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bpf, docs: Add signed comparison example

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Improve clarity by adding an example of a signed comparison instruction

Signed-off-by: Dave Thaler <dthaler@microsoft.com>
Acked-by: David Vernet <void@manifault.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/r/20230310233814.4641-1-dthaler1968@googlemail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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Dave Thaler 2023-03-10 23:38:14 +00:00 committed by Alexei Starovoitov
parent ab4c15feb2
commit b9fe8e8d03
1 changed files with 10 additions and 1 deletions
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11
Documentation/bpf/instruction-set.rst
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@ -11,7 +11,8 @@ Documentation conventions
========================= =========================
For brevity, this document uses the type notion "u64", "u32", etc. For brevity, this document uses the type notion "u64", "u32", etc.
to mean an unsigned integer whose width is the specified number of bits. to mean an unsigned integer whose width is the specified number of bits,
and "s32", etc. to mean a signed integer of the specified number of bits.
Registers and calling convention Registers and calling convention
================================ ================================
@ -264,6 +265,14 @@ BPF_JSLE 0xd0 PC += off if dst <= src signed
The eBPF program needs to store the return value into register R0 before doing a The eBPF program needs to store the return value into register R0 before doing a
BPF_EXIT. BPF_EXIT.
Example:
``BPF_JSGE | BPF_X | BPF_JMP32`` (0x7e) means::
if (s32)dst s>= (s32)src goto +offset
where 's>=' indicates a signed '>=' comparison.
Helper functions Helper functions
~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~