[PATCH v3 0/8] kallsyms: Optimizes the performance of lookup symbols

[PATCH v3 0/8] kallsyms: Optimizes the performance of lookup symbols

[Zhen Lei]

v2 --> v3:
1. Improve test cases, perform complete functional tests on functions
   kallsyms_lookup_name(), kallsyms_on_each_symbol() and
   kallsyms_on_each_match_symbol().
2. Add patch [PATCH v3 2/8] scripts/kallsyms: ensure that all possible
   combinations are compressed.
3. The symbol type is not compressed regardless of whether
   CONFIG_KALLSYMS_ALL is set or not. The memory overhead is increased
   by less than 20KiB if CONFIG_KALLSYMS_ALL=n.
4. Discard [PATCH v2 3/8] kallsyms: Adjust the types of some local variables

v1 --> v2:
Add self-test facility

v1:
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. This is very slow.

In fact, we can first compress the name being looked up and then use
it for comparison when traversing 'kallsyms_names'.

This patch series optimizes the performance of function kallsyms_lookup_name(),
and function klp_find_object_symbol() in the livepatch module. Based on the
test results, the performance overhead is reduced to 5%. That is, the
performance of these functions is improved by 20 times.

To avoid increasing the kernel size in non-debug mode, the optimization is only
for the case CONFIG_KALLSYMS_ALL=y.

Zhen Lei (8):
  scripts/kallsyms: rename build_initial_tok_table()
  scripts/kallsyms: ensure that all possible combinations are compressed
  scripts/kallsyms: don't compress symbol types
  kallsyms: Improve the performance of kallsyms_lookup_name()
  kallsyms: Add helper kallsyms_on_each_match_symbol()
  livepatch: Use kallsyms_on_each_match_symbol() to improve performance
  livepatch: Improve the search performance of
    module_kallsyms_on_each_symbol()
  kallsyms: Add self-test facility

 include/linux/kallsyms.h   |   8 +
 init/Kconfig               |  13 ++
 kernel/Makefile            |   1 +
 kernel/kallsyms.c          | 106 +++++++++-
 kernel/kallsyms_selftest.c | 424 +++++++++++++++++++++++++++++++++++++
 kernel/livepatch/core.c    |  25 ++-
 kernel/module/kallsyms.c   |  13 +-
 scripts/kallsyms.c         |  24 ++-
 8 files changed, 598 insertions(+), 16 deletions(-)
 create mode 100644 kernel/kallsyms_selftest.c

-- 
2.25.1

[PATCH v3 1/8] scripts/kallsyms: rename build_initial_tok_table()

[Zhen Lei]

Except for the function build_initial_tok_table(), no token abbreviation
is used elsewhere.

$ cat scripts/kallsyms.c | grep tok | wc -l
33
$ cat scripts/kallsyms.c | grep token | wc -l
31

Here, it would be clearer to use the full name.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
 scripts/kallsyms.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index f18e6dfc68c5839..8caccc8f4a23703 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -525,7 +525,7 @@ static void forget_symbol(const unsigned char *symbol, int len)
 }
 
 /* do the initial token count */
-static void build_initial_tok_table(void)
+static void build_initial_token_table(void)
 {
 	unsigned int i;
 
@@ -650,7 +650,7 @@ static void insert_real_symbols_in_table(void)
 
 static void optimize_token_table(void)
 {
-	build_initial_tok_table();
+	build_initial_token_table();
 
 	insert_real_symbols_in_table();
 
-- 
2.25.1

[PATCH v3 2/8] scripts/kallsyms: ensure that all possible combinations are compressed

[Zhen Lei]

For a symbol, there may be more than one place that can be merged. For
example: nfs_fs_proc_net_init, there are two "f"+"s_" combinations.
And we're only compressing the first combination at the moment. Let's
compress all possible combinations.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
 scripts/kallsyms.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 8caccc8f4a23703..3319d9f38d7a5f2 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -553,7 +553,7 @@ static void compress_symbols(const unsigned char *str, int idx)
 	unsigned char *p1, *p2;
 
 	for (i = 0; i < table_cnt; i++) {
-
+retry:
 		len = table[i]->len;
 		p1 = table[i]->sym;
 
@@ -585,6 +585,9 @@ static void compress_symbols(const unsigned char *str, int idx)
 
 		/* increase the counts for this symbol's new tokens */
 		learn_symbol(table[i]->sym, len);
+
+		/* May be more than one place that can be merged, try again */
+		goto retry;
 	}
 }
 
-- 
2.25.1

[PATCH v3 3/8] scripts/kallsyms: don't compress symbol types

[Zhen Lei]

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. Because we do not know the symbol type, and the symbol type
may be combined with the following characters to form a token.

So if we don't compress the symbol type, we can first compress the
searched symbol and then make a quick comparison based on the compressed
length and content. In this way, for entries with mismatched lengths,
there is no need to expand and compare strings. And for those matching
lengths, there's no need to expand the symbol. This saves a lot of time.
According to my test results, the average performance of
kallsyms_lookup_name() can be improved by 20 to 30 times.

Of course, because the symbol type is forcibly not compressed, the
compression rate also decreases. Here are the test results with
defconfig:

arm64: <<<<<<
        ---------------------------------------------------------------
       | ALL | nr_symbols | compressed size | original size | ratio(%) |
        -----|---------------------------------------------------------|
Before |  Y  |     174094 |       1884938   |      3750653  |  50.25   |
After  |  Y  |     174099 |       1960154   |      3750756  |  52.26   |
Before |  N  |      61744 |        725507   |      1222737  |  59.33   |
After  |  N  |      61747 |        745733   |      1222801  |  60.98   |
        ---------------------------------------------------------------
The memory overhead is increased by:
  73.5KiB and 4.0% if CONFIG_KALLSYMS_ALL=y.
  19.8KiB and 2.8% if CONFIG_KALLSYMS_ALL=n.

x86: <<<<<<<<
       ---------------------------------------------------------------
       | ALL | nr_symbols | compressed size | original size | ratio(%) |
        -----|---------------------------------------------------------|
Before |  Y  |     131415 |       1697542   |      3161216  |  53.69   |
After  |  Y  |     131540 |       1747769   |      3163933  |  55.24   |
Before |  N  |      60695 |        737627   |      1283046  |  57.49   |
After  |  N  |      60699 |        754797   |      1283149  |  58.82   |
        ---------------------------------------------------------------
The memory overhead is increased by:
  49.0KiB and 3.0% if CONFIG_KALLSYMS_ALL=y.
  16.8KiB and 2.3% if CONFIG_KALLSYMS_ALL=n.

