Documentation/bpf/instruction-set.rst - linux - Git at Google


 ====================
 eBPF Instruction Set
 ====================

 Registers and calling convention
 ================================

 eBPF has 10 general purpose registers and a read-only frame pointer register,
 all of which are 64-bits wide.

 The eBPF calling convention is defined as:

  * R0: return value from function calls, and exit value for eBPF programs
  * R1 - R5: arguments for function calls
  * R6 - R9: callee saved registers that function calls will preserve
  * R10: read-only frame pointer to access stack

 R0 - R5 are scratch registers and eBPF programs needs to spill/fill them if
 necessary across calls.

 Instruction encoding
 ====================

 eBPF has two instruction encodings:

  * the basic instruction encoding, which uses 64 bits to encode an instruction
  * the wide instruction encoding, which appends a second 64-bit immediate value
    (imm64) after the basic instruction for a total of 128 bits.

 The basic instruction encoding looks as follows:

  =============  =======  ===============  ====================  ============
  32 bits (MSB)  16 bits  4 bits           4 bits                8 bits (LSB)
  =============  =======  ===============  ====================  ============
  immediate      offset   source register  destination register  opcode
  =============  =======  ===============  ====================  ============

 Note that most instructions do not use all of the fields.
 Unused fields shall be cleared to zero.

 Instruction classes
 -------------------

 The three LSB bits of the 'opcode' field store the instruction class:

   =========  =====  ===============================
   class      value  description
   =========  =====  ===============================
   BPF_LD     0x00   non-standard load operations
   BPF_LDX    0x01   load into register operations
   BPF_ST     0x02   store from immediate operations
   BPF_STX    0x03   store from register operations
   BPF_ALU    0x04   32-bit arithmetic operations
   BPF_JMP    0x05   64-bit jump operations
   BPF_JMP32  0x06   32-bit jump operations
   BPF_ALU64  0x07   64-bit arithmetic operations
   =========  =====  ===============================

 Arithmetic and jump instructions
 ================================

 For arithmetic and jump instructions (BPF_ALU, BPF_ALU64, BPF_JMP and
 BPF_JMP32), the 8-bit 'opcode' field is divided into three parts:

   ==============  ======  =================
   4 bits (MSB)    1 bit   3 bits (LSB)
   ==============  ======  =================
   operation code  source  instruction class
   ==============  ======  =================

 The 4th bit encodes the source operand:

   ======  =====  ========================================
   source  value  description
   ======  =====  ========================================
   BPF_K   0x00   use 32-bit immediate as source operand
   BPF_X   0x08   use 'src_reg' register as source operand
   ======  =====  ========================================

 The four MSB bits store the operation code.


 Arithmetic instructions
 -----------------------

 BPF_ALU uses 32-bit wide operands while BPF_ALU64 uses 64-bit wide operands for
 otherwise identical operations.
 The code field encodes the operation as below:

   ========  =====  =================================================
   code      value  description
   ========  =====  =================================================
   BPF_ADD   0x00   dst += src
   BPF_SUB   0x10   dst -= src
   BPF_MUL   0x20   dst \*= src
   BPF_DIV   0x30   dst /= src
   BPF_OR    0x40   dst \|= src
   BPF_AND   0x50   dst &= src
   BPF_LSH   0x60   dst <<= src
   BPF_RSH   0x70   dst >>= src
   BPF_NEG   0x80   dst = ~src
   BPF_MOD   0x90   dst %= src
   BPF_XOR   0xa0   dst ^= src
   BPF_MOV   0xb0   dst = src
   BPF_ARSH  0xc0   sign extending shift right
   BPF_END   0xd0   byte swap operations (see separate section below)
   ========  =====  =================================================

 BPF_ADD | BPF_X | BPF_ALU means::

   dst_reg = (u32) dst_reg + (u32) src_reg;

 BPF_ADD | BPF_X | BPF_ALU64 means::

   dst_reg = dst_reg + src_reg

 BPF_XOR | BPF_K | BPF_ALU means::

   src_reg = (u32) src_reg ^ (u32) imm32

 BPF_XOR | BPF_K | BPF_ALU64 means::

   src_reg = src_reg ^ imm32


 Byte swap instructions
 ----------------------

 The byte swap instructions use an instruction class of ``BFP_ALU`` and a 4-bit
 code field of ``BPF_END``.

 The byte swap instructions operate on the destination register
 only and do not use a separate source register or immediate value.

