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(dhcp-9320.meeting.ietf.org. [31.133.147.32]) by smtp.gmail.com with ESMTPSA id w10-20020a0cff0a000000b005dd8b934585sm1748012qvt.29.2023.03.25.15.43.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 25 Mar 2023 15:43:16 -0700 (PDT) From: Dave Thaler To: bpf@vger.kernel.org Cc: bpf@ietf.org, Dave Thaler Subject: [PATCH bpf-next v3] bpf, docs: Add docs on extended 64-bit immediate instructions Date: Sat, 25 Mar 2023 22:43:05 +0000 Message-Id: <20230325224305.2157-1-dthaler1968@googlemail.com> X-Mailer: git-send-email 2.33.4 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net From: Dave Thaler Add docs on extended 64-bit immediate instructions, including six instructions previously undocumented. Include a brief description of map objects, and variables, as used by those instructions. --- V1 -> V2: rebased on top of latest master V2 -> V3: addressed comments from Alexei Signed-off-by: Dave Thaler --- Documentation/bpf/instruction-set.rst | 56 +++++++++++++++++++++++---- Documentation/bpf/linux-notes.rst | 13 +++++++ 2 files changed, 61 insertions(+), 8 deletions(-) diff --git a/Documentation/bpf/instruction-set.rst b/Documentation/bpf/instruction-set.rst index db8789e6969..2c8347d63e7 100644 --- a/Documentation/bpf/instruction-set.rst +++ b/Documentation/bpf/instruction-set.rst @@ -385,14 +385,54 @@ and loaded back to ``R0``. ----------------------------- Instructions with the ``BPF_IMM`` 'mode' modifier use the wide instruction -encoding for an extra imm64 value. - -There is currently only one such instruction. - -``BPF_LD | BPF_DW | BPF_IMM`` means:: - - dst = imm64 - +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 = map_val(map_by_fd(imm)) + next_imm map fd data pointer +BPF_IMM | BPF_DW | BPF_LD 0x18 0x3 dst = var_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 = map_val(map_by_idx(imm)) + next_imm map index data pointer +========================= ====== === ========================================= =========== ============== + +where + +* map_by_fd(imm) means to convert a 32-bit POSIX file descriptor into an address of a map object (see `Map objects`_) +* map_by_idx(imm) means to convert a 32-bit index into an address of a map object +* map_val(map) gets the address of the first value in a given map object +* var_addr(imm) gets the address of a platform variable (see `Platform Variables`_) with a given id +* code_addr(imm) gets the address of the instruction at a specified relative offset in number of (64-bit) instructions +* 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 'map_val(map)' is currently only defined for maps that do have a single +contiguous memory region. + +Each map object can have a POSIX file descriptor (fd) if supported by the platform, +where 'map_by_fd(imm)' means to get the map with the specified file descriptor. +Each BPF program can also be defined to use a set of maps associated with the program +at load time, and 'map_by_idx(imm)' means to get the map with the given index in the set +associated with the BPF program containing the instruction. + +Platform Variables +~~~~~~~~~~~~~~~~~~ + +Platform variables are memory regions, identified by integer ids, exposed by the runtime and accessible by BPF programs on +some platforms. The 'var_addr(imm)' operation means to get the address of the memory region +identified by the given id. Legacy BPF Packet access instructions ------------------------------------- diff --git a/Documentation/bpf/linux-notes.rst b/Documentation/bpf/linux-notes.rst index 956b0c86699..2d161467105 100644 --- a/Documentation/bpf/linux-notes.rst +++ b/Documentation/bpf/linux-notes.rst @@ -12,6 +12,19 @@ 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 'map_val(map)' operation on array maps with a single element. + +Linux uses an fd_array to store maps associated with a BPF program. Thus, +map_by_index(index) uses the fd at that index in the array. + +Variables +========= + +Linux uses BTF ids to identify variables. + Legacy BPF Packet access instructions =====================================