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DEFINITIONS
This source file includes following definitions.
- usage
- is_arm_mapping_symbol
- read_symbol
- symbol_valid
- read_map
- output_label
- expand_symbol
- write_src
- learn_symbol
- forget_symbol
- build_initial_tok_table
- find_token
- compress_symbols
- find_best_token
- optimize_result
- insert_real_symbols_in_table
- optimize_token_table
- compare_symbols
- sort_symbols
- main
/* 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>
#define KSYM_NAME_LEN 128
struct sym_entry {
unsigned long long addr;
unsigned int len;
unsigned int start_pos;
unsigned char *sym;
};
static struct sym_entry *table;
static unsigned int table_size, table_cnt;
static unsigned long long _text, _stext, _etext, _sinittext, _einittext;
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(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) {
/* skip line */
fgets(str, 500, in);
}
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 (strcmp(sym, "_stext") == 0)
_stext = s->addr;
else if (strcmp(sym, "_etext") == 0)
_etext = s->addr;
else if (strcmp(sym, "_sinittext") == 0)
_sinittext = s->addr;
else if (strcmp(sym, "_einittext") == 0)
_einittext = s->addr;
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(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 ((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 _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 == _etext &&
strcmp((char *)s->sym + offset, "_etext")) ||
(s->addr == _einittext &&
strcmp((char *)s->sym + offset, "_einittext")))
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();
/* 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();
}
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 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;
}