Move almost all of cg_llvm/back/link.rs to cg_ssa

5 files changed, 1560 insertions, 5 deletions

diff --git a/src/librustc_codegen_ssa/Cargo.toml b/src/librustc_codegen_ssa/Cargo.toml
index 4702e34aa19..af99d39182c 100644
--- a/src/librustc_codegen_ssa/Cargo.toml
+++ b/src/librustc_codegen_ssa/Cargo.toml
@@ -20,6 +20,7 @@ log = "0.4.5"
 libc = "0.2.44"
 jobserver = "0.1.11"
 parking_lot = "0.7"
+tempfile = "3.0.5"
 
 serialize = { path = "../libserialize" }
 syntax = { path = "../libsyntax" }
diff --git a/src/librustc_codegen_ssa/back/link.rs b/src/librustc_codegen_ssa/back/link.rs
index f97f78b7feb..acd2237617f 100644
--- a/src/librustc_codegen_ssa/back/link.rs
+++ b/src/librustc_codegen_ssa/back/link.rs
@@ -1,24 +1,36 @@
 /// For all the linkers we support, and information they might
 /// need out of the shared crate context before we get rid of it.
 
-use rustc::session::{Session, config};
+use rustc::session::{Session, filesearch};
+use rustc::session::config::{
+    self, RUST_CGU_EXT, DebugInfo, OutputFilenames, OutputType, PrintRequest, Sanitizer
+};
 use rustc::session::search_paths::PathKind;
 use rustc::middle::dependency_format::Linkage;
 use rustc::middle::cstore::{LibSource, NativeLibrary, NativeLibraryKind};
-use rustc_target::spec::LinkerFlavor;
+use rustc::util::common::{time, time_ext};
 use rustc::hir::def_id::CrateNum;
+use rustc_data_structures::fx::FxHashSet;
 use rustc_fs_util::fix_windows_verbatim_for_gcc;
+use rustc_target::spec::{PanicStrategy, RelroLevel, LinkerFlavor};
 
+use crate::{METADATA_FILENAME, RLIB_BYTECODE_EXTENSION, CrateInfo, CodegenResults};
+use super::archive::ArchiveBuilder;
 use super::command::Command;
-use crate::{CrateInfo, CodegenResults};
-use crate::back::linker::Linker;
+use super::linker::Linker;
+use super::rpath::{self, RPathConfig};
 
 use cc::windows_registry;
+use tempfile::{Builder as TempFileBuilder, TempDir};
+
+use std::ascii;
+use std::char;
 use std::fmt;
 use std::fs;
 use std::io;
 use std::path::{Path, PathBuf};
 use std::process::{Output, Stdio};
+use std::str;
 use std::env;
 
 pub use rustc_codegen_utils::link::*;
@@ -31,6 +43,122 @@ pub fn remove(sess: &Session, path: &Path) {
     }
 }
 
+/// Performs the linkage portion of the compilation phase. This will generate all
+/// of the requested outputs for this compilation session.
+pub fn link_binary<'a, B: ArchiveBuilder<'a>>(sess: &'a Session,
+                          codegen_results: &CodegenResults,
+                          outputs: &OutputFilenames,
+                          crate_name: &str,
+                          target_cpu: &str) -> Vec<PathBuf> {
+    let mut out_filenames = Vec::new();
+    for &crate_type in sess.crate_types.borrow().iter() {
+        // Ignore executable crates if we have -Z no-codegen, as they will error.
