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To build: $ make -C tools/testing/selftests/kcov kcov_test Signed-off-by: Alexander Potapenko --- MAINTAINERS | 1 + tools/testing/selftests/kcov/Makefile | 6 + tools/testing/selftests/kcov/kcov_test.c | 364 +++++++++++++++++++++++ 3 files changed, 371 insertions(+) create mode 100644 tools/testing/selftests/kcov/Makefile create mode 100644 tools/testing/selftests/kcov/kcov_test.c diff --git a/MAINTAINERS b/MAINTAINERS index 5bbc78b0fa6ed..0ec909e085077 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -12833,6 +12833,7 @@ 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/ =20 KCSAN M: Marco Elver diff --git a/tools/testing/selftests/kcov/Makefile b/tools/testing/selftest= s/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 +=3D -static + +TEST_GEN_PROGS :=3D kcov_test + +include ../lib.mk diff --git a/tools/testing/selftests/kcov/kcov_test.c b/tools/testing/selft= ests/kcov/kcov_test.c new file mode 100644 index 0000000000000..4d3ca41f28af4 --- /dev/null +++ b/tools/testing/selftests/kcov/kcov_test.c @@ -0,0 +1,364 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Test the kernel coverage (/sys/kernel/debug/kcov). + * + * Copyright 2025 Google LLC. + */ +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include "../kselftest_harness.h" + +/* Normally these defines should be provided by linux/kcov.h, but they are= n't there yet. */ +#define KCOV_UNIQUE_ENABLE _IOW('c', 103, unsigned long) +#define KCOV_RESET_TRACE _IO('c', 104) + +#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 =3D KCOV_TRACE_PC, + .fast_reset =3D true, + .map_readonly =3D false, +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(kcov, mode_trace_cmp) +{ + /* clang-format on */ + .mode =3D KCOV_TRACE_CMP, + .fast_reset =3D true, + .map_readonly =3D false, +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(kcov, reset_ioctl_rw) +{ + /* clang-format on */ + .mode =3D KCOV_TRACE_PC, + .fast_reset =3D false, + .map_readonly =3D false, +}; + +FIXTURE_VARIANT_ADD(kcov, reset_ioctl_ro) +/* clang-format off */ +{ + /* clang-format on */ + .mode =3D KCOV_TRACE_PC, + .fast_reset =3D false, + .map_readonly =3D 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 =3D open("/sys/kernel/debug/kcov", O_RDWR); + + ASSERT_NE(fd, -1) + { + perror("open"); + } + + EXPECT_EQ(ioctl(fd, KCOV_INIT_TRACE, COVER_SIZE), 0) + { + perror("ioctl KCOV_INIT_TRACE"); + close(fd); + } + + /* Mmap buffer shared between kernel- and user-space. */ + mapping =3D (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 =3D mapping; + + return fd; +} + +FIXTURE_SETUP(kcov) +{ + int prot =3D 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 =3D COVER_SIZE; + self->fd =3D 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"); + munmap(self->mapping, COVER_SIZE * sizeof(unsigned long)); + close(self->fd); + } +} + +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 =3D 0; + + TH_LOG("Collected %lu PCs", end - start); +#if DEBUG_COVER_PCS + for (i =3D 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 =3D __atomic_load_n(&cover[0], __ATOMIC_RELAXED); + /* + * Call the target syscall call. Here we use read(-1, NULL, 0) as an exam= ple. + * 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 =3D __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 =3D + 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 =3D __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 =3D collect_coverage_once(_metadata, self->mapping); + second =3D 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 =3D __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 =3D __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 =3D true, + .map_readonly =3D false, +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(kcov_uniq, slow_rw) +{ + /* clang-format on */ + .fast_reset =3D false, + .map_readonly =3D false, +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(kcov_uniq, slow_ro) +{ + /* clang-format on */ + .fast_reset =3D false, + .map_readonly =3D true, +}; + +FIXTURE_SETUP(kcov_uniq) +{ + int prot =3D 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 =3D COVER_SIZE; + self->fd =3D kcov_open_init(_metadata, self->mapping_size, prot, + &(self->mapping)); + + /* Enable coverage collection on the current thread. */ + EXPECT_EQ(ioctl(self->fd, KCOV_UNIQUE_ENABLE, BITMAP_SIZE), 0) + { + perror("ioctl KCOV_ENABLE"); + munmap(self->mapping, COVER_SIZE * sizeof(unsigned long)); + close(self->fd); + } +} + +FIXTURE_TEARDOWN(kcov_uniq) +{ + kcov_uninit_close(_metadata, self->fd, self->mapping, + self->mapping_size); +} + +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_coverage(_metadata, variant->fast_reset, self->fd, self->mapping); + + /* + * Collect the coverage for a single syscall two times in a row. + * Use collect_coverage_unchecked(), because it may return zero coverage. + */ + first =3D collect_coverage_unchecked(_metadata, self->mapping, + /*dump*/ true); + second =3D collect_coverage_unchecked(_metadata, self->mapping, + /*dump*/ true); + + /* 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 saturate the unique coverage bitmap. */ + reset_coverage(_metadata, variant->fast_reset, self->fd, self->mapping); + for (i =3D 0; i < 1000; i++) + collect_coverage_unchecked(_metadata, self->mapping, + /*dump*/ false); + /* Another invocation of collect_coverage_unchecked() should not produce = new coverage. */ + EXPECT_EQ(collect_coverage_unchecked(_metadata, self->mapping, + /*dump*/ false), + 0); + + before =3D __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 =3D __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); +} + +TEST_HARNESS_MAIN --=20 2.50.0.727.gbf7dc18ff4-goog