/* 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
*
* ChangeLog:
*
* (25/Aug/2004) Paulo Marques <pmarques@grupopie.com>
* Changed the compression method from stem compression to "table lookup"
* compression
*
* 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>
/* maximum token length used. It doesn't pay to increase it a lot, because
* very long substrings probably don't repeat themselves too often. */
#define MAX_TOK_SIZE 11
#define KSYM_NAME_LEN 127
/* we use only a subset of the complete symbol table to gather the token count,
* to speed up compression, at the expense of a little compression ratio */
#define WORKING_SET 1024
/* first find the best token only on the list of tokens that would profit more
* than GOOD_BAD_THRESHOLD. Only if this list is empty go to the "bad" list.
* Increasing this value will put less tokens on the "good" list, so the search
* is faster. However, if the good list runs out of tokens, we must painfully
* search the bad list. */
#define GOOD_BAD_THRESHOLD 10
/* token hash parameters */
#define HASH_BITS 18
#define HASH_TABLE_SIZE (1 << HASH_BITS)
#define HASH_MASK (HASH_TABLE_SIZE - 1)
#define HASH_BASE_OFFSET 2166136261U
#define HASH_FOLD(a) ((a)&(HASH_MASK))
/* flags to mark symbols */
#define SYM_FLAG_VALID 1
#define SYM_FLAG_SAMPLED 2
struct sym_entry {
unsigned long long addr;
char type;
unsigned char flags;
unsigned char len;
unsigned char *sym;
};
static struct sym_entry *table;
static int size, cnt;
static unsigned long long _stext, _etext, _sinittext, _einittext;
static int all_symbols = 0;
struct token {
unsigned char data[MAX_TOK_SIZE];
unsigned char len;
/* profit: the number of bytes that could be saved by inserting this
* token into the table */
int profit;
struct token *next; /* next token on the hash list */
struct token *right; /* next token on the good/bad list */
struct token *left; /* previous token on the good/bad list */
struct token *smaller; /* token that is less one letter than this one */
};
struct token bad_head, good_head;
struct token *hash_table[HASH_TABLE_SIZE];
/* the table that holds the result of the compression */
unsigned char best_table[256][MAX_TOK_SIZE+1];
unsigned char best_table_len[256];
static void
usage(void)
{
fprintf(stderr, "Usage: kallsyms [--all-symbols] < 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(FILE *in, struct sym_entry *s)
{
char str[500];
int rc;
rc = fscanf(in, "%llx %c %499s\n", &s->addr, &s->type, str);
if (rc != 3) {
if (rc != EOF) {
/* skip line */
fgets(str, 500, in);
}
return -1;
}
/* Ignore most absolute/undefined (?) symbols. */
if (strcmp(str, "_stext") == 0)
_stext = s->addr;
else if (strcmp(str, "_etext") == 0)
_etext = s->addr;
else if (strcmp(str, "_sinittext") == 0)
_sinittext = s->addr;
else if (strcmp(str, "_einittext") == 0)
_einittext = s->addr;
else if (toupper(s->type) == 'A')
{
/* Keep these useful absolute symbols */
if (strcmp(str, "__kernel_syscall_via_break") &&
strcmp(str, "__kernel_syscall_via_epc") &&
strcmp(str, "__kernel_sigtramp") &&
strcmp(str, "__gp"))
return -1;
}
else if (toupper(s->type) == 'U' ||
is_arm_mapping_symbol(str))
return -1;
/* include the type field in the symbol name, so that it gets
* compressed together */
s->len = strlen(str) + 1;
s->sym = (char *) malloc(s->len + 1);
strcpy(s->sym + 1, str);
s->sym[0] = s->type;
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;
/* if --all-symbols is not specified, then symbols outside the text
* and inittext sections are discarded */
if (!all_symbols) {
if ((s->addr < _stext || s->addr > _etext)
&& (s->addr < _sinittext || s->addr > _einittext))
return 0;
/* Corner case. Discard any symbols with the same value as
* _etext or _einittext, they can move between pass 1 and 2
* when the kallsyms data is added. If these symbols move then
* they may get dropped in pass 2, which breaks the kallsyms
* rules.