+        let output_metadata = sess.opts.output_types.contains_key(&OutputType::Metadata);
+        if (sess.opts.debugging_opts.no_codegen || !sess.opts.output_types.should_codegen()) &&
+           !output_metadata &&
+           crate_type == config::CrateType::Executable {
+            continue;
+        }
+
+        if invalid_output_for_target(sess, crate_type) {
+           bug!("invalid output type `{:?}` for target os `{}`",
+                crate_type, sess.opts.target_triple);
+        }
+        let out_files = link_binary_output::<B>(sess,
+                                           codegen_results,
+                                           crate_type,
+                                           outputs,
+                                           crate_name,
+                                           target_cpu);
+        out_filenames.extend(out_files);
+    }
+
+    // Remove the temporary object file and metadata if we aren't saving temps
+    if !sess.opts.cg.save_temps {
+        if sess.opts.output_types.should_codegen() && !preserve_objects_for_their_debuginfo(sess) {
+            for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
+                remove(sess, obj);
+            }
+        }
+        for obj in codegen_results.modules.iter().filter_map(|m| m.bytecode_compressed.as_ref()) {
+            remove(sess, obj);
+        }
+        if let Some(ref obj) = codegen_results.metadata_module.object {
+            remove(sess, obj);
+        }
+        if let Some(ref allocator) = codegen_results.allocator_module {
+            if let Some(ref obj) = allocator.object {
+                remove(sess, obj);
+            }
+            if let Some(ref bc) = allocator.bytecode_compressed {
+                remove(sess, bc);
+            }
+        }
+    }
+
+    out_filenames
+}
+
+fn link_binary_output<'a, B: ArchiveBuilder<'a>>(sess: &'a Session,
+                      codegen_results: &CodegenResults,
+                      crate_type: config::CrateType,
+                      outputs: &OutputFilenames,
+                      crate_name: &str,
+                      target_cpu: &str) -> Vec<PathBuf> {
+    for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
+        check_file_is_writeable(obj, sess);
+    }
+
+    let mut out_filenames = vec![];
+
+    if outputs.outputs.contains_key(&OutputType::Metadata) {
+        let out_filename = filename_for_metadata(sess, crate_name, outputs);
+        // To avoid races with another rustc process scanning the output directory,
+        // we need to write the file somewhere else and atomically move it to its
+        // final destination, with a `fs::rename` call. In order for the rename to
+        // always succeed, the temporary file needs to be on the same filesystem,
+        // which is why we create it inside the output directory specifically.
+        let metadata_tmpdir = TempFileBuilder::new()
+            .prefix("rmeta")
+            .tempdir_in(out_filename.parent().unwrap())
+            .unwrap_or_else(|err| sess.fatal(&format!("couldn't create a temp dir: {}", err)));
+        let metadata = emit_metadata(sess, codegen_results, &metadata_tmpdir);
+        if let Err(e) = fs::rename(metadata, &out_filename) {
+            sess.fatal(&format!("failed to write {}: {}", out_filename.display(), e));
+        }
+        out_filenames.push(out_filename);
+    }
+
+    let tmpdir = TempFileBuilder::new().prefix("rustc").tempdir().unwrap_or_else(|err|
+        sess.fatal(&format!("couldn't create a temp dir: {}", err)));
+
+    if outputs.outputs.should_codegen() {
+        let out_filename = out_filename(sess, crate_type, outputs, crate_name);
+        match crate_type {
+            config::CrateType::Rlib => {
+                link_rlib::<B>(sess,
+                          codegen_results,
+                          RlibFlavor::Normal,
+                          &out_filename,
+                          &tmpdir).build();
+            }
+            config::CrateType::Staticlib => {
+                link_staticlib::<B>(sess, codegen_results, &out_filename, &tmpdir);
+            }
+            _ => {
+                link_natively::<B>(sess, crate_type, &out_filename, codegen_results, tmpdir.path(), target_cpu);
+            }
+        }
+        out_filenames.push(out_filename);
+    }
+
+    if sess.opts.cg.save_temps {
+        let _ = tmpdir.into_path();
+    }
+
+    out_filenames
+}
+
 // The third parameter is for env vars, used on windows to set up the
 // path for MSVC to find its DLLs, and gcc to find its bundled
 // toolchain
@@ -123,6 +251,444 @@ pub fn each_linked_rlib(sess: &Session,
     Ok(())
 }
 
+/// We use a temp directory here to avoid races between concurrent rustc processes,
+/// such as builds in the same directory using the same filename for metadata while
+/// building an `.rlib` (stomping over one another), or writing an `.rmeta` into a
+/// directory being searched for `extern crate` (observing an incomplete file).
+/// The returned path is the temporary file containing the complete metadata.
+fn emit_metadata<'a>(
+    sess: &'a Session,
+    codegen_results: &CodegenResults,
+    tmpdir: &TempDir
+) -> PathBuf {
+    let out_filename = tmpdir.path().join(METADATA_FILENAME);
+    let result = fs::write(&out_filename, &codegen_results.metadata.raw_data);
+
+    if let Err(e) = result {
+        sess.fatal(&format!("failed to write {}: {}", out_filename.display(), e));
+    }
+
+    out_filename
+}
+
+// Create an 'rlib'
+//
+// An rlib in its current incarnation is essentially a renamed .a file. The
+// rlib primarily contains the object file of the crate, but it also contains
+// all of the object files from native libraries. This is done by unzipping
+// native libraries and inserting all of the contents into this archive.