 The 1-bit source operand field in the opcode is used to to select what byte
 order the operation convert from or to:

   =========  =====  =================================================
   source     value  description
   =========  =====  =================================================
   BPF_TO_LE  0x00   convert between host byte order and little endian
   BPF_TO_BE  0x08   convert between host byte order and big endian
   =========  =====  =================================================

 The imm field encodes the width of the swap operations.  The following widths
 are supported: 16, 32 and 64.

 Examples:

 ``BPF_ALU | BPF_TO_LE | BPF_END`` with imm = 16 means::

   dst_reg = htole16(dst_reg)

 ``BPF_ALU | BPF_TO_BE | BPF_END`` with imm = 64 means::

   dst_reg = htobe64(dst_reg)

 ``BPF_FROM_LE`` and ``BPF_FROM_BE`` exist as aliases for ``BPF_TO_LE`` and
 ``BPF_TO_BE`` respectively.


 Jump instructions
 -----------------

 BPF_JMP32 uses 32-bit wide operands while BPF_JMP uses 64-bit wide operands for
 otherwise identical operations.
 The code field encodes the operation as below:

   ========  =====  =========================  ============
   code      value  description                notes
   ========  =====  =========================  ============
   BPF_JA    0x00   PC += off                  BPF_JMP only
   BPF_JEQ   0x10   PC += off if dst == src
   BPF_JGT   0x20   PC += off if dst > src     unsigned
   BPF_JGE   0x30   PC += off if dst >= src    unsigned
   BPF_JSET  0x40   PC += off if dst & src
   BPF_JNE   0x50   PC += off if dst != src
   BPF_JSGT  0x60   PC += off if dst > src     signed
   BPF_JSGE  0x70   PC += off if dst >= src    signed
   BPF_CALL  0x80   function call
   BPF_EXIT  0x90   function / program return  BPF_JMP only
   BPF_JLT   0xa0   PC += off if dst < src     unsigned
   BPF_JLE   0xb0   PC += off if dst <= src    unsigned
   BPF_JSLT  0xc0   PC += off if dst < src     signed
   BPF_JSLE  0xd0   PC += off if dst <= src    signed
   ========  =====  =========================  ============

 The eBPF program needs to store the return value into register R0 before doing a
 BPF_EXIT.


 Load and store instructions
 ===========================

 For load and store instructions (BPF_LD, BPF_LDX, BPF_ST and BPF_STX), the
 8-bit 'opcode' field is divided as:

   ============  ======  =================
   3 bits (MSB)  2 bits  3 bits (LSB)
   ============  ======  =================
   mode          size    instruction class
   ============  ======  =================

 The size modifier is one of:

   =============  =====  =====================
   size modifier  value  description
   =============  =====  =====================
   BPF_W          0x00   word        (4 bytes)
   BPF_H          0x08   half word   (2 bytes)
   BPF_B          0x10   byte
   BPF_DW         0x18   double word (8 bytes)
   =============  =====  =====================

 The mode modifier is one of:

   =============  =====  ====================================
   mode modifier  value  description
   =============  =====  ====================================
   BPF_IMM        0x00   64-bit immediate instructions
   BPF_ABS        0x20   legacy BPF packet access (absolute)
   BPF_IND        0x40   legacy BPF packet access (indirect)
   BPF_MEM        0x60   regular load and store operations
   BPF_ATOMIC     0xc0   atomic operations
   =============  =====  ====================================


 Regular load and store operations
 ---------------------------------

 The ``BPF_MEM`` mode modifier is used to encode regular load and store
 instructions that transfer data between a register and memory.

 ``BPF_MEM | <size> | BPF_STX`` means::

   *(size *) (dst_reg + off) = src_reg

 ``BPF_MEM | <size> | BPF_ST`` means::

   *(size *) (dst_reg + off) = imm32

 ``BPF_MEM | <size> | BPF_LDX`` means::

   dst_reg = *(size *) (src_reg + off)

 Where size is one of: ``BPF_B``, ``BPF_H``, ``BPF_W``, or ``BPF_DW``.

 Atomic operations
 -----------------

 Atomic operations are operations that operate on memory and can not be
 interrupted or corrupted by other access to the same memory region
 by other eBPF programs or means outside of this specification.

