Unofficial eBPF spec

The official documentation for the eBPF instruction set is in the Linux repository. However, while it is concise, it isn't always easy to use as a reference. This document lists each valid eBPF opcode.

Instruction encoding

An eBPF program is a sequence of 64-bit instructions. This project assumes each instruction is encoded in host byte order, but the byte order is not relevant to this spec.

All eBPF instructions have the same basic encoding:

msb                                                        lsb
+------------------------+----------------+----+----+--------+
|immediate               |offset          |src |dst |opcode  |
+------------------------+----------------+----+----+--------+

From least significant to most significant bit:

• 8 bit opcode
• 4 bit destination register (dst)
• 4 bit source register (src)
• 16 bit offset
• 32 bit immediate (imm)

Most instructions do not use all of these fields. Unused fields should be zeroed.

The low 3 bits of the opcode field are the "instruction class". This groups together related opcodes.

LD/LDX/ST/STX opcode structure:

msb      lsb
+---+--+---+
|mde|sz|cls|
+---+--+---+

The sz field specifies the size of the memory location. The mde field is the memory access mode. uBPF only supports the generic "MEM" access mode.

ALU/ALU64/JMP opcode structure:

msb      lsb
+----+-+---+
|op  |s|cls|
+----+-+---+

If the s bit is zero, then the source operand is imm. If s is one, then the source operand is src. The op field specifies which ALU or branch operation is to be performed.

ALU Instructions

64-bit

Opcode	Mnemonic	Pseudocode
0x07	add dst, imm	dst += imm
0x0f	add dst, src	dst += src
0x17	sub dst, imm	dst -= imm
0x1f	sub dst, src	dst -= src
0x27	mul dst, imm	dst *= imm
0x2f	mul dst, src	dst *= src
0x37	div dst, imm	dst /= imm
0x3f	div dst, src	dst /= src
0x47	or dst, imm	dst |= imm
0x4f	or dst, src	dst |= src
0x57	and dst, imm	dst &= imm
0x5f	and dst, src	dst &= src
0x67	lsh dst, imm	dst <<= imm
0x6f	lsh dst, src	dst <<= src
0x77	rsh dst, imm	dst >>= imm (logical)
0x7f	rsh dst, src	dst >>= src (logical)
0x87	neg dst	dst = -dst
0x97	mod dst, imm	dst %= imm
0x9f	mod dst, src	dst %= src
0xa7	xor dst, imm	dst ^= imm
0xaf	xor dst, src	dst ^= src
0xb7	mov dst, imm	dst = imm
0xbf	mov dst, src	dst = src
0xc7	arsh dst, imm	dst >>= imm (arithmetic)
0xcf	arsh dst, src	dst >>= src (arithmetic)

32-bit

These instructions use only the lower 32 bits of their operands and zero the upper 32 bits of the destination register.

Opcode	Mnemonic	Pseudocode
0x04	add32 dst, imm	dst += imm
0x0c	add32 dst, src	dst += src
0x14	sub32 dst, imm	dst -= imm
0x1c	sub32 dst, src	dst -= src
0x24	mul32 dst, imm	dst *= imm
0x2c	mul32 dst, src	dst *= src
0x34	div32 dst, imm	dst /= imm
0x3c	div32 dst, src	dst /= src
0x44	or32 dst, imm	dst |= imm
0x4c	or32 dst, src	dst |= src
0x54	and32 dst, imm	dst &= imm
0x5c	and32 dst, src	dst &= src
0x64	lsh32 dst, imm	dst <<= imm
0x6c	lsh32 dst, src	dst <<= src
0x74	rsh32 dst, imm	dst >>= imm (logical)
0x7c	rsh32 dst, src	dst >>= src (logical)
0x84	neg32 dst	dst = -dst
0x94	mod32 dst, imm	dst %= imm
0x9c	mod32 dst, src	dst %= src
0xa4	xor32 dst, imm	dst ^= imm
0xac	xor32 dst, src	dst ^= src
0xb4	mov32 dst, imm	dst = imm
0xbc	mov32 dst, src	dst = src
0xc4	arsh32 dst, imm	dst >>= imm (arithmetic)
0xcc	arsh32 dst, src	dst >>= src (arithmetic)