+fn link_rlib<'a, B: ArchiveBuilder<'a>>(sess: &'a Session,
+                 codegen_results: &CodegenResults,
+                 flavor: RlibFlavor,
+                 out_filename: &Path,
+                 tmpdir: &TempDir) -> B {
+    info!("preparing rlib to {:?}", out_filename);
+    let mut ab = <B as ArchiveBuilder>::new(sess, out_filename, None);
+
+    for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
+        ab.add_file(obj);
+    }
+
+    // Note that in this loop we are ignoring the value of `lib.cfg`. That is,
+    // we may not be configured to actually include a static library if we're
+    // adding it here. That's because later when we consume this rlib we'll
+    // decide whether we actually needed the static library or not.
+    //
+    // To do this "correctly" we'd need to keep track of which libraries added
+    // which object files to the archive. We don't do that here, however. The
+    // #[link(cfg(..))] feature is unstable, though, and only intended to get
+    // liblibc working. In that sense the check below just indicates that if
+    // there are any libraries we want to omit object files for at link time we
+    // just exclude all custom object files.
+    //
+    // Eventually if we want to stabilize or flesh out the #[link(cfg(..))]
+    // feature then we'll need to figure out how to record what objects were
+    // loaded from the libraries found here and then encode that into the
+    // metadata of the rlib we're generating somehow.
+    for lib in codegen_results.crate_info.used_libraries.iter() {
+        match lib.kind {
+            NativeLibraryKind::NativeStatic => {}
+            NativeLibraryKind::NativeStaticNobundle |
+            NativeLibraryKind::NativeFramework |
+            NativeLibraryKind::NativeUnknown => continue,
+        }
+        if let Some(name) = lib.name {
+            ab.add_native_library(&name.as_str());
+        }
+    }
+
+    // After adding all files to the archive, we need to update the
+    // symbol table of the archive.
+    ab.update_symbols();
+
+    // Note that it is important that we add all of our non-object "magical
+    // files" *after* all of the object files in the archive. The reason for
+    // this is as follows:
+    //
+    // * When performing LTO, this archive will be modified to remove
+    //   objects from above. The reason for this is described below.
+    //
+    // * When the system linker looks at an archive, it will attempt to
+    //   determine the architecture of the archive in order to see whether its
+    //   linkable.
+    //
+    //   The algorithm for this detection is: iterate over the files in the
+    //   archive. Skip magical SYMDEF names. Interpret the first file as an
+    //   object file. Read architecture from the object file.
+    //
+    // * As one can probably see, if "metadata" and "foo.bc" were placed
+    //   before all of the objects, then the architecture of this archive would
+    //   not be correctly inferred once 'foo.o' is removed.
+    //
+    // Basically, all this means is that this code should not move above the
+    // code above.
+    match flavor {
+        RlibFlavor::Normal => {
+            // Instead of putting the metadata in an object file section, rlibs
+            // contain the metadata in a separate file.
+            ab.add_file(&emit_metadata(sess, codegen_results, tmpdir));
+
+            // For LTO purposes, the bytecode of this library is also inserted
+            // into the archive.
+            for bytecode in codegen_results
+                .modules
+                .iter()
+                .filter_map(|m| m.bytecode_compressed.as_ref())
+            {
+                ab.add_file(bytecode);
+            }
+
+            // After adding all files to the archive, we need to update the
+            // symbol table of the archive. This currently dies on macOS (see
+            // #11162), and isn't necessary there anyway
+            if !sess.target.target.options.is_like_osx {
+                ab.update_symbols();
+            }
+        }
+
+        RlibFlavor::StaticlibBase => {
+            let obj = codegen_results.allocator_module
+                .as_ref()
+                .and_then(|m| m.object.as_ref());
+            if let Some(obj) = obj {
+                ab.add_file(obj);
+            }
+        }
+    }
+
+    ab
+}
+
+// Create a static archive
+//
+// This is essentially the same thing as an rlib, but it also involves adding
+// all of the upstream crates' objects into the archive. This will slurp in
+// all of the native libraries of upstream dependencies as well.
