Re: [PATCH bpf-next] selftests/bpf: add helper retval linked scalar pruning selftest

[bot+bpf-ci]

> selftests/bpf: add helper retval linked scalar pruning selftest
>
>     Add a verifier runtime test for a branch pattern where a helper return
>     value and a related scalar stay live across the same control-flow
>     sequence. Rust/Aya-generated eBPF can naturally produce this shape when
>     a match on a helper status keeps data derived before the helper call
>     live across the same branches. Such code commonly uses the helper return
>     value in r0, where 0 means success, producing an r0 == 0 / r0 != 0
>     branch shape.
>
>     The test preserves that branch shape but shifts the success value to 1
>     before branching. Using r0 == 1 / r0 != 1 avoids depending on the
>     verifier's not-equal-zero refinement, so the test exercises linked
>     scalar precision and pruning behavior directly instead of being masked
>     by zero-specific range refinement.
>
>     On affected kernels the verifier can explore an impossible path where
>     r0 and r7 are linked by scalar ID, keep the wrong branch, and make the
>     test return 1. With linked scalar precision tracked per instruction,
>     state pruning keeps the real success path, and the test returns 0.
>
>     Suggested-by: Shung-Hsi Yu <shung-hsi.yu@xxxxxxxx>
>     Signed-off-by: Zhenzhong Wu <jt26wzz@xxxxxxxxx>

This adds a regression test for a verifier state-pruning issue with
scalars linked by scalar ID, but there is no Fixes: tag.

The test structure (success path keeps r7 independent with id=0, failure
path links r7 to r0) matches the "registers with id=0 in cached state vs
linked in current state" pruning scenario that was addressed by changing
check_scalar_ids() and regsafe() to treat rold->id == 0 as independent.

Should this carry:

  Fixes: b0388bafa494 ("bpf: Relax scalar id equivalence for state pruning")


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