*/
if ((s->addr == _etext && strcmp(s->sym + 1, "_etext")) ||
(s->addr == _einittext && strcmp(s->sym + 1, "_einittext")))
return 0;
}
/* Exclude symbols which vary between passes. */
if (strstr(s->sym + 1, "_compiled."))
return 0;
for (i = 0; special_symbols[i]; i++)
if( strcmp(s->sym + 1, special_symbols[i]) == 0 )
return 0;
return 1;
}
static void
read_map(FILE *in)
{
while (!feof(in)) {
if (cnt >= size) {
size += 10000;
table = realloc(table, sizeof(*table) * size);
if (!table) {
fprintf(stderr, "out of memory\n");
exit (1);
}
}
if (read_symbol(in, &table[cnt]) == 0)
cnt++;
}
}
static void output_label(char *label)
{
printf(".globl %s\n",label);
printf("\tALGN\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(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)
{
int i, k, off, valid;
unsigned int best_idx[256];
unsigned int *markers;
char buf[KSYM_NAME_LEN+1];
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(".data\n");
output_label("kallsyms_addresses");
valid = 0;
for (i = 0; i < cnt; i++) {
if (table[i].flags & SYM_FLAG_VALID) {
printf("\tPTR\t%#llx\n", table[i].addr);
valid++;
}
}
printf("\n");
output_label("kallsyms_num_syms");
printf("\tPTR\t%d\n", valid);
printf("\n");
/* table of offset markers, that give the offset in the compressed stream
* every 256 symbols */
markers = (unsigned int *) malloc(sizeof(unsigned int)*((valid + 255) / 256));
output_label("kallsyms_names");
valid = 0;
off = 0;
for (i = 0; i < cnt; i++) {
if (!table[i].flags & SYM_FLAG_VALID)
continue;
if ((valid & 0xFF) == 0)
markers[valid >> 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;
valid++;
}
printf("\n");
output_label("kallsyms_markers");
for (i = 0; i < ((valid + 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 */
static inline unsigned int rehash_token(unsigned int hash, unsigned char data)
{
return ((hash * 16777619) ^ data);
}
static unsigned int hash_token(unsigned char *data, int len)
{
unsigned int hash=HASH_BASE_OFFSET;
int i;
for (i = 0; i < len; i++)
hash = rehash_token(hash, data[i]);
return HASH_FOLD(hash);
}
/* find a token given its data and hash value */
static struct token *find_token_hash(unsigned char *data, int len, unsigned int hash)
{
struct token *ptr;
ptr = hash_table[hash];
while (ptr) {
if ((ptr->len == len) && (memcmp(ptr->data, data, len) == 0))
return ptr;
ptr=ptr->next;
}
return NULL;
}
static inline void insert_token_in_group(struct token *head, struct token *ptr)
{
ptr->right = head->right;
ptr->right->left = ptr;
head->right = ptr;
ptr->left = head;
}
static inline void remove_token_from_group(struct token *ptr)
{
ptr->left->right = ptr->right;
ptr->right->left = ptr->left;
}
/* build the counts for all the tokens that start with "data", and have lenghts
* from 2 to "len" */
static void learn_token(unsigned char *data, int len)
{
struct token *ptr,*last_ptr;
int i, newprofit;
unsigned int hash = HASH_BASE_OFFSET;
unsigned int hashes[MAX_TOK_SIZE + 1];
if (len > MAX_TOK_SIZE)
len = MAX_TOK_SIZE;
/* calculate and store the hash values for all the sub-tokens */
hash = rehash_token(hash, data[0]);
for (i = 2; i <= len; i++) {
hash = rehash_token(hash, data[i-1]);
hashes[i] = HASH_FOLD(hash);
}
last_ptr = NULL;
ptr = NULL;
for (i = len; i >= 2; i--) {
hash = hashes[i];
if (!ptr) ptr = find_token_hash(data, i, hash);
if (!ptr) {
/* create a new token entry */
ptr = (struct token *) malloc(sizeof(*ptr));
memcpy(ptr->data, data, i);
ptr->len = i;
/* when we create an entry, it's profit is 0 because
* we also take into account the size of the token on
* the compressed table. We then subtract GOOD_BAD_THRESHOLD
* so that the test to see if this token belongs to
* the good or bad list, is a comparison to zero */
ptr->profit = -GOOD_BAD_THRESHOLD;
ptr->next = hash_table[hash];
hash_table[hash] = ptr;
insert_token_in_group(&bad_head, ptr);
ptr->smaller = NULL;
} else {
newprofit = ptr->profit + (ptr->len - 1);
/* check to see if this token needs to be moved to a
* different list */
if((ptr->profit < 0) && (newprofit >= 0)) {
remove_token_from_group(ptr);
insert_token_in_group(&good_head,ptr);
}
ptr->profit = newprofit;
}
if (last_ptr) last_ptr->smaller = ptr;
last_ptr = ptr;
ptr = ptr->smaller;
}
}
/* decrease the counts for all the tokens that start with "data", and have lenghts
* from 2 to "len". This function is much simpler than learn_token because we have
* more guarantees (tho tokens exist, the ->smaller pointer is set, etc.)
