/* 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] [--pc-relative] [--sysmap=out.map] in out.bin > out.S * kallsyms --sysmap=out.map in * * in is vmlinux; an empty file stands for the first link, which has no * symbols yet, and gives an empty table. --sysmap also writes the symbols * in System.map format. * * The byte tables go to out.bin and are pulled into out.S with .incbin; * wider tables stay assembler source for endianness and relocations. * * 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 #include #include #include #include #include #include #include #include #include "../kernel/kallsyms_internal.h" #include "kallsyms.h" #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; /* A dynamic array of symbols, encoded by symbol index. */ struct sym_arr { unsigned int *sym_indexes; unsigned int cnt, cap; }; /* Every pair of bytes is a token. */ #define NR_TOKENS 0x10000 static int token_profit[NR_TOKENS]; static struct sym_arr token_syms[NR_TOKENS]; /* the table that holds the result of the compression */ static unsigned char best_table[256][2]; static unsigned char best_table_len[256]; static unsigned int sym_arr_last(const struct sym_arr *arr) { return arr->cnt ? arr->sym_indexes[arr->cnt - 1] : UINT_MAX; } static void sym_arr_maybe_expand(struct sym_arr *arr) { if (arr->cap > arr->cnt) return; arr->cap = arr->cap ? arr->cap * 2 : 16; arr->sym_indexes = xrealloc(arr->sym_indexes, arr->cap * sizeof(*arr->sym_indexes)); } static void sym_arr_add(struct sym_arr *arr, unsigned int sym_idx) { sym_arr_maybe_expand(arr); arr->sym_indexes[arr->cnt++] = sym_idx; } static void sym_arr_free(struct sym_arr *arr) { free(arr->sym_indexes); arr->sym_indexes = NULL; arr->cnt = 0; arr->cap = 0; } static void usage(void) { fprintf(stderr, "Usage: kallsyms [--all-symbols] [--pc-relative] [--sysmap=out.map]\n" " in out.bin > out.S\n" " kallsyms --sysmap=out.map vmlinux\n"); exit(1); } static char *sym_entry_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 *add_symbol(unsigned long long addr, char type, const char *name) { size_t len = strlen(name); struct sym_entry *sym; 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_entry_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 int symbol_valid(const struct sym_entry *s) { const char *name = sym_entry_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 add_table_entry(struct sym_entry *sym) { sym->seq = table_cnt; if (table_cnt >= table_size) { table_size = table_size ? table_size * 2 : 10000; table = xrealloc(table, sizeof(*table) * table_size); } table[table_cnt++] = sym; } static bool file_is_empty(const char *path) { struct stat st; if (stat(path, &st)) { perror(path); exit(EXIT_FAILURE); } return st.st_size == 0; } /* * Read the symbols from vmlinux, writing System.map if asked to. The first * link has no symbols yet: an empty file gives an empty table. */ static void read_elf(const char *path, FILE *sysmap_out) { struct sysmap *map; size_t i; if (file_is_empty(path)) return; map = sysmap_read(path); if (sysmap_out) sysmap_write(map, sysmap_out); for (i = 0; i < map->nr_syms; i++) { const struct sysmap_symbol *s = &map->syms[i]; struct sym_entry *sym = add_symbol(s->addr, s->type, s->name); if (sym) add_table_entry(sym); } sysmap_free(map); } static void output_label(const char *label) { printf(".globl %s\n", label); printf("\t.balign 4\n"); printf("%s:\n", label); } static long bin_pos(FILE *file) { const long pos = ftell(file); if (pos < 0) { perror("kallsyms: ftell"); exit(EXIT_FAILURE); } return pos; } static void write_incbin(const char *filename, long start, long end) { if (start >= end) return; printf("\t.incbin \"%s\", %ld, %ld\n", filename, start, end - start); } /* 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_entry_name(sa), sym_entry_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(FILE *out_bin_file, const char *out_bin_name) { unsigned int i, off; unsigned int best_idx[256]; unsigned int *markers, markers_cnt; long bin_start; 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, giving the offset in the compressed stream * every (1 << KALLSYMS_MARKER_SHIFT) symbols. */ markers_cnt = (table_cnt + KALLSYMS_MARKER_MASK) >> KALLSYMS_MARKER_SHIFT; markers = xmalloc(sizeof(*markers) * markers_cnt); output_label("kallsyms_names"); bin_start = bin_pos(out_bin_file); off = 0; for (i = 0; i < table_cnt; i++) { if ((i & KALLSYMS_MARKER_MASK) == 0) markers[i >> KALLSYMS_MARKER_SHIFT] = 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. */ fputc(table[i]->len, out_bin_file); off += table[i]->len + 1; } else { /* "Big" symbols use two bytes. */ fputc((table[i]->len & 0x7F) | 0x80, out_bin_file); fputc((table[i]->len >> 7) & 0x7F, out_bin_file); off += table[i]->len + 2; } fwrite(table[i]->sym, 1, table[i]->len, out_bin_file); /* * Now that we wrote out the compressed symbol name, restore the * original name for the comments below. */ expand_symbol(table[i]->sym, table[i]->len, buf); strcpy((char *)table[i]->sym, buf); } write_incbin(out_bin_name, bin_start, bin_pos(out_bin_file)); printf(".size kallsyms_names, . - kallsyms_names\n"); printf("\n"); output_label("kallsyms_markers"); for (i = 0; i < markers_cnt; i++) printf("\t.long\t%u\n", markers[i]); printf(".size