+//
+// Additionally, there's no way for us to link dynamic libraries, so we warn
+// about all dynamic library dependencies that they're not linked in.
+//
+// There's no need to include metadata in a static archive, so ensure to not
+// link in the metadata object file (and also don't prepare the archive with a
+// metadata file).
+fn link_staticlib<'a, B: ArchiveBuilder<'a>>(sess: &'a Session,
+                  codegen_results: &CodegenResults,
+                  out_filename: &Path,
+                  tempdir: &TempDir) {
+    let mut ab = link_rlib::<B>(sess,
+                           codegen_results,
+                           RlibFlavor::StaticlibBase,
+                           out_filename,
+                           tempdir);
+    let mut all_native_libs = vec![];
+
+    let res = each_linked_rlib(sess, &codegen_results.crate_info, &mut |cnum, path| {
+        let name = &codegen_results.crate_info.crate_name[&cnum];
+        let native_libs = &codegen_results.crate_info.native_libraries[&cnum];
+
+        // Here when we include the rlib into our staticlib we need to make a
+        // decision whether to include the extra object files along the way.
+        // These extra object files come from statically included native
+        // libraries, but they may be cfg'd away with #[link(cfg(..))].
+        //
+        // This unstable feature, though, only needs liblibc to work. The only
+        // use case there is where musl is statically included in liblibc.rlib,
+        // so if we don't want the included version we just need to skip it. As
+        // a result the logic here is that if *any* linked library is cfg'd away
+        // we just skip all object files.
+        //
+        // Clearly this is not sufficient for a general purpose feature, and
+        // we'd want to read from the library's metadata to determine which
+        // object files come from where and selectively skip them.
+        let skip_object_files = native_libs.iter().any(|lib| {
+            lib.kind == NativeLibraryKind::NativeStatic && !relevant_lib(sess, lib)
+        });
+        ab.add_rlib(path,
+                    &name.as_str(),
+                    are_upstream_rust_objects_already_included(sess) &&
+                        !ignored_for_lto(sess, &codegen_results.crate_info, cnum),
+                    skip_object_files).unwrap();
+
+        all_native_libs.extend(codegen_results.crate_info.native_libraries[&cnum].iter().cloned());
+    });
+    if let Err(e) = res {
+        sess.fatal(&e);
+    }
+
+    ab.update_symbols();
+    ab.build();
+
+    if !all_native_libs.is_empty() {
+        if sess.opts.prints.contains(&PrintRequest::NativeStaticLibs) {
+            print_native_static_libs(sess, &all_native_libs);
+        }
+    }
+}
+
+// Create a dynamic library or executable
+//
+// This will invoke the system linker/cc to create the resulting file. This
+// links to all upstream files as well.
+fn link_natively<'a, B: ArchiveBuilder<'a>>(sess: &'a Session,
+                 crate_type: config::CrateType,
+                 out_filename: &Path,
+                 codegen_results: &CodegenResults,
+                 tmpdir: &Path,
+                 target_cpu: &str) {
+    info!("preparing {:?} to {:?}", crate_type, out_filename);
+    let (linker, flavor) = linker_and_flavor(sess);
+
+    // The invocations of cc share some flags across platforms
+    let (pname, mut cmd) = get_linker(sess, &linker, flavor);
+
+    if let Some(args) = sess.target.target.options.pre_link_args.get(&flavor) {
+        cmd.args(args);
+    }
+    if let Some(args) = sess.target.target.options.pre_link_args_crt.get(&flavor) {
+        if sess.crt_static() {
+            cmd.args(args);
+        }
+    }
+    if let Some(ref args) = sess.opts.debugging_opts.pre_link_args {
+        cmd.args(args);
+    }
+    cmd.args(&sess.opts.debugging_opts.pre_link_arg);
+
+    if sess.target.target.options.is_like_fuchsia {
+        let prefix = match sess.opts.debugging_opts.sanitizer {
