Kunit to check the longest symbol length

PATCH In review Sergio González Collado 4 participants 5 messages Mar 2, 2025 – May 26, 2025

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Sergio González Collado

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2025-03-02 22:15 UTC #0 lore raw

PATCH v9 1/1 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]/

Tested-by Martin Rodriguez Reboredo <[email protected]>

Reviewed-by Shuah Khan <[email protected]>

Reviewed-by Rae Moar <[email protected]>

Signed-off-by Sergio González Collado <[email protected]>

Link https://github.com/Rust-for-Linux/linux/issues/504

---
V8 -> V9: removed unused macro & corrected error message
---
V7 -> V8: typo fixed & rebased
---
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:

```
[20:04:35] =============== longest-symbol (4 subtests) ================
[20:04:35] [PASSED] test_longest_symbol
[20:04:35] [PASSED] test_longest_symbol_kallsyms
[20:04:35] ================= [PASSED] longest-symbol ==================
[20:04:35] ============================================================
[20:04:35] Testing complete. Ran 4 tests: passed: 4
```
---
 arch/x86/tools/insn_decoder_test.c |  3 +-
 lib/Kconfig.debug                  |  9 ++++
 lib/Makefile                       |  2 +
 lib/longest_symbol_kunit.c         | 82 ++++++++++++++++++++++++++++++
 4 files changed, 95 insertions(+), 1 deletion(-)
 create mode 100644 lib/longest_symbol_kunit.c

arch/x86/tools/insn_decoder_test.c +2 -1

index 472540aeabc2..6c2986d2ad11 100644
@@ -10,6 +10,7 @@
 #include <assert.h>
 #include <unistd.h>
 #include <stdarg.h>
+#include <linux/kallsyms.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)
 {

lib/Kconfig.debug +9 -0

index 1af972a92d06..62d43aa9e8f0 100644
@@ -2838,6 +2838,15 @@ 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

lib/Makefile +2 -0

index d5cfc7afbbb8..e8fec9defec2 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

lib/longest_symbol_kunit.c new file +82 -0

82 lines not on this page · raw message

base-commit: 7eb172143d5508b4da468ed59ee857c6e5e01da6

Signature · 1 line

2.39.2

Rae Moar

Reviewed-by on v9 1/1

2025-03-05 23:18 UTC #1 lore raw

Quoted 6 lines · Sergio González Collado

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.

Hello!

Thanks for all the updates! This is now applying cleanly for me and it looks good to me.

Reviewed-by Rae Moar <[email protected]>

Thanks!
-Rae

Quoted 202 lines

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]/

Tested-by Martin Rodriguez Reboredo <[email protected]>

Reviewed-by Shuah Khan <[email protected]>

Reviewed-by Rae Moar <[email protected]>

Signed-off-by Sergio González Collado <[email protected]>

Link https://github.com/Rust-for-Linux/linux/issues/504

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

The test execution should result in something like:

```
[20:04:35] =============== longest-symbol (4 subtests) ================
[20:04:35] [PASSED] test_longest_symbol
[20:04:35] [PASSED] test_longest_symbol_kallsyms
[20:04:35] ================= [PASSED] longest-symbol ==================
[20:04:35] ============================================================
[20:04:35] Testing complete. Ran 4 tests: passed: 4
```
---
 arch/x86/tools/insn_decoder_test.c |  3 +-
 lib/Kconfig.debug                  |  9 ++++
 lib/Makefile                       |  2 +
 lib/longest_symbol_kunit.c         | 82 ++++++++++++++++++++++++++++++
 4 files changed, 95 insertions(+), 1 deletion(-)
 create mode 100644 lib/longest_symbol_kunit.c

arch/x86/tools/insn_decoder_test.c +2 -1

index 472540aeabc2..6c2986d2ad11 100644
@@ -10,6 +10,7 @@
 #include <assert.h>
 #include <unistd.h>
 #include <stdarg.h>
+#include <linux/kallsyms.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)
 {

lib/Kconfig.debug +9 -0

index 1af972a92d06..62d43aa9e8f0 100644
@@ -2838,6 +2838,15 @@ 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

lib/Makefile +2 -0

index d5cfc7afbbb8..e8fec9defec2 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

