "Symbol %s too long for kallsyms (%zu vs %d).\n"
                                "Please increase KSYM_NAME_LEN both in kernel and kallsyms.c\n",
                        str, strlen(str), KSYM_NAME_LEN);
                return -1;
        }

        sym = str;
        /* skip prefix char */
        if (symbol_prefix_char && str[0] == symbol_prefix_char)
                sym++;

        /* Ignore most absolute/undefined (?) symbols. */
        if (strcmp(sym, "_text") == 0)
                _text = s->addr;
        else if (check_symbol_range(sym, s->addr, text_ranges,
                                    ARRAY_SIZE(text_ranges)) == 0)
                /* nothing to do */;
        else if (toupper(stype) == 'A')
        {
                /* Keep these useful absolute symbols */
                if (strcmp(sym, "__kernel_syscall_via_break") &&
                    strcmp(sym, "__kernel_syscall_via_epc") &&
                    strcmp(sym, "__kernel_sigtramp") &&
                    strcmp(sym, "__gp"))
                        return -1;

        }
        else if (toupper(stype) == 'U' ||
                 is_arm_mapping_symbol(sym))
                return -1;
        /* exclude also MIPS ELF local symbols ($L123 instead of .L123) */
        else if (str[0] == '$')
                return -1;
        /* exclude debugging symbols */
        else if (stype == 'N')
                return -1;

        /* include the type field in the symbol name, so that it gets
         * compressed together */
        s->len = strlen(str) + 1;
        s->sym = malloc(s->len + 1);
        if (!s->sym) {
                fprintf(stderr, "kallsyms failure: "
                        "unable to allocate required amount of memory\n");
                exit(EXIT_FAILURE);
        }
        strcpy((char *)s->sym + 1, str);
        s->sym[0] = stype;

        /* Record if we've found __per_cpu_start/end. */
        check_symbol_range(sym, s->addr, &percpu_range, 1);

        return 0;
}

static int symbol_in_range(struct sym_entry *s, struct addr_range *ranges,
                           int entries)
{
        size_t i;
        struct addr_range *ar;

        for (i = 0; i < entries; ++i) {
                ar = &ranges[i];

                if (s->addr >= ar->start && s->addr <= ar->end)
                        return 1;
        }

        return 0;
}

static int symbol_valid(struct sym_entry *s)
{
        /* Symbols which vary between passes.  Passes 1 and 2 must have
         * identical symbol lists.  The kallsyms_* symbols below are only added
         * after pass 1, they would be included in pass 2 when --all-symbols is
         * specified so exclude them to get a stable symbol list.
         */
        static char *special_symbols[] = {
                "kallsyms_addresses",
                "kallsyms_num_syms",
                "kallsyms_names",
                "kallsyms_markers",
                "kallsyms_token_table",
                "kallsyms_token_index",

        /* Exclude linker generated symbols which vary between passes */
                "_SDA_BASE_",           /* ppc */
                "_SDA2_BASE_",          /* ppc */
                NULL };
        int i;
        int offset = 1;

        if (s->addr < kernel_start_addr)
                return 0;

        /* skip prefix char */
        if (symbol_prefix_char && *(s->sym + 1) == symbol_prefix_char)
                offset++;

        /* if --all-symbols is not specified, then symbols outside the text
         * and inittext sections are discarded */
        if (!all_symbols) {
                if (symbol_in_range(s, text_ranges,
                                    ARRAY_SIZE(text_ranges)) == 0)
                        return 0;
                /* Corner case.  Discard any symbols with the same value as
                 * _etext _einittext; they can move between pass 1 and 2 when
                 * the kallsyms data are added.  If these symbols move then
                 * they may get dropped in pass 2, which breaks the kallsyms
                 * rules.
                 */
                if ((s->addr == text_range_text->end &&
                                strcmp((char *)s->sym + offset,
                                       text_range_text->end_sym)) ||
                    (s->addr == text_range_inittext->end &&
                                strcmp((char *)s->sym + offset,
                                       text_range_inittext->end_sym)))
                        return 0;
        }

