[PATCH 1/5] bpf, docs: Document the byte swapping instructions
From: Christoph Hellwig <hch@lst.de>
Date: 2022-01-31 18:36:55
Also in:
bpf, linux-doc
Subsystem:
bpf [general] (safe dynamic programs and tools), documentation, the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Jonathan Corbet, Linus Torvalds
Add a section to document the byte swapping instructions. Signed-off-by: Christoph Hellwig <hch@lst.de> --- Documentation/bpf/instruction-set.rst | 44 ++++++++++++++++++++++++--- 1 file changed, 40 insertions(+), 4 deletions(-)
diff --git a/Documentation/bpf/instruction-set.rst b/Documentation/bpf/instruction-set.rst
index 3704836fe6df6..87f6ad62633a5 100644
--- a/Documentation/bpf/instruction-set.rst
+++ b/Documentation/bpf/instruction-set.rst@@ -82,9 +82,9 @@ 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
@@ -98,8 +98,8 @@ The code field encodes the operation as below: BPF_XOR 0xa0 dst ^= src BPF_MOV 0xb0 dst = src BPF_ARSH 0xc0 sign extending shift right - BPF_END 0xd0 endianness conversion - ======== ===== ========================== + BPF_END 0xd0 byte swap operations (see separate section below) + ======== ===== ================================================= BPF_ADD | BPF_X | BPF_ALU means::
@@ -118,6 +118,42 @@ 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 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_LE`` respetively. + + Jump instructions -----------------
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2.30.2