[PATCH] kallsyms: change compression algorithm

This patch changes the way the compression algorithm works.  The base
algorithm is similiar to the previous but we force the compressed token
size to 2.

Having a fixed size compressed token allows for a lot of optimizations, and
that in turn allows this code to run over *all* the symbols faster than it
did before over just a subset.

Having it work over all the symbols will make it behave better when symbols
change positions between passes, and the "inconsistent kallsyms" messages
should become less frequent.

In my tests the compression ratio was degraded by about 0.5%, but the
results will depend greatly on the number of symbols to compress.
Signed-off-by: Paulo Marques <pmarques@grupopie.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

scripts/kallsyms.c

@@ -24,75 +24,37 @@
  *
  */
 
+#define _GNU_SOURCE
+
 #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 int len;
 	unsigned char *sym;
 };
 
 
 static struct sym_entry *table;
-static int size, cnt;
+static unsigned int table_size, table_cnt;
 static unsigned long long _stext, _etext, _sinittext, _einittext, _sextratext, _eextratext;
 static int all_symbols = 0;
 static char symbol_prefix_char = '\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];
+int token_profit[0x10000];
 
 /* the table that holds the result of the compression */
-unsigned char best_table[256][MAX_TOK_SIZE+1];
+unsigned char best_table[256][2];
 unsigned char best_table_len[256];
 
 
-static void
-usage(void)
+static void usage(void)
 {
 	fprintf(stderr, "Usage: kallsyms [--all-symbols] [--symbol-prefix=<prefix char>] < in.map > out.S\n");
 	exit(1);
@@ -102,21 +64,19 @@ usage(void)
  * This ignores the intensely annoying "mapping symbols" found
  * in ARM ELF files: $a, $t and $d.
  */
-static inline int
-is_arm_mapping_symbol(const char *str)
+static inline int is_arm_mapping_symbol(const char *str)
 {
 	return str[0] == '$' && strchr("atd", str[1])
 	       && (str[2] == '\0' || str[2] == '.');
 }
 
-static int
-read_symbol(FILE *in, struct sym_entry *s)
+static int read_symbol(FILE *in, struct sym_entry *s)
 {
 	char str[500];
-	char *sym;
+	char *sym, stype;
 	int rc;
 
-	rc = fscanf(in, "%llx %c %499s\n", &s->addr, &s->type, str);
+	rc = fscanf(in, "%llx %c %499s\n", &s->addr, &stype, str);
 	if (rc != 3) {
 		if (rc != EOF) {
 			/* skip line */
@@ -143,7 +103,7 @@ read_symbol(FILE *in, struct sym_entry *s)
 		_sextratext = s->addr;
 	else if (strcmp(sym, "_eextratext") == 0)
 		_eextratext = s->addr;
-	else if (toupper(s->type) == 'A')
+	else if (toupper(stype) == 'A')
 	{
 		/* Keep these useful absolute symbols */
 		if (strcmp(sym, "__kernel_syscall_via_break") &&
@@ -153,22 +113,21 @@ read_symbol(FILE *in, struct sym_entry *s)
 			return -1;
 
 	}
-	else if (toupper(s->type) == 'U' ||
+	else if (toupper(stype) == 'U' ||
 		 is_arm_mapping_symbol(sym))
 		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;
+	s->sym = malloc(s->len + 1);
+	strcpy((char *)s->sym + 1, str);
+	s->sym[0] = stype;
 
 	return 0;
 }
 
-static int
-symbol_valid(struct sym_entry *s)
+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
@@ -214,30 +173,29 @@ symbol_valid(struct sym_entry *s)
 	}
 
 	/* Exclude symbols which vary between passes. */
-	if (strstr(s->sym + offset, "_compiled."))
+	if (strstr((char *)s->sym + offset, "_compiled."))
 		return 0;
 
 	for (i = 0; special_symbols[i]; i++)
-		if( strcmp(s->sym + offset, special_symbols[i]) == 0 )
+		if( strcmp((char *)s->sym + offset, special_symbols[i]) == 0 )
 			return 0;
 
 	return 1;
 }
 
-static void
-read_map(FILE *in)
+static void read_map(FILE *in)
 {
 	while (!feof(in)) {
-		if (cnt >= size) {
-			size += 10000;
-			table = realloc(table, sizeof(*table) * size);
+		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[cnt]) == 0)
-			cnt++;
+		if (read_symbol(in, &table[table_cnt]) == 0)
+			table_cnt++;
 	}
 }
 
@@ -281,10 +239,9 @@ static int expand_symbol(unsigned char *data, int len, char *result)
 	return total;
 }
 
