blob: bd9e9ce20e8b70afb5b3c24cc9352b46508907e3 [file]
/* 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 <getopt.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <limits.h>
#include <sys/stat.h>
#include <xalloc.h>
#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;
}