kallsyms.c

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/* 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 text_range {
    const char *stext, *etext;
    unsigned long long start, end;
};

static unsigned long long _text;
static struct text_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 sym_entry *table;
static unsigned int table_size, table_cnt;
static int all_symbols = 0;
static char symbol_prefix_char = '\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>] < 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("atd", str[1])
           && (str[2] == '\0' || str[2] == '.');
}

static int read_symbol_tr(const char *sym, unsigned long long addr)
{
    size_t i;
    struct text_range *tr;

    for (i = 0; i < ARRAY_SIZE(text_ranges); ++i) {
        tr = &text_ranges[i];

        if (strcmp(sym, tr->stext) == 0) {
            tr->start = addr;
            return 0;
        } else if (strcmp(sym, tr->etext) == 0) {
            tr->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;
    }

    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 (read_symbol_tr(sym, s->addr) == 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;

    return 0;
}

static int symbol_valid_tr(struct sym_entry *s)
{
    size_t i;
    struct text_range *tr;

    for (i = 0; i < ARRAY_SIZE(text_ranges); ++i) {
        tr = &text_ranges[i];

        if (s->addr >= tr->start && s->addr <= tr->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;

    /* 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_valid_tr(s) == 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->etext)) ||
            (s->addr == text_range_inittext->end &&
                strcmp((char *)s->sym + offset, text_range_inittext->etext)))
            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 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 (toupper(table[i].sym[0]) != 'A') {
            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);
}

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 (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
                usage();
        }
    } else if (argc != 1)
        usage();

    read_map(stdin);
    sort_symbols();
    optimize_token_table();
    write_src();

    return 0;
}