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 runtime, 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 */

          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 deleted 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 */

   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_bug.  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), "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 packets0, 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.


   In the current implementation, all bpf() commands require the caller to
   have the CAP_SYS_ADMIN capability.

   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.  The JIT
   compiler is disabled by default, but its operation can be controlled by
   writing   one   of   the   following   integer   strings  to  the  file

   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

   JIT compiler for eBPF is currently available for the x86-64, arm64, and
   s390 architectures.


   seccomp(2), 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 4.09 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


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