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docs/bpf: Default cpu version changed from v1 to v3 in llvm 20 

The default cpu version is changed from v1 to v3 in llvm version 20.
See [1] for more detailed reasoning. Update bpf_devel_QA.rst so
developers can find such information easily.

  [1] https://github.com/llvm/llvm-project/pull/107008

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20250612043049.2411989-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Yonghong Song 2025-06-11 21:30:49 -07:00 committed by Alexei Starovoitov
parent 6a4bd31f68
commit 50034d9362
1 changed files with 4 additions and 3 deletions
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7
Documentation/bpf/bpf_devel_QA.rst
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@ -611,9 +611,10 @@ Q: I have added a new BPF instruction to the kernel, how can I integrate
it into LLVM?
A: LLVM has a ``-mcpu`` selector for the BPF back end in order to allow
the selection of BPF instruction set extensions. By default the
``generic`` processor target is used, which is the base instruction set
(v1) of BPF.
the selection of BPF instruction set extensions. Before llvm version 20,
the ``generic`` processor target is used, which is the base instruction
set (v1) of BPF. Since llvm 20, the default processor target has changed
to instruction set v3.
LLVM has an option to select ``-mcpu=probe`` where it will probe the host
kernel for supported BPF instruction set extensions and selects the