diff options
| -rw-r--r-- | Documentation/dev-tools/kcov.rst | 99 |
1 files changed, 95 insertions, 4 deletions
diff --git a/Documentation/dev-tools/kcov.rst b/Documentation/dev-tools/kcov.rst index 44886c91e112..c2f6452e38ed 100644 --- a/Documentation/dev-tools/kcov.rst +++ b/Documentation/dev-tools/kcov.rst @@ -12,19 +12,30 @@ To achieve this goal it does not collect coverage in soft/hard interrupts and instrumentation of some inherently non-deterministic parts of kernel is disabled (e.g. scheduler, locking). -Usage ------ +kcov is also able to collect comparison operands from the instrumented code +(this feature currently requires that the kernel is compiled with clang). + +Prerequisites +------------- Configure the kernel with:: CONFIG_KCOV=y CONFIG_KCOV requires gcc built on revision 231296 or later. + +If the comparison operands need to be collected, set:: + + CONFIG_KCOV_ENABLE_COMPARISONS=y + Profiling data will only become accessible once debugfs has been mounted:: mount -t debugfs none /sys/kernel/debug -The following program demonstrates kcov usage from within a test program: +Coverage collection +------------------- +The following program demonstrates coverage collection from within a test +program using kcov: .. code-block:: c @@ -44,6 +55,9 @@ The following program demonstrates kcov usage from within a test program: #define KCOV_DISABLE _IO('c', 101) #define COVER_SIZE (64<<10) + #define KCOV_TRACE_PC 0 + #define KCOV_TRACE_CMP 1 + int main(int argc, char **argv) { int fd; @@ -64,7 +78,7 @@ The following program demonstrates kcov usage from within a test program: if ((void*)cover == MAP_FAILED) perror("mmap"), exit(1); /* Enable coverage collection on the current thread. */ - if (ioctl(fd, KCOV_ENABLE, 0)) + if (ioctl(fd, KCOV_ENABLE, KCOV_TRACE_PC)) perror("ioctl"), exit(1); /* Reset coverage from the tail of the ioctl() call. */ __atomic_store_n(&cover[0], 0, __ATOMIC_RELAXED); @@ -111,3 +125,80 @@ The interface is fine-grained to allow efficient forking of test processes. That is, a parent process opens /sys/kernel/debug/kcov, enables trace mode, mmaps coverage buffer and then forks child processes in a loop. Child processes only need to enable coverage (disable happens automatically on thread end). + +Comparison operands collection +------------------------------ +Comparison operands collection is similar to coverage collection: + +.. code-block:: c + + /* Same includes and defines as above. */ + + /* Number of 64-bit words per record. */ + #define KCOV_WORDS_PER_CMP 4 + + /* + * The format for the types of collected comparisons. + * + * Bit 0 shows whether one of the arguments is a compile-time constant. + * Bits 1 & 2 contain log2 of the argument size, up to 8 bytes. + */ + + #define KCOV_CMP_CONST (1 << 0) + #define KCOV_CMP_SIZE(n) ((n) << 1) + #define KCOV_CMP_MASK KCOV_CMP_SIZE(3) + + int main(int argc, char **argv) + { + int fd; + uint64_t *cover, type, arg1, arg2, is_const, size; + unsigned long n, i; + + fd = open("/sys/kernel/debug/kcov", O_RDWR); + if (fd == -1) + perror("open"), exit(1); + if (ioctl(fd, KCOV_INIT_TRACE, COVER_SIZE)) + perror("ioctl"), exit(1); + /* + * Note that the buffer pointer is of type uint64_t*, because all + * the comparison operands are promoted to uint64_t. + */ + cover = (uint64_t *)mmap(NULL, COVER_SIZE * sizeof(unsigned long), + PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); + if ((void*)cover == MAP_FAILED) + perror("mmap"), exit(1); + /* Note KCOV_TRACE_CMP instead of KCOV_TRACE_PC. */ + if (ioctl(fd, KCOV_ENABLE, KCOV_TRACE_CMP)) + perror("ioctl"), exit(1); + __atomic_store_n(&cover[0], 0, __ATOMIC_RELAXED); + read(-1, NULL, 0); + /* Read number of comparisons collected. */ + n = __atomic_load_n(&cover[0], __ATOMIC_RELAXED); + for (i = 0; i < n; i++) { + type = cover[i * KCOV_WORDS_PER_CMP + 1]; + /* arg1 and arg2 - operands of the comparison. */ + arg1 = cover[i * KCOV_WORDS_PER_CMP + 2]; + arg2 = cover[i * KCOV_WORDS_PER_CMP + 3]; + /* ip - caller address. */ + ip = cover[i * KCOV_WORDS_PER_CMP + 4]; + /* size of the operands. */ + size = 1 << ((type & KCOV_CMP_MASK) >> 1); + /* is_const - true if either operand is a compile-time constant.*/ + is_const = type & KCOV_CMP_CONST; + printf("ip: 0x%lx type: 0x%lx, arg1: 0x%lx, arg2: 0x%lx, " + "size: %lu, %s\n", + ip, type, arg1, arg2, size, + is_const ? "const" : "non-const"); + } + if (ioctl(fd, KCOV_DISABLE, 0)) + perror("ioctl"), exit(1); + /* Free resources. */ + if (munmap(cover, COVER_SIZE * sizeof(unsigned long))) + perror("munmap"), exit(1); + if (close(fd)) + perror("close"), exit(1); + return 0; + } + +Note that the kcov modes (coverage collection or comparison operands) are +mutually exclusive. |