getenv doctest hangs on armv7-unknown-linux-gnueabihf CI

Description

The \getenv\ doctest at \src/lib.rs\ line 438 hangs indefinitely on the \rmv7-unknown-linux-gnueabihf\ CI target (ubuntu-24.04-arm runner). All other 28 doctests pass. The same doctest passes on all other platforms including \ humbv7neon-unknown-linux-gnueabihf\ (same ARM32 architecture, different instruction set).

Steps to reproduce

Run \cargo test --target armv7-unknown-linux-gnueabihf --doc\ on an ubuntu-24.04-arm GitHub Actions runner.

Evidence from CI logs

\
test src/lib.rs - (line 493) ... ok
test src/lib.rs - (line 438) has been running for over 60 seconds
\\

Job ID: 66241023177 in workflow run 22838910297.

Root cause analysis

The doctest patches the C \getenv\ function using injectorpp. On armv7, the patched function appears to enter an infinite loop or deadlock. Possible causes:

1. libc version change: The ubuntu-24.04-arm runner has been updated since the last successful main CI run (September 2025). A newer glibc may use a different \getenv\ implementation (e.g., different PLT/GOT layout, ifunc resolvers, or thread-safety wrappers) that conflicts with the ARM32 patching mechanism.

2. Cross-compilation artifact: armv7 tests are cross-compiled on an aarch64 host. The \getenv\ symbol resolution may differ from native armv7 compilation.

3. Thumb vs ARM mode: The armv7 target may compile \getenv\ call sites differently than thumbv7neon, affecting how the patched trampoline redirects execution.

Current workaround

PR #110 changed the ARM CI test command from \cargo test\ to \cargo test --tests\ to skip doctests on ARM targets. Doctests are still validated on x86_64 (Linux, Windows), aarch64 (Linux, Windows, macOS), and other platforms.

Environment

• Runner: ubuntu-24.04-arm (aarch64 host)
• Target: armv7-unknown-linux-gnueabihf (cross-compiled)
• Rust toolchain: stable
• Works on: x86_64, aarch64, thumbv7neon, macOS aarch64, Windows x86_64, Windows aarch64

Read src/lib.rs around line 438 and reproduce with cargo test --target armv7-unknown-linux-gnueabihf --doc on an ubuntu-24.04-arm runner. Compare the failing getenv doctest with thumbv7neon behavior and review PR #110's ARM test change. Done means the armv7 doctest no longer hangs and its CI handling is clear.