Re: [PATCH v2] selftests: harness: Support KCOV.

[Shuah Khan <skhan@linuxfoundation.org>]

On 10/27/25 20:42, Kuniyuki Iwashima wrote:
> While writing a selftest with kselftest_harness.h, I often want to
> check which paths are actually exercised.
> 
> Let's support generating KCOV coverage data.
> 
> We can specify the output directory via the KCOV_OUTPUT environment
> variable, and the number of instructions to collect via the KCOV_SLOTS
> environment variable.
> 
>    # KCOV_OUTPUT=$PWD/kcov KCOV_SLOTS=$((4096 * 2)) \
>      ./tools/testing/selftests/net/af_unix/scm_inq
> 
> Both variables can also be specified as the make variable.
> 
>    # make -C tools/testing/selftests/ \
>      KCOV_OUTPUT=$PWD/kcov KCOV_SLOTS=$((4096 * 4)) \
>      kselftest_override_timeout=60 TARGETS=net/af_unix run_tests
> 
> The coverage data can be simply decoded with addr2line:
> 
>    $ cat kcov/* | sort | uniq | addr2line -e vmlinux | grep unix
>    net/unix/af_unix.c:1056
>    net/unix/af_unix.c:3138
>    net/unix/af_unix.c:3834
>    net/unix/af_unix.c:3838
>    net/unix/af_unix.c:311 (discriminator 2)
>    ...
> 
> or more nicely with a script embedded in vock [0]:
> 
>    $ cat kcov/* | sort | uniq > local.log
>    $ python3 ~/kernel/tools/vock/report.py \
>      --kernel-src ./ --vmlinux ./vmlinux \
>      --mode local --local-log local.log --filter unix
>    ...
>    ------------------------------- Coverage Report --------------------------------
>    📄 net/unix/af_unix.c (276 lines)
>     ...
>    942 | static int unix_setsockopt(struct socket *sock, int level, int optname,
>    943 | 			   sockptr_t optval, unsigned int optlen)
>    944 | {
>     ...
>    961 | 	switch (optname) {
>    962 | 	case SO_INQ:
>    963 > 		if (sk->sk_type != SOCK_STREAM)
>    964 | 			return -EINVAL;
>    965 |
>    966 > 		if (val > 1 || val < 0)
>    967 | 			return -EINVAL;
>    968 |
>    969 > 		WRITE_ONCE(u->recvmsg_inq, val);
>    970 | 		break;
> 
> Link: https://github.com/kzall0c/vock/blob/f3d97de9954f9df758c0ab287ca7e24e654288c7/report.py #[0]
> Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
> ---
> v2: Support TEST()
> v1: https://lore.kernel.org/linux-kselftest/20251017084022.3721950-1-kuniyu@google.com/
> ---
>   Documentation/dev-tools/kselftest.rst       |  41 ++++++
>   tools/testing/selftests/Makefile            |  14 ++-
>   tools/testing/selftests/kselftest_harness.h | 133 +++++++++++++++++++-
>   3 files changed, 178 insertions(+), 10 deletions(-)
> 

I am okay with kcov support being added. You probably have to fix a few things.
kernel test robot is still complaining on v2.

thanks,
-- Shuah