Implement test fixtures for testing different combinations of coverage
collection modes:
- unique and non-unique coverage;
- collecting PCs and comparison arguments;
- mapping the buffer as RO and RW.
To build:
$ make -C tools/testing/selftests/kcov kcov_test
Signed-off-by: Alexander Potapenko <glider@google.com>
---
v3:
- Address comments by Dmitry Vyukov:
- add tools/testing/selftests/kcov/config
- add ifdefs to KCOV_UNIQUE_ENABLE and KCOV_RESET_TRACE
- Properly handle/reset the coverage buffer when collecting unique
coverage
Change-Id: I0793f1b91685873c77bcb222a03f64321244df8f
---
MAINTAINERS | 1 +
tools/testing/selftests/kcov/Makefile | 6 +
tools/testing/selftests/kcov/config | 1 +
tools/testing/selftests/kcov/kcov_test.c | 401 +++++++++++++++++++++++
4 files changed, 409 insertions(+)
create mode 100644 tools/testing/selftests/kcov/Makefile
create mode 100644 tools/testing/selftests/kcov/config
create mode 100644 tools/testing/selftests/kcov/kcov_test.c
diff --git a/MAINTAINERS b/MAINTAINERS
index 6906eb9d88dae..c1d64cef693b9 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -13018,6 +13018,7 @@ F: include/linux/kcov_types.h
F: include/uapi/linux/kcov.h
F: kernel/kcov.c
F: scripts/Makefile.kcov
+F: tools/testing/selftests/kcov/
KCSAN
M: Marco Elver <elver@google.com>
diff --git a/tools/testing/selftests/kcov/Makefile b/tools/testing/selftests/kcov/Makefile
new file mode 100644
index 0000000000000..08abf8b60bcf9
--- /dev/null
+++ b/tools/testing/selftests/kcov/Makefile
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0-only
+LDFLAGS += -static
+
+TEST_GEN_PROGS := kcov_test
+
+include ../lib.mk
diff --git a/tools/testing/selftests/kcov/config b/tools/testing/selftests/kcov/config
new file mode 100644
index 0000000000000..75726b2aa9979
--- /dev/null
+++ b/tools/testing/selftests/kcov/config
@@ -0,0 +1 @@
+CONFIG_KCOV=y
diff --git a/tools/testing/selftests/kcov/kcov_test.c b/tools/testing/selftests/kcov/kcov_test.c
new file mode 100644
index 0000000000000..daf12aeb374b5
--- /dev/null
+++ b/tools/testing/selftests/kcov/kcov_test.c
@@ -0,0 +1,401 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test the kernel coverage (/sys/kernel/debug/kcov).
+ *
+ * Copyright 2025 Google LLC.
+ */
+#include <fcntl.h>
+#include <linux/kcov.h>
+#include <stdint.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "../kselftest_harness.h"
+
+/* Normally these defines should be provided by linux/kcov.h, but they aren't there yet. */
+#ifndef KCOV_UNIQUE_ENABLE
+#define KCOV_UNIQUE_ENABLE _IOW('c', 103, unsigned long)
+#endif
+#ifndef KCOV_RESET_TRACE
+#define KCOV_RESET_TRACE _IO('c', 104)
+#endif
+
+#define COVER_SIZE (64 << 10)
+#define BITMAP_SIZE (4 << 10)
+
+#define DEBUG_COVER_PCS 0
+
+FIXTURE(kcov)
+{
+ int fd;
+ unsigned long *mapping;
+ size_t mapping_size;
+};
+
+FIXTURE_VARIANT(kcov)
+{
+ int mode;
+ bool fast_reset;
+ bool map_readonly;
+};
+
+/* clang-format off */
+FIXTURE_VARIANT_ADD(kcov, mode_trace_pc)
+{
+ /* clang-format on */
+ .mode = KCOV_TRACE_PC,
+ .fast_reset = true,
+ .map_readonly = false,
+};
+
