diff options
| author | Christoph Hellwig <hch@lst.de> | 2022-01-03 19:35:52 +0100 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2022-01-05 22:11:26 +0100 |
| commit | be3193cded9d5c030be1713bf52d307427e88d19 (patch) | |
| tree | 9c4ba903760e05dbfa337472b01fdc4ba30236cd /Documentation/bpf | |
| parent | bpf, docs: Add a setion to explain the basic instruction encoding (diff) | |
| download | linux-be3193cded9d5c030be1713bf52d307427e88d19.tar.xz linux-be3193cded9d5c030be1713bf52d307427e88d19.zip | |
bpf, docs: Add subsections for ALU and JMP instructions
Add a little more stucture to the ALU/JMP documentation with sections and
improve the example text.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220103183556.41040-3-hch@lst.de
Diffstat (limited to 'Documentation/bpf')
| -rw-r--r-- | Documentation/bpf/instruction-set.rst | 52 |
1 files changed, 32 insertions, 20 deletions
diff --git a/Documentation/bpf/instruction-set.rst b/Documentation/bpf/instruction-set.rst index 80f42984b594..03bf3c6c5577 100644 --- a/Documentation/bpf/instruction-set.rst +++ b/Documentation/bpf/instruction-set.rst @@ -74,7 +74,13 @@ The 4th bit encodes the source operand: The four MSB bits store the operation code. -For class BPF_ALU or BPF_ALU64: + +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 @@ -95,7 +101,29 @@ For class BPF_ALU or BPF_ALU64: BPF_END 0xd0 endianness conversion ======== ===== ========================= -For class BPF_JMP or BPF_JMP32: +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 + + +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 @@ -116,24 +144,8 @@ For class BPF_JMP or BPF_JMP32: BPF_JSLE 0xd0 signed '<=' ======== ===== ========================= -So BPF_ADD | BPF_X | BPF_ALU means:: - - dst_reg = (u32) dst_reg + (u32) src_reg; - -Similarly, BPF_XOR | BPF_K | BPF_ALU means:: - - src_reg = (u32) src_reg ^ (u32) imm32 - -eBPF is using BPF_MOV | BPF_X | BPF_ALU to represent A = B moves. BPF_ALU64 -is used to mean exactly the same operations as BPF_ALU, but with 64-bit wide -operands instead. So BPF_ADD | BPF_X | BPF_ALU64 means 64-bit addition, i.e.:: - - dst_reg = dst_reg + src_reg - -BPF_JMP | BPF_EXIT means function exit only. The eBPF program needs to store -the return value into register R0 before doing a BPF_EXIT. Class 6 is used as -BPF_JMP32 to mean exactly the same operations as BPF_JMP, but with 32-bit wide -operands for the comparisons instead. +The eBPF program needs to store the return value into register R0 before doing a +BPF_EXIT. Load and store instructions |