BPF(2)                     Linux Programmer's Manual                    BPF(2)

       bpf - perform a command on an extended BPF map or program

       #include <linux/bpf.h>

       int bpf(int cmd, union bpf_attr *attr, unsigned int size);

       The bpf() system call performs a range of operations related to
       extended Berkeley Packet Filters.  Extended BPF (or eBPF) is similar to
       the original ("classic") BPF (cBPF) used to filter network packets.
       For both cBPF and eBPF programs, the kernel statically analyzes the
       programs before loading them, in order to ensure that they cannot harm
       the running system.

       eBPF extends cBPF in multiple ways, including the ability to call a
       fixed set of in-kernel helper functions (via the BPF_CALL opcode
       extension provided by eBPF) and access shared data structures such as
       eBPF maps.

   Extended BPF Design/Architecture
       eBPF maps are a generic data structure for storage of different data
       types.  Data types are generally treated as binary blobs, so a user
       just specifies the size of the key and the size of the value at map-
       creation time.  In other words, a key/value for a given map can have an
       arbitrary structure.

       A user process can create multiple maps (with key/value-pairs being
       opaque bytes of data) and access them via file descriptors.  Different
       eBPF programs can access the same maps in parallel.  It's up to the
       user process and eBPF program to decide what they store inside maps.

       There's one special map type, called a program array.  This type of map
       stores file descriptors referring to other eBPF programs.  When a
       lookup in the map is performed, the program flow is redirected in-place
       to the beginning of another eBPF program and does not return back to
       the calling program.  The level of nesting has a fixed limit of 32, so
       that infinite loops cannot be crafted.  At run time, the program file
       descriptors stored in the map can be modified, so program functionality
       can be altered based on specific requirements.  All programs referred
       to in a program-array map must have been previously loaded into the
       kernel via bpf().  If a map lookup fails, the current program continues
       its execution.  See BPF_MAP_TYPE_PROG_ARRAY below for further details.

       Generally, eBPF programs are loaded by the user process and
       automatically unloaded when the process exits.  In some cases, for
       example, tc-bpf(8), the program will continue to stay alive inside the
       kernel even after the process that loaded the program exits.  In that
       case, the tc subsystem holds a reference to the eBPF program after the
       file descriptor has been closed by the user-space program.  Thus,
       whether a specific program continues to live inside the kernel depends
       on how it is further attached to a given kernel subsystem after it was
       loaded via bpf().

       Each eBPF program is a set of instructions that is safe to run until
       its completion.  An in-kernel verifier statically determines that the
       eBPF program terminates and is safe to execute.  During verification,
       the kernel increments reference counts for each of the maps that the
       eBPF program uses, so that the attached maps can't be removed until the
       program is unloaded.

       eBPF programs can be attached to different events.  These events can be
       the arrival of network packets, tracing events, classification events
       by network queueing  disciplines (for eBPF programs attached to a tc(8)
       classifier), and other types that may be added in the future.  A new
       event triggers execution of the eBPF program, which may store
       information about the event in eBPF maps.  Beyond storing data, eBPF
       programs may call a fixed set of in-kernel helper functions.

       The same eBPF program can be attached to multiple events and different
       eBPF programs can access the same map:

           tracing     tracing    tracing    packet      packet     packet
           event A     event B    event C    on eth0     on eth1    on eth2
            |             |         |          |           |          ^
            |             |         |          |           v          |
            --> tracing <--     tracing      socket    tc ingress   tc egress
                 prog_1          prog_2      prog_3    classifier    action
                 |  |              |           |         prog_4      prog_5
              |---  -----|  |------|          map_3        |           |
            map_1       map_2                              --| map_4 |--

       The operation to be performed by the bpf() system call is determined by
       the cmd argument.  Each operation takes an accompanying argument,
       provided via attr, which is a pointer to a union of type bpf_attr (see
       below).  The size argument is the size of the union pointed to by attr.

