Re: [PATCH v4] Kunit to check the longest symbol length

[Shuah Khan <skhan@linuxfoundation.org>]

On 9/24/24 11:23, Sergio González Collado wrote:
> The longest length of a symbol (KSYM_NAME_LEN) was increased to 512
> in the reference [1]. This patch adds a kunit test to check the longest
> symbol length.
> 
> This test can also help other efforts for longer symbol lenght,
Spelling - length

Can you explain what kind of tests does it run and how it is useful?
Include test output in the change log.

> like [2].
> 
> [1] https://lore.kernel.org/lkml/20220802015052.10452-6-ojeda@kernel.org/
> [2] https://lore.kernel.org/lkml/20240605032120.3179157-1-song@kernel.org/
> 
> Tested-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
> Signed-off-by: Sergio González Collado <sergio.collado@gmail.com>
> ---
> V1 -> V2: corrected CI tests. Added fix proposed at [3]
> 
> [3] https://lore.kernel.org/lkml/Y9ES4UKl%2F+DtvAVS@gmail.com/T/#m3ef0e12bb834d01ed1ebdcae12ef5f2add342077
> ---
> V2 -> V3: updated base and added MODULE_DESCRIPTION() and MODULE_AUTHOR()
> ---
> V3 -> V4: add x86 mantainers, add new reference.
> ---
>   arch/x86/tools/insn_decoder_test.c |   3 +-
>   lib/Kconfig.debug                  |   9 +++
>   lib/Makefile                       |   2 +
>   lib/longest_symbol_kunit.c         | 124 +++++++++++++++++++++++++++++
>   4 files changed, 137 insertions(+), 1 deletion(-)
>   create mode 100644 lib/longest_symbol_kunit.c
> 
> diff --git a/arch/x86/tools/insn_decoder_test.c b/arch/x86/tools/insn_decoder_test.c
> index 472540aeabc2..3bde35ea4188 100644
> --- a/arch/x86/tools/insn_decoder_test.c
> +++ b/arch/x86/tools/insn_decoder_test.c
> @@ -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)
>   {
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index bc8faa4509e1..09015e7e07f3 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -2805,6 +2805,15 @@ 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

Can you add more detail why one would want to enable this test?

> +
> +	  If unsure, say N.
> +
>   config HW_BREAKPOINT_KUNIT_TEST
>   	bool "Test hw_breakpoint constraints accounting" if !KUNIT_ALL_TESTS
>   	depends on HAVE_HW_BREAKPOINT
> diff --git a/lib/Makefile b/lib/Makefile
> index 773adf88af41..fc878e716825 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -389,6 +389,8 @@ CFLAGS_fortify_kunit.o += $(DISABLE_STRUCTLEAK_PLUGIN)
>   obj-$(CONFIG_FORTIFY_KUNIT_TEST) += fortify_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
>   
> diff --git a/lib/longest_symbol_kunit.c b/lib/longest_symbol_kunit.c
> new file mode 100644
> index 000000000000..557ad6eae56c
> --- /dev/null
> +++ b/lib/longest_symbol_kunit.c
> @@ -0,0 +1,124 @@
> +// 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
> + */
> +
> +#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)
> +
> +#define PLUS1(name) __PASTE(name, e)
> +
> +/*Generate a symbol whose name length is 511 */
> +#define LONGEST_SYM_NAME  DDDDDI(g1h2i3j4k5l6m7n)
> +
> +/*Generate a symbol whose name length is 512 */
> +#define LONGEST_SYM_NAME_PLUS1 PLUS1(LONGEST_SYM_NAME)
> +
> +#define RETURN_LONGEST_SYM 0xAAAAA
> +#define RETURN_LONGEST_SYM_PLUS1 0x55555
> +
> +noinline int LONGEST_SYM_NAME(void);
> +noinline int LONGEST_SYM_NAME(void)
> +{
> +	return RETURN_LONGEST_SYM;
> +}
> +
> +noinline int LONGEST_SYM_NAME_PLUS1(void);
> +noinline int LONGEST_SYM_NAME_PLUS1(void)
> +{
> +	return RETURN_LONGEST_SYM_PLUS1;
> +}
> +
> +_Static_assert(sizeof(__stringify(LONGEST_SYM_NAME)) == KSYM_NAME_LEN,
> +"Incorrect symbol length found. Expected KSYM_NAME_LEN: "
> +__stringify(KSYM_NAME) ", 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\n", __func__);
> +		KUNIT_FAIL(test, "test_longest_symbol kallsysms: 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 void test_longest_symbol_plus1(struct kunit *test)
> +{
> +	KUNIT_EXPECT_EQ(test, RETURN_LONGEST_SYM_PLUS1, LONGEST_SYM_NAME_PLUS1());
> +};
> +
> +static void test_longest_symbol_plus1_kallsyms(struct kunit *test)
> +{
> +	unsigned long (*kallsyms_lookup_name)(const char *name);
> +	static int (*longest_sym_plus1)(void);
> +
> +	struct kprobe kp = {
> +		.symbol_name = "kallsyms_lookup_name",
> +	};
> +
> +	if (register_kprobe(&kp) < 0) {
> +		pr_info("%s: kprobe not registered\n", __func__);
> +		KUNIT_FAIL(test, "test_longest_symbol kallsysms: kprobe not registered\n");
> +		return;
> +	}
> +
> +	kunit_warn(test, "test_longest_symbol_plus1 kallsyms: kprobe registered\n");
> +	kallsyms_lookup_name = (unsigned long (*)(const char *name))kp.addr;
> +	unregister_kprobe(&kp);
> +
> +	longest_sym_plus1 =
> +		(void *) kallsyms_lookup_name(__stringify(LONGEST_SYM_NAME_PLUS1));
> +	KUNIT_EXPECT_NULL(test, longest_sym_plus1);
> +};
> +
> +static struct kunit_case longest_symbol_test_cases[] = {
> +	KUNIT_CASE(test_longest_symbol),
> +	KUNIT_CASE(test_longest_symbol_kallsyms),
> +	KUNIT_CASE(test_longest_symbol_plus1),
> +	KUNIT_CASE(test_longest_symbol_plus1_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: abf2050f51fdca0fd146388f83cddd95a57a008d

thanks,
-- Shuah