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bpf, docs: Explain helper functions

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Add brief text about existence of helper functions, with details to go in
separate psABI text.

Note that text about runtime functions (kfuncs) is part of a separate patch,
not this one.

Signed-off-by: Dave Thaler <dthaler@microsoft.com>
Link: https://lore.kernel.org/r/20230308205303.1308-1-dthaler1968@googlemail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Dave Thaler
2023-03-08 20:53:03 +00:00
committed by Alexei Starovoitov
parent 74843b57ec
commit c1f9e14e3b
3 changed files with 22 additions and 1 deletions
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6
Documentation/bpf/clang-notes.rst
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@@ -20,6 +20,12 @@ Arithmetic instructions
For CPU versions prior to 3, Clang v7.0 and later can enable ``BPF_ALU`` support with
``-Xclang -target-feature -Xclang +alu32``. In CPU version 3, support is automatically included.
Jump instructions
=================
If ``-O0`` is used, Clang will generate the ``BPF_CALL | BPF_X | BPF_JMP`` (0x8d)
instruction, which is not supported by the Linux kernel verifier.
Atomic operations
=================