        /* Exclude symbols which vary between passes. */
        if (strstr((char *)s->sym + offset, "_compiled."))
                return 0;

        for (i = 0; special_symbols[i]; i++)
                if( strcmp((char *)s->sym + offset, special_symbols[i]) == 0 )
                        return 0;

        return 1;
}

static void read_map(FILE *in)
{
        while (!feof(in)) {
                if (table_cnt >= table_size) {
                        table_size += 10000;
                        table = realloc(table, sizeof(*table) * table_size);
                        if (!table) {
                                fprintf(stderr, "out of memory\n");
                                exit (1);
                        }
                }
                if (read_symbol(in, &table[table_cnt]) == 0) {
                        table[table_cnt].start_pos = table_cnt;
                        table_cnt++;
                }
        }
}

static void output_label(char *label)
{
        if (symbol_prefix_char)
                printf(".globl %c%s\n", symbol_prefix_char, label);
        else
                printf(".globl %s\n", label);
        printf("\tALGN\n");
        if (symbol_prefix_char)
                printf("%c%s:\n", symbol_prefix_char, label);
        else
                printf("%s:\n", label);
}

/* uncompress a compressed symbol. When this function is called, the best table
 * might still be compressed itself, so the function needs to be recursive */
static int expand_symbol(unsigned char *data, int len, char *result)
{
        int c, rlen, total=0;

        while (len) {
                c = *data;
                /* if the table holds a single char that is the same as the one
                 * we are looking for, then end the search */
                if (best_table[c][0]==c && best_table_len[c]==1) {
                        *result++ = c;
                        total++;
                } else {
                        /* if not, recurse and expand */
                        rlen = expand_symbol(best_table[c], best_table_len[c], result);
                        total += rlen;
                        result += rlen;
                }
                data++;
                len--;
        }
        *result=0;

        return total;
}

static int symbol_absolute(struct sym_entry *s)
{
        return toupper(s->sym[0]) == 'A';
}

static void write_src(void)
{
        unsigned int i, k, off;
        unsigned int best_idx[256];
        unsigned int *markers;
        char buf[KSYM_NAME_LEN];

        printf("#include <asm/types.h>\n");
        printf("#if BITS_PER_LONG == 64\n");
        printf("#define PTR .quad\n");
        printf("#define ALGN .align 8\n");
        printf("#else\n");
        printf("#define PTR .long\n");
        printf("#define ALGN .align 4\n");
        printf("#endif\n");

        printf("\t.section .rodata, \"a\"\n");

        /* Provide proper symbols relocatability by their '_text'
         * relativeness.  The symbol names cannot be used to construct
         * normal symbol references as the list of symbols contains
         * symbols that are declared static and are private to their
         * .o files.  This prevents .tmp_kallsyms.o or any other
         * object from referencing them.
         */
        output_label("kallsyms_addresses");
        for (i = 0; i < table_cnt; i++) {
                if (!symbol_absolute(&table[i])) {
                        if (_text <= table[i].addr)
                                printf("\tPTR\t_text + %#llx\n",
                                        table[i].addr - _text);
                        else
                                printf("\tPTR\t_text - %#llx\n",
                                        _text - table[i].addr);
                } else {
                        printf("\tPTR\t%#llx\n", table[i].addr);
                }
        }
        printf("\n");

        output_label("kallsyms_num_syms");
        printf("\tPTR\t%d\n", table_cnt);
        printf("\n");

        /* table of offset markers, that give the offset in the compressed stream
         * every 256 symbols */
        markers = malloc(sizeof(unsigned int) * ((table_cnt + 255) / 256));
        if (!markers) {
                fprintf(stderr, "kallsyms failure: "
                        "unable to allocate required memory\n");
                exit(EXIT_FAILURE);
        }

        output_label("kallsyms_names");
        off = 0;
        for (i = 0; i < table_cnt; i++) {
                if ((i & 0xFF) == 0)
                        markers[i >> 8] = off;

                printf("\t.byte 0x%02x", table[i].len);
                for (k = 0; k < table[i].len; k++)
                        printf(", 0x%02x", table[i].sym[k]);
                printf("\n");

                off += table[i].len + 1;
        }
        printf("\n");