+/* clang-format off */
+FIXTURE_VARIANT_ADD(kcov, mode_trace_cmp)
+{
+ /* clang-format on */
+ .mode = KCOV_TRACE_CMP,
+ .fast_reset = true,
+ .map_readonly = false,
+};
+
+/* clang-format off */
+FIXTURE_VARIANT_ADD(kcov, reset_ioctl_rw)
+{
+ /* clang-format on */
+ .mode = KCOV_TRACE_PC,
+ .fast_reset = false,
+ .map_readonly = false,
+};
+
+FIXTURE_VARIANT_ADD(kcov, reset_ioctl_ro)
+/* clang-format off */
+{
+ /* clang-format on */
+ .mode = KCOV_TRACE_PC,
+ .fast_reset = false,
+ .map_readonly = true,
+};
+
+int kcov_open_init(struct __test_metadata *_metadata, unsigned long size,
+ int prot, unsigned long **out_mapping)
+{
+ unsigned long *mapping;
+
+ /* A single fd descriptor allows coverage collection on a single thread. */
+ int fd = open("/sys/kernel/debug/kcov", O_RDWR);
+
+ ASSERT_NE(fd, -1)
+ {
+ perror("open");
+ }
+
+ EXPECT_EQ(ioctl(fd, KCOV_INIT_TRACE, size), 0)
+ {
+ perror("ioctl KCOV_INIT_TRACE");
+ close(fd);
+ }
+
+ /* Mmap buffer shared between kernel- and user-space. */
+ mapping = (unsigned long *)mmap(NULL, size * sizeof(unsigned long),
+ prot, MAP_SHARED, fd, 0);
+ ASSERT_NE((void *)mapping, MAP_FAILED)
+ {
+ perror("mmap");
+ close(fd);
+ }
+ *out_mapping = mapping;
+
+ return fd;
+}
+
+FIXTURE_SETUP(kcov)
+{
+ int prot = variant->map_readonly ? PROT_READ : (PROT_READ | PROT_WRITE);
+
+ /* Read-only mapping is incompatible with fast reset. */
+ ASSERT_FALSE(variant->map_readonly && variant->fast_reset);
+
+ self->mapping_size = COVER_SIZE;
+ self->fd = kcov_open_init(_metadata, self->mapping_size, prot,
+ &(self->mapping));
+
+ /* Enable coverage collection on the current thread. */
+ EXPECT_EQ(ioctl(self->fd, KCOV_ENABLE, variant->mode), 0)
+ {
+ perror("ioctl KCOV_ENABLE");
+ /* Cleanup will be handled by FIXTURE_TEARDOWN. */
+ return;
+ }
+}
+
+void kcov_uninit_close(struct __test_metadata *_metadata, int fd,
+ unsigned long *mapping, size_t size)
+{
+ /* Disable coverage collection for the current thread. */
+ EXPECT_EQ(ioctl(fd, KCOV_DISABLE, 0), 0)
+ {
+ perror("ioctl KCOV_DISABLE");
+ }
+
+ /* Free resources. */
+ EXPECT_EQ(munmap(mapping, size * sizeof(unsigned long)), 0)
+ {
+ perror("munmap");
+ }
+
+ EXPECT_EQ(close(fd), 0)
+ {
+ perror("close");
+ }
+}
+
+FIXTURE_TEARDOWN(kcov)
+{
+ kcov_uninit_close(_metadata, self->fd, self->mapping,
+ self->mapping_size);
+}
+
+void dump_collected_pcs(struct __test_metadata *_metadata, unsigned long *cover,
+ size_t start, size_t end)
+{
+ int i = 0;
+
+ TH_LOG("Collected %lu PCs", end - start);
+#if DEBUG_COVER_PCS
+ for (i = start; i < end; i++)
+ TH_LOG("0x%lx", cover[i + 1]);
+#endif
+}
+
+/* Coverage collection helper without assertions. */
+unsigned long collect_coverage_unchecked(struct __test_metadata *_metadata,
+ unsigned long *cover, bool dump)
+{
+ unsigned long before, after;
+
+ before = __atomic_load_n(&cover[0], __ATOMIC_RELAXED);
+ /*
+ * Call the target syscall call. Here we use read(-1, NULL, 0) as an example.
+ * This will likely return an error (-EFAULT or -EBADF), but the goal is to
+ * collect coverage for the syscall's entry/exit paths.
