s390x-unknown-linux-gnu: cfg!(target_feature = "backchain") is always true · Issue #129927 · rust-lang/rust (original) (raw)

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Description

#127506 introduced what I think is a logic error: cfg!(target_feature = "backchain") is now always true on s390x targets, even if the feature gate is not set. I verified this with Miri, which shares the cfg logic with rustc so it should be a correct test.

This should print false when built without -Ctarget-feature=+backchain (as the feature seems off-by-default), but prints true instead:

fn main() { dbg!(cfg!(target_feature = "backchain")); }

Cc @liushuyu