+            Some(Sanitizer::Address) => "asan/",
+            _ => "",
+        };
+        cmd.arg(format!("--dynamic-linker={}ld.so.1", prefix));
+    }
+
+    let pre_link_objects = if crate_type == config::CrateType::Executable {
+        &sess.target.target.options.pre_link_objects_exe
+    } else {
+        &sess.target.target.options.pre_link_objects_dll
+    };
+    for obj in pre_link_objects {
+        cmd.arg(get_file_path(sess, obj));
+    }
+
+    if crate_type == config::CrateType::Executable && sess.crt_static() {
+        for obj in &sess.target.target.options.pre_link_objects_exe_crt {
+            cmd.arg(get_file_path(sess, obj));
+        }
+    }
+
+    if sess.target.target.options.is_like_emscripten {
+        cmd.arg("-s");
+        cmd.arg(if sess.panic_strategy() == PanicStrategy::Abort {
+            "DISABLE_EXCEPTION_CATCHING=1"
+        } else {
+            "DISABLE_EXCEPTION_CATCHING=0"
+        });
+    }
+
+    {
+        let mut linker = codegen_results.linker_info.to_linker(cmd, &sess, flavor, target_cpu);
+        link_args::<B>(&mut *linker, flavor, sess, crate_type, tmpdir,
+                  out_filename, codegen_results);
+        cmd = linker.finalize();
+    }
+    if let Some(args) = sess.target.target.options.late_link_args.get(&flavor) {
+        cmd.args(args);
+    }
+    for obj in &sess.target.target.options.post_link_objects {
+        cmd.arg(get_file_path(sess, obj));
+    }
+    if sess.crt_static() {
+        for obj in &sess.target.target.options.post_link_objects_crt {
+            cmd.arg(get_file_path(sess, obj));
+        }
+    }
+    if let Some(args) = sess.target.target.options.post_link_args.get(&flavor) {
+        cmd.args(args);
+    }
+    for &(ref k, ref v) in &sess.target.target.options.link_env {
+        cmd.env(k, v);
+    }
+
+    if sess.opts.debugging_opts.print_link_args {
+        println!("{:?}", &cmd);
+    }
+
+    // May have not found libraries in the right formats.
+    sess.abort_if_errors();
+
+    // Invoke the system linker
+    //
+    // Note that there's a terribly awful hack that really shouldn't be present
+    // in any compiler. Here an environment variable is supported to
+    // automatically retry the linker invocation if the linker looks like it
+    // segfaulted.
+    //
+    // Gee that seems odd, normally segfaults are things we want to know about!
+    // Unfortunately though in rust-lang/rust#38878 we're experiencing the
+    // linker segfaulting on Travis quite a bit which is causing quite a bit of
+    // pain to land PRs when they spuriously fail due to a segfault.
+    //
+    // The issue #38878 has some more debugging information on it as well, but
+    // this unfortunately looks like it's just a race condition in macOS's linker
+    // with some thread pool working in the background. It seems that no one
+    // currently knows a fix for this so in the meantime we're left with this...
+    info!("{:?}", &cmd);
+    let retry_on_segfault = env::var("RUSTC_RETRY_LINKER_ON_SEGFAULT").is_ok();
+    let mut prog;
+    let mut i = 0;
+    loop {
+        i += 1;
+        prog = time(sess, "running linker", || {
+            exec_linker(sess, &mut cmd, out_filename, tmpdir)
+        });
+        let output = match prog {
+            Ok(ref output) => output,
+            Err(_) => break,
+        };
+        if output.status.success() {
+            break
+        }
+        let mut out = output.stderr.clone();
+        out.extend(&output.stdout);
+        let out = String::from_utf8_lossy(&out);
+
+        // Check to see if the link failed with "unrecognized command line option:
+        // '-no-pie'" for gcc or "unknown argument: '-no-pie'" for clang. If so,
+        // reperform the link step without the -no-pie option. This is safe because
+        // if the linker doesn't support -no-pie then it should not default to
+        // linking executables as pie. Different versions of gcc seem to use
+        // different quotes in the error message so don't check for them.