This additional memory overhead is worth it compared to the performance
improvement, I think.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
 scripts/kallsyms.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 3319d9f38d7a5f2..1ae9ce773d2a31d 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -61,6 +61,15 @@ static int all_symbols;
 static int absolute_percpu;
 static int base_relative;
 
+/*
+ * Each entry in the symbol table consists of the symbol type and the symbol
+ * itself. To optimize the performance of finding or traversing symbols in
+ * kernel, do not compress the symbol type. In this way, when looking for a
+ * symbol of unknown type, we can first compress the searched symbol and then
+ * make a quick comparison based on the compressed length and content.
+ */
+static int sym_start_idx = 1;
+
 static int token_profit[0x10000];
 
 /* the table that holds the result of the compression */
@@ -511,7 +520,7 @@ static void learn_symbol(const unsigned char *symbol, int len)
 {
 	int i;
 
-	for (i = 0; i < len - 1; i++)
+	for (i = sym_start_idx; i < len - 1; i++)
 		token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++;
 }
 
@@ -520,7 +529,7 @@ static void forget_symbol(const unsigned char *symbol, int len)
 {
 	int i;
 
-	for (i = 0; i < len - 1; i++)
+	for (i = sym_start_idx; i < len - 1; i++)
 		token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--;
 }
 
@@ -538,7 +547,7 @@ static unsigned char *find_token(unsigned char *str, int len,
 {
 	int i;
 
-	for (i = 0; i < len - 1; i++) {
+	for (i = sym_start_idx; i < len - 1; i++) {
 		if (str[i] == token[0] && str[i+1] == token[1])
 			return &str[i];
 	}
-- 
2.25.1

[PATCH v3 4/8] kallsyms: Improve the performance of kallsyms_lookup_name()

[Zhen Lei]

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. This process can be optimized.

And now scripts/kallsyms no longer compresses the symbol types, each
symbol type always occupies one byte. So we can first compress the
searched symbol and then make a quick comparison based on the compressed
length and content. In this way, for entries with mismatched lengths,
there is no need to expand and compare strings. And for those matching
lengths, there's no need to expand the symbol. This saves a lot of time.
According to my test results, the average performance of
kallsyms_lookup_name() can be improved by 20 to 30 times.

The pseudo code of the test case is as follows:
static int stat_find_name(...)
{
	start = sched_clock();
	(void)kallsyms_lookup_name(name);
	end = sched_clock();
	//Update min, max, cnt, sum
}

/*
 * Traverse all symbols in sequence and collect statistics on the time
 * taken by kallsyms_lookup_name() to lookup each symbol.
 */
kallsyms_on_each_symbol(stat_find_name, NULL);

The test results are as follows (twice):
After : min=5250, max=  726560, avg= 302132
After : min=5320, max=  726850, avg= 301978
Before: min=170,  max=15949190, avg=7553906
Before: min=160,  max=15877280, avg=7517784

The average time consumed is only 4.01% and the maximum time consumed is
only 4.57% of the time consumed before optimization.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
 kernel/kallsyms.c | 79 +++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 76 insertions(+), 3 deletions(-)

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 3e7e2c2ad2f75ef..2d76196cfe89f34 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -87,6 +87,71 @@ static unsigned int kallsyms_expand_symbol(unsigned int off,
 	return off;
 }
 
+static int kallsyms_name_to_tokens(const char *name, char *buf)
+{
+	int i, j, k, n;
+	int len, token_len;
+	const char *token;
+	unsigned char token_idx[KSYM_NAME_LEN];
+	unsigned char token_bak[KSYM_NAME_LEN];
+
+	/*
+	 * n, number of tokens in the string name.
+	 * token_idx[i], the start index of the ith token.
+	 * token_idx[n] is used to calculate the length of the last token.
+	 */
+	n = strlen(name);
+	if (n >= KSYM_NAME_LEN) {
+		buf[0] = 0;
+		return 0;
+	}
+	for (i = 0; i <= n; i++)
+		token_idx[i] = (unsigned char)i;
+
+	/*
+	 * For tokens whose token_len >= 2, a larger index value indicates
+	 * a higher occurrence frequency. See scripts/kallsyms.c
+	 */
+	for (i = 255; i >= 0; i--) {
+		token = &kallsyms_token_table[kallsyms_token_index[i]];
+		token_len = strlen(token);
+		if (token_len <= 1)
+			continue;
+
+		/*
+		 * Find and merge two tokens into one.
+		 *
+		 *                |<-- new_token -->|
+		 *                | token1 | token2 |
+		 * token_idx[]:   j       j+1      j+2
+		 *
+		 */
+		for (j = 0; j < n - 1; j++) {
+			len = token_idx[j + 2] - token_idx[j];
+			if (len == token_len &&
+			    !strncmp(name + token_idx[j], token, len)) {
+				token_bak[token_idx[j]] = (unsigned char)i;
+				for (k = j + 1; k < n; k++)
+					token_idx[k] = token_idx[k + 1];
+				n--;
+			}
+		}
+	}
+
+	for (j = 0; j < n; j++) {
+		len = token_idx[j + 1] - token_idx[j];
+		if (len <= 1) {
+			buf[j] = name[token_idx[j]];
+			continue;
+		}
+
+		buf[j] = token_bak[token_idx[j]];
+	}
+	buf[n] = 0;
+
+	return n;
+}
+
 /*
  * Get symbol type information. This is encoded as a single char at the
  * beginning of the symbol name.
@@ -192,20 +257,28 @@ unsigned long kallsyms_lookup_name(const char *name)
 	char namebuf[KSYM_NAME_LEN];
 	unsigned long i;
 	unsigned int off;
+	int len;
 
