€•	      Œsphinx.addnodes”Œdocument”“”)”}”(Œ	rawsource”Œ ”Œchildren”]”(Œtranslations”ŒLanguagesNode”“”)”}”(hhh]”(h Œpending_xref”“”)”}”(hhh]”Œdocutils.nodes”ŒText”“”ŒChinese (Simplified)”…””}”Œparent”hsbaŒ
attributes”}”(Œids”]”Œclasses”]”Œnames”]”Œdupnames”]”Œbackrefs”]”Œ	refdomain”Œstd”Œreftype”Œdoc”Œ	reftarget”Œ"/translations/zh_CN/dev-tools/kcov”Œmodname”NŒ	classname”NŒrefexplicit”ˆuŒtagname”hhhubh)”}”(hhh]”hŒChinese (Traditional)”…””}”hh2sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ"/translations/zh_TW/dev-tools/kcov”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒItalian”…””}”hhFsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ"/translations/it_IT/dev-tools/kcov”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒJapanese”…””}”hhZsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ"/translations/ja_JP/dev-tools/kcov”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒKorean”…””}”hhnsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ"/translations/ko_KR/dev-tools/kcov”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒSpanish”…””}”hh‚sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ"/translations/sp_SP/dev-tools/kcov”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubeh}”(h]”h ]”h"]”h$]”h&]”Œcurrent_language”ŒEnglish”uh1h
hhŒ	_document”hŒsource”NŒline”NubhŒsection”“”)”}”(hhh]”(hŒtitle”“”)”}”(hŒKCOV: code coverage for fuzzing”h]”hŒKCOV: code coverage for fuzzing”…””}”(hh¨hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hh£hžhhŸŒ</var/lib/git/docbuild/linux/Documentation/dev-tools/kcov.rst”h KubhŒ	paragraph”“”)”}”(hX+  KCOV collects and exposes kernel code coverage information in a form suitable
for coverage-guided fuzzing. Coverage data of a running kernel is exported via
the ``kcov`` debugfs file. Coverage collection is enabled on a task basis, and
thus KCOV can capture precise coverage of a single system call.”h]”(hŒ¡KCOV collects and exposes kernel code coverage information in a form suitable
for coverage-guided fuzzing. Coverage data of a running kernel is exported via
the ”…””}”(hh¹hžhhŸNh NubhŒliteral”“”)”}”(hŒ``kcov``”h]”hŒkcov”…””}”(hhÃhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhh¹ubhŒ‚ debugfs file. Coverage collection is enabled on a task basis, and
thus KCOV can capture precise coverage of a single system call.”…””}”(hh¹hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hXy  Note that KCOV does not aim to collect as much coverage as possible. It aims
to collect more or less stable coverage that is a function of syscall inputs.
To achieve this goal, it does not collect coverage in soft/hard interrupts
(unless remove coverage collection is enabled, see below) and from some
inherently non-deterministic parts of the kernel (e.g. scheduler, locking).”h]”hXy  Note that KCOV does not aim to collect as much coverage as possible. It aims
to collect more or less stable coverage that is a function of syscall inputs.
To achieve this goal, it does not collect coverage in soft/hard interrupts
(unless remove coverage collection is enabled, see below) and from some
inherently non-deterministic parts of the kernel (e.g. scheduler, locking).”…””}”(hhÛhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K	hh£hžhubh¸)”}”(hŒŠBesides collecting code coverage, KCOV can also collect comparison operands.
See the "Comparison operands collection" section for details.”h]”hŒŽBesides collecting code coverage, KCOV can also collect comparison operands.
See the â€œComparison operands collectionâ€ section for details.”…””}”(hhéhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hŒëBesides collecting coverage data from syscall handlers, KCOV can also collect
coverage for annotated parts of the kernel executing in background kernel
tasks or soft interrupts. See the "Remote coverage collection" section for
details.”h]”hŒïBesides collecting coverage data from syscall handlers, KCOV can also collect
coverage for annotated parts of the kernel executing in background kernel
tasks or soft interrupts. See the â€œRemote coverage collectionâ€ section for
details.”…””}”(hh÷hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¢)”}”(hhh]”(h§)”}”(hŒPrerequisites”h]”hŒPrerequisites”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hj  hžhhŸh¶h Kubh¸)”}”(hŒuKCOV relies on compiler instrumentation and requires GCC 6.1.0 or later
or any Clang version supported by the kernel.”h]”hŒuKCOV relies on compiler instrumentation and requires GCC 6.1.0 or later