 All atomic operations supported by eBPF are encoded as store operations
 that use the ``BPF_ATOMIC`` mode modifier as follows:

   * ``BPF_ATOMIC | BPF_W | BPF_STX`` for 32-bit operations
   * ``BPF_ATOMIC | BPF_DW | BPF_STX`` for 64-bit operations
   * 8-bit and 16-bit wide atomic operations are not supported.

 The imm field is used to encode the actual atomic operation.
 Simple atomic operation use a subset of the values defined to encode
 arithmetic operations in the imm field to encode the atomic operation:

   ========  =====  ===========
   imm       value  description
   ========  =====  ===========
   BPF_ADD   0x00   atomic add
   BPF_OR    0x40   atomic or
   BPF_AND   0x50   atomic and
   BPF_XOR   0xa0   atomic xor
   ========  =====  ===========


 ``BPF_ATOMIC | BPF_W  | BPF_STX`` with imm = BPF_ADD means::

   *(u32 *)(dst_reg + off16) += src_reg

 ``BPF_ATOMIC | BPF_DW | BPF_STX`` with imm = BPF ADD means::

   *(u64 *)(dst_reg + off16) += src_reg

 ``BPF_XADD`` is a deprecated name for ``BPF_ATOMIC | BPF_ADD``.

 In addition to the simple atomic operations, there also is a modifier and
 two complex atomic operations:

   ===========  ================  ===========================
   imm          value             description
   ===========  ================  ===========================
   BPF_FETCH    0x01              modifier: return old value
   BPF_XCHG     0xe0 | BPF_FETCH  atomic exchange
   BPF_CMPXCHG  0xf0 | BPF_FETCH  atomic compare and exchange
   ===========  ================  ===========================

 The ``BPF_FETCH`` modifier is optional for simple atomic operations, and
 always set for the complex atomic operations.  If the ``BPF_FETCH`` flag
 is set, then the operation also overwrites ``src_reg`` with the value that
 was in memory before it was modified.

 The ``BPF_XCHG`` operation atomically exchanges ``src_reg`` with the value
 addressed by ``dst_reg + off``.

 The ``BPF_CMPXCHG`` operation atomically compares the value addressed by
 ``dst_reg + off`` with ``R0``. If they match, the value addressed by
 ``dst_reg + off`` is replaced with ``src_reg``. In either case, the
 value that was at ``dst_reg + off`` before the operation is zero-extended
 and loaded back to ``R0``.

 Clang can generate atomic instructions by default when ``-mcpu=v3`` is
 enabled. If a lower version for ``-mcpu`` is set, the only atomic instruction
 Clang can generate is ``BPF_ADD`` *without* ``BPF_FETCH``. If you need to enable
 the atomics features, while keeping a lower ``-mcpu`` version, you can use
 ``-Xclang -target-feature -Xclang +alu32``.

 64-bit immediate instructions
 -----------------------------

 Instructions with the ``BPF_IMM`` mode modifier use the wide instruction
 encoding for an extra imm64 value.

 There is currently only one such instruction.

 ``BPF_LD | BPF_DW | BPF_IMM`` means::

   dst_reg = imm64


 Legacy BPF Packet access instructions
 -------------------------------------

 eBPF has special instructions for access to packet data that have been
 carried over from classic BPF to retain the performance of legacy socket
 filters running in the eBPF interpreter.

 The instructions come in two forms: ``BPF_ABS | <size> | BPF_LD`` and
 ``BPF_IND | <size> | BPF_LD``.

 These instructions are used to access packet data and can only be used when
 the program context is a pointer to networking packet.  ``BPF_ABS``
 accesses packet data at an absolute offset specified by the immediate data
 and ``BPF_IND`` access packet data at an offset that includes the value of
 a register in addition to the immediate data.

 These instructions have seven implicit operands:

  * Register R6 is an implicit input that must contain pointer to a
    struct sk_buff.
  * Register R0 is an implicit output which contains the data fetched from
    the packet.
  * Registers R1-R5 are scratch registers that are clobbered after a call to
    ``BPF_ABS | BPF_LD`` or ``BPF_IND`` | BPF_LD instructions.

 These instructions have an implicit program exit condition as well. When an
 eBPF program is trying to access the data beyond the packet boundary, the
 program execution will be aborted.