+        if sess.target.target.options.linker_is_gnu &&
+           flavor != LinkerFlavor::Ld &&
+           (out.contains("unrecognized command line option") ||
+            out.contains("unknown argument")) &&
+           out.contains("-no-pie") &&
+           cmd.get_args().iter().any(|e| e.to_string_lossy() == "-no-pie") {
+            info!("linker output: {:?}", out);
+            warn!("Linker does not support -no-pie command line option. Retrying without.");
+            for arg in cmd.take_args() {
+                if arg.to_string_lossy() != "-no-pie" {
+                    cmd.arg(arg);
+                }
+            }
+            info!("{:?}", &cmd);
+            continue;
+        }
+        if !retry_on_segfault || i > 3 {
+            break
+        }
+        let msg_segv = "clang: error: unable to execute command: Segmentation fault: 11";
+        let msg_bus  = "clang: error: unable to execute command: Bus error: 10";
+        if !(out.contains(msg_segv) || out.contains(msg_bus)) {
+            break
+        }
+
+        warn!(
+            "looks like the linker segfaulted when we tried to call it, \
+             automatically retrying again. cmd = {:?}, out = {}.",
+            cmd,
+            out,
+        );
+    }
+
+    match prog {
+        Ok(prog) => {
+            fn escape_string(s: &[u8]) -> String {
+                str::from_utf8(s).map(|s| s.to_owned())
+                    .unwrap_or_else(|_| {
+                        let mut x = "Non-UTF-8 output: ".to_string();
+                        x.extend(s.iter()
+                                  .flat_map(|&b| ascii::escape_default(b))
+                                  .map(char::from));
+                        x
+                    })
+            }
+            if !prog.status.success() {
+                let mut output = prog.stderr.clone();
+                output.extend_from_slice(&prog.stdout);
+                sess.struct_err(&format!("linking with `{}` failed: {}",
+                                         pname.display(),
+                                         prog.status))
+                    .note(&format!("{:?}", &cmd))
+                    .note(&escape_string(&output))
+                    .emit();
+                sess.abort_if_errors();
+            }
+            info!("linker stderr:\n{}", escape_string(&prog.stderr));
+            info!("linker stdout:\n{}", escape_string(&prog.stdout));
+        },
+        Err(e) => {
+            let linker_not_found = e.kind() == io::ErrorKind::NotFound;
+
+            let mut linker_error = {
+                if linker_not_found {
+                    sess.struct_err(&format!("linker `{}` not found", pname.display()))
+                } else {
+                    sess.struct_err(&format!("could not exec the linker `{}`", pname.display()))
+                }
+            };
+
+            linker_error.note(&e.to_string());
+
+            if !linker_not_found {
+                linker_error.note(&format!("{:?}", &cmd));
+            }
+
+            linker_error.emit();
+
+            if sess.target.target.options.is_like_msvc && linker_not_found {
+                sess.note_without_error("the msvc targets depend on the msvc linker \
+                    but `link.exe` was not found");
+                sess.note_without_error("please ensure that VS 2013, VS 2015 or VS 2017 \
+                    was installed with the Visual C++ option");
+            }
+            sess.abort_if_errors();
+        }
+    }
+
+
+    // On macOS, debuggers need this utility to get run to do some munging of
+    // the symbols. Note, though, that if the object files are being preserved
+    // for their debug information there's no need for us to run dsymutil.
+    if sess.target.target.options.is_like_osx &&
+        sess.opts.debuginfo != DebugInfo::None &&
+        !preserve_objects_for_their_debuginfo(sess)
+    {
+        if let Err(e) = Command::new("dsymutil").arg(out_filename).output() {
+            sess.fatal(&format!("failed to run dsymutil: {}", e))
+        }
+    }
+
+    if sess.opts.target_triple.triple() == "wasm32-unknown-unknown" {
+        super::wasm::add_producer_section(
+            &out_filename,
+            &sess.edition().to_string(),
+            option_env!("CFG_VERSION").unwrap_or("unknown"),
+        );
+    }
+}
+
 /// Returns a boolean indicating whether the specified crate should be ignored
 /// during LTO.
 ///
@@ -258,7 +824,7 @@ pub fn archive_search_paths(sess: &Session) -> Vec<PathBuf> {
     sess.target_filesearch(PathKind::Native).search_path_dirs()
 }
 
-pub enum RlibFlavor {
+enum RlibFlavor {
     Normal,
     StaticlibBase,
 }
@@ -451,6 +1017,209 @@ pub fn exec_linker(sess: &Session, cmd: &mut Command, out_filename: &Path, tmpdi
     }
 }
 
+fn link_args<'a, B: ArchiveBuilder<'a>>(cmd: &mut dyn Linker,
+             flavor: LinkerFlavor,
+             sess: &'a Session,
+             crate_type: config::CrateType,
+             tmpdir: &Path,
+             out_filename: &Path,
+             codegen_results: &CodegenResults) {
+
+    // Linker plugins should be specified early in the list of arguments
+    cmd.linker_plugin_lto();
+
+    // The default library location, we need this to find the runtime.