       The value provided in cmd is one of the following:

              Create a map and return a file descriptor that refers to the
              map.  The close-on-exec file descriptor flag (see fcntl(2)) is
              automatically enabled for the new file descriptor.

              Look up an element by key in a specified map and return its

              Create or update an element (key/value pair) in a specified map.

              Look up and delete an element by key in a specified map.

              Look up an element by key in a specified map and return the key
              of the next element.

              Verify and load an eBPF program, returning a new file descriptor
              associated with the program.  The close-on-exec file descriptor
              flag (see fcntl(2)) is automatically enabled for the new file

              The bpf_attr union consists of various anonymous structures that
              are used by different bpf() commands:

           union bpf_attr {
               struct {    /* Used by BPF_MAP_CREATE */
                   __u32         map_type;
                   __u32         key_size;    /* size of key in bytes */
                   __u32         value_size;  /* size of value in bytes */
                   __u32         max_entries; /* maximum number of entries
                                                 in a map */

               struct {    /* Used by BPF_MAP_*_ELEM and BPF_MAP_GET_NEXT_KEY
                              commands */
                   __u32         map_fd;
                   __aligned_u64 key;
                   union {
                       __aligned_u64 value;
                       __aligned_u64 next_key;
                   __u64         flags;

               struct {    /* Used by BPF_PROG_LOAD */
                   __u32         prog_type;
                   __u32         insn_cnt;
                   __aligned_u64 insns;      /* 'const struct bpf_insn *' */
                   __aligned_u64 license;    /* 'const char *' */
                   __u32         log_level;  /* verbosity level of verifier */
                   __u32         log_size;   /* size of user buffer */
                   __aligned_u64 log_buf;    /* user supplied 'char *'
                                                buffer */
                   __u32         kern_version;
                                             /* checked when prog_type=kprobe
                                                (since Linux 4.1) */
           } __attribute__((aligned(8)));

   eBPF maps
       Maps are a generic data structure for storage of different types of
       data.  They allow sharing of data between eBPF kernel programs, and
       also between kernel and user-space applications.

       Each map type has the following attributes:

       *  type

       *  maximum number of elements

       *  key size in bytes

       *  value size in bytes

       The following wrapper functions demonstrate how various bpf() commands
       can be used to access the maps.  The functions use the cmd argument to
       invoke different operations.

              The BPF_MAP_CREATE command creates a new map, returning a new
              file descriptor that refers to the map.

                  bpf_create_map(enum bpf_map_type map_type,
                                 unsigned int key_size,
                                 unsigned int value_size,
                                 unsigned int max_entries)
                      union bpf_attr attr = {
                          .map_type    = map_type,
                          .key_size    = key_size,
                          .value_size  = value_size,
                          .max_entries = max_entries

                      return bpf(BPF_MAP_CREATE, &attr, sizeof(attr));

              The new map has the type specified by map_type, and attributes
              as specified in key_size, value_size, and max_entries.  On
              success, this operation returns a file descriptor.  On error, -1
              is returned and errno is set to EINVAL, EPERM, or ENOMEM.

              The key_size and value_size attributes will be used by the
              verifier during program loading to check that the program is
              calling bpf_map_*_elem() helper functions with a correctly
              initialized key and to check that the program doesn't access the
              map element value beyond the specified value_size.  For example,
              when a map is created with a key_size of 8 and the eBPF program

                  bpf_map_lookup_elem(map_fd, fp - 4)

              the program will be rejected, since the in-kernel helper

                  bpf_map_lookup_elem(map_fd, void *key)

              expects to read 8 bytes from the location pointed to by key, but
              the fp - 4 (where fp is the top of the stack) starting address
              will cause out-of-bounds stack access.

              Similarly, when a map is created with a value_size of 1 and the
              eBPF program contains

                  value = bpf_map_lookup_elem(...);
                  *(u32 *) value = 1;

              the program will be rejected, since it accesses the value
              pointer beyond the specified 1 byte value_size limit.