 	/* Skip the search for empty string. */
 	if (!*name)
 		return 0;
 
+	len = kallsyms_name_to_tokens(name, namebuf);
+	for (i = 0, off = 0; len && i < kallsyms_num_syms; i++) {
+		if (kallsyms_names[off] == len + 1 &&
+		    !memcmp(&kallsyms_names[off + 2], namebuf, len))
+			return kallsyms_sym_address(i);
+
+		off += kallsyms_names[off] + 1;
+	}
+
 	for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
 		off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
 
-		if (strcmp(namebuf, name) == 0)
-			return kallsyms_sym_address(i);
-
 		if (cleanup_symbol_name(namebuf) && strcmp(namebuf, name) == 0)
 			return kallsyms_sym_address(i);
 	}
+
 	return module_kallsyms_lookup_name(name);
 }
 
-- 
2.25.1

[PATCH v3 5/8] kallsyms: Add helper kallsyms_on_each_match_symbol()

[Zhen Lei]

Function kallsyms_on_each_symbol() traverses all symbols and submits each
symbol to the hook 'fn' for judgment and processing. For some cases, the
hook actually only handles the matched symbol, such as livepatch.

So that, we can first compress the name being looked up and then use
it for comparison when traversing 'kallsyms_names', this greatly reduces
the time consumed by traversing.

The pseudo code of the test case is as follows:
static int tst_find(void *data, const char *name,
		    struct module *mod, unsigned long addr)
{
	if (strcmp(name, "vmap") == 0)
		*(unsigned long *)data = addr;
        return 0;
}

static int tst_match(void *data, unsigned long addr)
{
        *(unsigned long *)data = addr;
        return 0;
}

start = sched_clock();
kallsyms_on_each_match_symbol(tst_match, "vmap", &addr);
end = sched_clock();

start = sched_clock();
kallsyms_on_each_symbol(tst_find, &addr);
end = sched_clock();

The test results are as follows (twice):
kallsyms_on_each_match_symbol:   557400,   583900
kallsyms_on_each_symbol      : 16659500, 16113950

kallsyms_on_each_match_symbol() consumes only 3.48% of
kallsyms_on_each_symbol()'s time.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
 include/linux/kallsyms.h |  8 ++++++++
 kernel/kallsyms.c        | 25 +++++++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h
index ad39636e0c3f122..f9f2cc084cab16b 100644
--- a/include/linux/kallsyms.h
+++ b/include/linux/kallsyms.h
@@ -69,6 +69,8 @@ static inline void *dereference_symbol_descriptor(void *ptr)
 int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
 				      unsigned long),
 			    void *data);
+extern int kallsyms_on_each_match_symbol(int (*fn)(void *, unsigned long),
+					 const char *name, void *data);
 
 /* Lookup the address for a symbol. Returns 0 if not found. */
 unsigned long kallsyms_lookup_name(const char *name);
@@ -168,6 +170,12 @@ static inline int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct
 {
 	return -EOPNOTSUPP;
 }
+
+static inline int kallsyms_on_each_match_symbol(int (*fn)(void *, unsigned long),
+						const char *name, void *data)
+{
+	return -EOPNOTSUPP;
+}
 #endif /*CONFIG_KALLSYMS*/
 
 static inline void print_ip_sym(const char *loglvl, unsigned long ip)
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 2d76196cfe89f34..cbcc9c560f5c188 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -305,6 +305,31 @@ int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
 	return 0;
 }
 
+int kallsyms_on_each_match_symbol(int (*fn)(void *, unsigned long),
+				  const char *name, void *data)
+{
+	unsigned int i, off;
+	int len, ret;
+	char namebuf[KSYM_NAME_LEN];
+
+	len = kallsyms_name_to_tokens(name, namebuf);
+	for (i = 0, off = 0; len && i < kallsyms_num_syms; i++) {
+		if ((i & 0xfff) == 0)
+			cond_resched();
+
+		if ((kallsyms_names[off] == len + 1) &&
+		    !memcmp(&kallsyms_names[off + 2], namebuf, len)) {
+			ret = fn(data, kallsyms_sym_address(i));
+			if (ret != 0)
+				return ret;
+			cond_resched();
+		}
+		off += kallsyms_names[off] + 1;
+	}
+
+	return 0;
+}
+
 static unsigned long get_symbol_pos(unsigned long addr,
 				    unsigned long *symbolsize,
 				    unsigned long *offset)
-- 
2.25.1

[PATCH v3 6/8] livepatch: Use kallsyms_on_each_match_symbol() to improve performance

[Zhen Lei]

Based on the test results of kallsyms_on_each_match_symbol() and
kallsyms_on_each_symbol(), the average performance can be improved by 20
to 30 times.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
 kernel/livepatch/core.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 42f7e716d56bf72..31b57ccf908017e 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -153,6 +153,24 @@ static int klp_find_callback(void *data, const char *name,
 	return 0;
 }
 
+static int klp_match_callback(void *data, unsigned long addr)
+{
+	struct klp_find_arg *args = data;
+
+	args->addr = addr;
+	args->count++;
+
+	/*
+	 * Finish the search when the symbol is found for the desired position
+	 * or the position is not defined for a non-unique symbol.
+	 */
+	if ((args->pos && (args->count == args->pos)) ||
+	    (!args->pos && (args->count > 1)))
+		return 1;
+
+	return 0;
+}
+
 static int klp_find_object_symbol(const char *objname, const char *name,
 				  unsigned long sympos, unsigned long *addr)
 {
@@ -167,7 +185,7 @@ static int klp_find_object_symbol(const char *objname, const char *name,
 	if (objname)
 		module_kallsyms_on_each_symbol(klp_find_callback, &args);
 	else
-		kallsyms_on_each_symbol(klp_find_callback, &args);
+		kallsyms_on_each_match_symbol(klp_match_callback, name, &args);
 
 	/*
 	 * Ensure an address was found. If sympos is 0, ensure symbol is unique;
-- 
2.25.1

[PATCH v3 7/8] livepatch: Improve the search performance of module_kallsyms_on_each_symbol()

[Zhen Lei]

Currently we traverse all symbols of all modules to find the specified
function for the specified module. But in reality, we just need to find
the given module and then traverse all the symbols in it.

