From 2cc34df784a2c1b67fdd6fbae8cbf0dfbbcd0a2b Mon Sep 17 00:00:00 2001
From: Gris Ge <fge@redhat.com>
Date: Jan 18 2024 00:46:32 +0000
Subject: rust: Add document on how to set SONAME for c library written in Rust


There are many ways to set SONAME for rust C library, some of them
requires you to modify `RUSTFLAGS` which is not suggested by Fedora rust
packaging tools.

Including suggestions for this use case which works with Fedora rust
packaging tools.

Signed-off-by: Gris Ge <fge@redhat.com>

---

diff --git a/guidelines/modules/ROOT/pages/Rust.adoc b/guidelines/modules/ROOT/pages/Rust.adoc
index 9a88e40..2aca701 100644
--- a/guidelines/modules/ROOT/pages/Rust.adoc
+++ b/guidelines/modules/ROOT/pages/Rust.adoc
@@ -819,6 +819,31 @@ that apply to the statically linked Python extension.
 The packager also *MUST* ensure
 that the default link:#_compiler_flags[compiler flags] are passed to rustc.
 
+== Exposing C library written in Rust
+
+When exposing C library written in Rust through `cdylib` crate type,
+due to https://github.com/rust-lang/cargo/issues/5045[a bug of cargo],
+your C library will not have `SONAME` defined which will cause rpm build tools
+setting the rpm dependency incorrectly.
+
+To workaround that, you could use
+https://doc.rust-lang.org/cargo/reference/build-scripts.html[`build.rs`] with
+content of
+
+....
+fn main() {
+    #[cfg(target_os = "linux")]
+    println!("cargo:rustc-cdylib-link-arg=-Wl,-soname=libabc.so.1");
+}
+....
+
+If you prefer doing it in downstream, you may use `patchelf` to fix the
+`SONAME` during rpm packaging:
+
+....
+patchelf --set-soname libabc.so.1 %{buildroot}/%{_libdir}/libabc.so.%{version}
+....
+
 == Mixed Rust / C/C++ projects
 
 Handling of projects that include both C/C++ and Rust code