 ``BPF_ABS | BPF_W | BPF_LD`` means::

   R0 = ntohl(*(u32 *) (((struct sk_buff *) R6)->data + imm32))

 ``BPF_IND | BPF_W | BPF_LD`` means::

   R0 = ntohl(*(u32 *) (((struct sk_buff *) R6)->data + src_reg + imm32))

	====================
	eBPF Instruction Set
	====================

	Registers and calling convention
	================================

	eBPF has 10 general purpose registers and a read-only frame pointer register,
	all of which are 64-bits wide.

	The eBPF calling convention is defined as:

	* R0: return value from function calls, and exit value for eBPF programs
	* R1 - R5: arguments for function calls
	* R6 - R9: callee saved registers that function calls will preserve
	* R10: read-only frame pointer to access stack

	R0 - R5 are scratch registers and eBPF programs needs to spill/fill them if
	necessary across calls.

	Instruction encoding
	====================

	eBPF has two instruction encodings:

	* the basic instruction encoding, which uses 64 bits to encode an instruction
	* the wide instruction encoding, which appends a second 64-bit immediate value
	(imm64) after the basic instruction for a total of 128 bits.

	The basic instruction encoding looks as follows:

	============= ======= =============== ==================== ============
	32 bits (MSB) 16 bits 4 bits 4 bits 8 bits (LSB)
	============= ======= =============== ==================== ============
	immediate offset source register destination register opcode
	============= ======= =============== ==================== ============

	Note that most instructions do not use all of the fields.
	Unused fields shall be cleared to zero.

	Instruction classes
	-------------------

	The three LSB bits of the 'opcode' field store the instruction class:

	========= ===== ===============================
	class value description
	========= ===== ===============================
	BPF_LD 0x00 non-standard load operations
	BPF_LDX 0x01 load into register operations
	BPF_ST 0x02 store from immediate operations
	BPF_STX 0x03 store from register operations
	BPF_ALU 0x04 32-bit arithmetic operations
	BPF_JMP 0x05 64-bit jump operations
	BPF_JMP32 0x06 32-bit jump operations
	BPF_ALU64 0x07 64-bit arithmetic operations
	========= ===== ===============================

	Arithmetic and jump instructions
	================================

	For arithmetic and jump instructions (BPF_ALU, BPF_ALU64, BPF_JMP and
	BPF_JMP32), the 8-bit 'opcode' field is divided into three parts:

	============== ====== =================
	4 bits (MSB) 1 bit 3 bits (LSB)
	============== ====== =================
	operation code source instruction class
	============== ====== =================

	The 4th bit encodes the source operand:

	====== ===== ========================================
	source value description
	====== ===== ========================================
	BPF_K 0x00 use 32-bit immediate as source operand
	BPF_X 0x08 use 'src_reg' register as source operand
	====== ===== ========================================

	The four MSB bits store the operation code.


	Arithmetic instructions
	-----------------------

	BPF_ALU uses 32-bit wide operands while BPF_ALU64 uses 64-bit wide operands for
	otherwise identical operations.
	The code field encodes the operation as below:

	======== ===== =================================================
	code value description
	======== ===== =================================================
	BPF_ADD 0x00 dst += src
	BPF_SUB 0x10 dst -= src
	BPF_MUL 0x20 dst \*= src
	BPF_DIV 0x30 dst /= src
	BPF_OR 0x40 dst \\|= src
	BPF_AND 0x50 dst &= src
	BPF_LSH 0x60 dst <<= src
	BPF_RSH 0x70 dst >>= src
	BPF_NEG 0x80 dst = ~src
	BPF_MOD 0x90 dst %= src
	BPF_XOR 0xa0 dst ^= src
	BPF_MOV 0xb0 dst = src
	BPF_ARSH 0xc0 sign extending shift right
	BPF_END 0xd0 byte swap operations (see separate section below)
	======== ===== =================================================

	BPF_ADD \| BPF_X \| BPF_ALU means::

	dst_reg = (u32) dst_reg + (u32) src_reg;

	BPF_ADD \| BPF_X \| BPF_ALU64 means::

	dst_reg = dst_reg + src_reg

	BPF_XOR \| BPF_K \| BPF_ALU means::

	src_reg = (u32) src_reg ^ (u32) imm32

	BPF_XOR \| BPF_K \| BPF_ALU64 means::

	src_reg = src_reg ^ imm32


	Byte swap instructions
	----------------------

	The byte swap instructions use an instruction class of ``BFP_ALU`` and a 4-bit
	code field of ``BPF_END``.

	The byte swap instructions operate on the destination register
	only and do not use a separate source register or immediate value.