or any Clang version supported by the kernel.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khj  hžhubh¸)”}”(hŒFCollecting comparison operands is supported with GCC 8+ or with Clang.”h]”hŒFCollecting comparison operands is supported with GCC 8+ or with Clang.”…””}”(hj$  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khj  hžhubh¸)”}”(hŒ+To enable KCOV, configure the kernel with::”h]”hŒ*To enable KCOV, configure the kernel with:”…””}”(hj2  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khj  hžhubhŒliteral_block”“”)”}”(hŒCONFIG_KCOV=y”h]”hŒCONFIG_KCOV=y”…””}”hjB  sbah}”(h]”h ]”h"]”h$]”h&]”Œ	xml:space”Œpreserve”uh1j@  hŸh¶h K!hj  hžhubh¸)”}”(hŒ/To enable comparison operands collection, set::”h]”hŒ.To enable comparison operands collection, set:”…””}”(hjR  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K#hj  hžhubjA  )”}”(hŒ CONFIG_KCOV_ENABLE_COMPARISONS=y”h]”hŒ CONFIG_KCOV_ENABLE_COMPARISONS=y”…””}”hj`  sbah}”(h]”h ]”h"]”h$]”h&]”jP  jQ  uh1j@  hŸh¶h K%hj  hžhubh¸)”}”(hŒECoverage data only becomes accessible once debugfs has been mounted::”h]”hŒDCoverage data only becomes accessible once debugfs has been mounted:”…””}”(hjn  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K'hj  hžhubjA  )”}”(hŒ'mount -t debugfs none /sys/kernel/debug”h]”hŒ'mount -t debugfs none /sys/kernel/debug”…””}”hj|  sbah}”(h]”h ]”h"]”h$]”h&]”jP  jQ  uh1j@  hŸh¶h K)hj  hžhubeh}”(h]”Œprerequisites”ah ]”h"]”Œprerequisites”ah$]”h&]”uh1h¡hh£hžhhŸh¶h Kubh¢)”}”(hhh]”(h§)”}”(hŒCoverage collection”h]”hŒCoverage collection”…””}”(hj•  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hj’  hžhhŸh¶h K,ubh¸)”}”(hŒwThe following program demonstrates how to use KCOV to collect coverage for a
single syscall from within a test program:”h]”hŒwThe following program demonstrates how to use KCOV to collect coverage for a
single syscall from within a test program:”…””}”(hj£  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K.hj’  hžhubjA  )”}”(hX2  #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>
#include <linux/types.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);
    /* Call the target syscall 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;
}”h]”hX2  #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>
#include <linux/types.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);
    /* Call the target syscall 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;
}”…””}”hj±  sbah}”(h]”h ]”h"]”h$]”h&]”jP  jQ  Œforce”‰Œlanguage”Œc”Œhighlight_args”}”uh1j@  hŸh¶h K1hj’  hžhubh¸)”}”(hŒOAfter piping through ``addr2line`` the output of the program looks as follows::”h]”(hŒAfter piping through ”…””}”(hjÄ  hžhhŸNh NubhÂ)”}”(hŒ``addr2line``”h]”hŒ	addr2line”…””}”(hjÌ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhjÄ  ubhŒ, the output of the program looks as follows:”…””}”(hjÄ  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Krhj’  hžhubjA  )”}”(hŒ¾SyS_read
fs/read_write.c:562
__fdget_pos
fs/file.c:774
__fget_light
fs/file.c:746
__fget_light
fs/file.c:750
__fget_light
fs/file.c:760
__fdget_pos
fs/file.c:784
SyS_read
fs/read_write.c:562”h]”hŒ¾SyS_read
fs/read_write.c:562
__fdget_pos
fs/file.c:774
__fget_light
fs/file.c:746
__fget_light
fs/file.c:750
__fget_light
fs/file.c:760
__fdget_pos
fs/file.c:784
SyS_read
fs/read_write.c:562”…””}”hjä  sbah}”(h]”h ]”h"]”h$]”h&]”jP  jQ  uh1j@  hŸh¶h Kthj’  hžhubh¸)”}”(hŒ“If a program needs to collect coverage from several threads (independently),
it needs to open ``/sys/kernel/debug/kcov`` in each thread separately.”h]”(hŒ^If a program needs to collect coverage from several threads (independently),
it needs to open ”…””}”(hjò  hžhhŸNh NubhÂ)”}”(hŒ``/sys/kernel/debug/kcov``”h]”hŒ/sys/kernel/debug/kcov”…””}”(hjú  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhjò  ubhŒ in each thread separately.”…””}”(hjò  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kƒhj’  hžhubh¸)”}”(hXC  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. The child
processes only need to enable coverage (it gets disabled automatically when
a thread exits).”h]”(hŒlThe interface is fine-grained to allow efficient forking of test processes.
That is, a parent process opens ”…””}”(hj  hžhhŸNh NubhÂ)”}”(hŒ``/sys/kernel/debug/kcov``”h]”hŒ/sys/kernel/debug/kcov”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhj  ubhŒ½, enables trace mode,
mmaps coverage buffer, and then forks child processes in a loop. The child
processes only need to enable coverage (it gets disabled automatically when
a thread exits).”…””}”(hj  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K†hj’  hžhubeh}”(h]”Œcoverage-collection”ah ]”h"]”Œcoverage collection”ah$]”h&]”uh1h¡hh£hžhhŸh¶h K,ubh¢)”}”(hhh]”(h§)”}”(hŒComparison operands collection”h]”hŒComparison operands collection”…””}”(hj=  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hj:  hžhhŸh¶h Kubh¸)”}”(hŒAComparison operands collection is similar to coverage collection:”h]”hŒAComparison operands collection is similar to coverage collection:”…””}”(hjK  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khj:  hžhubjA  )”}”(hXÖ	  /* 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++) {
            uint64_t ip;