        output_label("kallsyms_markers");
        for (i = 0; i < ((table_cnt + 255) >> 8); i++)
                printf("\tPTR\t%d\n", markers[i]);
        printf("\n");

        free(markers);

        output_label("kallsyms_token_table");
        off = 0;
        for (i = 0; i < 256; i++) {
                best_idx[i] = off;
                expand_symbol(best_table[i], best_table_len[i], buf);
                printf("\t.asciz\t\"%s\"\n", buf);
                off += strlen(buf) + 1;
        }
        printf("\n");

        output_label("kallsyms_token_index");
        for (i = 0; i < 256; i++)
                printf("\t.short\t%d\n", best_idx[i]);
        printf("\n");
}


/* table lookup compression functions */

/* count all the possible tokens in a symbol */
static void learn_symbol(unsigned char *symbol, int len)
{
        int i;

        for (i = 0; i < len - 1; i++)
                token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++;
}

/* decrease the count for all the possible tokens in a symbol */
static void forget_symbol(unsigned char *symbol, int len)
{
        int i;

        for (i = 0; i < len - 1; i++)
                token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--;
}

/* remove all the invalid symbols from the table and do the initial token count */
static void build_initial_tok_table(void)
{
        unsigned int i, pos;

        pos = 0;
        for (i = 0; i < table_cnt; i++) {
                if ( symbol_valid(&table[i]) ) {
                        if (pos != i)
                                table[pos] = table[i];
                        learn_symbol(table[pos].sym, table[pos].len);
                        pos++;
                }
        }
        table_cnt = pos;
}

static void *find_token(unsigned char *str, int len, unsigned char *token)
{
        int i;

        for (i = 0; i < len - 1; i++) {
                if (str[i] == token[0] && str[i+1] == token[1])
                        return &str[i];
        }
        return NULL;
}

/* replace a given token in all the valid symbols. Use the sampled symbols
 * to update the counts */
static void compress_symbols(unsigned char *str, int idx)
{
        unsigned int i, len, size;
        unsigned char *p1, *p2;

        for (i = 0; i < table_cnt; i++) {

                len = table[i].len;
                p1 = table[i].sym;

                /* find the token on the symbol */
                p2 = find_token(p1, len, str);
                if (!p2) continue;

                /* decrease the counts for this symbol's tokens */
                forget_symbol(table[i].sym, len);

                size = len;

                do {
                        *p2 = idx;
                        p2++;
                        size -= (p2 - p1);
                        memmove(p2, p2 + 1, size);
                        p1 = p2;
                        len--;

                        if (size < 2) break;

                        /* find the token on the symbol */
                        p2 = find_token(p1, size, str);

                } while (p2);

                table[i].len = len;

                /* increase the counts for this symbol's new tokens */
                learn_symbol(table[i].sym, len);
        }
}

/* search the token with the maximum profit */
static int find_best_token(void)
{
        int i, best, bestprofit;

        bestprofit=-10000;
        best = 0;

        for (i = 0; i < 0x10000; i++) {
                if (token_profit[i] > bestprofit) {
                        best = i;
                        bestprofit = token_profit[i];
                }
        }
        return best;
}

/* this is the core of the algorithm: calculate the "best" table */
static void optimize_result(void)
{
        int i, best;

        /* using the '\0' symbol last allows compress_symbols to use standard
         * fast string functions */
        for (i = 255; i >= 0; i--) {

                /* if this table slot is empty (it is not used by an actual
                 * original char code */
                if (!best_table_len[i]) {

                        /* find the token with the breates profit value */
                        best = find_best_token();
                        if (token_profit[best] == 0)
                                break;

                        /* place it in the "best" table */
                        best_table_len[i] = 2;
                        best_table[i][0] = best & 0xFF;
                        best_table[i][1] = (best >> 8) & 0xFF;

                        /* replace this token in all the valid symbols */
                        compress_symbols(best_table[i], i);
                }
        }
}

