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| author | Dave Thaler <dthaler1968@googlemail.com> | 2024-01-19 00:29:54 +0100 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2024-01-24 00:10:08 +0100 |
| commit | 20e109ea9842158a153b24ef42ec5cc3d44e9485 (patch) | |
| tree | ba89b7c2fba858d3ad06c588e2cf7c5621ca0a84 /Documentation/bpf | |
| parent | bpf: Define struct bpf_tcp_req_attrs when CONFIG_SYN_COOKIES=n. (diff) | |
| download | linux-20e109ea9842158a153b24ef42ec5cc3d44e9485.tar.xz linux-20e109ea9842158a153b24ef42ec5cc3d44e9485.zip | |
bpf, docs: Clarify that MOVSX is only for BPF_X not BPF_K
Per discussion on the mailing list at
https://mailarchive.ietf.org/arch/msg/bpf/uQiqhURdtxV_ZQOTgjCdm-seh74/
the MOVSX operation is only defined to support register extension.
The document didn't previously state this and incorrectly implied
that one could use an immediate value.
Signed-off-by: Dave Thaler <dthaler1968@gmail.com>
Acked-by: David Vernet <void@manifault.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20240118232954.27206-1-dthaler1968@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'Documentation/bpf')
| -rw-r--r-- | Documentation/bpf/standardization/instruction-set.rst | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/Documentation/bpf/standardization/instruction-set.rst b/Documentation/bpf/standardization/instruction-set.rst index eb0f234a8001..d17a96c6254f 100644 --- a/Documentation/bpf/standardization/instruction-set.rst +++ b/Documentation/bpf/standardization/instruction-set.rst @@ -317,7 +317,8 @@ The ``BPF_MOVSX`` instruction does a move operation with sign extension. ``BPF_ALU | BPF_MOVSX`` :term:`sign extends<Sign Extend>` 8-bit and 16-bit operands into 32 bit operands, and zeroes the remaining upper 32 bits. ``BPF_ALU64 | BPF_MOVSX`` :term:`sign extends<Sign Extend>` 8-bit, 16-bit, and 32-bit -operands into 64 bit operands. +operands into 64 bit operands. Unlike other arithmetic instructions, +``BPF_MOVSX`` is only defined for register source operands (``BPF_X``). Shift operations use a mask of 0x3F (63) for 64-bit operations and 0x1F (31) for 32-bit operations. |