Re: [PATCH 2/2] lib/tests: Add KUnit test for struct stack_trace __counted_by_ptr attribute

[Thomas Weißschuh]

On Sun, Aug 23, 2026 at 12:35:33PM +0000, Bill Wendling wrote:
> Add a custom KUnit test suite 'stacktrace_counted_by' to verify that the
> __counted_by_ptr annotation on the 'entries' field of 'struct stack_trace'
> behaves correctly.

The implementation of __counted_by_ptr should be tested by a dedicated unittest
for that feature. And I am fairly sure that already exists. It should not be
tested in random subsystems.

> The test verifies that 'max_entries' correctly limits and validates access
> to 'entries' when CONFIG_ARCH_STACKWALK is not defined. If it is defined,
> the test is cleanly skipped at runtime to prevent compile-time or runtime
> failures due to 'struct stack_trace' being undefined on modern
> architectures.
> 
> Assisted-by: Gemini Next
> Signed-off-by: Bill Wendling <morbo@xxxxxxxxxx>
> ---
> Cc: Kees Cook <kees@xxxxxxxxxx>
> Cc: "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Brendan Higgins <brendan.higgins@xxxxxxxxx>
> Cc: David Gow <david@xxxxxxxxxxxx>
> Cc: Rae Moar <raemoar63@xxxxxxxxx>
> Cc: Ryota Sakamoto <sakamo.ryota@xxxxxxxxx>
> Cc: Kuan-Wei Chiu <visitorckw@xxxxxxxxx>
> Cc: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
> Cc: Dmitry Antipov <dmantipov@xxxxxxxxx>
> Cc: Petr Mladek <pmladek@xxxxxxxx>
> Cc: Kir Chou <note351@xxxxxxxxxxx>
> Cc: codemender-patching+linux@xxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: linux-hardening@xxxxxxxxxxxxxxx
> Cc: linux-kselftest@xxxxxxxxxxxxxxx
> Cc: kunit-dev@xxxxxxxxxxxxxxxx
> Cc: linux-hardening@xxxxxxxxxxxxxxx
> ---
>  lib/Kconfig.debug            | 10 +++++++
>  lib/kunit/.kunitconfig       |  1 +
>  lib/tests/Makefile           |  1 +
>  lib/tests/stacktrace_kunit.c | 51 ++++++++++++++++++++++++++++++++++++
>  4 files changed, 63 insertions(+)
>  create mode 100644 lib/tests/stacktrace_kunit.c

(...)

> diff --git a/lib/tests/stacktrace_kunit.c b/lib/tests/stacktrace_kunit.c
> new file mode 100644
> index 000000000000..7ec48edf84fe
> --- /dev/null
> +++ b/lib/tests/stacktrace_kunit.c
> @@ -0,0 +1,51 @@

(...)

> +}
> +#else
> +static void test_stack_trace_counted_by(struct kunit *test)
> +{
> +	kunit_skip(test, "CONFIG_ARCH_STACKWALK is enabled, struct stack_trace is not defined");

If the test requires a specific kconfig symbol, then depend on it in kconfig.
Putting all of the code behind a single, giant ifdef is pointless.

> +}
> +#endif

(...)