+ */
+ read(-1, NULL, 0);
+
+ after = __atomic_load_n(&cover[0], __ATOMIC_RELAXED);
+
+ if (dump)
+ dump_collected_pcs(_metadata, cover, before, after);
+ return after - before;
+}
+
+unsigned long collect_coverage_once(struct __test_metadata *_metadata,
+ unsigned long *cover)
+{
+ unsigned long collected =
+ collect_coverage_unchecked(_metadata, cover, /*dump*/ true);
+
+ /* Coverage must be non-zero. */
+ EXPECT_GT(collected, 0);
+ return collected;
+}
+
+void reset_coverage(struct __test_metadata *_metadata, bool fast, int fd,
+ unsigned long *mapping)
+{
+ unsigned long count;
+
+ if (fast) {
+ __atomic_store_n(&mapping[0], 0, __ATOMIC_RELAXED);
+ } else {
+ EXPECT_EQ(ioctl(fd, KCOV_RESET_TRACE, 0), 0)
+ {
+ perror("ioctl KCOV_RESET_TRACE");
+ }
+ count = __atomic_load_n(&mapping[0], __ATOMIC_RELAXED);
+ EXPECT_NE(count, 0);
+ }
+}
+
+TEST_F(kcov, kcov_basic_syscall_coverage)
+{
+ unsigned long first, second, before, after, i;
+
+ /* Reset coverage that may be left over from the fixture setup. */
+ reset_coverage(_metadata, variant->fast_reset, self->fd, self->mapping);
+
+ /* Collect the coverage for a single syscall two times in a row. */
+ first = collect_coverage_once(_metadata, self->mapping);
+ second = collect_coverage_once(_metadata, self->mapping);
+ /* Collected coverage should not differ too much. */
+ EXPECT_GT(first * 10, second);
+ EXPECT_GT(second * 10, first);
+
+ /* Now reset the buffer and collect the coverage again. */
+ reset_coverage(_metadata, variant->fast_reset, self->fd, self->mapping);
+ collect_coverage_once(_metadata, self->mapping);
+
+ /* Now try many times to fill up the buffer. */
+ reset_coverage(_metadata, variant->fast_reset, self->fd, self->mapping);
+ while (collect_coverage_unchecked(_metadata, self->mapping,
+ /*dump*/ false)) {
+ /* Do nothing. */
+ }
+ before = __atomic_load_n(&(self->mapping[0]), __ATOMIC_RELAXED);
+ /*
+ * Resetting with ioctl may still generate some coverage, but much less
+ * than there was before.
+ */
+ reset_coverage(_metadata, variant->fast_reset, self->fd, self->mapping);
+ after = __atomic_load_n(&(self->mapping[0]), __ATOMIC_RELAXED);
+ EXPECT_GT(before, after);
+ /* Collecting coverage after reset will now succeed. */
+ collect_coverage_once(_metadata, self->mapping);
+}
+
+FIXTURE(kcov_uniq)
+{
+ int fd;
+ unsigned long *mapping;
+ size_t mapping_size;
+ unsigned long *bitmap;
+ size_t bitmap_size;
+ unsigned long *cover;
+ size_t cover_size;
+};
+
+FIXTURE_VARIANT(kcov_uniq)
+{
+ bool fast_reset;
+ bool map_readonly;
+};
+
+/* clang-format off */
+FIXTURE_VARIANT_ADD(kcov_uniq, fast_rw)
+{
+ /* clang-format on */
+ .fast_reset = true,
+ .map_readonly = false,
+};
+
+/* clang-format off */
+FIXTURE_VARIANT_ADD(kcov_uniq, slow_rw)
+{
+ /* clang-format on */
+ .fast_reset = false,
+ .map_readonly = false,
+};
+
+/* clang-format off */
+FIXTURE_VARIANT_ADD(kcov_uniq, slow_ro)
+{
+ /* clang-format on */
+ .fast_reset = false,
+ .map_readonly = true,
+};
+
+FIXTURE_SETUP(kcov_uniq)
+{
+ int prot = variant->map_readonly ? PROT_READ : (PROT_READ | PROT_WRITE);
+
+ /* Read-only mapping is incompatible with fast reset. */
+ ASSERT_FALSE(variant->map_readonly && variant->fast_reset);
+
+ self->mapping_size = COVER_SIZE;
+ self->fd = kcov_open_init(_metadata, self->mapping_size, prot,
+ &(self->mapping));
+
+ self->bitmap = self->mapping;
+ self->bitmap_size = BITMAP_SIZE;
+ /*
+ * Enable unique coverage collection on the current thread. Carve out
+ * self->bitmap_size unsigned long's for the bitmap.
+ */
+ EXPECT_EQ(ioctl(self->fd, KCOV_UNIQUE_ENABLE, self->bitmap_size), 0)
+ {
+ perror("ioctl KCOV_ENABLE");
+ /* Cleanup will be handled by FIXTURE_TEARDOWN. */
+ return;
+ }
+ self->cover = self->mapping + BITMAP_SIZE;
+ self->cover_size = self->mapping_size - BITMAP_SIZE;
+}
+
+FIXTURE_TEARDOWN(kcov_uniq)
+{
+ kcov_uninit_close(_metadata, self->fd, self->mapping,
+ self->mapping_size);
+}
+
+void reset_uniq_coverage(struct __test_metadata *_metadata, bool fast, int fd,
+ unsigned long *bitmap, unsigned long *cover)
+{
+ unsigned long count;
+
+ if (fast) {
+ /*
+ * Resetting the buffer for unique coverage collection requires
+ * zeroing out the bitmap and cover[0]. We are assuming that
+ * the coverage buffer immediately follows the bitmap, as they
+ * belong to the same memory mapping.
