bpf(2) — Linux manual page


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

NAME         top

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

SYNOPSIS         top

       #include <linux/bpf.h>

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

DESCRIPTION         top

       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

       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

              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 descrip‐
              tor associated with the program.  The close-on-exec file
              descriptor flag (see fcntl(2)) is automatically enabled for
              the new file descriptor.

              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() com‐
       mands 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 calls

                  bpf_map_lookup_elem(map_fd, fp - 4)

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

                  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 below.

              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 follow‐

                     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 ele‐
              ment 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

              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 ele‐
                 ment 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 time

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

              *  map_delete_elem() fails with the error EINVAL, since ele‐
                 ments 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 events.

              *  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), exe‐
              cution 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 net‐
              working, to handle individual system calls or protocols in
              their own subprograms and use their identifiers as an individ‐
              ual map index.  This approach may result in performance bene‐
              fits, and also makes it possible to overcome the maximum
              instruction limit of a single eBPF program.  In dynamic envi‐
              ronments, a user-space daemon might atomically replace indi‐
              vidual subprograms at run-time with newer versions to alter
              overall program behavior, for instance, if global policies

   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 insns.

       *  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 pro‐
       grams.  For example, eBPF programs can process various events (like
       kprobe, packets) and store their data into a map, and user-space pro‐
       grams can then fetch data from the map.  Conversely, user-space pro‐
       grams 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_con‐
       text (which is the data blob passed into the eBPF program as the
       first argument).

       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 trac‐
       ing 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_FIL‐
              TER is:

                  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

           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);

EXAMPLES         top

       /* 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.

RETURN VALUE         top

       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.

ERRORS         top

       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

       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

       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).

VERSIONS         top

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

CONFORMING TO         top

       The bpf() system call is Linux-specific.

NOTES         top

       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

       *  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 closed.

       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 tree.

       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

       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).

SEE ALSO         top

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

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

COLOPHON         top

       This page is part of release 5.07 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)

Pages that refer to this page: perf_event_open(2)seccomp(2)syscalls(2)lirc(4)proc(5)procfs(5)bpf-helpers(7)BPF-HELPERS(7)capabilities(7)socket(7)BPF(8)tc-bpf(8)