From aee1720eeb87a3adc242eb07e5d4f7ba3eb8c736 Mon Sep 17 00:00:00 2001 From: David Vernet Date: Mon, 28 Aug 2023 10:59:46 -0500 Subject: bpf, docs: Move linux-notes.rst to root bpf docs tree In commit 4d496be9ca05 ("bpf,docs: Create new standardization subdirectory"), I added a standardization/ directory to the BPF documentation, which will contain the docs that will be standardized as part of the effort with the IETF. I included linux-notes.rst in that directory, but I shouldn't have. It doesn't contain anything that will be standardized. Let's move it back to Documentation/bpf. Signed-off-by: David Vernet Signed-off-by: Daniel Borkmann Link: https://lore.kernel.org/bpf/20230828155948.123405-2-void@manifault.com --- Documentation/bpf/index.rst | 1 + Documentation/bpf/linux-notes.rst | 84 +++++++++++++++++++++++ Documentation/bpf/standardization/index.rst | 1 - Documentation/bpf/standardization/linux-notes.rst | 84 ----------------------- 4 files changed, 85 insertions(+), 85 deletions(-) create mode 100644 Documentation/bpf/linux-notes.rst delete mode 100644 Documentation/bpf/standardization/linux-notes.rst (limited to 'Documentation/bpf') diff --git a/Documentation/bpf/index.rst b/Documentation/bpf/index.rst index 1ff177b89d66..aeaeb35e6d4a 100644 --- a/Documentation/bpf/index.rst +++ b/Documentation/bpf/index.rst @@ -29,6 +29,7 @@ that goes into great technical depth about the BPF Architecture. bpf_licensing test_debug clang-notes + linux-notes other redirect diff --git a/Documentation/bpf/linux-notes.rst b/Documentation/bpf/linux-notes.rst new file mode 100644 index 000000000000..00d2693de025 --- /dev/null +++ b/Documentation/bpf/linux-notes.rst @@ -0,0 +1,84 @@ +.. contents:: +.. sectnum:: + +========================== +Linux implementation notes +========================== + +This document provides more details specific to the Linux kernel implementation of the eBPF instruction set. + +Byte swap instructions +====================== + +``BPF_FROM_LE`` and ``BPF_FROM_BE`` exist as aliases for ``BPF_TO_LE`` and ``BPF_TO_BE`` respectively. + +Jump instructions +================= + +``BPF_CALL | BPF_X | BPF_JMP`` (0x8d), where the helper function +integer would be read from a specified register, is not currently supported +by the verifier. Any programs with this instruction will fail to load +until such support is added. + +Maps +==== + +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_idx(imm) uses the fd at that index in the array. + +Variables +========= + +The following 64-bit immediate instruction specifies that a variable address, +which corresponds to some integer stored in the 'imm' field, should be loaded: + +========================= ====== === ========================================= =========== ============== +opcode construction opcode src pseudocode imm type dst type +========================= ====== === ========================================= =========== ============== +BPF_IMM | BPF_DW | BPF_LD 0x18 0x3 dst = var_addr(imm) variable id data pointer +========================= ====== === ========================================= =========== ============== + +On Linux, this integer is a BTF ID. + +Legacy BPF Packet access instructions +===================================== + +As mentioned in the `ISA standard documentation +`_, +Linux has special eBPF 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 | | BPF_LD`` and +``BPF_IND | | BPF_LD``. + +These instructions are used to access packet data and can only be used when +the program context is a pointer to a 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 a 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 by the + instruction. + +These instructions have an implicit program exit condition as well. If an +eBPF program attempts access data beyond the packet boundary, the +program execution will be aborted. + +``BPF_ABS | BPF_W | BPF_LD`` (0x20) means:: + + R0 = ntohl(*(u32 *) ((struct sk_buff *) R6->data + imm)) + +where ``ntohl()`` converts a 32-bit value from network byte order to host byte order. + +``BPF_IND | BPF_W | BPF_LD`` (0x40) means:: + + R0 = ntohl(*(u32 *) ((struct sk_buff *) R6->data + src + imm)) diff --git a/Documentation/bpf/standardization/index.rst b/Documentation/bpf/standardization/index.rst index 09c6ba055fd7..d7b946f71261 100644 --- a/Documentation/bpf/standardization/index.rst +++ b/Documentation/bpf/standardization/index.rst @@ -12,7 +12,6 @@ for the working group charter, documents, and more. :maxdepth: 1 instruction-set - linux-notes .. Links: .. _IETF BPF Working Group: https://datatracker.ietf.org/wg/bpf/about/ diff --git a/Documentation/bpf/standardization/linux-notes.rst b/Documentation/bpf/standardization/linux-notes.rst deleted file mode 100644 index 00d2693de025..000000000000 --- a/Documentation/bpf/standardization/linux-notes.rst +++ /dev/null @@ -1,84 +0,0 @@ -.. contents:: -.. sectnum:: - -========================== -Linux implementation notes -========================== - -This document provides more details specific to the Linux kernel implementation of the eBPF instruction set. - -Byte swap instructions -====================== - -``BPF_FROM_LE`` and ``BPF_FROM_BE`` exist as aliases for ``BPF_TO_LE`` and ``BPF_TO_BE`` respectively. - -Jump instructions -================= - -``BPF_CALL | BPF_X | BPF_JMP`` (0x8d), where the helper function -integer would be read from a specified register, is not currently supported -by the verifier. Any programs with this instruction will fail to load -until such support is added. - -Maps -==== - -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_idx(imm) uses the fd at that index in the array. - -Variables -========= - -The following 64-bit immediate instruction specifies that a variable address, -which corresponds to some integer stored in the 'imm' field, should be loaded: - -========================= ====== === ========================================= =========== ============== -opcode construction opcode src pseudocode imm type dst type -========================= ====== === ========================================= =========== ============== -BPF_IMM | BPF_DW | BPF_LD 0x18 0x3 dst = var_addr(imm) variable id data pointer -========================= ====== === ========================================= =========== ============== - -On Linux, this integer is a BTF ID. - -Legacy BPF Packet access instructions -===================================== - -As mentioned in the `ISA standard documentation -`_, -Linux has special eBPF 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 | | BPF_LD`` and -``BPF_IND | | BPF_LD``. - -These instructions are used to access packet data and can only be used when -the program context is a pointer to a 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 a 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 by the - instruction. - -These instructions have an implicit program exit condition as well. If an -eBPF program attempts access data beyond the packet boundary, the -program execution will be aborted. - -``BPF_ABS | BPF_W | BPF_LD`` (0x20) means:: - - R0 = ntohl(*(u32 *) ((struct sk_buff *) R6->data + imm)) - -where ``ntohl()`` converts a 32-bit value from network byte order to host byte order. - -``BPF_IND | BPF_W | BPF_LD`` (0x40) means:: - - R0 = ntohl(*(u32 *) ((struct sk_buff *) R6->data + src + imm)) -- cgit v1.2.3