mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-25 13:43:55 +08:00
57131dd3fd
Now that we don't have automatic syntax highlighting, use the code-block directive with the explicitly selected language, where appropriate. Signed-off-by: Jani Nikula <jani.nikula@intel.com>
114 lines
3.6 KiB
ReStructuredText
114 lines
3.6 KiB
ReStructuredText
kcov: code coverage for fuzzing
|
|
===============================
|
|
|
|
kcov exposes kernel code coverage information in a form suitable for coverage-
|
|
guided fuzzing (randomized testing). Coverage data of a running kernel is
|
|
exported via the "kcov" debugfs file. Coverage collection is enabled on a task
|
|
basis, and thus it can capture precise coverage of a single system call.
|
|
|
|
Note that kcov does not aim to collect as much coverage as possible. It aims
|
|
to collect more or less stable coverage that is function of syscall inputs.
|
|
To achieve this goal it does not collect coverage in soft/hard interrupts
|
|
and instrumentation of some inherently non-deterministic parts of kernel is
|
|
disbled (e.g. scheduler, locking).
|
|
|
|
Usage
|
|
-----
|
|
|
|
Configure the kernel with::
|
|
|
|
CONFIG_KCOV=y
|
|
|
|
CONFIG_KCOV requires gcc built on revision 231296 or later.
|
|
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:
|
|
|
|
.. code-block:: c
|
|
|
|
#include <stdio.h>
|
|
#include <stddef.h>
|
|
#include <stdint.h>
|
|
#include <stdlib.h>
|
|
#include <sys/types.h>
|
|
#include <sys/stat.h>
|
|
#include <sys/ioctl.h>
|
|
#include <sys/mman.h>
|
|
#include <unistd.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;
|
|
unsigned long *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"), exit(1);
|
|
/* Setup trace mode and trace size. */
|
|
if (ioctl(fd, KCOV_INIT_TRACE, COVER_SIZE))
|
|
perror("ioctl"), exit(1);
|
|
/* Mmap buffer shared between kernel- and user-space. */
|
|
cover = (unsigned long*)mmap(NULL, COVER_SIZE * sizeof(unsigned long),
|
|
PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
|
|
if ((void*)cover == MAP_FAILED)
|
|
perror("mmap"), exit(1);
|
|
/* Enable coverage collection on the current thread. */
|
|
if (ioctl(fd, KCOV_ENABLE, 0))
|
|
perror("ioctl"), exit(1);
|
|
/* 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);
|
|
for (i = 0; i < n; i++)
|
|
printf("0x%lx\n", 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"), 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;
|
|
}
|
|
|
|
After piping through addr2line output of the program looks as follows::
|
|
|
|
SyS_read
|
|
fs/read_write.c:562
|
|
__fdget_pos
|
|
fs/file.c:774
|
|
__fget_light
|
|
fs/file.c:746
|
|
__fget_light
|
|
fs/file.c:750
|
|
__fget_light
|
|
fs/file.c:760
|
|
__fdget_pos
|
|
fs/file.c:784
|
|
SyS_read
|
|
fs/read_write.c:562
|
|
|
|
If a program needs to collect coverage from several threads (independently),
|
|
it needs to open /sys/kernel/debug/kcov in each thread separately.
|
|
|
|
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).
|