lib/longest_symbol_kunit.c new file +82 -0

new file mode 100644
index 000000000000..e3c28ff1807f
@@ -0,0 +1,82 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test the longest symbol length. Execute with:
+ *  ./tools/testing/kunit/kunit.py run longest-symbol
+ *  --arch=x86_64 --kconfig_add CONFIG_KPROBES=y --kconfig_add CONFIG_MODULES=y
+ *  --kconfig_add CONFIG_RETPOLINE=n --kconfig_add CONFIG_CFI_CLANG=n
+ *  --kconfig_add CONFIG_MITIGATION_RETPOLINE=n
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <kunit/test.h>
+#include <linux/stringify.h>
+#include <linux/kprobes.h>
+#include <linux/kallsyms.h>
+
+#define DI(name) s##name##name
+#define DDI(name) DI(n##name##name)
+#define DDDI(name) DDI(n##name##name)
+#define DDDDI(name) DDDI(n##name##name)
+#define DDDDDI(name) DDDDI(n##name##name)
+
+/*Generate a symbol whose name length is 511 */
+#define LONGEST_SYM_NAME  DDDDDI(g1h2i3j4k5l6m7n)
+
+#define RETURN_LONGEST_SYM 0xAAAAA
+
+noinline int LONGEST_SYM_NAME(void);
+noinline int LONGEST_SYM_NAME(void)
+{
+       return RETURN_LONGEST_SYM;
+}
+
+_Static_assert(sizeof(__stringify(LONGEST_SYM_NAME)) == KSYM_NAME_LEN,
+"Incorrect symbol length found. Expected KSYM_NAME_LEN: "
+__stringify(KSYM_NAME_LEN) ", but found: "
+__stringify(sizeof(LONGEST_SYM_NAME)));
+
+static void test_longest_symbol(struct kunit *test)
+{
+       KUNIT_EXPECT_EQ(test, RETURN_LONGEST_SYM, LONGEST_SYM_NAME());
+};
+
+static void test_longest_symbol_kallsyms(struct kunit *test)
+{
+       unsigned long (*kallsyms_lookup_name)(const char *name);
+       static int (*longest_sym)(void);
+
+       struct kprobe kp = {
+               .symbol_name = "kallsyms_lookup_name",
+       };
+
+       if (register_kprobe(&kp) < 0) {
+               pr_info("%s: kprobe not registered", __func__);
+               KUNIT_FAIL(test, "test_longest_symbol kallsyms: kprobe not registered\n");
+               return;
+       }
+
+       kunit_warn(test, "test_longest_symbol kallsyms: kprobe registered\n");
+       kallsyms_lookup_name = (unsigned long (*)(const char *name))kp.addr;
+       unregister_kprobe(&kp);
+
+       longest_sym =
+               (void *) kallsyms_lookup_name(__stringify(LONGEST_SYM_NAME));
+       KUNIT_EXPECT_EQ(test, RETURN_LONGEST_SYM, longest_sym());
+};
+
+static struct kunit_case longest_symbol_test_cases[] = {
+       KUNIT_CASE(test_longest_symbol),
+       KUNIT_CASE(test_longest_symbol_kallsyms),
+       {}
+};
+
+static struct kunit_suite longest_symbol_test_suite = {
+       .name = "longest-symbol",
+       .test_cases = longest_symbol_test_cases,
+};
+kunit_test_suite(longest_symbol_test_suite);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Test the longest symbol length");
+MODULE_AUTHOR("Sergio González Collado");

base-commit: 7eb172143d5508b4da468ed59ee857c6e5e01da6 --
2.39.2

David Gow

Acked-by on v9 1/1

2025-03-14 05:44 UTC #2 lore raw

In reply to Sergio González Collado

Quoted 20 lines · Sergio González Collado

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]/

Quoted 6 lines

Tested-by Martin Rodriguez Reboredo <[email protected]>
Reviewed-by Shuah Khan <[email protected]>
Reviewed-by Rae Moar <[email protected]>
Signed-off-by Sergio González Collado <[email protected]>
Link https://github.com/Rust-for-Linux/linux/issues/504
---

Acked-by David Gow <[email protected]>

I suspect that this might end up finding issues with some tools, so I'd not be surprised if it breaks something, but given the whole point is to uncover issues, we should accept it and find out. :-)

Thanks for putting so much time into this -- sorry it ended up taking so long. -- David

Quoted 182 lines

V8 -> V9: removed unused macro & corrected error message
---
V7 -> V8: typo fixed & rebased
---
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:

```
[20:04:35] =============== longest-symbol (4 subtests) ================
[20:04:35] [PASSED] test_longest_symbol
[20:04:35] [PASSED] test_longest_symbol_kallsyms
[20:04:35] ================= [PASSED] longest-symbol ==================
[20:04:35] ============================================================
[20:04:35] Testing complete. Ran 4 tests: passed: 4
```
---
 arch/x86/tools/insn_decoder_test.c |  3 +-
 lib/Kconfig.debug                  |  9 ++++
 lib/Makefile                       |  2 +
 lib/longest_symbol_kunit.c         | 82 ++++++++++++++++++++++++++++++
 4 files changed, 95 insertions(+), 1 deletion(-)
 create mode 100644 lib/longest_symbol_kunit.c

