Kunit to check the longest symbol length

The longest length of a symbol (KSYM_NAME_LEN) was increased to 512 in the reference [1]. This patch adds kunit test suite to check the longest symbol length. These tests verify that the longest symbol length defined is supported.

This test can also help other efforts for longer symbol length, like [2].

The test suite defines one symbol with the longest possible length.

The first test verify that functions with names of the created symbol, can be called or not.

The second test, verify that the symbols are created (or not) in the kernel symbol table.

[1] https://lore.kernel.org/lkml/[email protected]/
[2] https://lore.kernel.org/lkml/[email protected]/

---
V6 -> V7: rebased
---
V5 -> V6: remove tests with symbols of length KSYM_NAME_LEN+1
---
V4 -> V5: fixed typo, added improved description
---
V3 -> V4: add x86 mantainers, add new reference.
---
V2 -> V3: updated base and added MODULE_DESCRIPTION() and MODULE_AUTHOR()
---
V1 -> V2: corrected CI tests. Added fix proposed at [3]

[3] https://lore.kernel.org/lkml/Y9ES4UKl%[email protected]/T/#m3ef0e12bb834d01ed1ebdcae12ef5f2add342077

The test execution should result in something like:
```

---
 arch/x86/tools/insn_decoder_test.c |  3 +-
 lib/Kconfig.debug                  |  9 ++++
 lib/Makefile                       |  2 +
 lib/longest_symbol_kunit.c         | 84 ++++++++++++++++++++++++++++++
 4 files changed, 97 insertions(+), 1 deletion(-)
 create mode 100644 lib/longest_symbol_kunit.c

index 472540aeabc2..3bde35ea4188 100644
@@ -10,6 +10,7 @@
 #include <assert.h>
 #include <unistd.h>
 #include <stdarg.h>
+#include <linux/kallsysms.h>
 
 #define unlikely(cond) (cond)
 

@@ -106,7 +107,7 @@ static void parse_args(int argc, char **argv)
 	}
 }
 
-#define BUFSIZE 256
+#define BUFSIZE (256 + KSYM_NAME_LEN)
 
 int main(int argc, char **argv)
 {

index 775966cf6114..9bab160efa4a 100644
@@ -2852,6 +2852,15 @@ config FORTIFY_KUNIT_TEST
 	  by the str*() and mem*() family of functions. For testing runtime
 	  traps of FORTIFY_SOURCE, see LKDTM's "FORTIFY_*" tests.
 
+config LONGEST_SYM_KUNIT_TEST
+	tristate "Test the longest symbol possible" if !KUNIT_ALL_TESTS
+	depends on KUNIT && KPROBES
+	default KUNIT_ALL_TESTS
+	help
+	  Tests the longest symbol possible
+
+	  If unsure, say N.
+
 config HW_BREAKPOINT_KUNIT_TEST
 	bool "Test hw_breakpoint constraints accounting" if !KUNIT_ALL_TESTS
 	depends on HAVE_HW_BREAKPOINT

index f1c6e9d76a7c..33b5ef908764 100644
@@ -393,6 +393,8 @@ obj-$(CONFIG_FORTIFY_KUNIT_TEST) += fortify_kunit.o
 obj-$(CONFIG_CRC_KUNIT_TEST) += crc_kunit.o
 obj-$(CONFIG_SIPHASH_KUNIT_TEST) += siphash_kunit.o
 obj-$(CONFIG_USERCOPY_KUNIT_TEST) += usercopy_kunit.o
+obj-$(CONFIG_LONGEST_SYM_KUNIT_TEST) += longest_symbol_kunit.o
+CFLAGS_longest_symbol_kunit.o += $(call cc-disable-warning, missing-prototypes)
 
 obj-$(CONFIG_GENERIC_LIB_DEVMEM_IS_ALLOWED) += devmem_is_allowed.o
 

base-commit: 6d61a53dd6f55405ebcaea6ee38d1ab5a8856c2c

2.39.2