            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;
}”h]”hXÖ	  /* 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++) {
            uint64_t ip;

            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;
}”…””}”hjY  sbah}”(h]”h ]”h"]”h$]”h&]”jP  jQ  j¿  ‰jÀ  jÁ  jÂ  }”uh1j@  hŸh¶h K‘hj:  hžhubh¸)”}”(hŒeNote that the KCOV modes (collection of code coverage or comparison operands)
are mutually exclusive.”h]”hŒeNote that the KCOV modes (collection of code coverage or comparison operands)
are mutually exclusive.”…””}”(hjh  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KÙhj:  hžhubeh}”(h]”Œcomparison-operands-collection”ah ]”h"]”Œcomparison operands collection”ah$]”h&]”uh1h¡hh£hžhhŸh¶h Kubh¢)”}”(hhh]”(h§)”}”(hŒRemote coverage collection”h]”hŒRemote coverage collection”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hj~  hžhhŸh¶h KÝubh¸)”}”(hŒÍBesides collecting coverage data from handlers of syscalls issued from a
userspace process, KCOV can also collect coverage for parts of the kernel
executing in other contexts - so-called "remote" coverage.”h]”hŒÑBesides collecting coverage data from handlers of syscalls issued from a
userspace process, KCOV can also collect coverage for parts of the kernel
executing in other contexts - so-called â€œremoteâ€ coverage.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kßhj~  hžhubh¸)”}”(hŒ/Using KCOV to collect remote coverage requires:”h]”hŒ/Using KCOV to collect remote coverage requires:”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kãhj~  hžhubhŒenumerated_list”“”)”}”(hhh]”(hŒ	list_item”“”)”}”(hŒModifying kernel code to annotate the code section from where coverage
should be collected with ``kcov_remote_start`` and ``kcov_remote_stop``.
”h]”h¸)”}”(hŒModifying kernel code to annotate the code section from where coverage
should be collected with ``kcov_remote_start`` and ``kcov_remote_stop``.”h]”(hŒ`Modifying kernel code to annotate the code section from where coverage
should be collected with ”…””}”(hj¶  hžhhŸNh NubhÂ)”}”(hŒ``kcov_remote_start``”h]”hŒkcov_remote_start”…””}”(hj¾  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhj¶  ubhŒ and ”…””}”(hj¶  hžhhŸNh NubhÂ)”}”(hŒ``kcov_remote_stop``”h]”hŒkcov_remote_stop”…””}”(hjÐ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhj¶  ubhŒ.”…””}”(hj¶  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kåhj²  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j°  hj­  hžhhŸh¶h Nubj±  )”}”(hŒiUsing ``KCOV_REMOTE_ENABLE`` instead of ``KCOV_ENABLE`` in the userspace
process that collects coverage.
”h]”h¸)”}”(hŒhUsing ``KCOV_REMOTE_ENABLE`` instead of ``KCOV_ENABLE`` in the userspace
process that collects coverage.”h]”(hŒUsing ”…””}”(hjò  hžhhŸNh NubhÂ)”}”(hŒ``KCOV_REMOTE_ENABLE``”h]”hŒKCOV_REMOTE_ENABLE”…””}”(hjú  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhjò  ubhŒ instead of ”…””}”(hjò  hžhhŸNh NubhÂ)”}”(hŒ``KCOV_ENABLE``”h]”hŒKCOV_ENABLE”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhjò  ubhŒ1 in the userspace
process that collects coverage.”…””}”(hjò  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kèhjî  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j°  hj­  hžhhŸh¶h Nubeh}”(h]”h ]”h"]”h$]”h&]”Œenumtype”Œarabic”Œprefix”hŒsuffix”Œ.”uh1j«  hj~  hžhhŸh¶h Kåubh¸)”}”(hX  Both ``kcov_remote_start`` and ``kcov_remote_stop`` annotations and the
``KCOV_REMOTE_ENABLE`` ioctl accept handles that identify particular coverage
collection sections. The way a handle is used depends on the context where the
matching code section executes.”h]”(hŒBoth ”…””}”(hj5  hžhhŸNh NubhÂ)”}”(hŒ``kcov_remote_start``”h]”hŒkcov_remote_start”…””}”(hj=  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhj5  ubhŒ and ”…””}”(hj5  hžhhŸNh NubhÂ)”}”(hŒ``kcov_remote_stop``”h]”hŒkcov_remote_stop”…””}”(hjO  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhj5  ubhŒ annotations and the
”…””}”(hj5  hžhhŸNh NubhÂ)”}”(hŒ``KCOV_REMOTE_ENABLE``”h]”hŒKCOV_REMOTE_ENABLE”…””}”(hja  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhj5  ubhŒ¦ ioctl accept handles that identify particular coverage
collection sections. The way a handle is used depends on the context where the
matching code section executes.”…””}”(hj5  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Këhj~  hžhubh¸)”}”(hŒEKCOV supports collecting remote coverage from the following contexts:”h]”hŒEKCOV supports collecting remote coverage from the following contexts:”…””}”(hjy  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kðhj~  hžhubj¬  )”}”(hhh]”(j±  )”}”(hŒ¹Global kernel background tasks. These are the tasks that are spawned during
