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| author | Dave Thaler <dthaler@microsoft.com> | 2023-03-26 08:49:46 +0300 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2023-04-03 03:02:54 +0300 |
| commit | 16b7c970cc8192e929dbd5192ccc1867e19d7bda (patch) | |
| tree | 44b5b5d57108cdf54b4896b686b369e97f20a1e4 /Documentation/bpf/linux-notes.rst | |
| parent | 92b2e810f0d3a2c05d8cf12a800592b238d458df (diff) | |
| download | linux-16b7c970cc8192e929dbd5192ccc1867e19d7bda.tar.xz | |
bpf, docs: Add docs on extended 64-bit immediate instructions
Add docs on extended 64-bit immediate instructions, including six instructions
previously undocumented. Include a brief description of maps and variables,
as used by those instructions.
V1 -> V2: rebased on top of latest master
V2 -> V3: addressed comments from Alexei
V3 -> V4: addressed comments from David Vernet
Signed-off-by: Dave Thaler <dthaler@microsoft.com>
Link: https://lore.kernel.org/r/20230326054946.2331-1-dthaler1968@googlemail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'Documentation/bpf/linux-notes.rst')
| -rw-r--r-- | Documentation/bpf/linux-notes.rst | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/Documentation/bpf/linux-notes.rst b/Documentation/bpf/linux-notes.rst index f43b9c797bcb..508d009d3bed 100644 --- a/Documentation/bpf/linux-notes.rst +++ b/Documentation/bpf/linux-notes.rst @@ -20,6 +20,28 @@ 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 ===================================== |