1.1 BPF Virtual Machine OPCODES

BPF Virtual Machine Instruction Set

The JNetRuntime BPF VM supports both standard Berkeley Packet Filter instructions and extended operations for advanced packet processing capabilities.

Instruction Categories

1. Load Operations (LOAD)

Load operations move data into the accumulator (A) or index register (X) from various sources:

• Immediate values
• Packet data (absolute or indexed addressing)
• Packet length
• Memory locations

2. Store Operations (STORE)

Store operations move data from registers to memory locations.

3. Arithmetic and Logical Operations (ALU)

ALU operations perform calculations on the accumulator using either:

• Immediate values
• X register contents

4. Jump Operations (JUMP)

Jump operations control program flow through:

• Unconditional jumps
• Conditional jumps based on accumulator value

5. Return Operations (RET)

Return operations terminate program execution and return a value.

6. Miscellaneous Operations (MISC)

Utility operations for register transfers.

7. Extended Operations (EXTENSION)

Custom extensions for specialized packet processing.

Instruction Set Reference

Load Instructions (LD/LDX)

Opcode	Mnemonic	Format	Description
0x00	ld #k	IMMEDIATE	Load immediate into A
0x20	ld [k]	MEMORY_ABS	Load word from packet offset k
0x28	ldh [k]	MEMORY_ABS	Load half-word from packet offset k
0x30	ldb [k]	MEMORY_ABS	Load byte from packet offset k
0x40	ld [x + k]	MEMORY_IND	Load word from packet offset X + k
0x48	ldh [x + k]	MEMORY_IND	Load half-word from packet offset X + k
0x50	ldb [x + k]	MEMORY_IND	Load byte from packet offset X + k
0x80	ld len	REG_ONLY	Load packet length into A
0x60	ld M[k]	MEMORY_REG	Load word from memory location M[k]
0xA0	ld #([k]&0xf)<<2	MEMORY_ABS	Load masked value and shift
0x01	ldx #k	IMMEDIATE	Load immediate into X
0x61	ldx M[k]	MEMORY_REG	Load word from memory into X
0x81	ldx len	REG_ONLY	Load packet length into X
0xA1	ldx #([k]&0xf)<<2	MEMORY_ABS	Load masked value into X and shift
0xB1	ldx M[k]	MEMORY_REG	Load word from indirect memory into X

Store Instructions

Opcode	Mnemonic	Format	Description
0x02	st M[k]	MEMORY_REG	Store A into memory M[k]
0x03	stx M[k]	MEMORY_REG	Store X into memory M[k]

ALU Instructions

Opcode	Mnemonic	Format	Description
0x04	add #k	IMMEDIATE	A += k
0x14	sub #k	IMMEDIATE	A -= k
0x24	mul #k	IMMEDIATE	A *= k
0x34	div #k	IMMEDIATE	A /= k
0x44	or #k	IMMEDIATE	A |= k
0x54	and #k	IMMEDIATE	A &= k
0x64	lsh #k	IMMEDIATE	A <<= k
0x74	rsh #k	IMMEDIATE	A >>= k
0x94	mod #k	IMMEDIATE	A %= k
0xA4	xor #k	IMMEDIATE	A ^= k
0x84	neg	REG_ONLY	A = -A
0x0C	add x	REG_ONLY	A += X
0x1C	sub x	REG_ONLY	A -= X
0x2C	mul x	REG_ONLY	A *= X
0x3C	div x	REG_ONLY	A /= X
0x4C	or x	REG_ONLY	A |= X
0x5C	and x	REG_ONLY	A &= X
0x6C	lsh x	REG_ONLY	A <<= X
0x7C	rsh x	REG_ONLY	A >>= X
0x9C	mod x	REG_ONLY	A %= X
0xAC	xor x	REG_ONLY	A ^= X

Jump Instructions

Opcode	Mnemonic	Format	Description
0x05	jmp +k	JUMP_UNCOND	Jump k instructions
0x15	jeq #k,jt,jf	JUMP_COND	Jump if A == k
0x25	jgt #k,jt,jf	JUMP_COND	Jump if A > k
0x35	jge #k,jt,jf	JUMP_COND	Jump if A >= k
0x45	jset #k,jt,jf	JUMP_COND	Jump if (A & k) != 0
0x1D	jeq x,jt,jf	JUMP_COND	Jump if A == X
0x2D	jgt x,jt,jf	JUMP_COND	Jump if A > X
0x3D	jge x,jt,jf	JUMP_COND	Jump if A >= X
0x4D	jset x,jt,jf	JUMP_COND	Jump if (A & X) != 0

Return Instructions

Opcode	Mnemonic	Format	Description
0x06	ret #k	IMMEDIATE	Return k
0x16	ret a	REG_ONLY	Return A

Miscellaneous Instructions

Opcode	Mnemonic	Format	Description
0x07	tax	REG_ONLY	X = A
0x87	txa	REG_ONLY	A = X

Extended Instructions

Opcode	Mnemonic	Format	Description
0xE0	chk_crc	EXTENDED	Check packet CRC
0xE1	chk_l3_csum	EXTENDED	Verify Layer 3 checksum
0xE2	chk_l4_csum	EXTENDED	Verify Layer 4 checksum
0xE3	chk_trunc	EXTENDED	Check packet truncation
0xE4	chk_frame_len	EXTENDED	Verify frame length
0xE5	chk_proto_loc	EXTENDED	Check protocol location

Instruction Encoding

Each BPF instruction is encoded in 64 bits:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    opcode     |    jt         |    jf         |     k         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                               k                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Where:

• opcode: 8-bit operation code
• jt: 8-bit jump target offset (true condition)
• jf: 8-bit jump target offset (false condition)
• k: 32-bit immediate value or offset