* The two separate functions exist only because of compression performance */
static void forget_token(unsigned char *data, int len)
{
struct token *ptr;
int i, newprofit;
unsigned int hash=0;
if (len > MAX_TOK_SIZE) len = MAX_TOK_SIZE;
hash = hash_token(data, len);
ptr = find_token_hash(data, len, hash);
for (i = len; i >= 2; i--) {
newprofit = ptr->profit - (ptr->len - 1);
if ((ptr->profit >= 0) && (newprofit < 0)) {
remove_token_from_group(ptr);
insert_token_in_group(&bad_head, ptr);
}
ptr->profit=newprofit;
ptr=ptr->smaller;
}
}
/* 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++)
learn_token(symbol + i, len - i);
}
/* 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++)
forget_token(symbol + i, len - i);
}
/* set all the symbol flags and do the initial token count */
static void build_initial_tok_table(void)
{
int i, use_it, valid;
valid = 0;
for (i = 0; i < cnt; i++) {
table[i].flags = 0;
if ( symbol_valid(&table[i]) ) {
table[i].flags |= SYM_FLAG_VALID;
valid++;
}
}
use_it = 0;
for (i = 0; i < cnt; i++) {
/* subsample the available symbols. This method is almost like
* a Bresenham's algorithm to get uniformly distributed samples
* across the symbol table */
if (table[i].flags & SYM_FLAG_VALID) {
use_it += WORKING_SET;
if (use_it >= valid) {
table[i].flags |= SYM_FLAG_SAMPLED;
use_it -= valid;
}
}
if (table[i].flags & SYM_FLAG_SAMPLED)
learn_symbol(table[i].sym, table[i].len);
}
}
/* 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 tlen, int idx)
{
int i, len, learn, size;
unsigned char *p;
for (i = 0; i < cnt; i++) {
if (!(table[i].flags & SYM_FLAG_VALID)) continue;
len = table[i].len;
learn = 0;
p = table[i].sym;
do {
/* find the token on the symbol */
p = (unsigned char *) strstr((char *) p, (char *) str);
if (!p) break;
if (!learn) {
/* if this symbol was used to count, decrease it */
if (table[i].flags & SYM_FLAG_SAMPLED)
forget_symbol(table[i].sym, len);
learn = 1;
}
*p = idx;
size = (len - (p - table[i].sym)) - tlen + 1;
memmove(p + 1, p + tlen, size);
p++;
len -= tlen - 1;
} while (size >= tlen);
if(learn) {
table[i].len = len;
/* if this symbol was used to count, learn it again */
if(table[i].flags & SYM_FLAG_SAMPLED)
learn_symbol(table[i].sym, len);
}
}
}
/* search the token with the maximum profit */
static struct token *find_best_token(void)
{
struct token *ptr,*best,*head;
int bestprofit;
bestprofit=-10000;
/* failsafe: if the "good" list is empty search from the "bad" list */
if(good_head.right == &good_head) head = &bad_head;
else head = &good_head;
ptr = head->right;
best = NULL;
while (ptr != head) {
if (ptr->profit > bestprofit) {
bestprofit = ptr->profit;
best = ptr;
}
ptr = ptr->right;
}
return best;
}
/* this is the core of the algorithm: calculate the "best" table */
static void optimize_result(void)
{
struct token *best;
int i;
/* 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();
/* place it in the "best" table */
best_table_len[i] = best->len;
memcpy(best_table[i], best->data, best_table_len[i]);
/* zero terminate the token so that we can use strstr
in compress_symbols */
best_table[i][best_table_len[i]]='\0';
/* replace this token in all the valid symbols */
compress_symbols(best_table[i], best_table_len[i], i);
}
}
}
/* start by placing the symbols that are actually used on the table */
static void insert_real_symbols_in_table(void)
{
int i, j, c;
memset(best_table, 0, sizeof(best_table));
memset(best_table_len, 0, sizeof(best_table_len));
for (i = 0; i < cnt; i++) {
if (table[i].flags & SYM_FLAG_VALID) {
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)
{
memset(hash_table, 0, sizeof(hash_table));
good_head.left = &good_head;
good_head.right = &good_head;
bad_head.left = &bad_head;
bad_head.right = &bad_head;
build_initial_tok_table();
insert_real_symbols_in_table();
optimize_result();
}
int
main(int argc, char **argv)
{
if (argc == 2 && strcmp(argv[1], "--all-symbols") == 0)
all_symbols = 1;
else if (argc != 1)
usage();
read_map(stdin);
optimize_token_table();
write_src();
return 0;
}
