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代码覆盖率（Code Coverage）是反映测试用例对被测软件覆盖程序的重要指标，kcov是用于随机测试中合适表达代码覆盖率的一种工具。

前置需求

内核需要配置

CONFIG_KCOV=y

CONFIG_KCOV需要231296以上版本的gcc，如果需要收集比较操作

CONFIG_KCOV_ENABLE_COMPARISONS=y

只有挂载了debugfs，才可以访问配置数据。

使用方法

#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)



#define KCOV_TRACE_PC 0

#define KCOV_TRACE_CMP 1



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, KCOV_TRACE_PC))

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;

}

输出信息

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

/* 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;

}