/* start by placing the symbols that are actually used on the table */
static void insert_real_symbols_in_table(void)
{
        unsigned int i, j, c;

        memset(best_table, 0, sizeof(best_table));
        memset(best_table_len, 0, sizeof(best_table_len));

        for (i = 0; i < table_cnt; i++) {
                for (j = 0; j < table[i].len; j++) {
                        c = table[i].sym[j];
                        best_table[c][0]=c;
                        best_table_len[c]=1;
                }
        }
}

static void optimize_token_table(void)
{
        build_initial_tok_table();

        insert_real_symbols_in_table();

        /* When valid symbol is not registered, exit to error */
        if (!table_cnt) {
                fprintf(stderr, "No valid symbol.\n");
                exit(1);
        }

        optimize_result();
}

/* guess for "linker script provide" symbol */
static int may_be_linker_script_provide_symbol(const struct sym_entry *se)
{
        const char *symbol = (char *)se->sym + 1;
        int len = se->len - 1;

        if (len < 8)
                return 0;

        if (symbol[0] != '_' || symbol[1] != '_')
                return 0;

        /* __start_XXXXX */
        if (!memcmp(symbol + 2, "start_", 6))
                return 1;

        /* __stop_XXXXX */
        if (!memcmp(symbol + 2, "stop_", 5))
                return 1;

        /* __end_XXXXX */
        if (!memcmp(symbol + 2, "end_", 4))
                return 1;

        /* __XXXXX_start */
        if (!memcmp(symbol + len - 6, "_start", 6))
                return 1;

        /* __XXXXX_end */
        if (!memcmp(symbol + len - 4, "_end", 4))
                return 1;

        return 0;
}

static int prefix_underscores_count(const char *str)
{
        const char *tail = str;

        while (*tail == '_')
                tail++;

        return tail - str;
}

static int compare_symbols(const void *a, const void *b)
{
        const struct sym_entry *sa;
        const struct sym_entry *sb;
        int wa, wb;

        sa = a;
        sb = b;

        /* sort by address first */
        if (sa->addr > sb->addr)
                return 1;
        if (sa->addr < sb->addr)
                return -1;

        /* sort by "weakness" type */
        wa = (sa->sym[0] == 'w') || (sa->sym[0] == 'W');
        wb = (sb->sym[0] == 'w') || (sb->sym[0] == 'W');
        if (wa != wb)
                return wa - wb;

        /* sort by "linker script provide" type */
        wa = may_be_linker_script_provide_symbol(sa);
        wb = may_be_linker_script_provide_symbol(sb);
        if (wa != wb)
                return wa - wb;

        /* sort by the number of prefix underscores */
        wa = prefix_underscores_count((const char *)sa->sym + 1);
        wb = prefix_underscores_count((const char *)sb->sym + 1);
        if (wa != wb)
                return wa - wb;

        /* sort by initial order, so that other symbols are left undisturbed */
        return sa->start_pos - sb->start_pos;
}

static void sort_symbols(void)
{
        qsort(table, table_cnt, sizeof(struct sym_entry), compare_symbols);
}

static void make_percpus_absolute(void)
{
        unsigned int i;

        for (i = 0; i < table_cnt; i++)
                if (symbol_in_range(&table[i], &percpu_range, 1))
                        table[i].sym[0] = 'A';
}

int main(int argc, char **argv)
{
        if (argc >= 2) {
                int i;
                for (i = 1; i < argc; i++) {
                        if(strcmp(argv[i], "--all-symbols") == 0)
                                all_symbols = 1;
                        else if (strcmp(argv[i], "--absolute-percpu") == 0)
                                absolute_percpu = 1;
                        else if (strncmp(argv[i], "--symbol-prefix=", 16) == 0) {
                                char *p = &argv[i][16];
                                /* skip quote */
                                if ((*p == '"' && *(p+2) == '"') || (*p == '\'' && *(p+2) == '\''))
                                        p++;
                                symbol_prefix_char = *p;
                        } else if (strncmp(argv[i], "--page-offset=", 14) == 0) {
                                const char *p = &argv[i][14];
                                kernel_start_addr = strtoull(p, NULL, 16);
                        } else
                                usage();
                }
        } else if (argc != 1)
                usage();

        read_map(stdin);
        if (absolute_percpu)
                make_percpus_absolute();
        sort_symbols();
        optimize_token_table();
        write_src();

        return 0;
}