In order to achieve this purpose, split the call to hook 'fn' into two
phases:
1. Finds the given module. Pass pointer 'mod'. Hook 'fn' directly returns
   the comparison result of the module name without comparing the function
   name.
2. Finds the given function in that module. Pass pointer 'mod = NULL'.
   Hook 'fn' skip the comparison of module name and directly compare
   function names.

Phase1: mod1-->mod2..(subsequent modules do not need to be compared)
                |
Phase2:          -->f1-->f2-->f3

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
 kernel/livepatch/core.c  |  7 ++-----
 kernel/module/kallsyms.c | 13 ++++++++++++-
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 31b57ccf908017e..98e23137e4133bc 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -130,15 +130,12 @@ static int klp_find_callback(void *data, const char *name,
 {
 	struct klp_find_arg *args = data;
 
-	if ((mod && !args->objname) || (!mod && args->objname))
-		return 0;
+	if (mod)
+		return strcmp(args->objname, mod->name);
 
 	if (strcmp(args->name, name))
 		return 0;
 
-	if (args->objname && strcmp(args->objname, mod->name))
-		return 0;
-
 	args->addr = addr;
 	args->count++;
 
diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
index f5c5c9175333df7..b033613e6c7e3bb 100644
--- a/kernel/module/kallsyms.c
+++ b/kernel/module/kallsyms.c
@@ -510,6 +510,11 @@ int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *,
 		if (mod->state == MODULE_STATE_UNFORMED)
 			continue;
 
+		/* check mod->name first */
+		ret = fn(data, NULL, mod, 0);
+		if (ret)
+			continue;
+
 		/* Use rcu_dereference_sched() to remain compliant with the sparse tool */
 		preempt_disable();
 		kallsyms = rcu_dereference_sched(mod->kallsyms);
@@ -522,10 +527,16 @@ int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *,
 				continue;
 
 			ret = fn(data, kallsyms_symbol_name(kallsyms, i),
-				 mod, kallsyms_symbol_value(sym));
+				 NULL, kallsyms_symbol_value(sym));
 			if (ret != 0)
 				goto out;
 		}
+
+		/*
+		 * The given module is found, the subsequent modules do not
+		 * need to be compared.
+		 */
+		break;
 	}
 out:
 	mutex_unlock(&module_mutex);
-- 
2.25.1

[PATCH v3 8/8] kallsyms: Add self-test facility

[Zhen Lei]

Added test cases for basic functions and performance of functions
kallsyms_lookup_name(), kallsyms_on_each_symbol() and
kallsyms_on_each_match_symbol(). It also calculates the compression rate
of the kallsyms compression algorithm for the current symbol set.

The basic functions test begins by testing a set of symbols whose address
values are known. Then, traverse all symbol addresses and find the
corresponding symbol name based on the address. It's impossible to
determine whether these addresses are correct, but we can use the above
three functions along with the addresses to test each other. Due to the
traversal operation of kallsyms_on_each_symbol() is too slow, only 60
symbols can be tested in one second, so let it test on average once
every 128 symbols. The other two functions validate all symbols.

If the basic functions test is passed, print only performance test
results. If the test fails, print error information, but do not perform
subsequent performance tests.

Start self-test automatically after system startup if
CONFIG_KALLSYMS_SELFTEST=y.

Example of output content: (prefix 'kallsyms_selftest:' is omitted)
 start
  ---------------------------------------------------------
 | nr_symbols | compressed size | original size | ratio(%) |
 |---------------------------------------------------------|
 |     174099 |       1960154   |      3750756  |  52.26   |
  ---------------------------------------------------------
 kallsyms_lookup_name() looked up 174099 symbols
 The time spent on each symbol is (ns): min=5250, max=726560, avg=302132
 kallsyms_on_each_symbol() traverse all: 16659500 ns
 kallsyms_on_each_match_symbol() traverse all: 557400 ns
 finish

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
 init/Kconfig               |  13 ++
 kernel/Makefile            |   1 +
 kernel/kallsyms.c          |   2 +-
 kernel/kallsyms_selftest.c | 424 +++++++++++++++++++++++++++++++++++++
 4 files changed, 439 insertions(+), 1 deletion(-)
 create mode 100644 kernel/kallsyms_selftest.c

diff --git a/init/Kconfig b/init/Kconfig
index 532362fcfe31fd3..2fcace3b9f063bf 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1716,6 +1716,19 @@ config KALLSYMS
 	  symbolic stack backtraces. This increases the size of the kernel
 	  somewhat, as all symbols have to be loaded into the kernel image.
 