              Currently, the following values are supported for map_type:

                  enum bpf_map_type {
                      BPF_MAP_TYPE_UNSPEC,  /* Reserve 0 as invalid map type */
                      /* See /usr/include/linux/bpf.h for the full list. */

              map_type selects one of the available map implementations in the
              kernel.  For all map types, eBPF programs access maps with the
              same bpf_map_lookup_elem() and bpf_map_update_elem() helper
              functions.  Further details of the various map types are given

              The BPF_MAP_LOOKUP_ELEM command looks up an element with a given
              key in the map referred to by the file descriptor fd.

                  bpf_lookup_elem(int fd, const void *key, void *value)
                      union bpf_attr attr = {
                          .map_fd = fd,
                          .key    = ptr_to_u64(key),
                          .value  = ptr_to_u64(value),

                      return bpf(BPF_MAP_LOOKUP_ELEM, &attr, sizeof(attr));

              If an element is found, the operation returns zero and stores
              the element's value into value, which must point to a buffer of
              value_size bytes.

              If no element is found, the operation returns -1 and sets errno
              to ENOENT.

              The BPF_MAP_UPDATE_ELEM command creates or updates an element
              with a given key/value in the map referred to by the file
              descriptor fd.

                  bpf_update_elem(int fd, const void *key, const void *value,
                                  uint64_t flags)
                      union bpf_attr attr = {
                          .map_fd = fd,
                          .key    = ptr_to_u64(key),
                          .value  = ptr_to_u64(value),
                          .flags  = flags,

                      return bpf(BPF_MAP_UPDATE_ELEM, &attr, sizeof(attr));

              The flags argument should be specified as one of the following:

                     Create a new element or update an existing element.

                     Create a new element only if it did not exist.

                     Update an existing element.

              On success, the operation returns zero.  On error, -1 is
              returned and errno is set to EINVAL, EPERM, ENOMEM, or E2BIG.
              E2BIG indicates that the number of elements in the map reached
              the max_entries limit specified at map creation time.  EEXIST
              will be returned if flags specifies BPF_NOEXIST and the element
              with key already exists in the map.  ENOENT will be returned if
              flags specifies BPF_EXIST and the element with key doesn't exist
              in the map.

              The BPF_MAP_DELETE_ELEM command deletes the element whose key is
              key from the map referred to by the file descriptor fd.

                  bpf_delete_elem(int fd, const void *key)
                      union bpf_attr attr = {
                          .map_fd = fd,
                          .key    = ptr_to_u64(key),

                      return bpf(BPF_MAP_DELETE_ELEM, &attr, sizeof(attr));

              On success, zero is returned.  If the element is not found, -1
              is returned and errno is set to ENOENT.

              The BPF_MAP_GET_NEXT_KEY command looks up an element by key in
              the map referred to by the file descriptor fd and sets the
              next_key pointer to the key of the next element.

                  bpf_get_next_key(int fd, const void *key, void *next_key)
                      union bpf_attr attr = {
                          .map_fd   = fd,
                          .key      = ptr_to_u64(key),
                          .next_key = ptr_to_u64(next_key),

                      return bpf(BPF_MAP_GET_NEXT_KEY, &attr, sizeof(attr));

              If key is found, the operation returns zero and sets the
              next_key pointer to the key of the next element.  If key is not
              found, the operation returns zero and sets the next_key pointer
              to the key of the first element.  If key is the last element, -1
              is returned and errno is set to ENOENT.  Other possible errno
              values are ENOMEM, EFAULT, EPERM, and EINVAL.  This method can
              be used to iterate over all elements in the map.

              Delete the map referred to by the file descriptor map_fd.  When
              the user-space program that created a map exits, all maps will
              be deleted automatically (but see NOTES).

   eBPF map types
       The following map types are supported:

              Hash-table maps have the following characteristics:

              *  Maps are created and destroyed by user-space programs.  Both
                 user-space and eBPF programs can perform lookup, update, and
                 delete operations.

