kallsyms: Add self-test facility

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(%) |
 |---------------------------------------------------------|
 |     107543 |       1357912   |      2407433  |  56.40   |
  ---------------------------------------------------------
 kallsyms_lookup_name() looked up 107543 symbols
 The time spent on each symbol is (ns): min=630, max=35295, avg=7353
 kallsyms_on_each_symbol() traverse all: 11782628 ns
 kallsyms_on_each_match_symbol() traverse all: 9261 ns
 finish
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

include/linux/kallsyms.h

@@ -66,6 +66,7 @@ static inline void *dereference_symbol_descriptor(void *ptr)
 }
 
 #ifdef CONFIG_KALLSYMS
+unsigned long kallsyms_sym_address(int idx);
 int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
 				      unsigned long),
 			    void *data);

init/Kconfig

@@ -1723,6 +1723,19 @@ 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 basic functions and performance of kallsyms"
+	depends on KALLSYMS
+	default n
+	help
+	  Test the basic functions 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

kernel/Makefile

@@ -69,6 +69,7 @@ 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

kernel/kallsyms.c

@@ -146,7 +146,7 @@ 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];

kernel/kallsyms_selftest.h

+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef LINUX_KALLSYMS_SELFTEST_H_
+#define LINUX_KALLSYMS_SELFTEST_H_
+
+#include <linux/types.h>
+
+extern int kallsyms_test_var_bss;
+extern int kallsyms_test_var_data;
+
+extern int kallsyms_test_func(void);
+extern int kallsyms_test_func_weak(void);
+
+#endif // LINUX_KALLSYMS_SELFTEST_H_