	The 1-bit source operand field in the opcode is used to to select what byte
	order the operation convert from or to:

	========= ===== =================================================
	source value description
	========= ===== =================================================
	BPF_TO_LE 0x00 convert between host byte order and little endian
	BPF_TO_BE 0x08 convert between host byte order and big endian
	========= ===== =================================================

	The imm field encodes the width of the swap operations. The following widths
	are supported: 16, 32 and 64.

	Examples:

	``BPF_ALU \| BPF_TO_LE \| BPF_END`` with imm = 16 means::

	dst_reg = htole16(dst_reg)

	``BPF_ALU \| BPF_TO_BE \| BPF_END`` with imm = 64 means::

	dst_reg = htobe64(dst_reg)

	``BPF_FROM_LE`` and ``BPF_FROM_BE`` exist as aliases for ``BPF_TO_LE`` and
	``BPF_TO_BE`` respectively.


	Jump instructions
	-----------------

	BPF_JMP32 uses 32-bit wide operands while BPF_JMP uses 64-bit wide operands for
	otherwise identical operations.
	The code field encodes the operation as below:

	======== ===== ========================= ============
	code value description notes
	======== ===== ========================= ============
	BPF_JA 0x00 PC += off BPF_JMP only
	BPF_JEQ 0x10 PC += off if dst == src
	BPF_JGT 0x20 PC += off if dst > src unsigned
	BPF_JGE 0x30 PC += off if dst >= src unsigned
	BPF_JSET 0x40 PC += off if dst & src
	BPF_JNE 0x50 PC += off if dst != src
	BPF_JSGT 0x60 PC += off if dst > src signed
	BPF_JSGE 0x70 PC += off if dst >= src signed
	BPF_CALL 0x80 function call
	BPF_EXIT 0x90 function / program return BPF_JMP only
	BPF_JLT 0xa0 PC += off if dst < src unsigned
	BPF_JLE 0xb0 PC += off if dst <= src unsigned
	BPF_JSLT 0xc0 PC += off if dst < src signed
	BPF_JSLE 0xd0 PC += off if dst <= src signed
	======== ===== ========================= ============

	The eBPF program needs to store the return value into register R0 before doing a
	BPF_EXIT.


	Load and store instructions
	===========================

	For load and store instructions (BPF_LD, BPF_LDX, BPF_ST and BPF_STX), the
	8-bit 'opcode' field is divided as:

	============ ====== =================
	3 bits (MSB) 2 bits 3 bits (LSB)
	============ ====== =================
	mode size instruction class
	============ ====== =================

	The size modifier is one of:

	============= ===== =====================
	size modifier value description
	============= ===== =====================
	BPF_W 0x00 word (4 bytes)
	BPF_H 0x08 half word (2 bytes)
	BPF_B 0x10 byte
	BPF_DW 0x18 double word (8 bytes)
	============= ===== =====================

	The mode modifier is one of:

	============= ===== ====================================
	mode modifier value description
	============= ===== ====================================
	BPF_IMM 0x00 64-bit immediate instructions
	BPF_ABS 0x20 legacy BPF packet access (absolute)
	BPF_IND 0x40 legacy BPF packet access (indirect)
	BPF_MEM 0x60 regular load and store operations
	BPF_ATOMIC 0xc0 atomic operations
	============= ===== ====================================


	Regular load and store operations
	---------------------------------

	The ``BPF_MEM`` mode modifier is used to encode regular load and store
	instructions that transfer data between a register and memory.

	``BPF_MEM \| <size> \| BPF_STX`` means::

	(size ) (dst_reg + off) = src_reg

	``BPF_MEM \| <size> \| BPF_ST`` means::

	(size ) (dst_reg + off) = imm32

	``BPF_MEM \| <size> \| BPF_LDX`` means::

	dst_reg = (size ) (src_reg + off)

	Where size is one of: ``BPF_B``, ``BPF_H``, ``BPF_W``, or ``BPF_DW``.

	Atomic operations
	-----------------

	Atomic operations are operations that operate on memory and can not be
	interrupted or corrupted by other access to the same memory region
	by other eBPF programs or means outside of this specification.

	All atomic operations supported by eBPF are encoded as store operations
	that use the ``BPF_ATOMIC`` mode modifier as follows:

	* ``BPF_ATOMIC \| BPF_W \| BPF_STX`` for 32-bit operations
	* ``BPF_ATOMIC \| BPF_DW \| BPF_STX`` for 64-bit operations
	* 8-bit and 16-bit wide atomic operations are not supported.