              *  The kernel takes care of allocating and freeing key/value

              *  The map_update_elem() helper will fail to insert new element
                 when the max_entries limit is reached.  (This ensures that
                 eBPF programs cannot exhaust memory.)

              *  map_update_elem() replaces existing elements atomically.

              Hash-table maps are optimized for speed of lookup.

              Array maps have the following characteristics:

              *  Optimized for fastest possible lookup.  In the future the
                 verifier/JIT compiler may recognize lookup() operations that
                 employ a constant key and optimize it into constant pointer.
                 It is possible to optimize a non-constant key into direct
                 pointer arithmetic as well, since pointers and value_size are
                 constant for the life of the eBPF program.  In other words,
                 array_map_lookup_elem() may be 'inlined' by the verifier/JIT
                 compiler while preserving concurrent access to this map from
                 user space.

              *  All array elements pre-allocated and zero initialized at init

              *  The key is an array index, and must be exactly four bytes.

              *  map_delete_elem() fails with the error EINVAL, since elements
                 cannot be deleted.

              *  map_update_elem() replaces elements in a nonatomic fashion;
                 for atomic updates, a hash-table map should be used instead.
                 There is however one special case that can also be used with
                 arrays: the atomic built-in __sync_fetch_and_add() can be
                 used on 32 and 64 bit atomic counters.  For example, it can
                 be applied on the whole value itself if it represents a
                 single counter, or in case of a structure containing multiple
                 counters, it could be used on individual counters.  This is
                 quite often useful for aggregation and accounting of events.

              Among the uses for array maps are the following:

              *  As "global" eBPF variables: an array of 1 element whose key
                 is (index) 0 and where the value is a collection of 'global'
                 variables which eBPF programs can use to keep state between

              *  Aggregation of tracing events into a fixed set of buckets.

              *  Accounting of networking events, for example, number of
                 packets and packet sizes.

       BPF_MAP_TYPE_PROG_ARRAY (since Linux 4.2)
              A program array map is a special kind of array map whose map
              values contain only file descriptors referring to other eBPF
              programs.  Thus, both the key_size and value_size must be
              exactly four bytes.  This map is used in conjunction with the
              bpf_tail_call() helper.

              This means that an eBPF program with a program array map
              attached to it can call from kernel side into

                  void bpf_tail_call(void *context, void *prog_map,
                                     unsigned int index);

              and therefore replace its own program flow with the one from the
              program at the given program array slot, if present.  This can
              be regarded as kind of a jump table to a different eBPF program.
              The invoked program will then reuse the same stack.  When a jump
              into the new program has been performed, it won't return to the
              old program anymore.

              If no eBPF program is found at the given index of the program
              array (because the map slot doesn't contain a valid program file
              descriptor, the specified lookup index/key is out of bounds, or
              the limit of 32 nested calls has been exceed), execution
              continues with the current eBPF program.  This can be used as a
              fall-through for default cases.

              A program array map is useful, for example, in tracing or
              networking, to handle individual system calls or protocols in
              their own subprograms and use their identifiers as an individual
              map index.  This approach may result in performance benefits,
              and also makes it possible to overcome the maximum instruction
              limit of a single eBPF program.  In dynamic environments, a
              user-space daemon might atomically replace individual
              subprograms at run-time with newer versions to alter overall
              program behavior, for instance, if global policies change.

   eBPF programs
       The BPF_PROG_LOAD command is used to load an eBPF program into the
       kernel.  The return value for this command is a new file descriptor
       associated with this eBPF program.

