Hi Shuah,
Could you take a look at this patch?
Thanks!
On Fri, Oct 17, 2025 at 1:40 AM Kuniyuki Iwashima kuniyu@google.com 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/f3d97de9954f9df758c0ab287ca7e24e654288c... #[0] Signed-off-by: Kuniyuki Iwashima kuniyu@google.com
Documentation/dev-tools/kselftest.rst | 41 +++++++ tools/testing/selftests/Makefile | 14 ++- tools/testing/selftests/kselftest_harness.h | 128 +++++++++++++++++++- 3 files changed, 174 insertions(+), 9 deletions(-)
diff --git a/Documentation/dev-tools/kselftest.rst b/Documentation/dev-tools/kselftest.rst index 18c2da67fae42..5c2b92ac4a300 100644 --- a/Documentation/dev-tools/kselftest.rst +++ b/Documentation/dev-tools/kselftest.rst @@ -200,6 +200,47 @@ You can look at the TAP output to see if you ran into the timeout. Test runners which know a test must run under a specific time can then optionally treat these timeouts then as fatal.
+KCOV for selftests +==================
+Selftests built with `kselftest_harness.h` natively support generating +KCOV coverage data. See :doc:`KCOV: code coverage for fuzzing </dev-tools/kcov>` +for prerequisites.
+You can specify the output directory with the `KCOV_OUTPUT` environment +variable. Additionally, you can specify the number of instructions to +collect with the `KCOV_SLOTS` environment variable ::
- # KCOV_OUTPUT=$PWD/kcov KCOV_SLOTS=$((4096 * 2)) \
./tools/testing/selftests/net/af_unix/scm_inq+In the output directory, a coverage file is generated for each test +case in the selftest ::
- $ ls kcov/
- scm_inq.dgram.basic scm_inq.seqpacket.basic scm_inq.stream.basic
+The default value of `KCOV_SLOTS` is `4096`, and `KCOV_SLOTS` multiplied +by `sizeof(unsigned long)` must be multiple of `4096`, so the smallest +value is `512`.
+Both `KCOV_OUTPUT` and `KCOV_SLOTS` can be specified as the variables +on the `make` command line ::
- # make -C tools/testing/selftests/ \
kselftest_override_timeout=60 \KCOV_OUTPUT=$PWD/kcov KCOV_SLOTS=$((4096 * 4)) \TARGETS=net/af_unix run_tests+The collected data can be 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
- ...
Packaging selftests
diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile index c46ebdb9b8ef7..40e70fb1a3478 100644 --- a/tools/testing/selftests/Makefile +++ b/tools/testing/selftests/Makefile @@ -218,12 +218,14 @@ all: done; exit $$ret;
run_tests: all
@for TARGET in $(TARGETS); do \BUILD_TARGET=$$BUILD/$$TARGET; \$(MAKE) OUTPUT=$$BUILD_TARGET -C $$TARGET run_tests \SRC_PATH=$(shell readlink -e $$(pwd)) \OBJ_PATH=$(BUILD) \O=$(abs_objtree); \
@for TARGET in $(TARGETS); do \BUILD_TARGET=$$BUILD/$$TARGET; \$(MAKE) OUTPUT=$$BUILD_TARGET \KCOV_OUTPUT=$(abspath $(KCOV_OUTPUT)) \-C $$TARGET run_tests \SRC_PATH=$(shell readlink -e $$(pwd)) \OBJ_PATH=$(BUILD) \O=$(abs_objtree); \ done;hotplug: diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h index 3f66e862e83eb..cba8020853b5d 100644 --- a/tools/testing/selftests/kselftest_harness.h +++ b/tools/testing/selftests/kselftest_harness.h @@ -56,6 +56,8 @@ #include <asm/types.h> #include <ctype.h> #include <errno.h> +#include <fcntl.h> +#include <linux/kcov.h> #include <linux/unistd.h> #include <poll.h> #include <stdbool.h> @@ -63,7 +65,9 @@ #include <stdio.h> #include <stdlib.h> #include <string.h> +#include <sys/ioctl.h> #include <sys/mman.h> +#include <sys/stat.h> #include <sys/types.h> #include <sys/wait.h> #include <unistd.h> @@ -401,7 +405,8 @@ const FIXTURE_VARIANT(fixture_name) *variant); \ static void wrapper_##fixture_name##_##test_name( \ struct __test_metadata *_metadata, \
struct __fixture_variant_metadata *variant) \
struct __fixture_variant_metadata *variant, \char *test_full_name) \ { \ /* fixture data is alloced, setup, and torn down per call. */ \ FIXTURE_DATA(fixture_name) self_private, *self = NULL; \@@ -430,7 +435,9 @@ if (_metadata->exit_code) \ _exit(0); \ *_metadata->no_teardown = false; \