+    // The location of crates will be determined as needed.
+    let lib_path = sess.target_filesearch(PathKind::All).get_lib_path();
+
+    // target descriptor
+    let t = &sess.target.target;
+
+    cmd.include_path(&fix_windows_verbatim_for_gcc(&lib_path));
+    for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
+        cmd.add_object(obj);
+    }
+    cmd.output_filename(out_filename);
+
+    if crate_type == config::CrateType::Executable &&
+       sess.target.target.options.is_like_windows {
+        if let Some(ref s) = codegen_results.windows_subsystem {
+            cmd.subsystem(s);
+        }
+    }
+
+    // If we're building a dynamic library then some platforms need to make sure
+    // that all symbols are exported correctly from the dynamic library.
+    if crate_type != config::CrateType::Executable ||
+       sess.target.target.options.is_like_emscripten {
+        cmd.export_symbols(tmpdir, crate_type);
+    }
+
+    // When linking a dynamic library, we put the metadata into a section of the
+    // executable. This metadata is in a separate object file from the main
+    // object file, so we link that in here.
+    if crate_type == config::CrateType::Dylib ||
+       crate_type == config::CrateType::ProcMacro {
+        if let Some(obj) = codegen_results.metadata_module.object.as_ref() {
+            cmd.add_object(obj);
+        }
+    }
+
+    let obj = codegen_results.allocator_module
+        .as_ref()
+        .and_then(|m| m.object.as_ref());
+    if let Some(obj) = obj {
+        cmd.add_object(obj);
+    }
+
+    // Try to strip as much out of the generated object by removing unused
+    // sections if possible. See more comments in linker.rs
+    if !sess.opts.cg.link_dead_code {
+        let keep_metadata = crate_type == config::CrateType::Dylib;
+        cmd.gc_sections(keep_metadata);
+    }
+
+    let used_link_args = &codegen_results.crate_info.link_args;
+
+    if crate_type == config::CrateType::Executable {
+        let mut position_independent_executable = false;
+
+        if t.options.position_independent_executables {
+            let empty_vec = Vec::new();
+            let args = sess.opts.cg.link_args.as_ref().unwrap_or(&empty_vec);
+            let more_args = &sess.opts.cg.link_arg;
+            let mut args = args.iter().chain(more_args.iter()).chain(used_link_args.iter());
+
+            if is_pic(sess) && !sess.crt_static() && !args.any(|x| *x == "-static") {
+                position_independent_executable = true;
+            }
+        }
+
+        if position_independent_executable {
+            cmd.position_independent_executable();
+        } else {
+            // recent versions of gcc can be configured to generate position
+            // independent executables by default. We have to pass -no-pie to
+            // explicitly turn that off. Not applicable to ld.
+            if sess.target.target.options.linker_is_gnu
+                && flavor != LinkerFlavor::Ld {
+                cmd.no_position_independent_executable();
+            }
+        }
+    }
+
+    let relro_level = match sess.opts.debugging_opts.relro_level {
+        Some(level) => level,
+        None => t.options.relro_level,
+    };
+    match relro_level {
+        RelroLevel::Full => {
+            cmd.full_relro();
+        },
+        RelroLevel::Partial => {
+            cmd.partial_relro();
+        },
+        RelroLevel::Off => {
+            cmd.no_relro();
+        },
+        RelroLevel::None => {
+        },
+    }
+
+    // Pass optimization flags down to the linker.
+    cmd.optimize();
+
+    // Pass debuginfo flags down to the linker.
+    cmd.debuginfo();
+
+    // We want to, by default, prevent the compiler from accidentally leaking in
+    // any system libraries, so we may explicitly ask linkers to not link to any
+    // libraries by default. Note that this does not happen for windows because
+    // windows pulls in some large number of libraries and I couldn't quite
+    // figure out which subset we wanted.
+    //
+    // This is all naturally configurable via the standard methods as well.
