kallsyms: Improve the performance of kallsyms_lookup_name()

[ Upstream commit 60443c88f3a89fd303a9e8c0e84895910675c316 ]

Currently, to search for a symbol, we need to expand the symbols in
'kallsyms_names' one by one, and then use the expanded string for
comparison. It's O(n).

If we sort names in ascending order like addresses, we can also use
binary search. It's O(log(n)).

In order not to change the implementation of "/proc/kallsyms", the table
kallsyms_names[] is still stored in a one-to-one correspondence with the
address in ascending order.

Add array kallsyms_seqs_of_names[], it's indexed by the sequence number
of the sorted names, and the corresponding content is the sequence number
of the sorted addresses. For example:
Assume that the index of NameX in array kallsyms_seqs_of_names[] is 'i',
the content of kallsyms_seqs_of_names[i] is 'k', then the corresponding
address of NameX is kallsyms_addresses[k]. The offset in kallsyms_names[]
is get_symbol_offset(k).

Note that the memory usage will increase by (4 * kallsyms_num_syms)
bytes, the next two patches will reduce (1 * kallsyms_num_syms) bytes
and properly handle the case CONFIG_LTO_CLANG=y.

Performance test results: (x86)
Before:
min=234, max=10364402, avg=5206926
min=267, max=11168517, avg=5207587
After:
min=1016, max=90894, avg=7272
min=1014, max=93470, avg=7293

The average lookup performance of kallsyms_lookup_name() improved 715x.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Stable-dep-of: 8cc32a9bbf29 ("kallsyms: strip LTO-only suffixes from promoted global functions")
Signed-off-by: Sasha Levin <sashal@kernel.org>

1 files changed, 37 insertions, 0 deletions

diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 03fa07ad45d9..dcb744a067e5 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -49,6 +49,7 @@ _Static_assert(
 struct sym_entry {
 	unsigned long long addr;
 	unsigned int len;
+	unsigned int seq;
 	unsigned int start_pos;
 	unsigned int percpu_absolute;
 	unsigned char sym[];
@@ -410,6 +411,35 @@ static int symbol_absolute(const struct sym_entry *s)
 	return s->percpu_absolute;
 }
 
+static int compare_names(const void *a, const void *b)
+{
+	int ret;
+	char sa_namebuf[KSYM_NAME_LEN];
+	char sb_namebuf[KSYM_NAME_LEN];
+	const struct sym_entry *sa = *(const struct sym_entry **)a;
+	const struct sym_entry *sb = *(const struct sym_entry **)b;
+
+	expand_symbol(sa->sym, sa->len, sa_namebuf);
+	expand_symbol(sb->sym, sb->len, sb_namebuf);
+	ret = strcmp(&sa_namebuf[1], &sb_namebuf[1]);
+	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(void)
 {
 	unsigned int i, k, off;
@@ -495,6 +525,7 @@ static void write_src(void)
 	for (i = 0; i < table_cnt; i++) {
 		if ((i & 0xFF) == 0)
 			markers[i >> 8] = off;
+		table[i]->seq = i;
 
 		/* There cannot be any symbol of length zero. */
 		if (table[i]->len == 0) {
@@ -535,6 +566,12 @@ static void write_src(void)
 
 	free(markers);
 
+	sort_symbols_by_name();
+	output_label("kallsyms_seqs_of_names");
+	for (i = 0; i < table_cnt; i++)
+		printf("\t.long\t%u\n", table[i]->seq);
+	printf("\n");
+
 	output_label("kallsyms_token_table");
 	off = 0;
 	for (i = 0; i < 256; i++) {