enable_kcov(_metadata); \ fixture_name##_##test_name(_metadata, self, variant->data); \disable_kcov(_metadata, test_full_name); \ _metadata->teardown_fn(false, _metadata, self, variant->data); \ _exit(0); \ } else if (child < 0 || child != waitpid(child, &status, 0)) { \@@ -470,6 +477,8 @@ object->teardown_fn = &wrapper_##fixture_name##_##test_name##_teardown; \ object->termsig = signal; \ object->timeout = tmout; \
object->kcov_fd = -1; \object->kcov_slots = -1; \ _##fixture_name##_##test_name##_object = object; \ __register_test(object); \ } \@@ -908,7 +917,8 @@ __register_fixture_variant(struct __fixture_metadata *f, struct __test_metadata { const char *name; void (*fn)(struct __test_metadata *,
struct __fixture_variant_metadata *);
struct __fixture_variant_metadata *,char *test_name); pid_t pid; /* pid of test when being run */ struct __fixture_metadata *fixture; void (*teardown_fn)(bool in_parent, struct __test_metadata *_metadata,@@ -923,6 +933,10 @@ struct __test_metadata { const void *variant; struct __test_results *results; struct __test_metadata *prev, *next;
int kcov_fd;int kcov_slots;char *kcov_dir;unsigned long *kcov_mem;};
static inline bool __test_passed(struct __test_metadata *metadata) @@ -1185,6 +1199,114 @@ static bool test_enabled(int argc, char **argv, return !has_positive; }
+#define KCOV_SLOTS 4096
+static void enable_kcov(struct __test_metadata *t) +{
char *slots;int err;t->kcov_dir = getenv("KCOV_OUTPUT");if (!t->kcov_dir || *t->kcov_dir == '\0')return;slots = getenv("KCOV_SLOTS");if (slots && *slots != '\0')sscanf(slots, "%d", &t->kcov_slots);if (t->kcov_slots <= 0)t->kcov_slots = KCOV_SLOTS;t->kcov_fd = open("/sys/kernel/debug/kcov", O_RDWR);if (t->kcov_fd < 0) {ksft_print_msg("ERROR OPENING KCOV FD\n");goto err;}err = ioctl(t->kcov_fd, KCOV_INIT_TRACE, t->kcov_slots);if (err) {ksft_print_msg("ERROR INITIALISING KCOV\n");goto err;}t->kcov_mem = mmap(NULL, sizeof(unsigned long) * t->kcov_slots,PROT_READ | PROT_WRITE, MAP_SHARED, t->kcov_fd, 0);if ((void *)t->kcov_mem == MAP_FAILED) {ksft_print_msg("ERROR ALLOCATING MEMORY FOR KCOV\n");goto err;}err = ioctl(t->kcov_fd, KCOV_ENABLE, KCOV_TRACE_PC);if (err) {ksft_print_msg("ERROR ENABLING KCOV\n");goto err;}__atomic_store_n(&t->kcov_mem[0], 0, __ATOMIC_RELAXED);return;+err:
t->exit_code = KSFT_FAIL;_exit(KSFT_FAIL);+}
+static void disable_kcov(struct __test_metadata *t, char *test_name) +{
int slots, err, dir, fd, i;if (t->kcov_fd == -1)return;slots = __atomic_load_n(&t->kcov_mem[0], __ATOMIC_RELAXED);if (slots == t->kcov_slots - 1)ksft_print_msg("Set KCOV_SLOTS to a value greater than %d\n", t->kcov_slots);err = ioctl(t->kcov_fd, KCOV_DISABLE, 0);if (err) {ksft_print_msg("ERROR DISABLING KCOV\n");goto out;}err = mkdir(t->kcov_dir, 0755);if (err == -1 && errno != EEXIST) {ksft_print_msg("ERROR CREATING '%s'\n", t->kcov_dir);goto out;}err = 0;dir = open(t->kcov_dir, O_DIRECTORY);if (dir < 0) {ksft_print_msg("ERROR OPENING %s\n", t->kcov_dir);err = dir;goto out;}fd = openat(dir, test_name, O_RDWR | O_CREAT | O_TRUNC);close(dir);if (fd == -1) {ksft_print_msg("ERROR CREATING '%s' at '%s'\n", test_name, t->kcov_dir);err = fd;goto out;}for (i = 0; i < slots; i++) {char buf[64];int size;size = snprintf(buf, 64, "0x%lx\n", t->kcov_mem[i + 1]);write(fd, buf, size);}+out:
munmap(t->kcov_mem, sizeof(t->kcov_mem[0]) * t->kcov_slots);close(t->kcov_fd);if (err) {t->exit_code = KSFT_FAIL;_exit(KSFT_FAIL);}+}
static void __run_test(struct __fixture_metadata *f, struct __fixture_variant_metadata *variant, struct __test_metadata *t) @@ -1216,7 +1338,7 @@ static void __run_test(struct __fixture_metadata *f, t->exit_code = KSFT_FAIL; } else if (child == 0) { setpgrp();
t->fn(t, variant);
t->fn(t, variant, test_name); _exit(t->exit_code); } else { t->pid = child;-- 2.51.0.858.gf9c4a03a3a-goog