           char bpf_log_buf[LOG_BUF_SIZE];

           bpf_prog_load(enum bpf_prog_type type,
                         const struct bpf_insn *insns, int insn_cnt,
                         const char *license)
               union bpf_attr attr = {
                   .prog_type = type,
                   .insns     = ptr_to_u64(insns),
                   .insn_cnt  = insn_cnt,
                   .license   = ptr_to_u64(license),
                   .log_buf   = ptr_to_u64(bpf_log_buf),
                   .log_size  = LOG_BUF_SIZE,
                   .log_level = 1,

               return bpf(BPF_PROG_LOAD, &attr, sizeof(attr));

       prog_type is one of the available program types:

                  enum bpf_prog_type {
                      BPF_PROG_TYPE_UNSPEC,        /* Reserve 0 as invalid
                                                      program type */
                      /* See /usr/include/linux/bpf.h for the full list. */

       For further details of eBPF program types, see below.

       The remaining fields of bpf_attr are set as follows:

       *  insns is an array of struct bpf_insn instructions.

       *  insn_cnt is the number of instructions in the program referred to by

       *  license is a license string, which must be GPL compatible to call
          helper functions marked gpl_only.  (The licensing rules are the same
          as for kernel modules, so that also dual licenses, such as "Dual
          BSD/GPL", may be used.)

       *  log_buf is a pointer to a caller-allocated buffer in which the in-
          kernel verifier can store the verification log.  This log is a
          multi-line string that can be checked by the program author in order
          to understand how the verifier came to the conclusion that the eBPF
          program is unsafe.  The format of the output can change at any time
          as the verifier evolves.

       *  log_size size of the buffer pointed to by log_buf.  If the size of
          the buffer is not large enough to store all verifier messages, -1 is
          returned and errno is set to ENOSPC.

       *  log_level verbosity level of the verifier.  A value of zero means
          that the verifier will not provide a log; in this case, log_buf must
          be a NULL pointer, and log_size must be zero.

       Applying close(2) to the file descriptor returned by BPF_PROG_LOAD will
       unload the eBPF program (but see NOTES).

       Maps are accessible from eBPF programs and are used to exchange data
       between eBPF programs and between eBPF programs and user-space
       programs.  For example, eBPF programs can process various events (like
       kprobe, packets) and store their data into a map, and user-space
       programs can then fetch data from the map.  Conversely, user-space
       programs can use a map as a configuration mechanism, populating the map
       with values checked by the eBPF program, which then modifies its
       behavior on the fly according to those values.

   eBPF program types
       The eBPF program type (prog_type) determines the subset of kernel
       helper functions that the program may call.  The program type also
       determines the program input (context)—the format of struct bpf_context
       (which is the data blob passed into the eBPF program as the first

       For example, a tracing program does not have the exact same subset of
       helper functions as a socket filter program (though they may have some
       helpers in common).  Similarly, the input (context) for a tracing
       program is a set of register values, while for a socket filter it is a
       network packet.

       The set of functions available to eBPF programs of a given type may
       increase in the future.

       The following program types are supported:

       BPF_PROG_TYPE_SOCKET_FILTER (since Linux 3.19)
              Currently, the set of functions for BPF_PROG_TYPE_SOCKET_FILTER

                  bpf_map_lookup_elem(map_fd, void *key)
                                      /* look up key in a map_fd */
                  bpf_map_update_elem(map_fd, void *key, void *value)
                                      /* update key/value */
                  bpf_map_delete_elem(map_fd, void *key)
                                      /* delete key in a map_fd */

              The bpf_context argument is a pointer to a struct __sk_buff.

       BPF_PROG_TYPE_KPROBE (since Linux 4.1)
              [To be documented]

       BPF_PROG_TYPE_SCHED_CLS (since Linux 4.1)
              [To be documented]

       BPF_PROG_TYPE_SCHED_ACT (since Linux 4.1)
              [To be documented]

       Once a program is loaded, it can be attached to an event.  Various
       kernel subsystems have different ways to do so.