+ */
+ if (cover > bitmap)
+ memset(bitmap, 0, sizeof(unsigned long) * (cover - bitmap));
+ __atomic_store_n(&cover[0], 0, __ATOMIC_RELAXED);
+ } else {
+ EXPECT_EQ(ioctl(fd, KCOV_RESET_TRACE, 0), 0)
+ {
+ perror("ioctl KCOV_RESET_TRACE");
+ }
+ count = __atomic_load_n(&cover[0], __ATOMIC_RELAXED);
+ EXPECT_NE(count, 0);
+ }
+}
+
+TEST_F(kcov_uniq, kcov_uniq_coverage)
+{
+ unsigned long first, second, before, after, i;
+
+ /* Reset coverage that may be left over from the fixture setup. */
+ reset_uniq_coverage(_metadata, variant->fast_reset, self->fd, self->bitmap, self->cover);
+
+ /*
+ * Collect the coverage for a single syscall two times in a row.
+ * Use collect_coverage_unchecked(), because it may return zero coverage.
+ */
+ first = collect_coverage_unchecked(_metadata, self->cover,
+ /*dump*/ true);
+ second = collect_coverage_unchecked(_metadata, self->cover,
+ /*dump*/ true);
+
+ /* Now reset the buffer and collect the coverage again. */
+ reset_uniq_coverage(_metadata, variant->fast_reset, self->fd, self->bitmap, self->cover);
+ collect_coverage_once(_metadata, self->cover);
+
+ /* Now try many times to saturate the unique coverage bitmap. */
+ reset_uniq_coverage(_metadata, variant->fast_reset, self->fd, self->bitmap, self->cover);
+ for (i = 0; i < 1000; i++)
+ collect_coverage_unchecked(_metadata, self->cover,
+ /*dump*/ false);
+
+ /* Another invocation of collect_coverage_unchecked() should not produce new coverage. */
+ EXPECT_EQ(collect_coverage_unchecked(_metadata, self->cover,
+ /*dump*/ false),
+ 0);
+
+ before = __atomic_load_n(&(self->cover[0]), __ATOMIC_RELAXED);
+ /*
+ * Resetting with ioctl may still generate some coverage, but much less
+ * than there was before.
+ */
+ reset_uniq_coverage(_metadata, variant->fast_reset, self->fd, self->bitmap, self->cover);
+ after = __atomic_load_n(&(self->cover[0]), __ATOMIC_RELAXED);
+ EXPECT_GT(before, after);
+ /* Collecting coverage after reset will now succeed. */
+ collect_coverage_once(_metadata, self->cover);
+}
+
+TEST_HARNESS_MAIN
--
2.50.1.470.g6ba607880d-googOn Mon, 28 Jul 2025 at 17:26, Alexander Potapenko <glider@google.com> wrote:
>
> Implement test fixtures for testing different combinations of coverage
> collection modes:
> - unique and non-unique coverage;
> - collecting PCs and comparison arguments;
> - mapping the buffer as RO and RW.
>
> To build:
> $ make -C tools/testing/selftests/kcov kcov_test
>
> Signed-off-by: Alexander Potapenko <glider@google.com>
> ---
> v3:
> - Address comments by Dmitry Vyukov:
> - add tools/testing/selftests/kcov/config
> - add ifdefs to KCOV_UNIQUE_ENABLE and KCOV_RESET_TRACE
> - Properly handle/reset the coverage buffer when collecting unique
> coverage
>
> Change-Id: I0793f1b91685873c77bcb222a03f64321244df8f
> ---
> MAINTAINERS | 1 +
> tools/testing/selftests/kcov/Makefile | 6 +
> tools/testing/selftests/kcov/config | 1 +
> tools/testing/selftests/kcov/kcov_test.c | 401 +++++++++++++++++++++++
> 4 files changed, 409 insertions(+)
> create mode 100644 tools/testing/selftests/kcov/Makefile
> create mode 100644 tools/testing/selftests/kcov/config
> create mode 100644 tools/testing/selftests/kcov/kcov_test.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 6906eb9d88dae..c1d64cef693b9 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -13018,6 +13018,7 @@ F: include/linux/kcov_types.h
> F: include/uapi/linux/kcov.h
> F: kernel/kcov.c
> F: scripts/Makefile.kcov
> +F: tools/testing/selftests/kcov/
>
> KCSAN
> M: Marco Elver <elver@google.com>
> diff --git a/tools/testing/selftests/kcov/Makefile b/tools/testing/selftests/kcov/Makefile
> new file mode 100644
> index 0000000000000..08abf8b60bcf9
> --- /dev/null
> +++ b/tools/testing/selftests/kcov/Makefile
> @@ -0,0 +1,6 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +LDFLAGS += -static
> +
> +TEST_GEN_PROGS := kcov_test
> +
> +include ../lib.mk
> diff --git a/tools/testing/selftests/kcov/config b/tools/testing/selftests/kcov/config
> new file mode 100644
> index 0000000000000..75726b2aa9979
> --- /dev/null
> +++ b/tools/testing/selftests/kcov/config
> @@ -0,0 +1 @@
> +CONFIG_KCOV=y
Doesn't it also need CONFIG_KCOV_UNIQUE=y since it tests the unique
mode as well?