kallsyms_markers, . - kallsyms_markers\n"); printf("\n"); free(markers); output_label("kallsyms_token_table"); bin_start = bin_pos(out_bin_file); off = 0; for (i = 0; i < 256; i++) { best_idx[i] = off; expand_symbol(best_table[i], best_table_len[i], buf); fwrite(buf, 1, strlen(buf) + 1, out_bin_file); off += strlen(buf) + 1; } write_incbin(out_bin_name, bin_start, bin_pos(out_bin_file)); printf(".size kallsyms_token_table, . - kallsyms_token_table\n"); 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(".size kallsyms_offsets, . - kallsyms_offsets\n"); printf("\n"); sort_symbols_by_name(); output_label("kallsyms_seqs_of_names"); bin_start = bin_pos(out_bin_file); for (i = 0; i < table_cnt; i++) { fputc(table[i]->seq >> 16, out_bin_file); fputc(table[i]->seq >> 8, out_bin_file); fputc(table[i]->seq >> 0, out_bin_file); } write_incbin(out_bin_name, bin_start, bin_pos(out_bin_file)); printf("\n"); } static unsigned int token_index(unsigned char first, unsigned char second) { return first + (second << 8); } static unsigned int sym_token_index(const unsigned char *symbol, int first_idx) { return token_index(symbol[first_idx], symbol[first_idx + 1]); } /* 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[sym_token_index(symbol, i)]++; } /* 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[sym_token_index(symbol, i)]--; } static void token_add_symbol(unsigned int token_idx, unsigned int sym_idx) { struct sym_arr *arr = &token_syms[token_idx]; /* Symbol indexes kept in sorted order, check for duplicate. */ if (sym_arr_last(arr) == sym_idx) return; sym_arr_add(arr, sym_idx); } static void symbol_index_all_tokens(const unsigned char *symbol, int len, unsigned int sym_idx) { int i; for (i = 0; i < len - 1; i++) { const unsigned int token_idx = sym_token_index(symbol, i); token_add_symbol(token_idx, sym_idx); } } /* * The symbol just got compressed. The only parts of the symbol that changed * meaningfully are those containing the newly assigned compressed char, so * index those. */ static void symbol_index_new_tokens(const unsigned char *symbol, int len, unsigned int sym_idx, int compressed_chr) { int i; for (i = 0; i < len - 1; i++) { const unsigned int token_idx = sym_token_index(symbol, i); if (symbol[i] == compressed_chr || symbol[i + 1] == compressed_chr) token_add_symbol(token_idx, sym_idx); } } 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); /* * The initial occurrence counts tell us exactly how much memory should * be reserved for each token's symbol array. */ for (i = 0; i < ARRAY_SIZE(token_syms); i++) { const int nr_syms = token_profit[i]; if (!nr_syms) continue; token_syms[i].cap = nr_syms; token_syms[i].sym_indexes = xmalloc(nr_syms * sizeof(unsigned int)); } /* For every symbol, index every token -> symbol it is present in. */ for (i = 0; i < table_cnt; i++) symbol_index_all_tokens(table[i]->sym, table[i]->len, i); } 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 compressed_chr) { const unsigned int token_idx = sym_token_index(str, 0); struct sym_arr *arr = &token_syms[token_idx]; unsigned int sym_idx, j, len, size; unsigned char *p1, *p2; /* Iterate through all symbols this token is found in and compress. */ for (j = 0; j < arr->cnt; j++) { sym_idx = arr->sym_indexes[j]; len = table[sym_idx]->len; p1 = table[sym_idx]->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[sym_idx]->sym, len); size = len; do { *p2 = compressed_chr; 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[sym_idx]->len = len; /* increase the counts for this symbol's new tokens */ learn_symbol(table[sym_idx]->sym, len); symbol_index_new_tokens(table[sym_idx]->sym, len, sym_idx, compressed_chr); } sym_arr_free(arr); /* No symbol contains this token any more. */ } /* 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 < ARRAY_SIZE(token_profit); 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_entry_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_entry_name(sa), "_"); wb = strspn(sym_entry_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) { const char *in, *sysmap = NULL, *out_bin_name; FILE *sysmap_out = NULL, *out_bin_file; while (1) { static const struct option long_options[] = { {"all-symbols", no_argument, &all_symbols, 1}, {"pc-relative", no_argument, &pc_relative, 1}, {"sysmap", required_argument, NULL, 's'}, {}, }; int c = getopt_long(argc, argv, "", long_options, NULL); if (c == -1) break; if (c == 's') sysmap = optarg; else if (c != 0) usage(); } if (optind + 2 != argc && !(sysmap && optind + 1 == argc)) usage(); in = argv[optind]; if (sysmap) { sysmap_out = fopen(sysmap, "w"); if (!sysmap_out) { perror(sysmap); exit(EXIT_FAILURE); } } if (optind + 1 == argc) { read_elf(in, sysmap_out); if (ferror(sysmap_out) || fclose(sysmap_out)) { perror(sysmap); exit(EXIT_FAILURE); } return 0; } out_bin_name = argv[optind + 1]; out_bin_file = fopen(out_bin_name, "w"); if (!out_bin_file) { perror(out_bin_name); exit(EXIT_FAILURE); } read_elf(in, sysmap_out); if (sysmap_out && (ferror(sysmap_out) || fclose(sysmap_out))) { perror(sysmap); exit(EXIT_FAILURE); } shrink_table(); sort_symbols(); optimize_token_table(); write_src(out_bin_file, out_bin_name); /* Write errors are latched in the stream, so one check at the end covers them all. */ if (ferror(out_bin_file) || fclose(out_bin_file)) { perror(out_bin_name); exit(EXIT_FAILURE); } return 0; }