       Since Linux 3.19, the following call will attach the program prog_fd to
       the socket sockfd, which was created by an earlier call to socket(2):

           setsockopt(sockfd, SOL_SOCKET, SO_ATTACH_BPF,
                      &prog_fd, sizeof(prog_fd));

       Since Linux 4.1, the following call may be used to attach the eBPF
       program referred to by the file descriptor prog_fd to a perf event file
       descriptor, event_fd, that was created by a previous call to

           ioctl(event_fd, PERF_EVENT_IOC_SET_BPF, prog_fd);

       /* bpf+sockets example:
        * 1. create array map of 256 elements
        * 2. load program that counts number of packets received
        *    r0 = skb->data[ETH_HLEN + offsetof(struct iphdr, protocol)]
        *    map[r0]++
        * 3. attach prog_fd to raw socket via setsockopt()
        * 4. print number of received TCP/UDP packets every second
       main(int argc, char **argv)
           int sock, map_fd, prog_fd, key;
           long long value = 0, tcp_cnt, udp_cnt;

           map_fd = bpf_create_map(BPF_MAP_TYPE_ARRAY, sizeof(key),
                                   sizeof(value), 256);
           if (map_fd < 0) {
               printf("failed to create map '%s'\n", strerror(errno));
               /* likely not run as root */
               return 1;

           struct bpf_insn prog[] = {
               BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),        /* r6 = r1 */
               BPF_LD_ABS(BPF_B, ETH_HLEN + offsetof(struct iphdr, protocol)),
                                       /* r0 = ip->proto */
               BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_0, -4),
                                       /* *(u32 *)(fp - 4) = r0 */
               BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),       /* r2 = fp */
               BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4),      /* r2 = r2 - 4 */
               BPF_LD_MAP_FD(BPF_REG_1, map_fd),           /* r1 = map_fd */
                                       /* r0 = map_lookup(r1, r2) */
               BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
                                       /* if (r0 == 0) goto pc+2 */
               BPF_MOV64_IMM(BPF_REG_1, 1),                /* r1 = 1 */
               BPF_XADD(BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0),
                                       /* lock *(u64 *) r0 += r1 */
               BPF_MOV64_IMM(BPF_REG_0, 0),                /* r0 = 0 */
               BPF_EXIT_INSN(),                            /* return r0 */

           prog_fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, prog,
                                   sizeof(prog) / sizeof(prog[0]), "GPL");

           sock = open_raw_sock("lo");

           assert(setsockopt(sock, SOL_SOCKET, SO_ATTACH_BPF, &prog_fd,
                             sizeof(prog_fd)) == 0);

           for (;;) {
               key = IPPROTO_TCP;
               assert(bpf_lookup_elem(map_fd, &key, &tcp_cnt) == 0);
               key = IPPROTO_UDP;
               assert(bpf_lookup_elem(map_fd, &key, &udp_cnt) == 0);
               printf("TCP %lld UDP %lld packets\n", tcp_cnt, udp_cnt);

           return 0;

       Some complete working code can be found in the samples/bpf directory in
       the kernel source tree.

       For a successful call, the return value depends on the operation:

              The new file descriptor associated with the eBPF map.

              The new file descriptor associated with the eBPF program.

       All other commands

       On error, -1 is returned, and errno is set appropriately.

       E2BIG  The eBPF program is too large or a map reached the max_entries
              limit (maximum number of elements).

       EACCES For BPF_PROG_LOAD, even though all program instructions are
              valid, the program has been rejected because it was deemed
              unsafe.  This may be because it may have accessed a disallowed
              memory region or an uninitialized stack/register or because the
              function constraints don't match the actual types or because
              there was a misaligned memory access.  In this case, it is
              recommended to call bpf() again with log_level = 1 and examine
              log_buf for the specific reason provided by the verifier.

       EBADF  fd is not an open file descriptor.

       EFAULT One of the pointers (key or value or log_buf or insns) is
              outside the accessible address space.

       EINVAL The value specified in cmd is not recognized by this kernel.

