Description: Set DT_SONAME when building dylibs
 In Rust, library filenames include a version-specific hash to help
 the run-time linker find the correct version.  Unlike in C/C++, the
 compiler looks for all libraries matching a glob that ignores the
 hash and reads embedded metadata to work out versions, etc.
 .
 The upshot is that there is no need for the usual "libfoo.so ->
 libfoo-1.2.3.so" symlink common with C/C++ when building with Rust,
 and no need to communicate an alternate filename to use at run-time
 vs compile time.  If linking to a Rust dylib from C/C++ however, a
 "libfoo.so -> libfoo-$hash.so" symlink may well be useful and in
 this case DT_SONAME=libfoo-$hash.so would be required.  More
 mundanely, various tools (eg: dpkg-shlibdeps) complain if they don't
 find DT_SONAME on shared libraries in public directories.
 .
 This patch passes -Wl,-soname=$outfile when building dylibs (and
 using a GNU linker).
Author: Angus Lees <gus@debian.org>
Forwarded: no

--- a/src/librustc_codegen_ssa/back/link.rs
+++ b/src/librustc_codegen_ssa/back/link.rs
@@ -1034,6 +1034,13 @@
         cmd.args(&rpath::get_rpath_flags(&mut rpath_config));
     }
 
+    if (crate_type == config::CrateType::Dylib || crate_type == config::CrateType::Cdylib)
+       && t.options.linker_is_gnu {
+        let filename = String::from(out_filename.file_name().unwrap().to_str().unwrap());
+        let soname = [String::from("-Wl,-soname=") + &filename];
+        cmd.args(&soname);
+    }
+
     // Finally add all the linker arguments provided on the command line along
     // with any #[link_args] attributes found inside the crate
     if let Some(ref args) = sess.opts.cg.link_args {