arch/x86/tools/insn_decoder_test.c +2 -1

index 472540aeabc2..6c2986d2ad11 100644
@@ -10,6 +10,7 @@
 #include <assert.h>
 #include <unistd.h>
 #include <stdarg.h>
+#include <linux/kallsyms.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)
 {

lib/Kconfig.debug +9 -0

index 1af972a92d06..62d43aa9e8f0 100644
@@ -2838,6 +2838,15 @@ 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

lib/Makefile +2 -0

index d5cfc7afbbb8..e8fec9defec2 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

lib/longest_symbol_kunit.c new file +82 -0

new file mode 100644
index 000000000000..e3c28ff1807f
@@ -0,0 +1,82 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test the longest symbol length. Execute with:
+ *  ./tools/testing/kunit/kunit.py run longest-symbol
+ *  --arch=x86_64 --kconfig_add CONFIG_KPROBES=y --kconfig_add CONFIG_MODULES=y
+ *  --kconfig_add CONFIG_RETPOLINE=n --kconfig_add CONFIG_CFI_CLANG=n
+ *  --kconfig_add CONFIG_MITIGATION_RETPOLINE=n
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <kunit/test.h>
+#include <linux/stringify.h>
+#include <linux/kprobes.h>
+#include <linux/kallsyms.h>
+
+#define DI(name) s##name##name
+#define DDI(name) DI(n##name##name)
+#define DDDI(name) DDI(n##name##name)
+#define DDDDI(name) DDDI(n##name##name)
+#define DDDDDI(name) DDDDI(n##name##name)
+
+/*Generate a symbol whose name length is 511 */
+#define LONGEST_SYM_NAME  DDDDDI(g1h2i3j4k5l6m7n)
+
+#define RETURN_LONGEST_SYM 0xAAAAA
+
+noinline int LONGEST_SYM_NAME(void);
+noinline int LONGEST_SYM_NAME(void)
+{
+       return RETURN_LONGEST_SYM;
+}
+
+_Static_assert(sizeof(__stringify(LONGEST_SYM_NAME)) == KSYM_NAME_LEN,
+"Incorrect symbol length found. Expected KSYM_NAME_LEN: "
+__stringify(KSYM_NAME_LEN) ", but found: "
+__stringify(sizeof(LONGEST_SYM_NAME)));
+
+static void test_longest_symbol(struct kunit *test)
+{
+       KUNIT_EXPECT_EQ(test, RETURN_LONGEST_SYM, LONGEST_SYM_NAME());
+};
+
+static void test_longest_symbol_kallsyms(struct kunit *test)
+{
+       unsigned long (*kallsyms_lookup_name)(const char *name);
+       static int (*longest_sym)(void);
+
+       struct kprobe kp = {
+               .symbol_name = "kallsyms_lookup_name",
+       };
+
+       if (register_kprobe(&kp) < 0) {
+               pr_info("%s: kprobe not registered", __func__);
+               KUNIT_FAIL(test, "test_longest_symbol kallsyms: kprobe not registered\n");
+               return;
+       }
+
+       kunit_warn(test, "test_longest_symbol kallsyms: kprobe registered\n");
+       kallsyms_lookup_name = (unsigned long (*)(const char *name))kp.addr;
+       unregister_kprobe(&kp);
+
+       longest_sym =
+               (void *) kallsyms_lookup_name(__stringify(LONGEST_SYM_NAME));
+       KUNIT_EXPECT_EQ(test, RETURN_LONGEST_SYM, longest_sym());
+};
+
+static struct kunit_case longest_symbol_test_cases[] = {
+       KUNIT_CASE(test_longest_symbol),
+       KUNIT_CASE(test_longest_symbol_kallsyms),
+       {}
+};
+
+static struct kunit_suite longest_symbol_test_suite = {
+       .name = "longest-symbol",
+       .test_cases = longest_symbol_test_cases,
+};
+kunit_test_suite(longest_symbol_test_suite);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Test the longest symbol length");
+MODULE_AUTHOR("Sergio González Collado");

base-commit: 7eb172143d5508b4da468ed59ee857c6e5e01da6 --
2.39.2

Miguel Ojeda

2025-05-26 18:27 UTC #3 lore raw

In reply to Sergio González Collado

Quoted 2 lines · Sergio González Collado

 arch/x86/tools/insn_decoder_test.c |  3 +-

Should at least this part of the patch be backported to the LTSs?

Thanks!

Cheers,
Miguel

Miguel Ojeda

2025-05-26 18:49 UTC #4 lore raw

Quoted 2 lines · Miguel Ojeda

Should at least this part of the patch be backported to the LTSs?

For future reference/context, we had another report at:
https://github.com/Rust-for-Linux/linux/issues/1134.

Cheers,
Miguel