+config KALLSYMS_SELFTEST
+	bool "Test the function and performance of some interfaces in kallsyms"
+	depends on KALLSYMS
+	default n
+	help
+	  Test the function and performance of some interfaces, such as
+	  kallsyms_lookup_name. It also calculates the compression rate of the
+	  kallsyms compression algorithm for the current symbol set.
+
+	  Start self-test automatically after system startup. Suggest executing
+	  "dmesg | grep kallsyms_selftest" to collect test results. "finish" is
+	  displayed in the last line, indicating that the test is complete.
+
 config KALLSYMS_ALL
 	bool "Include all symbols in kallsyms"
 	depends on DEBUG_KERNEL && KALLSYMS
diff --git a/kernel/Makefile b/kernel/Makefile
index 318789c728d3290..122a5fed457bd98 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -68,6 +68,7 @@ endif
 obj-$(CONFIG_UID16) += uid16.o
 obj-$(CONFIG_MODULE_SIG_FORMAT) += module_signature.o
 obj-$(CONFIG_KALLSYMS) += kallsyms.o
+obj-$(CONFIG_KALLSYMS_SELFTEST) += kallsyms_selftest.o
 obj-$(CONFIG_BSD_PROCESS_ACCT) += acct.o
 obj-$(CONFIG_CRASH_CORE) += crash_core.o
 obj-$(CONFIG_KEXEC_CORE) += kexec_core.o
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index cbcc9c560f5c188..34e306eecbb60c8 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -193,7 +193,7 @@ static unsigned int get_symbol_offset(unsigned long pos)
 	return name - kallsyms_names;
 }
 