       EINVAL For BPF_MAP_CREATE, either map_type or attributes are invalid.

       EINVAL For BPF_MAP_*_ELEM commands, some of the fields of union
              bpf_attr that are not used by this command are not set to zero.

       EINVAL For BPF_PROG_LOAD, indicates an attempt to load an invalid
              program.  eBPF programs can be deemed invalid due to
              unrecognized instructions, the use of reserved fields, jumps out
              of range, infinite loops or calls of unknown functions.

              the element with the given key was not found.

       ENOMEM Cannot allocate sufficient memory.

       EPERM  The call was made without sufficient privilege (without the
              CAP_SYS_ADMIN capability).

       The bpf() system call first appeared in Linux 3.18.

       The bpf() system call is Linux-specific.

       Prior to Linux 4.4, all bpf() commands require the caller to have the
       CAP_SYS_ADMIN capability.  From Linux 4.4 onwards, an unprivileged user
       may create limited programs of type BPF_PROG_TYPE_SOCKET_FILTER and
       associated maps.  However they may not store kernel pointers within the
       maps and are presently limited to the following helper functions:

       *  get_random
       *  get_smp_processor_id
       *  tail_call
       *  ktime_get_ns

       Unprivileged access may be blocked by setting the sysctl

       eBPF objects (maps and programs) can be shared between processes.  For
       example, after fork(2), the child inherits file descriptors referring
       to the same eBPF objects.  In addition, file descriptors referring to
       eBPF objects can be transferred over UNIX domain sockets.  File
       descriptors referring to eBPF objects can be duplicated in the usual
       way, using dup(2) and similar calls.  An eBPF object is deallocated
       only after all file descriptors referring to the object have been

       eBPF programs can be written in a restricted C that is compiled (using
       the clang compiler) into eBPF bytecode.  Various features are omitted
       from this restricted C, such as loops, global variables, variadic
       functions, floating-point numbers, and passing structures as function
       arguments.  Some examples can be found in the samples/bpf/*_kern.c
       files in the kernel source tree.

       The kernel contains a just-in-time (JIT) compiler that translates eBPF
       bytecode into native machine code for better performance.  In kernels
       before Linux 4.15, the JIT compiler is disabled by default, but its
       operation can be controlled by writing one of the following integer
       strings to the file /proc/sys/net/core/bpf_jit_enable:

       0  Disable JIT compilation (default).

       1  Normal compilation.

       2  Debugging mode.  The generated opcodes are dumped in hexadecimal
          into the kernel log.  These opcodes can then be disassembled using
          the program tools/net/bpf_jit_disasm.c provided in the kernel source

       Since Linux 4.15, the kernel may configured with the
       CONFIG_BPF_JIT_ALWAYS_ON option.  In this case, the JIT compiler is
       always enabled, and the bpf_jit_enable is initialized to 1 and is
       immutable.  (This kernel configuration option was provided as a
       mitigation for one of the Spectre attacks against the BPF interpreter.)

       The JIT compiler for eBPF is currently available for the following

       *  x86-64 (since Linux 3.18; cBPF since Linux 3.0);
       *  ARM32 (since Linux 3.18; cBPF since Linux 3.4);
       *  SPARC 32 (since Linux 3.18; cBPF since Linux 3.5);
       *  ARM-64 (since Linux 3.18);
       *  s390 (since Linux 4.1; cBPF since Linux 3.7);
       *  PowerPC 64 (since Linux 4.8; cBPF since Linux 3.1);
       *  SPARC 64 (since Linux 4.12);
       *  x86-32 (since Linux 4.18);
       *  MIPS 64 (since Linux 4.18; cBPF since Linux 3.16);
       *  riscv (since Linux 5.1).

       seccomp(2), bpf-helpers(7), socket(7), tc(8), tc-bpf(8)

       Both classic and extended BPF are explained in the kernel source file

       This page is part of release 5.08 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                             2020-06-09                            BPF(2)