kernel boot in a limited number of instances (e.g. one USB ``hub_event``
worker is spawned per one USB HCD).
”h]”h¸)”}”(hŒ¸Global kernel background tasks. These are the tasks that are spawned during
kernel boot in a limited number of instances (e.g. one USB ``hub_event``
worker is spawned per one USB HCD).”h]”(hŒ‡Global kernel background tasks. These are the tasks that are spawned during
kernel boot in a limited number of instances (e.g. one USB ”…””}”(hjŽ  hžhhŸNh NubhÂ)”}”(hŒ``hub_event``”h]”hŒ	hub_event”…””}”(hj–  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhjŽ  ubhŒ$
worker is spawned per one USB HCD).”…””}”(hjŽ  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KòhjŠ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j°  hj‡  hžhhŸh¶h Nubj±  )”}”(hŒ³Local kernel background tasks. These are spawned when a userspace process
interacts with some kernel interface and are usually killed when the process
exits (e.g. vhost workers).
”h]”h¸)”}”(hŒ²Local kernel background tasks. These are spawned when a userspace process
interacts with some kernel interface and are usually killed when the process
exits (e.g. vhost workers).”h]”hŒ²Local kernel background tasks. These are spawned when a userspace process
interacts with some kernel interface and are usually killed when the process
exits (e.g. vhost workers).”…””}”(hj¸  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Köhj´  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j°  hj‡  hžhhŸh¶h Nubj±  )”}”(hŒSoft interrupts.
”h]”h¸)”}”(hŒSoft interrupts.”h]”hŒSoft interrupts.”…””}”(hjÐ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KúhjÌ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j°  hj‡  hžhhŸh¶h Nubeh}”(h]”h ]”h"]”h$]”h&]”j0  j1  j2  hj3  j4  uh1j«  hj~  hžhhŸh¶h Kòubh¸)”}”(hX£  For #1 and #3, a unique global handle must be chosen and passed to the
corresponding ``kcov_remote_start`` call. Then a userspace process must pass
this handle to ``KCOV_REMOTE_ENABLE`` in the ``handles`` array field of the
``kcov_remote_arg`` struct. This will attach the used KCOV device to the code
section referenced by this handle. Multiple global handles identifying
different code sections can be passed at once.”h]”(hŒUFor #1 and #3, a unique global handle must be chosen and passed to the
corresponding ”…””}”(hjê  hžhhŸNh NubhÂ)”}”(hŒ``kcov_remote_start``”h]”hŒkcov_remote_start”…””}”(hjò  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhjê  ubhŒ9 call. Then a userspace process must pass
this handle to ”…””}”(hjê  hžhhŸNh NubhÂ)”}”(hŒ``KCOV_REMOTE_ENABLE``”h]”hŒKCOV_REMOTE_ENABLE”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhjê  ubhŒ in the ”…””}”(hjê  hžhhŸNh NubhÂ)”}”(hŒ``handles``”h]”hŒhandles”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhjê  ubhŒ array field of the
”…””}”(hjê  hžhhŸNh NubhÂ)”}”(hŒ``kcov_remote_arg``”h]”hŒkcov_remote_arg”…””}”(hj(  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhjê  ubhŒ° struct. This will attach the used KCOV device to the code
section referenced by this handle. Multiple global handles identifying
different code sections can be passed at once.”…””}”(hjê  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kühj~  hžhubh¸)”}”(hX¶  For #2, the userspace process instead must pass a non-zero handle through the
``common_handle`` field of the ``kcov_remote_arg`` struct. This common handle
gets saved to the ``kcov_handle`` field in the current ``task_struct`` and
needs to be passed to the newly spawned local tasks via custom kernel code
modifications. Those tasks should in turn use the passed handle in their
``kcov_remote_start`` and ``kcov_remote_stop`` annotations.”h]”(hŒNFor #2, the userspace process instead must pass a non-zero handle through the
”…””}”(hj@  hžhhŸNh NubhÂ)”}”(hŒ``common_handle``”h]”hŒcommon_handle”…””}”(hjH  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhj@  ubhŒ field of the ”…””}”(hj@  hžhhŸNh NubhÂ)”}”(hŒ``kcov_remote_arg``”h]”hŒkcov_remote_arg”…””}”(hjZ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhj@  ubhŒ. struct. This common handle
gets saved to the ”…””}”(hj@  hžhhŸNh NubhÂ)”}”(hŒ``kcov_handle``”h]”hŒkcov_handle”…””}”(hjl  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhj@  ubhŒ field in the current ”…””}”(hj@  hžhhŸNh NubhÂ)”}”(hŒ``task_struct``”h]”hŒtask_struct”…””}”(hj~  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhj@  ubhŒ™ and