-static unsigned long kallsyms_sym_address(int idx)
+unsigned long kallsyms_sym_address(int idx)
 {
 	if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
 		return kallsyms_addresses[idx];
diff --git a/kernel/kallsyms_selftest.c b/kernel/kallsyms_selftest.c
new file mode 100644
index 000000000000000..756759d1f45a6e3
--- /dev/null
+++ b/kernel/kallsyms_selftest.c
@@ -0,0 +1,424 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Test the function and performance of kallsyms
+ *
+ * Copyright (C) Huawei Technologies Co., Ltd., 2022
+ *
+ * Authors: Zhen Lei <thunder.leizhen@huawei.com> Huawei
+ */
+
+#define pr_fmt(fmt) "kallsyms_selftest: " fmt
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/kallsyms.h>
+#include <linux/random.h>
+#include <linux/sched/clock.h>
+#include <linux/kthread.h>
+#include <linux/vmalloc.h>
+
+#include "kallsyms_internal.h"
+
+extern unsigned long kallsyms_sym_address(int idx);
+
+#define MAX_NUM_OF_RECORDS		64
+
+struct test_stat {
+	int min;
+	int max;
+	int save_cnt;
+	int real_cnt;
+	u64 sum;
+	char *name;
+	unsigned long addr;
+	unsigned long addrs[MAX_NUM_OF_RECORDS];
+};
+
+struct test_item {
+	char *name;
+	unsigned long addr;
+};
+
+#define ITEM_FUNC(s)				\
+	{					\
+		.name = #s,			\
+		.addr = (unsigned long)s,	\
+	}
+
+#define ITEM_DATA(s)				\
+	{					\
+		.name = #s,			\
+		.addr = (unsigned long)&s,	\
+	}
+
+static int test_var_bss_static;
+static int test_var_data_static = 1;
+int test_var_bss;
+int test_var_data = 1;
+
+static int test_func_static(void)
+{
+	test_var_bss_static++;
+	test_var_data_static++;
+
+	return 0;
+}
+
+int test_func(void)
+{
+	return test_func_static();
+}
+
+__weak int test_func_weak(void)
+{
+	test_var_bss++;
+	test_var_data++;
+	return 0;
+}
+
+static struct test_item test_items[] = {
+	ITEM_FUNC(test_func_static),
+	ITEM_FUNC(test_func),
+	ITEM_FUNC(test_func_weak),
+	ITEM_FUNC(vmalloc),
+	ITEM_FUNC(vfree),
+#ifdef CONFIG_KALLSYMS_ALL
+	ITEM_DATA(test_var_bss_static),
+	ITEM_DATA(test_var_data_static),
+	ITEM_DATA(test_var_bss),
+	ITEM_DATA(test_var_data),
+	ITEM_DATA(vmap_area_list),
+#endif
+};
+
+static char stub_name[KSYM_NAME_LEN];
+
+static int stat_symbol_len(void *data, const char *name,
+			   struct module *mod, unsigned long addr)
+{
+	*(u32 *)data += strlen(name);
+
+	return 0;
+}
+
+static void test_kallsyms_compression_ratio(void)
+{
+	int i;
+	const u8 *name;
+	u32 pos;
+	u32 ratio, total_size, total_len = 0;
+
+	kallsyms_on_each_symbol(stat_symbol_len, &total_len);
+
+	/*
+	 * A symbol name cannot start with a number. This stub name helps us
+	 * traverse the entire symbol table without finding a match. It's used
+	 * for subsequent performance tests, and its length is the average
+	 * length of all symbol names.
+	 */
+	memset(stub_name, '4', sizeof(stub_name));
+	pos = total_len / kallsyms_num_syms;
+	stub_name[pos] = 0;
+
+	pos = kallsyms_num_syms - 1;
+	name = &kallsyms_names[kallsyms_markers[pos >> 8]];
+	for (i = 0; i <= (pos & 0xff); i++)
+		name = name + (*name) + 1;
+
+	/*
+	 * 1. The length fields is not counted
+	 * 2. The memory occupied by array kallsyms_token_table[] and
+	 *    kallsyms_token_index[] needs to be counted.
+	 */
+	total_size = (name - kallsyms_names) - kallsyms_num_syms;
+	pos = kallsyms_token_index[0xff];
+	total_size += pos + strlen(&kallsyms_token_table[pos]) + 1;
+	total_size += 0x100 * sizeof(u16);
+
+	pr_info(" ---------------------------------------------------------\n");
+	pr_info("| nr_symbols | compressed size | original size | ratio(%%) |\n");
+	pr_info("|---------------------------------------------------------|\n");
+	ratio = 10000ULL * total_size / total_len;
+	pr_info("| %10d |    %10d   |   %10d  |  %2d.%-2d   |\n",
+		kallsyms_num_syms, total_size, total_len, ratio / 100, ratio % 100);
+	pr_info(" ---------------------------------------------------------\n");
+}
+
+static int lookup_name(void *data, const char *name, struct module *mod, unsigned long addr)
+{
+	u64 t0, t1, t;
+	unsigned long flags;
+	struct test_stat *stat = (struct test_stat *)data;
+
+	local_irq_save(flags);
+	t0 = sched_clock();
+	(void)kallsyms_lookup_name(name);
+	t1 = sched_clock();
+	local_irq_restore(flags);
+
+	t = t1 - t0;
+	if (t < stat->min)
+		stat->min = t;
+
+	if (t > stat->max)
+		stat->max = t;
+
+	stat->real_cnt++;
+	stat->sum += t;
+
+	return 0;
+}
+
+static void test_perf_kallsyms_lookup_name(void)
+{
+	struct test_stat stat;
+
+	memset(&stat, 0, sizeof(stat));
+	stat.min = INT_MAX;
+	kallsyms_on_each_symbol(lookup_name, &stat);
+	pr_info("kallsyms_lookup_name() looked up %d symbols\n", stat.real_cnt);
+	pr_info("The time spent on each symbol is (ns): min=%d, max=%d, avg=%lld\n",
+		stat.min, stat.max, stat.sum / stat.real_cnt);
+}
+
+static int find_symbol(void *data, const char *name,
+		       struct module *mod, unsigned long addr)
+{
+	struct test_stat *stat = (struct test_stat *)data;
+
+	if (strcmp(name, stat->name) == 0) {
+		stat->real_cnt++;
+		stat->addr = addr;
+
+		if (stat->save_cnt < MAX_NUM_OF_RECORDS) {
+			stat->addrs[stat->save_cnt] = addr;
+			stat->save_cnt++;
+		}
+
+		if (stat->real_cnt == stat->max)
+			return 1;
+	}
+
+	return 0;
+}
+
+static void test_perf_kallsyms_on_each_symbol(void)
+{
+	u64 t0, t1;
+	unsigned long flags;
+	struct test_stat stat;
+
+	memset(&stat, 0, sizeof(stat));
+	stat.max = INT_MAX;
+	stat.name = stub_name;
+	local_irq_save(flags);
+	t0 = sched_clock();
+	kallsyms_on_each_symbol(find_symbol, &stat);
+	t1 = sched_clock();
+	local_irq_restore(flags);
+	pr_info("kallsyms_on_each_symbol() traverse all: %lld ns\n", t1 - t0);
+}
+
+static int match_symbol(void *data, unsigned long addr)
+{
+	struct test_stat *stat = (struct test_stat *)data;
+
+	stat->real_cnt++;
+	stat->addr = addr;
+
+	if (stat->save_cnt < MAX_NUM_OF_RECORDS) {
+		stat->addrs[stat->save_cnt] = addr;
+		stat->save_cnt++;
+	}
+
+	if (stat->real_cnt == stat->max)
+		return 1;
+
+	return 0;
+}
+
+static void test_perf_kallsyms_on_each_match_symbol(void)
+{
+	u64 t0, t1;
+	unsigned long flags;
+	struct test_stat stat;
+
+	memset(&stat, 0, sizeof(stat));
+	stat.max = INT_MAX;
+	stat.name = stub_name;
+	local_irq_save(flags);
+	t0 = sched_clock();
+	kallsyms_on_each_match_symbol(match_symbol, stat.name, &stat);
+	t1 = sched_clock();
+	local_irq_restore(flags);
+	pr_info("kallsyms_on_each_match_symbol() traverse all: %lld ns\n", t1 - t0);
+}
+
+static int test_kallsyms_basic_function(void)
+{
+	int i, j, ret;
+	int next = 0, nr_failed = 0;
+	char *prefix;
+	unsigned short rand;
+	unsigned long addr;
+	char namebuf[KSYM_NAME_LEN];
+	struct test_stat stat, stat1, stat2;
+
+	prefix = "kallsyms_lookup_name() for";
+	for (i = 0; i < ARRAY_SIZE(test_items); i++) {
+		addr = kallsyms_lookup_name(test_items[i].name);
+		if (addr != test_items[i].addr) {
+			nr_failed++;
+			pr_info("%s %s failed: addr=%lx, expect %lx\n",
+				prefix, test_items[i].name, addr, test_items[i].addr);
+		}
+	}
+
+	prefix = "kallsyms_on_each_symbol() for";
+	for (i = 0; i < ARRAY_SIZE(test_items); i++) {
+		memset(&stat, 0, sizeof(stat));
+		stat.max = INT_MAX;
+		stat.name = test_items[i].name;
+		kallsyms_on_each_symbol(find_symbol, &stat);
+		if (stat.addr != test_items[i].addr || stat.real_cnt != 1) {
+			nr_failed++;
+			pr_info("%s %s failed: count=%d, addr=%lx, expect %lx\n",
+				prefix, test_items[i].name,
+				stat.real_cnt, stat.addr, test_items[i].addr);
+		}
+	}
+
+	prefix = "kallsyms_on_each_match_symbol() for";
+	for (i = 0; i < ARRAY_SIZE(test_items); i++) {
+		memset(&stat, 0, sizeof(stat));
+		stat.max = INT_MAX;
+		stat.name = test_items[i].name;
+		kallsyms_on_each_match_symbol(match_symbol, test_items[i].name, &stat);
+		if (stat.addr != test_items[i].addr || stat.real_cnt != 1) {
+			nr_failed++;
+			pr_info("%s %s failed: count=%d, addr=%lx, expect %lx\n",
+				prefix, test_items[i].name,
+				stat.real_cnt, stat.addr, test_items[i].addr);
+		}
+	}
+
+	if (nr_failed)
+		return -EFAULT;
+
+	for (i = 0; i < kallsyms_num_syms; i++) {
+		addr = kallsyms_sym_address(i);
+		if (!is_ksym_addr(addr))
+			continue;
+
+		ret = lookup_symbol_name(addr, namebuf);
+		if (unlikely(ret)) {
+			namebuf[0] = 0;
+			goto failed;
+		}
+
+		stat.addr = kallsyms_lookup_name(namebuf);
+
+		memset(&stat1, 0, sizeof(stat1));
+		stat1.max = INT_MAX;
+		kallsyms_on_each_match_symbol(match_symbol, namebuf, &stat1);
+
+		/*
+		 * kallsyms_on_each_symbol() is too slow, randomly select some
+		 * symbols for test.
+		 */
+		if (i >= next) {
+			memset(&stat2, 0, sizeof(stat2));
+			stat2.max = INT_MAX;
+			stat2.name = namebuf;
+			kallsyms_on_each_symbol(find_symbol, &stat2);
+
+			/*
+			 * kallsyms_on_each_symbol() and kallsyms_on_each_match_symbol()
+			 * need to get the same traversal result.
+			 */
+			if (stat1.addr != stat2.addr ||
+			    stat1.real_cnt != stat2.real_cnt ||
+			    memcmp(stat1.addrs, stat2.addrs,
+				   stat1.save_cnt * sizeof(stat1.addrs[0])))
+				goto failed;
+
+			/*
+			 * The average of random increments is 128, that is, one of
+			 * them is tested every 128 symbols.
+			 */
+			get_random_bytes(&rand, sizeof(rand));
+			next = i + (rand & 0xff) + 1;
+		}
+
+		/* Need to be found at least once */
+		if (!stat1.real_cnt)
+			goto failed;
+
+		/*
+		 * kallsyms_lookup_name() returns the address of the first
+		 * symbol found and cannot be NULL.
+		 */
+		if (!stat.addr || stat.addr != stat1.addrs[0])
+			goto failed;
+
+		/*
+		 * If the addresses of all matching symbols are recorded, the
+		 * target address needs to be exist.
+		 */
+		if (stat1.real_cnt <= MAX_NUM_OF_RECORDS) {
+			for (j = 0; j < stat1.save_cnt; j++) {
+				if (stat1.addrs[j] == addr)
+					break;
+			}
+
+			if (j == stat1.save_cnt)
+				goto failed;
+		}
+	}
+
+	return 0;
+
+failed:
+	pr_info("Test for %dth symbol failed: (%s) addr=%lx", i, namebuf, addr);
+	return -EFAULT;
+}
+
+static int test_entry(void *p)
+{
+	int ret;
+
+	do {
+		schedule_timeout(5 * HZ);
+	} while (system_state != SYSTEM_RUNNING);
+
+	pr_info("start\n");
+	ret = test_kallsyms_basic_function();
+	if (ret) {
+		pr_info("abort\n");
+		return ret;
+	}
+
+	test_kallsyms_compression_ratio();
+	test_perf_kallsyms_lookup_name();
+	test_perf_kallsyms_on_each_symbol();
+	test_perf_kallsyms_on_each_match_symbol();
+	pr_info("finish\n");
+
+	return 0;
+}
+
+static int __init kallsyms_test_init(void)
+{
+	struct task_struct *t;
+
+	t = kthread_create(test_entry, NULL, "kallsyms_test");
+	if (IS_ERR(t)) {
+		pr_info("Create kallsyms selftest task failed\n");
+		return PTR_ERR(t);
+	}
+	kthread_bind(t, 0);
+	wake_up_process(t);
+
+	return 0;
+}
+late_initcall(kallsyms_test_init);
-- 
2.25.1