> diff --git a/tools/testing/selftests/kcov/kcov_test.c b/tools/testing/selftests/kcov/kcov_test.c
> new file mode 100644
> index 0000000000000..daf12aeb374b5
> --- /dev/null
> +++ b/tools/testing/selftests/kcov/kcov_test.c
> @@ -0,0 +1,401 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Test the kernel coverage (/sys/kernel/debug/kcov).
> + *
> + * Copyright 2025 Google LLC.
> + */
> +#include <fcntl.h>
> +#include <linux/kcov.h>
> +#include <stdint.h>
> +#include <stddef.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <sys/ioctl.h>
> +#include <sys/mman.h>
> +#include <sys/types.h>
> +#include <unistd.h>
> +
> +#include "../kselftest_harness.h"
> +
> +/* Normally these defines should be provided by linux/kcov.h, but they aren't there yet. */
> +#ifndef KCOV_UNIQUE_ENABLE
> +#define KCOV_UNIQUE_ENABLE _IOW('c', 103, unsigned long)
> +#endif
> +#ifndef KCOV_RESET_TRACE
> +#define KCOV_RESET_TRACE _IO('c', 104)
> +#endif
> +
> +#define COVER_SIZE (64 << 10)
> +#define BITMAP_SIZE (4 << 10)
> +
> +#define DEBUG_COVER_PCS 0
> +
> +FIXTURE(kcov)
> +{
> + int fd;
> + unsigned long *mapping;
> + size_t mapping_size;
> +};
> +
> +FIXTURE_VARIANT(kcov)
> +{
> + int mode;
> + bool fast_reset;
> + bool map_readonly;
> +};
> +
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(kcov, mode_trace_pc)
> +{
> + /* clang-format on */
> + .mode = KCOV_TRACE_PC,
> + .fast_reset = true,
> + .map_readonly = false,
> +};
> +
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(kcov, mode_trace_cmp)
> +{
> + /* clang-format on */
> + .mode = KCOV_TRACE_CMP,
> + .fast_reset = true,
> + .map_readonly = false,
> +};
> +
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(kcov, reset_ioctl_rw)
> +{
> + /* clang-format on */
> + .mode = KCOV_TRACE_PC,
> + .fast_reset = false,
> + .map_readonly = false,
> +};
> +
> +FIXTURE_VARIANT_ADD(kcov, reset_ioctl_ro)
> +/* clang-format off */
> +{
> + /* clang-format on */
> + .mode = KCOV_TRACE_PC,
> + .fast_reset = false,
> + .map_readonly = true,
> +};
> +
> +int kcov_open_init(struct __test_metadata *_metadata, unsigned long size,
> + int prot, unsigned long **out_mapping)
> +{
> + unsigned long *mapping;
> +
> + /* A single fd descriptor allows coverage collection on a single thread. */
> + int fd = open("/sys/kernel/debug/kcov", O_RDWR);
> +
> + ASSERT_NE(fd, -1)
> + {
> + perror("open");
> + }
> +
> + EXPECT_EQ(ioctl(fd, KCOV_INIT_TRACE, size), 0)
> + {
> + perror("ioctl KCOV_INIT_TRACE");
> + close(fd);
> + }
> +
> + /* Mmap buffer shared between kernel- and user-space. */
> + mapping = (unsigned long *)mmap(NULL, size * sizeof(unsigned long),
> + prot, MAP_SHARED, fd, 0);
> + ASSERT_NE((void *)mapping, MAP_FAILED)
> + {
> + perror("mmap");
> + close(fd);
> + }
> + *out_mapping = mapping;
> +
> + return fd;
> +}
> +
> +FIXTURE_SETUP(kcov)
> +{
> + int prot = variant->map_readonly ? PROT_READ : (PROT_READ | PROT_WRITE);
> +
> + /* Read-only mapping is incompatible with fast reset. */
> + ASSERT_FALSE(variant->map_readonly && variant->fast_reset);
> +
> + self->mapping_size = COVER_SIZE;
> + self->fd = kcov_open_init(_metadata, self->mapping_size, prot,
> + &(self->mapping));
> +
> + /* Enable coverage collection on the current thread. */
> + EXPECT_EQ(ioctl(self->fd, KCOV_ENABLE, variant->mode), 0)
> + {
> + perror("ioctl KCOV_ENABLE");
> + /* Cleanup will be handled by FIXTURE_TEARDOWN. */
> + return;
> + }
> +}
> +
> +void kcov_uninit_close(struct __test_metadata *_metadata, int fd,
