Re: [PATCH v3] kernel: add kcov code coverage

Kirill A. Shutemov
2016-01-14T16:25:47Z

On Thu, Jan 14, 2016 at 03:22:21PM +0100, Dmitry Vyukov wrote:
> +The following program demonstrates kcov usage from within a test program:
> +
> +#include <stdio.h>
> +#include <stddef.h>
> +#include <stdint.h>
> +#include <sys/types.h>
> +#include <sys/stat.h>
> +#include <sys/ioctl.h>
> +#include <sys/mman.h>
> +#include <fcntl.h>
> +
> +#define KCOV_INIT_TRACE _IOR('c', 1, unsigned long)
> +#define KCOV_ENABLE _IO('c', 100)
> +#define KCOV_DISABLE _IO('c', 101)
> +#define COVER_SIZE (64<<10)
> +
> +int main(int argc, char **argv)
> +{
> + int fd;
> + uint32_t *cover, n, i;
> +
> + /* A single fd descriptor allows coverage collection on a single
> + * thread.
> + */
> + fd = open("/sys/kernel/debug/kcov", O_RDWR);
> + if (fd == -1)
> + perror("open");
> + /* Setup trace mode and trace size. */
> + if (ioctl(fd, KCOV_INIT_TRACE, COVER_SIZE))
> + perror("ioctl");
> + /* Mmap buffer shared between kernel- and user-space. */
> + cover = (uint32_t*)mmap(NULL, COVER_SIZE * sizeof(uint32_t),
> + PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
> + if ((void*)cover == MAP_FAILED)
> + perror("mmap");
> + /* Enable coverage collection on the current thread. */
> + if (ioctl(fd, KCOV_ENABLE, 0))
> + perror("ioctl");
> + /* Reset coverage from the tail of the ioctl() call. */
> + __atomic_store_n(&cover[0], 0, __ATOMIC_RELAXED);
> + /* That's the target syscal call. */
> + read(-1, NULL, 0);
> + /* Read number of PCs collected. */
> + n = __atomic_load_n(&cover[0], __ATOMIC_RELAXED);
> + /* PCs are shorten to uint32_t, so we need to restore the upper part. */
> + for (i = 0; i < n; i++)
> + printf("0xffffffff%0lx\n", (unsigned long)cover[i + 1]);
> + /* Disable coverage collection for the current thread. After this call
> + * coverage can be enabled for a different thread.
> + */
> + if (ioctl(fd, KCOV_DISABLE, 0))
> + perror("ioctl");
> + /* Free resources. */
> + if (munmap(cover, COVER_SIZE * sizeof(uint32_t)))
> + perror("munmap");
> + if (close(fd))
> + perror("close");
> + return 0;
> +}

Do we really need ioctl in this interface? Why not just plain write(2)?

--
Kirill A. Shutemov