-static void
-write_src(void)
+static void write_src(void)
 {
-	int i, k, off, valid;
+	unsigned int i, k, off;
 	unsigned int best_idx[256];
 	unsigned int *markers;
 	char buf[KSYM_NAME_LEN+1];
@@ -301,33 +258,24 @@ write_src(void)
 	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++;
-		}
+	for (i = 0; i < table_cnt; i++) {
+		printf("\tPTR\t%#llx\n", table[i].addr);
 	}
 	printf("\n");
 
 	output_label("kallsyms_num_syms");
-	printf("\tPTR\t%d\n", valid);
+	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 = (unsigned int *) malloc(sizeof(unsigned int)*((valid + 255) / 256));
+	markers = (unsigned int *) malloc(sizeof(unsigned int) * ((table_cnt + 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;
+	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++)
@@ -335,12 +283,11 @@ write_src(void)
 		printf("\n");
 
 		off += table[i].len + 1;
-		valid++;
 	}
 	printf("\n");
 
 	output_label("kallsyms_markers");
-	for (i = 0; i < ((valid + 255) >> 8); i++)
+	for (i = 0; i < ((table_cnt + 255) >> 8); i++)
 		printf("\tPTR\t%d\n", markers[i]);
 	printf("\n");
 
@@ -350,7 +297,7 @@ write_src(void)
 	off = 0;
 	for (i = 0; i < 256; i++) {
 		best_idx[i] = off;
-		expand_symbol(best_table[i],best_table_len[i],buf);
+		expand_symbol(best_table[i], best_table_len[i], buf);
 		printf("\t.asciz\t\"%s\"\n", buf);
 		off += strlen(buf) + 1;
 	}
@@ -365,153 +312,13 @@ write_src(void)
 
 /* 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);
+		token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++;
 }
 
 /* decrease the count for all the possible tokens in a symbol */
@@ -520,117 +327,90 @@ static void forget_symbol(unsigned char *symbol, int len)
 	int i;
 
 	for (i = 0; i < len - 1; i++)
-		forget_token(symbol + i, len - i);
+		token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--;
 }
 
-/* set all the symbol flags and do the initial token count */
+/* remove all the invalid symbols from the table and do the initial token count */
 static void build_initial_tok_table(void)
 {
-	int i, use_it, valid;
+	unsigned int i, pos;
 
-	valid = 0;
-	for (i = 0; i < cnt; i++) {
-		table[i].flags = 0;
+	pos = 0;
+	for (i = 0; i < table_cnt; i++) {
 		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 (pos != i)
+				table[pos] = table[i];
+			learn_symbol(table[pos].sym, table[pos].len);
+			pos++;
 		}
-		if (table[i].flags & SYM_FLAG_SAMPLED)
-			learn_symbol(table[i].sym, table[i].len);
 	}
+	table_cnt = pos;
 }
 
 /* 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)
+static void compress_symbols(unsigned char *str, int idx)
 {
-	int i, len, learn, size;
-	unsigned char *p;
+	unsigned int i, len, size;
+	unsigned char *p1, *p2;
 
-	for (i = 0; i < cnt; i++) {
-
-		if (!(table[i].flags & SYM_FLAG_VALID)) continue;
+	for (i = 0; i < table_cnt; i++) {
 
 		len = table[i].len;
-		learn = 0;
-		p = table[i].sym;
+		p1 = table[i].sym;
+
+		/* find the token on the symbol */
+		p2 = memmem(p1, len, str, 2);
+		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 */
-			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;
-			}
+			p2 = memmem(p1, size, str, 2);
 
-			*p = idx;
-			size = (len - (p - table[i].sym)) - tlen + 1;
-			memmove(p + 1, p + tlen, size);
-			p++;
-			len -= tlen - 1;
+		} while (p2);
 
-		} while (size >= tlen);
+		table[i].len = len;
 
-		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);
-		}
+		/* increase the counts for this symbol's new tokens */
+		learn_symbol(table[i].sym, len);
 	}
 }
 
 /* search the token with the maximum profit */
-static struct token *find_best_token(void)
+static int find_best_token(void)
 {
-	struct token *ptr,*best,*head;
-	int bestprofit;
+	int i, best, bestprofit;
 
 	bestprofit=-10000;
+	best = 0;
 
-	/* 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;
+	for (i = 0; i < 0x10000; i++) {
+		if (token_profit[i] > bestprofit) {
+			best = i;
+			bestprofit = token_profit[i];
 		}
-		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;
+	int i, best;
 
 	/* using the '\0' symbol last allows compress_symbols to use standard
 	 * fast string functions */
@@ -644,14 +424,12 @@ static void optimize_result(void)
 			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';
+			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], best_table_len[i], i);
+			compress_symbols(best_table[i], i);
 		}
 	}
 }
@@ -659,39 +437,28 @@ static void optimize_result(void)
 /* start by placing the symbols that are actually used on the table */
 static void insert_real_symbols_in_table(void)
 {
-	int i, j, c;
+	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 < 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;
-			}
+	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)
 {
-	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();
 
 	/* When valid symbol is not registered, exit to error */
-	if (good_head.left == good_head.right &&
-	    bad_head.left == bad_head.right) {
+	if (!table_cnt) {
 		fprintf(stderr, "No valid symbol.\n");
 		exit(1);
 	}
@@ -700,8 +467,7 @@ static void optimize_token_table(void)
 }
 
 
-int
-main(int argc, char **argv)
+int main(int argc, char **argv)
 {
 	if (argc >= 2) {
 		int i;