Bug description

Building std on the latest nightly fails for the espidf target (e.g., riscv32imac-esp-espidf) with the following error:

error[E0425]: cannot find value `SIGKILL` in crate `libc`
   --> /.../rustlib/src/rust/library/std/src/os/unix/process.rs:498:53
    |
498 |         self.handle.send_process_group_signal(libc::SIGKILL)
    |

Environment

• Target: riscv32imac-esp-espidf
• Container/Toolchain: Occurs when using the espressif/idf-rust:esp32c6_latest Docker image, which pulls the latest nightly.

Cause

This is an upstream regression caused by rust-lang/rust commit 7bf5fe7bf84f5b94e5970de18543abac0579209c.
rust-lang/rust@7bf5fe7

The commit added the unix_kill_process_group feature to std::os::unix::process. Because espidf is categorized under the unix family, it attempts to compile this code, but the espidf libc does not define SIGKILL.