Re: [PATCH v3 8/8] kallsyms: Add self-test facility

[kernel test robot]

Hi Zhen,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on mcgrof/modules-next]
[also build test WARNING on linus/master v6.0-rc6 next-20220919]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Zhen-Lei/kallsyms-Optimizes-the-performance-of-lookup-symbols/20220919-231916
base:   https://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux.git modules-next
config: i386-randconfig-a001-20220919 (https://download.01.org/0day-ci/archive/20220920/202209201123.hihIfjo1-lkp@intel.com/config)
compiler: clang version 14.0.6 (https://github.com/llvm/llvm-project f28c006a5895fc0e329fe15fead81e37457cb1d1)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/26fdb8f3984ffbdb57da2d1fac7e32ae418bfa96
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Zhen-Lei/kallsyms-Optimizes-the-performance-of-lookup-symbols/20220919-231916
        git checkout 26fdb8f3984ffbdb57da2d1fac7e32ae418bfa96
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=i386 SHELL=/bin/bash

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

>> kernel/kallsyms.c:196:15: warning: no previous prototype for function 'kallsyms_sym_address' [-Wmissing-prototypes]
   unsigned long kallsyms_sym_address(int idx)
                 ^
   kernel/kallsyms.c:196:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
   unsigned long kallsyms_sym_address(int idx)
   ^
   static 
   kernel/kallsyms.c:668:12: warning: no previous prototype for function 'arch_get_kallsym' [-Wmissing-prototypes]
   int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
              ^
   kernel/kallsyms.c:668:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
   int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
   ^
   static 
   2 warnings generated.


vim +/kallsyms_sym_address +196 kernel/kallsyms.c

   195	
 > 196	unsigned long kallsyms_sym_address(int idx)
   197	{
   198		if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
   199			return kallsyms_addresses[idx];
   200	
   201		/* values are unsigned offsets if --absolute-percpu is not in effect */
   202		if (!IS_ENABLED(CONFIG_KALLSYMS_ABSOLUTE_PERCPU))
   203			return kallsyms_relative_base + (u32)kallsyms_offsets[idx];
   204	
   205		/* ...otherwise, positive offsets are absolute values */
   206		if (kallsyms_offsets[idx] >= 0)
   207			return kallsyms_offsets[idx];
   208	
   209		/* ...and negative offsets are relative to kallsyms_relative_base - 1 */
   210		return kallsyms_relative_base - 1 - kallsyms_offsets[idx];
   211	}
   212	