	The imm field is used to encode the actual atomic operation.
	Simple atomic operation use a subset of the values defined to encode
	arithmetic operations in the imm field to encode the atomic operation:

	======== ===== ===========
	imm value description
	======== ===== ===========
	BPF_ADD 0x00 atomic add
	BPF_OR 0x40 atomic or
	BPF_AND 0x50 atomic and
	BPF_XOR 0xa0 atomic xor
	======== ===== ===========


	``BPF_ATOMIC \| BPF_W \| BPF_STX`` with imm = BPF_ADD means::

	(u32 )(dst_reg + off16) += src_reg

	``BPF_ATOMIC \| BPF_DW \| BPF_STX`` with imm = BPF ADD means::

	(u64 )(dst_reg + off16) += src_reg

	``BPF_XADD`` is a deprecated name for ``BPF_ATOMIC \| BPF_ADD``.

	In addition to the simple atomic operations, there also is a modifier and
	two complex atomic operations:

	=========== ================ ===========================
	imm value description
	=========== ================ ===========================
	BPF_FETCH 0x01 modifier: return old value
	BPF_XCHG 0xe0 \| BPF_FETCH atomic exchange
	BPF_CMPXCHG 0xf0 \| BPF_FETCH atomic compare and exchange
	=========== ================ ===========================

	The ``BPF_FETCH`` modifier is optional for simple atomic operations, and
	always set for the complex atomic operations. If the ``BPF_FETCH`` flag
	is set, then the operation also overwrites ``src_reg`` with the value that
	was in memory before it was modified.

	The ``BPF_XCHG`` operation atomically exchanges ``src_reg`` with the value
	addressed by ``dst_reg + off``.

	The ``BPF_CMPXCHG`` operation atomically compares the value addressed by
	``dst_reg + off`` with ``R0``. If they match, the value addressed by
	``dst_reg + off`` is replaced with ``src_reg``. In either case, the
	value that was at ``dst_reg + off`` before the operation is zero-extended
	and loaded back to ``R0``.

	Clang can generate atomic instructions by default when ``-mcpu=v3`` is
	enabled. If a lower version for ``-mcpu`` is set, the only atomic instruction
	Clang can generate is ``BPF_ADD`` without ``BPF_FETCH``. If you need to enable
	the atomics features, while keeping a lower ``-mcpu`` version, you can use
	``-Xclang -target-feature -Xclang +alu32``.

	64-bit immediate instructions
	-----------------------------

	Instructions with the ``BPF_IMM`` mode modifier use the wide instruction
	encoding for an extra imm64 value.

	There is currently only one such instruction.

	``BPF_LD \| BPF_DW \| BPF_IMM`` means::

	dst_reg = imm64


	Legacy BPF Packet access instructions
	-------------------------------------

	eBPF has special instructions for access to packet data that have been
	carried over from classic BPF to retain the performance of legacy socket
	filters running in the eBPF interpreter.

	The instructions come in two forms: ``BPF_ABS \| <size> \| BPF_LD`` and
	``BPF_IND \| <size> \| BPF_LD``.

	These instructions are used to access packet data and can only be used when
	the program context is a pointer to networking packet. ``BPF_ABS``
	accesses packet data at an absolute offset specified by the immediate data
	and ``BPF_IND`` access packet data at an offset that includes the value of
	a register in addition to the immediate data.

	These instructions have seven implicit operands:

	* Register R6 is an implicit input that must contain pointer to a
	struct sk_buff.
	* Register R0 is an implicit output which contains the data fetched from
	the packet.
	* Registers R1-R5 are scratch registers that are clobbered after a call to
	``BPF_ABS \| BPF_LD`` or ``BPF_IND`` \| BPF_LD instructions.

	These instructions have an implicit program exit condition as well. When an
	eBPF program is trying to access the data beyond the packet boundary, the
	program execution will be aborted.

	``BPF_ABS \| BPF_W \| BPF_LD`` means::

	R0 = ntohl((u32 ) (((struct sk_buff *) R6)->data + imm32))

	``BPF_IND \| BPF_W \| BPF_LD`` means::

	R0 = ntohl((u32 ) (((struct sk_buff *) R6)->data + src_reg + imm32))