/* 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: kallsyms [--all-symbols] in.map > out.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 <errno.h>
#include <getopt.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <limits.h>

#include <xalloc.h>

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

#define KSYM_NAME_LEN           512

struct sym_entry {
        unsigned long long addr;
        unsigned int len;
        unsigned int seq;
        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" },
};
#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;
static int pc_relative;

static int token_profit[0x10000];

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


static void usage(void)
{
        fprintf(stderr, "Usage: kallsyms [--all-symbols] in.map > out.S\n");
        exit(1);
}

static char *sym_name(const struct sym_entry *s)
{
        return (char *)s->sym + 1;
}

static bool is_ignored_symbol(const char *name, char type)
{
        if (type == 'u' || type == 'n')
                return true;

        if (toupper(type) == 'A') {
                /* Keep these useful absolute symbols */
                if (strcmp(name, "__kernel_syscall_via_break") &&
                    strcmp(name, "__kernel_syscall_via_epc") &&
                    strcmp(name, "__kernel_sigtramp") &&
                    strcmp(name, "__gp"))
                        return true;
        }

        return false;
}

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

static struct sym_entry *read_symbol(FILE *in, char **buf, size_t *buf_len)
{
        char *name, type, *p;
        unsigned long long addr;
        size_t len;
        ssize_t readlen;
        struct sym_entry *sym;

        errno = 0;
        readlen = getline(buf, buf_len, in);
        if (readlen < 0) {
                if (errno) {
                        perror("read_symbol");
                        exit(EXIT_FAILURE);
                }
                return NULL;
        }

        if ((*buf)[readlen - 1] == '\n')
                (*buf)[readlen - 1] = 0;

        addr = strtoull(*buf, &p, 16);

        if (*buf == p || *p++ != ' ' || !isascii((type = *p++)) || *p++ != ' ') {
                fprintf(stderr, "line format error\n");
                exit(EXIT_FAILURE);
        }

        name = p;
        len = strlen(name);

        if (len >= KSYM_NAME_LEN) {
                fprintf(stderr, "Symbol %s too long for kallsyms (%zu >= %d).\n"
                                "Please increase KSYM_NAME_LEN both in kernel and kallsyms.c\n",
                        name, len, KSYM_NAME_LEN);
                return NULL;
        }

        if (strcmp(name, "_text") == 0)
                _text = addr;

        /* Ignore most absolute/undefined (?) symbols. */
        if (is_ignored_symbol(name, type))
                return NULL;

        check_symbol_range(name, addr, text_ranges, ARRAY_SIZE(text_ranges));

        /* include the type field in the symbol name, so that it gets
         * compressed together */
        len++;

        sym = xmalloc(sizeof(*sym) + len + 1);
        sym->addr = addr;
        sym->len = len;
        sym->sym[0] = type;
        strcpy(sym_name(sym), name);

        return sym;
}

static int symbol_in_range(const struct sym_entry *s,
                           const struct addr_range *ranges, int entries)
{
        size_t i;
        const 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 bool string_starts_with(const char *s, const char *prefix)
{
        return strncmp(s, prefix, strlen(prefix)) == 0;
}

static int symbol_valid(const struct sym_entry *s)
{
        const char *name = sym_name(s);

        /* if --all-symbols is not specified, then symbols outside the text
         * and inittext sections are discarded */
        if (!all_symbols) {
                /*
                 * Symbols starting with __start and __stop are used to denote
                 * section boundaries, and should always be included:
                 */
                if (string_starts_with(name, "__start_") ||
                    string_starts_with(name, "__stop_"))
                        return 1;

                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(name, text_range_text->end_sym)) ||
                    (s->addr == text_range_inittext->end &&
                     strcmp(name, text_range_inittext->end_sym)))
                        return 0;
        }

        return 1;
}

/* remove all the invalid symbols from the table */
static void shrink_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];
                        pos++;
                } else {
                        free(table[i]);
                }
        }
        table_cnt = pos;
}

static void read_map(const char *in)
{
        FILE *fp;
        struct sym_entry *sym;
        char *buf = NULL;
        size_t buflen = 0;

        fp = fopen(in, "r");
        if (!fp) {
                perror(in);
                exit(1);
        }

        while (!feof(fp)) {
                sym = read_symbol(fp, &buf, &buflen);
                if (!sym)
                        continue;

                sym->seq = table_cnt;

                if (table_cnt >= table_size) {
                        table_size += 10000;
                        table = xrealloc(table, sizeof(*table) * table_size);
                }

                table[table_cnt++] = sym;
        }

        free(buf);
        fclose(fp);
}

static void output_label(const char *label)
{
        printf(".globl %s\n", label);
        printf("\t.balign 4\n");
        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(const 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 compare_names(const void *a, const void *b)
{
        int ret;
        const struct sym_entry *sa = *(const struct sym_entry **)a;
        const struct sym_entry *sb = *(const struct sym_entry **)b;

        ret = strcmp(sym_name(sa), sym_name(sb));
        if (!ret) {
                if (sa->addr > sb->addr)
                        return 1;
                else if (sa->addr < sb->addr)
                        return -1;