> + unsigned long *mapping, size_t size)
> +{
> + /* Disable coverage collection for the current thread. */
> + EXPECT_EQ(ioctl(fd, KCOV_DISABLE, 0), 0)
> + {
> + perror("ioctl KCOV_DISABLE");
> + }
> +
> + /* Free resources. */
> + EXPECT_EQ(munmap(mapping, size * sizeof(unsigned long)), 0)
> + {
> + perror("munmap");
> + }
> +
> + EXPECT_EQ(close(fd), 0)
> + {
> + perror("close");
> + }
> +}
> +
> +FIXTURE_TEARDOWN(kcov)
> +{
> + kcov_uninit_close(_metadata, self->fd, self->mapping,
> + self->mapping_size);
> +}
> +
> +void dump_collected_pcs(struct __test_metadata *_metadata, unsigned long *cover,
> + size_t start, size_t end)
> +{
> + int i = 0;
> +
> + TH_LOG("Collected %lu PCs", end - start);
> +#if DEBUG_COVER_PCS
> + for (i = start; i < end; i++)
> + TH_LOG("0x%lx", cover[i + 1]);
> +#endif
> +}
> +
> +/* Coverage collection helper without assertions. */
> +unsigned long collect_coverage_unchecked(struct __test_metadata *_metadata,
> + unsigned long *cover, bool dump)
> +{
> + unsigned long before, after;
> +
> + before = __atomic_load_n(&cover[0], __ATOMIC_RELAXED);
> + /*
> + * Call the target syscall call. Here we use read(-1, NULL, 0) as an example.
> + * This will likely return an error (-EFAULT or -EBADF), but the goal is to
> + * collect coverage for the syscall's entry/exit paths.
> + */
> + read(-1, NULL, 0);
> +
> + after = __atomic_load_n(&cover[0], __ATOMIC_RELAXED);
> +
> + if (dump)
> + dump_collected_pcs(_metadata, cover, before, after);
> + return after - before;
> +}
> +
> +unsigned long collect_coverage_once(struct __test_metadata *_metadata,
> + unsigned long *cover)
> +{
> + unsigned long collected =
> + collect_coverage_unchecked(_metadata, cover, /*dump*/ true);
> +
> + /* Coverage must be non-zero. */
> + EXPECT_GT(collected, 0);
> + return collected;
> +}
> +
> +void reset_coverage(struct __test_metadata *_metadata, bool fast, int fd,
> + unsigned long *mapping)
> +{
> + unsigned long count;
> +
> + if (fast) {
> + __atomic_store_n(&mapping[0], 0, __ATOMIC_RELAXED);
> + } else {
> + EXPECT_EQ(ioctl(fd, KCOV_RESET_TRACE, 0), 0)
> + {
> + perror("ioctl KCOV_RESET_TRACE");
> + }
> + count = __atomic_load_n(&mapping[0], __ATOMIC_RELAXED);
> + EXPECT_NE(count, 0);
> + }
> +}
> +
> +TEST_F(kcov, kcov_basic_syscall_coverage)
> +{
> + unsigned long first, second, before, after, i;
> +
> + /* Reset coverage that may be left over from the fixture setup. */
> + reset_coverage(_metadata, variant->fast_reset, self->fd, self->mapping);
> +
> + /* Collect the coverage for a single syscall two times in a row. */
> + first = collect_coverage_once(_metadata, self->mapping);
> + second = collect_coverage_once(_metadata, self->mapping);
> + /* Collected coverage should not differ too much. */
> + EXPECT_GT(first * 10, second);
> + EXPECT_GT(second * 10, first);
> +
> + /* Now reset the buffer and collect the coverage again. */
> + reset_coverage(_metadata, variant->fast_reset, self->fd, self->mapping);
> + collect_coverage_once(_metadata, self->mapping);
> +
> + /* Now try many times to fill up the buffer. */
> + reset_coverage(_metadata, variant->fast_reset, self->fd, self->mapping);
> + while (collect_coverage_unchecked(_metadata, self->mapping,
> + /*dump*/ false)) {
> + /* Do nothing. */
> + }
> + before = __atomic_load_n(&(self->mapping[0]), __ATOMIC_RELAXED);
> + /*
> + * Resetting with ioctl may still generate some coverage, but much less
> + * than there was before.
