Re: [PATCH bpf-next v3 1/6] bpf: Derive the atomic load register in one place

[Eduard Zingerman <eddyz87@gmail.com>]

On Tue, 2026-08-11 at 15:15 +0200, Daniel Borkmann wrote:
> check_atomic_rmw() open codes the mapping from a BPF_ATOMIC to the register
> it reads the old value into, the BPF_STX case of insn_def_regno() open codes
> the very same mapping a second time, the const folding and the liveness
> transfer functions a third and a fourth time, and BPF JITs need it as well
> to know which register a faulting BPF_PROBE_ATOMIC has to clear.
> 
> Add a small helper so that all of them can share it. No functional change.
> The BPF_LOAD_ACQ case is there for the JITs, which do walk all instruction
> classes. const_reg_xfer() loses its explicit BPF_ATOMIC mode test since the
> helper checks class and mode itself; the BPF_PROBE_ATOMIC it additionally
> accepts cannot be seen there as it is only set from bpf_do_misc_fixups(),
> that is, after const folding has run. arg_track_xfer() keeps its mode test
> since that also guards the stack clearing next to it.
> 
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> ---
>   v2 -> v3:
>    - Also use the helper for const_fold and liveness (bpf ci)
>    - Drop the return value comment in verifier since the helper
>      comment already covers it (Jakub)
>   v1 -> v2:
>    - also convert insn_def_regno (Eduard, sashiko)
> 
>  include/linux/filter.h  | 24 ++++++++++++++++++++++++
>  kernel/bpf/const_fold.c | 11 +++--------
>  kernel/bpf/fixups.c     | 11 +----------
>  kernel/bpf/liveness.c   |  9 +++------
>  kernel/bpf/verifier.c   | 13 ++-----------
>  5 files changed, 33 insertions(+), 35 deletions(-)

Acked-by: Eduard Zingerman <eddyz87@gmail.com>

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