--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libpam-sys/libpam-sys-helpers/build.rs	Thu Jul 03 14:28:04 2025 -0400
@@ -0,0 +1,96 @@
+#![allow(unexpected_cfgs)]
+
+use std::ffi::{c_void, CString};
+use std::ptr::NonNull;
+use std::{env, fs};
+
+include!("src/pam_impl.rs");
+
+fn main() {
+    let pam_impl = match option_env!("LIBPAMSYS_IMPL") {
+        // The default option: Guess what PAM impl we're using based on OS.
+        None | Some("") => LibPam::detect(),
+        Some(other) => match PamImpl::try_from(other) {
+            Ok(i) => i,
+            Err(_) => {
+                panic!(
+                    "unknown PAM implementation {other:?}. valid LIBPAMSYS_IMPLs are {:?}, or unset to detect", PamImpl::items()
+                )
+            }
+        },
+    };
+    let impl_str = format!("{pam_impl:?}");
+    println!("{}", generate_cfg(&impl_str));
+    // We set this environment variable to substitute into docstrings.
+    println!("cargo:rustc-env=LIBPAMSYS_IMPL={impl_str}");
+    fs::write(
+        format!("{}/pam_impl_const.rs", env::var("OUT_DIR").unwrap()),
+        generate_consts(&impl_str),
+    )
+    .unwrap();
+}
+
+fn generate_consts(impl_str: &str) -> String {
+    format!(
+        "\
+impl PamImpl {{
+/// The implementation of libpam this was built for (`{impl_str}`).
+pub const CURRENT: Self = Self::{impl_str};
+}}
+
+/// String name of [`PamImpl::CURRENT`], for substituting into docs.
+#[macro_export]
+macro_rules! pam_impl_name {{ () => ({impl_str:?}) }}
+        "
+    )
+}
+
+struct LibPam(NonNull<c_void>);
+
+impl LibPam {
+    fn detect() -> PamImpl {
+        if let Some(lib) = Self::open() {
+            if lib.has("pam_syslog") {
+                return PamImpl::LinuxPam;
+            } else if lib.has("_openpam_log") {
+                return PamImpl::OpenPam;
+            } else if lib.has("__pam_get_authtok") {
+                return PamImpl::Sun;
+            }
+        }
+        if cfg!(target_os = "linux") {
+            PamImpl::LinuxPam
+        } else if cfg!(any(
+            target_os = "macos",
+            target_os = "freebsd",
+            target_os = "netbsd",
+            target_os = "dragonfly",
+            target_os = "openbsd",
+        )) {
+            PamImpl::OpenPam
+        } else if cfg!(any(target_os = "illumos", target_os = "solaris")) {
+            PamImpl::Sun
+        } else {
+            PamImpl::XSso
+        }
+    }
+
+    fn open() -> Option<Self> {
+        NonNull::new(unsafe { libc::dlopen(b"libpam.so\0".as_ptr().cast(), libc::RTLD_LAZY) })
+            .map(Self)
+    }
+
+    fn has(&self, name: &str) -> bool {
+        let name = CString::new(name).unwrap();
+        let symbol = unsafe { libc::dlsym(self.0.as_ptr(), name.as_ptr()) };
+        !symbol.is_null()
+    }
+}
+
+impl Drop for LibPam {
+    fn drop(&mut self) {
+        unsafe {
+            libc::dlclose(self.0.as_ptr());
+        }
+    }
+}