needs to be passed to the newly spawned local tasks via custom kernel code
modifications. Those tasks should in turn use the passed handle in their
”…””}”(hj@  hžhhŸNh NubhÂ)”}”(hŒ``kcov_remote_start``”h]”hŒkcov_remote_start”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhj@  ubhŒ and ”…””}”(hj@  hžhhŸNh NubhÂ)”}”(hŒ``kcov_remote_stop``”h]”hŒkcov_remote_stop”…””}”(hj¢  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhj@  ubhŒ annotations.”…””}”(hj@  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Mhj~  hžhubh¸)”}”(hŒËKCOV follows a predefined format for both global and common handles. Each
handle is a ``u64`` integer. Currently, only the one top and the lower 4 bytes
are used. Bytes 4-7 are reserved and must be zero.”h]”(hŒVKCOV follows a predefined format for both global and common handles. Each
handle is a ”…””}”(hjº  hžhhŸNh NubhÂ)”}”(hŒ``u64``”h]”hŒu64”…””}”(hjÂ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhjº  ubhŒn integer. Currently, only the one top and the lower 4 bytes
are used. Bytes 4-7 are reserved and must be zero.”…””}”(hjº  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h M
hj~  hžhubh¸)”}”(hXO  For global handles, the top byte of the handle denotes the id of a subsystem
this handle belongs to. For example, KCOV uses ``1`` as the USB subsystem id.
The lower 4 bytes of a global handle denote the id of a task instance within
that subsystem. For example, each ``hub_event`` worker uses the USB bus number
as the task instance id.”h]”(hŒ|For global handles, the top byte of the handle denotes the id of a subsystem
this handle belongs to. For example, KCOV uses ”…””}”(hjÚ  hžhhŸNh NubhÂ)”}”(hŒ``1``”h]”hŒ1”…””}”(hjâ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhjÚ  ubhŒ‰ as the USB subsystem id.
The lower 4 bytes of a global handle denote the id of a task instance within
that subsystem. For example, each ”…””}”(hjÚ  hžhhŸNh NubhÂ)”}”(hŒ``hub_event``”h]”hŒ	hub_event”…””}”(hjô  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhjÚ  ubhŒ8 worker uses the USB bus number
as the task instance id.”…””}”(hjÚ  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Mhj~  hžhubh¸)”}”(hX,  For common handles, a reserved value ``0`` is used as a subsystem id, as such
handles don't belong to a particular subsystem. The lower 4 bytes of a common
handle identify a collective instance of all local tasks spawned by the
userspace process that passed a common handle to ``KCOV_REMOTE_ENABLE``.”h]”(hŒ%For common handles, a reserved value ”…””}”(hj  hžhhŸNh NubhÂ)”}”(hŒ``0``”h]”hŒ0”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhj  ubhŒí is used as a subsystem id, as such
handles donâ€™t belong to a particular subsystem. The lower 4 bytes of a common
handle identify a collective instance of all local tasks spawned by the
userspace process that passed a common handle to ”…””}”(hj  hžhhŸNh NubhÂ)”}”(hŒ``KCOV_REMOTE_ENABLE``”h]”hŒKCOV_REMOTE_ENABLE”…””}”(hj&  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÁhj  ubhŒ.”…””}”(hj  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Mhj~  hžhubh¸)”}”(hXA  In practice, any value can be used for common handle instance id if coverage
is only collected from a single userspace process on the system. However, if
common handles are used by multiple processes, unique instance ids must be
used for each process. One option is to use the process id as the common
handle instance id.”h]”hXA  In practice, any value can be used for common handle instance id if coverage
is only collected from a single userspace process on the system. However, if
common handles are used by multiple processes, unique instance ids must be
used for each process. One option is to use the process id as the common
handle instance id.”…””}”(hj>  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Mhj~  hžhubh¸)”}”(hŒ›The following program demonstrates using KCOV to collect coverage from both
local tasks spawned by the process and the global task that handles USB bus #1:”h]”hŒ›The following program demonstrates using KCOV to collect coverage from both
local tasks spawned by the process and the global task that handles USB bus #1:”…””}”(hjL  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Mhj~  hžhubjA  )”}”(hX‰
  /* Same includes and defines as above. */

