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Diffstat (limited to 'Documentation/bpf/instruction-set.rst')
| -rw-r--r-- | Documentation/bpf/instruction-set.rst | 318 |
1 files changed, 140 insertions, 178 deletions
diff --git a/Documentation/bpf/instruction-set.rst b/Documentation/bpf/instruction-set.rst index 1b0e6711dec9..5d798437dad4 100644 --- a/Documentation/bpf/instruction-set.rst +++ b/Documentation/bpf/instruction-set.rst @@ -1,7 +1,12 @@ +.. contents:: +.. sectnum:: + +======================================== +eBPF Instruction Set Specification, v1.0 +======================================== + +This document specifies version 1.0 of the eBPF instruction set. -==================== -eBPF Instruction Set -==================== Registers and calling convention ================================ @@ -11,10 +16,10 @@ 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: 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. @@ -24,17 +29,17 @@ 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, 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 - ============= ======= =============== ==================== ============ +============= ======= =============== ==================== ============ +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. @@ -44,30 +49,30 @@ 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 - ========= ===== =============================== +========= ===== =============================== =================================== +class value description reference +========= ===== =============================== =================================== +BPF_LD 0x00 non-standard load operations `Load and store instructions`_ +BPF_LDX 0x01 load into register operations `Load and store instructions`_ +BPF_ST 0x02 store from immediate operations `Load and store instructions`_ +BPF_STX 0x03 store from register operations `Load and store instructions`_ +BPF_ALU 0x04 32-bit arithmetic operations `Arithmetic and jump instructions`_ +BPF_JMP 0x05 64-bit jump operations `Arithmetic and jump instructions`_ +BPF_JMP32 0x06 32-bit jump operations `Arithmetic and jump instructions`_ +BPF_ALU64 0x07 64-bit arithmetic operations `Arithmetic and jump instructions`_ +========= ===== =============================== =================================== 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: +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 - ============== ====== ================= +============== ====== ================= +4 bits (MSB) 1 bit 3 bits (LSB) +============== ====== ================= +operation code source instruction class +============== ====== ================= The 4th bit encodes the source operand: @@ -84,66 +89,66 @@ 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 +``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:: +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 `Byte swap instructions`_ below) +======== ===== ========================================================== + +``BPF_ADD | BPF_X | BPF_ALU`` means:: dst_reg = (u32) dst_reg + (u32) src_reg; -BPF_ADD | BPF_X | BPF_ALU64 means:: +``BPF_ADD | BPF_X | BPF_ALU64`` means:: dst_reg = dst_reg + src_reg -BPF_XOR | BPF_K | BPF_ALU means:: +``BPF_XOR | BPF_K | BPF_ALU`` means:: src_reg = (u32) src_reg ^ (u32) imm32 -BPF_XOR | BPF_K | BPF_ALU64 means:: +``BPF_XOR | BPF_K | BPF_ALU64`` means:: src_reg = src_reg ^ imm32 Byte swap instructions ----------------------- +~~~~~~~~~~~~~~~~~~~~~~ The byte swap instructions use an instruction class of ``BPF_ALU`` and a 4-bit -code field of ``BPF_END``. +'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 +The 1-bit source operand field in the opcode is used 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 - ========= ===== ================================================= +========= ===== ================================================= +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 +The 'imm' field encodes the width of the swap operations. The following widths are supported: 16, 32 and 64. Examples: @@ -156,35 +161,31 @@ Examples: 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 +``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 '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. @@ -193,14 +194,26 @@ BPF_EXIT. Load and store instructions =========================== -For load and store instructions (BPF_LD, BPF_LDX, BPF_ST and BPF_STX), the +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 - ============ ====== ================= +============ ====== ================= +3 bits (MSB) 2 bits 3 bits (LSB) +============ ====== ================= +mode size instruction class +============ ====== ================= + +The mode modifier is one of: + + ============= ===== ==================================== ============= + mode modifier value description reference + ============= ===== ==================================== ============= + BPF_IMM 0x00 64-bit immediate instructions `64-bit immediate instructions`_ + BPF_ABS 0x20 legacy BPF packet access (absolute) `Legacy BPF Packet access instructions`_ + BPF_IND 0x40 legacy BPF packet access (indirect) `Legacy BPF Packet access instructions`_ + BPF_MEM 0x60 regular load and store operations `Regular load and store operations`_ + BPF_ATOMIC 0xc0 atomic operations `Atomic operations`_ + ============= ===== ==================================== ============= The size modifier is one of: @@ -213,19 +226,6 @@ The size modifier is one of: 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 --------------------------------- @@ -256,44 +256,42 @@ 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. +* ``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. +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: +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 - ======== ===== =========== +======== ===== =========== +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:: +``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:: +``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 - =========== ================ =========================== +=========== ================ =========================== +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 @@ -309,16 +307,10 @@ The ``BPF_CMPXCHG`` operation atomically compares the value addressed by 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 +Instructions with the ``BPF_IMM`` 'mode' modifier use the wide instruction encoding for an extra imm64 value. There is currently only one such instruction. @@ -331,36 +323,6 @@ There is currently only one such instruction. 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 previously introduced special instructions for access to packet data that were +carried over from classic BPF. However, these instructions are +deprecated and should no longer be used. |