Byteswap instructions

Opcode	Mnemonic	Pseudocode
0xd4 (imm == 16)	le16 dst	dst = htole16(dst)
0xd4 (imm == 32)	le32 dst	dst = htole32(dst)
0xd4 (imm == 64)	le64 dst	dst = htole64(dst)
0xdc (imm == 16)	be16 dst	dst = htobe16(dst)
0xdc (imm == 32)	be32 dst	dst = htobe32(dst)
0xdc (imm == 64)	be64 dst	dst = htobe64(dst)

Memory Instructions

Opcode	Mnemonic	Pseudocode
0x18	lddw dst, imm	dst = imm
0x20	ldabsw src, dst, imm	See kernel documentation
0x28	ldabsh src, dst, imm	...
0x30	ldabsb src, dst, imm	...
0x38	ldabsdw src, dst, imm	...
0x40	ldindw src, dst, imm	...
0x48	ldindh src, dst, imm	...
0x50	ldindb src, dst, imm	...
0x58	ldinddw src, dst, imm	...
0x61	ldxw dst, [src+off]	dst = *(uint32_t *) (src + off)
0x69	ldxh dst, [src+off]	dst = *(uint16_t *) (src + off)
0x71	ldxb dst, [src+off]	dst = *(uint8_t *) (src + off)
0x79	ldxdw dst, [src+off]	dst = *(uint64_t *) (src + off)
0x62	stw [dst+off], imm	*(uint32_t *) (dst + off) = imm
0x6a	sth [dst+off], imm	*(uint16_t *) (dst + off) = imm
0x72	stb [dst+off], imm	*(uint8_t *) (dst + off) = imm
0x7a	stdw [dst+off], imm	*(uint64_t *) (dst + off) = imm
0x63	stxw [dst+off], src	*(uint32_t *) (dst + off) = src
0x6b	stxh [dst+off], src	*(uint16_t *) (dst + off) = src
0x73	stxb [dst+off], src	*(uint8_t *) (dst + off) = src
0x7b	stxdw [dst+off], src	*(uint64_t *) (dst + off) = src

Branch Instructions

Opcode	Mnemonic	Pseudocode
0x05	ja +off	PC += off
0x15	jeq dst, imm, +off	PC += off if dst == imm
0x1d	jeq dst, src, +off	PC += off if dst == src
0x25	jgt dst, imm, +off	PC += off if dst > imm
0x2d	jgt dst, src, +off	PC += off if dst > src
0x35	jge dst, imm, +off	PC += off if dst >= imm
0x3d	jge dst, src, +off	PC += off if dst >= src
0xa5	jlt dst, imm, +off	PC += off if dst < imm
0xad	jlt dst, src, +off	PC += off if dst < src
0xb5	jle dst, imm, +off	PC += off if dst <= imm
0xbd	jle dst, src, +off	PC += off if dst <= src
0x45	jset dst, imm, +off	PC += off if dst & imm
0x4d	jset dst, src, +off	PC += off if dst & src
0x55	jne dst, imm, +off	PC += off if dst != imm
0x5d	jne dst, src, +off	PC += off if dst != src
0x65	jsgt dst, imm, +off	PC += off if dst > imm (signed)
0x6d	jsgt dst, src, +off	PC += off if dst > src (signed)
0x75	jsge dst, imm, +off	PC += off if dst >= imm (signed)
0x7d	jsge dst, src, +off	PC += off if dst >= src (signed)
0xc5	jslt dst, imm, +off	PC += off if dst < imm (signed)
0xcd	jslt dst, src, +off	PC += off if dst < src (signed)
0xd5	jsle dst, imm, +off	PC += off if dst <= imm (signed)
0xdd	jsle dst, src, +off	PC += off if dst <= src (signed)
0x85	call imm	Function call
0x95	exit	return r0