> + */
> + reset_coverage(_metadata, variant->fast_reset, self->fd, self->mapping);
> + after = __atomic_load_n(&(self->mapping[0]), __ATOMIC_RELAXED);
> + EXPECT_GT(before, after);
> + /* Collecting coverage after reset will now succeed. */
> + collect_coverage_once(_metadata, self->mapping);
> +}
> +
> +FIXTURE(kcov_uniq)
> +{
> + int fd;
> + unsigned long *mapping;
> + size_t mapping_size;
> + unsigned long *bitmap;
> + size_t bitmap_size;
> + unsigned long *cover;
> + size_t cover_size;
> +};
> +
> +FIXTURE_VARIANT(kcov_uniq)
> +{
> + bool fast_reset;
> + bool map_readonly;
> +};
> +
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(kcov_uniq, fast_rw)
> +{
> + /* clang-format on */
> + .fast_reset = true,
> + .map_readonly = false,
> +};
> +
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(kcov_uniq, slow_rw)
> +{
> + /* clang-format on */
> + .fast_reset = false,
> + .map_readonly = false,
> +};
> +
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(kcov_uniq, slow_ro)
> +{
> + /* clang-format on */
> + .fast_reset = false,
> + .map_readonly = true,
> +};
> +
> +FIXTURE_SETUP(kcov_uniq)
> +{
> + int prot = variant->map_readonly ? PROT_READ : (PROT_READ | PROT_WRITE);
> +
> + /* Read-only mapping is incompatible with fast reset. */
> + ASSERT_FALSE(variant->map_readonly && variant->fast_reset);
> +
> + self->mapping_size = COVER_SIZE;
> + self->fd = kcov_open_init(_metadata, self->mapping_size, prot,
> + &(self->mapping));
> +
> + self->bitmap = self->mapping;
> + self->bitmap_size = BITMAP_SIZE;
> + /*
> + * Enable unique coverage collection on the current thread. Carve out
> + * self->bitmap_size unsigned long's for the bitmap.
> + */
> + EXPECT_EQ(ioctl(self->fd, KCOV_UNIQUE_ENABLE, self->bitmap_size), 0)
> + {
> + perror("ioctl KCOV_ENABLE");
> + /* Cleanup will be handled by FIXTURE_TEARDOWN. */
> + return;
> + }
> + self->cover = self->mapping + BITMAP_SIZE;
> + self->cover_size = self->mapping_size - BITMAP_SIZE;
> +}
> +
> +FIXTURE_TEARDOWN(kcov_uniq)
> +{
> + kcov_uninit_close(_metadata, self->fd, self->mapping,
> + self->mapping_size);
> +}
> +
> +void reset_uniq_coverage(struct __test_metadata *_metadata, bool fast, int fd,
> + unsigned long *bitmap, unsigned long *cover)
> +{
> + unsigned long count;
> +
> + if (fast) {
> + /*
> + * Resetting the buffer for unique coverage collection requires
> + * zeroing out the bitmap and cover[0]. We are assuming that
> + * the coverage buffer immediately follows the bitmap, as they
> + * belong to the same memory mapping.
> + */
> + if (cover > bitmap)
> + memset(bitmap, 0, sizeof(unsigned long) * (cover - bitmap));
> + __atomic_store_n(&cover[0], 0, __ATOMIC_RELAXED);
> + } else {
> + EXPECT_EQ(ioctl(fd, KCOV_RESET_TRACE, 0), 0)
> + {
> + perror("ioctl KCOV_RESET_TRACE");
> + }
> + count = __atomic_load_n(&cover[0], __ATOMIC_RELAXED);
> + EXPECT_NE(count, 0);
> + }
> +}
> +
> +TEST_F(kcov_uniq, kcov_uniq_coverage)
> +{
> + unsigned long first, second, before, after, i;
> +
> + /* Reset coverage that may be left over from the fixture setup. */
> + reset_uniq_coverage(_metadata, variant->fast_reset, self->fd, self->bitmap, self->cover);
> +
> + /*
> + * Collect the coverage for a single syscall two times in a row.
> + * Use collect_coverage_unchecked(), because it may return zero coverage.