struct kcov_remote_arg {
    __u32           trace_mode;
    __u32           area_size;
    __u32           num_handles;
    __aligned_u64   common_handle;
    __aligned_u64   handles[0];
};

#define KCOV_INIT_TRACE                     _IOR('c', 1, unsigned long)
#define KCOV_DISABLE                        _IO('c', 101)
#define KCOV_REMOTE_ENABLE          _IOW('c', 102, struct kcov_remote_arg)

#define COVER_SIZE  (64 << 10)

#define KCOV_TRACE_PC       0

#define KCOV_SUBSYSTEM_COMMON       (0x00ull << 56)
#define KCOV_SUBSYSTEM_USB  (0x01ull << 56)

#define KCOV_SUBSYSTEM_MASK (0xffull << 56)
#define KCOV_INSTANCE_MASK  (0xffffffffull)

static inline __u64 kcov_remote_handle(__u64 subsys, __u64 inst)
{
    if (subsys & ~KCOV_SUBSYSTEM_MASK || inst & ~KCOV_INSTANCE_MASK)
            return 0;
    return subsys | inst;
}

#define KCOV_COMMON_ID      0x42
#define KCOV_USB_BUS_NUM    1

int main(int argc, char **argv)
{
    int fd;
    unsigned long *cover, n, i;
    struct kcov_remote_arg *arg;

