From: Dave Thaler <dthaler@xxxxxxxxxxxxx> Signed-off-by: Dave Thaler <dthaler@xxxxxxxxxxxxx> --- Documentation/bpf/instruction-set.rst | 54 +++++++++++++++++++++++++-- Documentation/bpf/linux-notes.rst | 10 +++++ 2 files changed, 60 insertions(+), 4 deletions(-) diff --git a/Documentation/bpf/instruction-set.rst b/Documentation/bpf/instruction-set.rst index 328207ff6..667d97715 100644 --- a/Documentation/bpf/instruction-set.rst +++ b/Documentation/bpf/instruction-set.rst @@ -430,14 +430,54 @@ and loaded back to ``R0``. ----------------------------- Instructions with the ``BPF_IMM`` 'mode' modifier use the wide instruction -encoding for an extra imm64 value. +encoding defined in `Instruction encoding`_, and use the 'src' field of the +basic instruction to hold an opcode subtype. + +The following instructions are defined, and use additional concepts defined below: + +========================= ====== === ===================================== =========== ============== +opcode construction opcode src pseudocode imm type dst type +========================= ====== === ===================================== =========== ============== +BPF_IMM | BPF_DW | BPF_LD 0x18 0x0 dst = imm64 integer integer +BPF_IMM | BPF_DW | BPF_LD 0x18 0x1 dst = map_by_fd(imm) map fd map +BPF_IMM | BPF_DW | BPF_LD 0x18 0x2 dst = mva(map_by_fd(imm)) + next_imm map fd data pointer +BPF_IMM | BPF_DW | BPF_LD 0x18 0x3 dst = variable_addr(imm) variable id data pointer +BPF_IMM | BPF_DW | BPF_LD 0x18 0x4 dst = code_addr(imm) integer code pointer +BPF_IMM | BPF_DW | BPF_LD 0x18 0x5 dst = map_by_idx(imm) map index map +BPF_IMM | BPF_DW | BPF_LD 0x18 0x6 dst = mva(map_by_idx(imm)) + next_imm map index data pointer +========================= ====== === ===================================== =========== ============== -There is currently only one such instruction. +where + +* map_by_fd(fd) means to convert a 32-bit POSIX file descriptor into an address of a map object (see `Map objects`_) +* map_by_index(index) means to convert a 32-bit index into an address of a map object +* mva(map) gets the address of the first value in a given map object +* variable_addr(id) gets the address of a variable (see `Variables`_) with a given id +* code_addr(offset) gets the address of the instruction at a specified relative offset in units of 64-bit blocks +* the 'imm type' can be used by disassemblers for display +* the 'dst type' can be used for verification and JIT compilation purposes + +Map objects +~~~~~~~~~~~ + +Maps are shared memory regions accessible by eBPF programs on some platforms, where we use the term "map object" +to refer to an object containing the data and metadata (e.g., size) about the memory region. +A map can have various semantics as defined in a separate document, and may or may not have a single +contiguous memory region, but the 'mva(map)' is currently only defined for maps that do have a single +contiguous memory region. Support for maps is optional. -``BPF_LD | BPF_DW | BPF_IMM`` means:: +Each map object can have a POSIX file descriptor (fd) if supported by the platform, +where 'map_by_fd(fd)' means to get the map with the specified file descriptor. +Each eBPF program can also be defined to use a set of maps associated with the program +at load time, and 'map_by_index(index)' means to get the map with the given index in the set +associated with the eBPF program containing the instruction. - dst = imm64 +Variables +~~~~~~~~~ +Variables are memory regions, identified by integer ids, accessible by eBPF programs on +some platforms. The 'variable_addr(id)' operation means to get the address of the memory region +identified by the given id. Support for such variables is optional. Legacy BPF Packet access instructions ------------------------------------- @@ -465,6 +505,12 @@ opcode src imm description referenc 0x16 0x0 any if (uint32_t)dst == imm goto +offset `Jump instructions`_ 0x17 0x0 any dst -= imm `Arithmetic instructions`_ 0x18 0x0 any dst = imm64 `64-bit immediate instructions`_ +0x18 0x1 any dst = map_by_fd(imm) `64-bit immediate instructions`_ +0x18 0x2 any dst = mva(map_by_fd(imm)) + next_imm `64-bit immediate instructions`_ +0x18 0x3 any dst = variable_addr(imm) `64-bit immediate instructions`_ +0x18 0x4 any dst = code_addr(imm) `64-bit immediate instructions`_ +0x18 0x5 any dst = map_by_idx(imm) `64-bit immediate instructions`_ +0x18 0x6 any dst = mva(map_by_idx(imm)) + next_imm `64-bit immediate instructions`_ 0x1c any 0x00 dst = (uint32_t)(dst - src) `Arithmetic instructions`_ 0x1d any 0x00 if dst == src goto +offset `Jump instructions`_ 0x1e any 0x00 if (uint32_t)dst == (uint32_t)src goto +offset `Jump instructions`_ diff --git a/Documentation/bpf/linux-notes.rst b/Documentation/bpf/linux-notes.rst index 0581ba326..e7f79242c 100644 --- a/Documentation/bpf/linux-notes.rst +++ b/Documentation/bpf/linux-notes.rst @@ -24,6 +24,16 @@ Byte swap instructions ``BPF_FROM_LE`` and ``BPF_FROM_BE`` exist as aliases for ``BPF_TO_LE`` and ``BPF_TO_BE`` respectively. +Map objects +=========== + +Linux only supports the 'mva(map)' operation on array maps with a single element. + +Variables +========= + +Linux uses BTF ids to identify variables. + Legacy BPF Packet access instructions ===================================== -- 2.33.4