                /* keep old order */
                return (int)(sa->seq - sb->seq);
        }

        return ret;
}

static void sort_symbols_by_name(void)
{
        qsort(table, table_cnt, sizeof(table[0]), compare_names);
}

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

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

        output_label("kallsyms_num_syms");
        printf("\t.long\t%u\n", table_cnt);
        printf("\n");

        /* table of offset markers, that give the offset in the compressed stream
         * every 256 symbols */
        markers_cnt = (table_cnt + 255) / 256;
        markers = xmalloc(sizeof(*markers) * markers_cnt);

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

                /* There cannot be any symbol of length zero. */
                if (table[i]->len == 0) {
                        fprintf(stderr, "kallsyms failure: "
                                "unexpected zero symbol length\n");
                        exit(EXIT_FAILURE);
                }

                /* Only lengths that fit in up-to-two-byte ULEB128 are supported. */
                if (table[i]->len > 0x3FFF) {
                        fprintf(stderr, "kallsyms failure: "
                                "unexpected huge symbol length\n");
                        exit(EXIT_FAILURE);
                }

                /* Encode length with ULEB128. */
                if (table[i]->len <= 0x7F) {
                        /* Most symbols use a single byte for the length. */
                        printf("\t.byte 0x%02x", table[i]->len);
                        off += table[i]->len + 1;
                } else {
                        /* "Big" symbols use two bytes. */
                        printf("\t.byte 0x%02x, 0x%02x",
                                (table[i]->len & 0x7F) | 0x80,
                                (table[i]->len >> 7) & 0x7F);
                        off += table[i]->len + 2;
                }
                for (k = 0; k < table[i]->len; k++)
                        printf(", 0x%02x", table[i]->sym[k]);

                /*
                 * Now that we wrote out the compressed symbol name, restore the
                 * original name and print it in the comment.
                 */
                expand_symbol(table[i]->sym, table[i]->len, buf);
                strcpy((char *)table[i]->sym, buf);
                printf("\t/* %s */\n", table[i]->sym);
        }
        printf("\n");

        output_label("kallsyms_markers");
        for (i = 0; i < markers_cnt; i++)
                printf("\t.long\t%u\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");

        output_label("kallsyms_offsets");

        for (i = 0; i < table_cnt; i++) {
                if (pc_relative) {
                        long long offset = table[i]->addr - _text;

                        if (offset < INT_MIN || offset > INT_MAX) {
                                fprintf(stderr, "kallsyms failure: "
                                        "relative symbol value %#llx out of range\n",
                                        table[i]->addr);
                                exit(EXIT_FAILURE);
                        }
                        printf("\t.long\t_text - . + (%d)\t/* %s */\n",
                               (int)offset, table[i]->sym);
                } else {
                        printf("\t.long\t%#x\t/* %s */\n",
                               (unsigned int)table[i]->addr, table[i]->sym);
                }
        }
        printf("\n");

        sort_symbols_by_name();
        output_label("kallsyms_seqs_of_names");
        for (i = 0; i < table_cnt; i++)
                printf("\t.byte 0x%02x, 0x%02x, 0x%02x\t/* %s */\n",
                        (unsigned char)(table[i]->seq >> 16),
                        (unsigned char)(table[i]->seq >> 8),
                        (unsigned char)(table[i]->seq >> 0),
                       table[i]->sym);
        printf("\n");
}


/* table lookup compression functions */

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

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

/* do the initial token count */
static void build_initial_token_table(void)
{
        unsigned int i;

        for (i = 0; i < table_cnt; i++)
                learn_symbol(table[i]->sym, table[i]->len);
}

static unsigned char *find_token(unsigned char *str, int len,
                                 const 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(const 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 best 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;

        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_token_table();

        insert_real_symbols_in_table();

        optimize_result();
}

/* guess for "linker script provide" symbol */
static int may_be_linker_script_provide_symbol(const struct sym_entry *se)
{
        const char *symbol = sym_name(se);
        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 compare_symbols(const void *a, const void *b)
{
        const struct sym_entry *sa = *(const struct sym_entry **)a;
        const struct sym_entry *sb = *(const struct sym_entry **)b;
        int wa, wb;

        /* 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 = strspn(sym_name(sa), "_");
        wb = strspn(sym_name(sb), "_");
        if (wa != wb)
                return wa - wb;

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

static void sort_symbols(void)
{
        qsort(table, table_cnt, sizeof(table[0]), compare_symbols);
}

int main(int argc, char **argv)
{
        while (1) {
                static const struct option long_options[] = {
                        {"all-symbols",     no_argument, &all_symbols,     1},
                        {"pc-relative",     no_argument, &pc_relative,     1},
                        {},
                };

                int c = getopt_long(argc, argv, "", long_options, NULL);

                if (c == -1)
                        break;
                if (c != 0)
                        usage();
        }

        if (optind >= argc)
                usage();

        read_map(argv[optind]);
        shrink_table();
        sort_symbols();
        optimize_token_table();
        write_src();

        return 0;
}