    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);
    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 via common handle and from USB bus #1. */
    arg = calloc(1, sizeof(*arg) + sizeof(uint64_t));
    if (!arg)
            perror("calloc"), exit(1);
    arg->trace_mode = KCOV_TRACE_PC;
    arg->area_size = COVER_SIZE;
    arg->num_handles = 1;
    arg->common_handle = kcov_remote_handle(KCOV_SUBSYSTEM_COMMON,
                                                    KCOV_COMMON_ID);
    arg->handles[0] = kcov_remote_handle(KCOV_SUBSYSTEM_USB,
                                            KCOV_USB_BUS_NUM);
    if (ioctl(fd, KCOV_REMOTE_ENABLE, arg))
            perror("ioctl"), free(arg), exit(1);
    free(arg);

    /*
     * Here the user needs to trigger execution of a kernel code section
     * that is either annotated with the common handle, or to trigger some
     * activity on USB bus #1.
     */
    sleep(2);

    n = __atomic_load_n(&cover[0], __ATOMIC_RELAXED);
    for (i = 0; i < n; i++)
            printf("0x%lx\n", cover[i + 1]);
    if (ioctl(fd, KCOV_DISABLE, 0))
            perror("ioctl"), exit(1);
    if (munmap(cover, COVER_SIZE * sizeof(unsigned long)))
            perror("munmap"), exit(1);
    if (close(fd))
            perror("close"), exit(1);
    return 0;
}”h]”hX‰
  /* Same includes and defines as above. */

struct kcov_remote_arg {
    __u32           trace_mode;
    __u32           area_size;
    __u32           num_handles;
    __aligned_u64   common_handle;
    __aligned_u64   handles[0];
};

#define KCOV_INIT_TRACE                     _IOR('c', 1, unsigned long)
#define KCOV_DISABLE                        _IO('c', 101)
#define KCOV_REMOTE_ENABLE          _IOW('c', 102, struct kcov_remote_arg)

#define COVER_SIZE  (64 << 10)

#define KCOV_TRACE_PC       0

#define KCOV_SUBSYSTEM_COMMON       (0x00ull << 56)
#define KCOV_SUBSYSTEM_USB  (0x01ull << 56)

#define KCOV_SUBSYSTEM_MASK (0xffull << 56)
#define KCOV_INSTANCE_MASK  (0xffffffffull)

static inline __u64 kcov_remote_handle(__u64 subsys, __u64 inst)
{
    if (subsys & ~KCOV_SUBSYSTEM_MASK || inst & ~KCOV_INSTANCE_MASK)
            return 0;
    return subsys | inst;
}

#define KCOV_COMMON_ID      0x42
#define KCOV_USB_BUS_NUM    1

int main(int argc, char **argv)
{
    int fd;
    unsigned long *cover, n, i;
    struct kcov_remote_arg *arg;

    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);
    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 via common handle and from USB bus #1. */
    arg = calloc(1, sizeof(*arg) + sizeof(uint64_t));
    if (!arg)
            perror("calloc"), exit(1);
    arg->trace_mode = KCOV_TRACE_PC;
    arg->area_size = COVER_SIZE;
    arg->num_handles = 1;
    arg->common_handle = kcov_remote_handle(KCOV_SUBSYSTEM_COMMON,
                                                    KCOV_COMMON_ID);
    arg->handles[0] = kcov_remote_handle(KCOV_SUBSYSTEM_USB,
                                            KCOV_USB_BUS_NUM);
    if (ioctl(fd, KCOV_REMOTE_ENABLE, arg))
            perror("ioctl"), free(arg), exit(1);
    free(arg);

    /*
     * Here the user needs to trigger execution of a kernel code section
     * that is either annotated with the common handle, or to trigger some
     * activity on USB bus #1.
     */
    sleep(2);

    n = __atomic_load_n(&cover[0], __ATOMIC_RELAXED);
    for (i = 0; i < n; i++)
            printf("0x%lx\n", cover[i + 1]);
    if (ioctl(fd, KCOV_DISABLE, 0))
            perror("ioctl"), exit(1);
    if (munmap(cover, COVER_SIZE * sizeof(unsigned long)))
            perror("munmap"), exit(1);
    if (close(fd))
            perror("close"), exit(1);
    return 0;
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