-- 
0-DAY CI Kernel Test Service
https://01.org/lkp

Re: [PATCH v3 8/8] kallsyms: Add self-test facility

[kernel test robot]

Hi Zhen,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on mcgrof/modules-next]
[also build test WARNING on linus/master v6.0-rc6 next-20220919]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Zhen-Lei/kallsyms-Optimizes-the-performance-of-lookup-symbols/20220919-231916
base:   https://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux.git modules-next
config: arm-nhk8815_defconfig (https://download.01.org/0day-ci/archive/20220920/202209201126.fpHaqBEx-lkp@intel.com/config)
compiler: arm-linux-gnueabi-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/26fdb8f3984ffbdb57da2d1fac7e32ae418bfa96
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Zhen-Lei/kallsyms-Optimizes-the-performance-of-lookup-symbols/20220919-231916
        git checkout 26fdb8f3984ffbdb57da2d1fac7e32ae418bfa96
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=arm SHELL=/bin/bash

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

>> kernel/kallsyms.c:196:15: warning: no previous prototype for 'kallsyms_sym_address' [-Wmissing-prototypes]
     196 | unsigned long kallsyms_sym_address(int idx)
         |               ^~~~~~~~~~~~~~~~~~~~
   kernel/kallsyms.c:668:12: warning: no previous prototype for 'arch_get_kallsym' [-Wmissing-prototypes]
     668 | int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
         |            ^~~~~~~~~~~~~~~~


vim +/kallsyms_sym_address +196 kernel/kallsyms.c

   195	
 > 196	unsigned long kallsyms_sym_address(int idx)
   197	{
   198		if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
   199			return kallsyms_addresses[idx];
   200	
   201		/* values are unsigned offsets if --absolute-percpu is not in effect */
   202		if (!IS_ENABLED(CONFIG_KALLSYMS_ABSOLUTE_PERCPU))
   203			return kallsyms_relative_base + (u32)kallsyms_offsets[idx];
   204	
   205		/* ...otherwise, positive offsets are absolute values */
   206		if (kallsyms_offsets[idx] >= 0)
   207			return kallsyms_offsets[idx];
   208	
   209		/* ...and negative offsets are relative to kallsyms_relative_base - 1 */
   210		return kallsyms_relative_base - 1 - kallsyms_offsets[idx];
   211	}
   212	

-- 
0-DAY CI Kernel Test Service
https://01.org/lkp

Re: [PATCH v3 8/8] kallsyms: Add self-test facility

[Leizhen (ThunderTown)]

On 2022/9/20 11:14, kernel test robot wrote:
> Hi Zhen,
> 
> Thank you for the patch! Perhaps something to improve:
> 
> [auto build test WARNING on mcgrof/modules-next]
> [also build test WARNING on linus/master v6.0-rc6 next-20220919]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch#_base_tree_information]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Zhen-Lei/kallsyms-Optimizes-the-performance-of-lookup-symbols/20220919-231916
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux.git modules-next
> config: i386-randconfig-a001-20220919 (https://download.01.org/0day-ci/archive/20220920/202209201123.hihIfjo1-lkp@intel.com/config)
> compiler: clang version 14.0.6 (https://github.com/llvm/llvm-project f28c006a5895fc0e329fe15fead81e37457cb1d1)
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # https://github.com/intel-lab-lkp/linux/commit/26fdb8f3984ffbdb57da2d1fac7e32ae418bfa96
>         git remote add linux-review https://github.com/intel-lab-lkp/linux
>         git fetch --no-tags linux-review Zhen-Lei/kallsyms-Optimizes-the-performance-of-lookup-symbols/20220919-231916
>         git checkout 26fdb8f3984ffbdb57da2d1fac7e32ae418bfa96
>         # save the config file
>         mkdir build_dir && cp config build_dir/.config
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=i386 SHELL=/bin/bash
> 
> If you fix the issue, kindly add following tag where applicable
> Reported-by: kernel test robot <lkp@intel.com>
> 
> All warnings (new ones prefixed by >>):
> 
>>> kernel/kallsyms.c:196:15: warning: no previous prototype for function 'kallsyms_sym_address' [-Wmissing-prototypes]
>    unsigned long kallsyms_sym_address(int idx)
>                  ^
>    kernel/kallsyms.c:196:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
>    unsigned long kallsyms_sym_address(int idx)
>    ^

Well, thanks. Because it's just for testing code, I'm thinking about not
changing the header file, but it looks like I'll have to change it.

>    static 
>    kernel/kallsyms.c:668:12: warning: no previous prototype for function 'arch_get_kallsym' [-Wmissing-prototypes]
>    int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
>               ^
>    kernel/kallsyms.c:668:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
>    int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
>    ^
>    static 
>    2 warnings generated.
> 
> 
> vim +/kallsyms_sym_address +196 kernel/kallsyms.c
> 
>    195	
>  > 196	unsigned long kallsyms_sym_address(int idx)
>    197	{
>    198		if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
>    199			return kallsyms_addresses[idx];
>    200	
>    201		/* values are unsigned offsets if --absolute-percpu is not in effect */
>    202		if (!IS_ENABLED(CONFIG_KALLSYMS_ABSOLUTE_PERCPU))
>    203			return kallsyms_relative_base + (u32)kallsyms_offsets[idx];
>    204	
>    205		/* ...otherwise, positive offsets are absolute values */
>    206		if (kallsyms_offsets[idx] >= 0)
>    207			return kallsyms_offsets[idx];
>    208	
>    209		/* ...and negative offsets are relative to kallsyms_relative_base - 1 */
>    210		return kallsyms_relative_base - 1 - kallsyms_offsets[idx];
>    211	}
>    212	
> 

-- 
Regards,
  Zhen Lei