> + */
> + first = collect_coverage_unchecked(_metadata, self->cover,
> + /*dump*/ true);
> + second = collect_coverage_unchecked(_metadata, self->cover,
> + /*dump*/ true);
> +
> + /* Now reset the buffer and collect the coverage again. */
> + reset_uniq_coverage(_metadata, variant->fast_reset, self->fd, self->bitmap, self->cover);
> + collect_coverage_once(_metadata, self->cover);
> +
> + /* Now try many times to saturate the unique coverage bitmap. */
> + reset_uniq_coverage(_metadata, variant->fast_reset, self->fd, self->bitmap, self->cover);
> + for (i = 0; i < 1000; i++)
> + collect_coverage_unchecked(_metadata, self->cover,
> + /*dump*/ false);
> +
> + /* Another invocation of collect_coverage_unchecked() should not produce new coverage. */
> + EXPECT_EQ(collect_coverage_unchecked(_metadata, self->cover,
> + /*dump*/ false),
> + 0);
> +
> + before = __atomic_load_n(&(self->cover[0]), __ATOMIC_RELAXED);
> + /*
> + * Resetting with ioctl may still generate some coverage, but much less
> + * than there was before.
> + */
> + reset_uniq_coverage(_metadata, variant->fast_reset, self->fd, self->bitmap, self->cover);
> + after = __atomic_load_n(&(self->cover[0]), __ATOMIC_RELAXED);
> + EXPECT_GT(before, after);
> + /* Collecting coverage after reset will now succeed. */
> + collect_coverage_once(_metadata, self->cover);
> +}
> +
> +TEST_HARNESS_MAIN
> --
> 2.50.1.470.g6ba607880d-goog
>
On Tue, Jul 29, 2025 at 1:20 PM Dmitry Vyukov <dvyukov@google.com> wrote: > > On Mon, 28 Jul 2025 at 17:26, Alexander Potapenko <glider@google.com> wrote: > > > > Implement test fixtures for testing different combinations of coverage > > collection modes: > > - unique and non-unique coverage; > > - collecting PCs and comparison arguments; > > - mapping the buffer as RO and RW. > > > > To build: > > $ make -C tools/testing/selftests/kcov kcov_test > > > > Signed-off-by: Alexander Potapenko <glider@google.com> > > --- > > v3: > > - Address comments by Dmitry Vyukov: > > - add tools/testing/selftests/kcov/config > > - add ifdefs to KCOV_UNIQUE_ENABLE and KCOV_RESET_TRACE > > - Properly handle/reset the coverage buffer when collecting unique > > coverage > > > > Change-Id: I0793f1b91685873c77bcb222a03f64321244df8f > > --- > > MAINTAINERS | 1 + > > tools/testing/selftests/kcov/Makefile | 6 + > > tools/testing/selftests/kcov/config | 1 + > > tools/testing/selftests/kcov/kcov_test.c | 401 +++++++++++++++++++++++ > > 4 files changed, 409 insertions(+) > > create mode 100644 tools/testing/selftests/kcov/Makefile > > create mode 100644 tools/testing/selftests/kcov/config > > create mode 100644 tools/testing/selftests/kcov/kcov_test.c > > > > diff --git a/MAINTAINERS b/MAINTAINERS > > index 6906eb9d88dae..c1d64cef693b9 100644 > > --- a/MAINTAINERS > > +++ b/MAINTAINERS > > @@ -13018,6 +13018,7 @@ F: include/linux/kcov_types.h > > F: include/uapi/linux/kcov.h > > F: kernel/kcov.c > > F: scripts/Makefile.kcov > > +F: tools/testing/selftests/kcov/ > > > > KCSAN > > M: Marco Elver <elver@google.com> > > diff --git a/tools/testing/selftests/kcov/Makefile b/tools/testing/selftests/kcov/Makefile > > new file mode 100644 > > index 0000000000000..08abf8b60bcf9 > > --- /dev/null > > +++ b/tools/testing/selftests/kcov/Makefile > > @@ -0,0 +1,6 @@ > > +# SPDX-License-Identifier: GPL-2.0-only > > +LDFLAGS += -static > > + > > +TEST_GEN_PROGS := kcov_test > > + > > +include ../lib.mk > > diff --git a/tools/testing/selftests/kcov/config b/tools/testing/selftests/kcov/config > > new file mode 100644 > > index 0000000000000..75726b2aa9979 > > --- /dev/null > > +++ b/tools/testing/selftests/kcov/config > > @@ -0,0 +1 @@ > > +CONFIG_KCOV=y > > Doesn't it also need CONFIG_KCOV_UNIQUE=y since it tests the unique > mode as well? You are right, I missed that. Another option would be to skip the test under #ifndef CONFIG_KCOV_UNIQUE, but I think for KCOV developers it is important to enable all the necessary config options.
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