+    if !sess.opts.cg.default_linker_libraries.unwrap_or(false) &&
+        t.options.no_default_libraries
+    {
+        cmd.no_default_libraries();
+    }
+
+    // Take careful note of the ordering of the arguments we pass to the linker
+    // here. Linkers will assume that things on the left depend on things to the
+    // right. Things on the right cannot depend on things on the left. This is
+    // all formally implemented in terms of resolving symbols (libs on the right
+    // resolve unknown symbols of libs on the left, but not vice versa).
+    //
+    // For this reason, we have organized the arguments we pass to the linker as
+    // such:
+    //
+    //  1. The local object that LLVM just generated
+    //  2. Local native libraries
+    //  3. Upstream rust libraries
+    //  4. Upstream native libraries
+    //
+    // The rationale behind this ordering is that those items lower down in the
+    // list can't depend on items higher up in the list. For example nothing can
+    // depend on what we just generated (e.g., that'd be a circular dependency).
+    // Upstream rust libraries are not allowed to depend on our local native
+    // libraries as that would violate the structure of the DAG, in that
+    // scenario they are required to link to them as well in a shared fashion.
+    //
+    // Note that upstream rust libraries may contain native dependencies as
+    // well, but they also can't depend on what we just started to add to the
+    // link line. And finally upstream native libraries can't depend on anything
+    // in this DAG so far because they're only dylibs and dylibs can only depend
+    // on other dylibs (e.g., other native deps).
+    add_local_native_libraries(cmd, sess, codegen_results);
+    add_upstream_rust_crates::<B>(cmd, sess, codegen_results, crate_type, tmpdir);
+    add_upstream_native_libraries(cmd, sess, codegen_results, crate_type);
+
+    // Tell the linker what we're doing.
+    if crate_type != config::CrateType::Executable {
+        cmd.build_dylib(out_filename);
+    }
+    if crate_type == config::CrateType::Executable && sess.crt_static() {
+        cmd.build_static_executable();
+    }
+
+    if sess.opts.debugging_opts.pgo_gen.enabled() {
+        cmd.pgo_gen();
+    }
+
+    // FIXME (#2397): At some point we want to rpath our guesses as to
+    // where extern libraries might live, based on the
+    // addl_lib_search_paths
+    if sess.opts.cg.rpath {
+        let target_triple = sess.opts.target_triple.triple();
+        let mut get_install_prefix_lib_path = || {
+            let install_prefix = option_env!("CFG_PREFIX").expect("CFG_PREFIX");
+            let tlib = filesearch::relative_target_lib_path(&sess.sysroot, target_triple);
+            let mut path = PathBuf::from(install_prefix);
+            path.push(&tlib);
+
+            path
+        };
+        let mut rpath_config = RPathConfig {
+            used_crates: &codegen_results.crate_info.used_crates_dynamic,
+            out_filename: out_filename.to_path_buf(),
+            has_rpath: sess.target.target.options.has_rpath,
+            is_like_osx: sess.target.target.options.is_like_osx,
+            linker_is_gnu: sess.target.target.options.linker_is_gnu,
+            get_install_prefix_lib_path: &mut get_install_prefix_lib_path,
+        };
+        cmd.args(&rpath::get_rpath_flags(&mut rpath_config));
+    }
+
+    // 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 {
+        cmd.args(args);
+    }
+    cmd.args(&sess.opts.cg.link_arg);
+    cmd.args(&used_link_args);
+}
+
 // # Native library linking
 //
 // User-supplied library search paths (-L on the command line). These are
@@ -493,6 +1262,319 @@ pub fn add_local_native_libraries(cmd: &mut dyn Linker,
     }
 }
 
+// # Rust Crate linking
+//
+// Rust crates are not considered at all when creating an rlib output. All
+// dependencies will be linked when producing the final output (instead of
+// the intermediate rlib version)
+fn add_upstream_rust_crates<'a, B: ArchiveBuilder<'a>>(cmd: &mut dyn Linker,
+                            sess: &'a Session,
+                            codegen_results: &CodegenResults,
+                            crate_type: config::CrateType,
+                            tmpdir: &Path) {
+    // All of the heavy lifting has previously been accomplished by the
+    // dependency_format module of the compiler. This is just crawling the
+    // output of that module, adding crates as necessary.
+    //
+    // Linking to a rlib involves just passing it to the linker (the linker
+    // will slurp up the object files inside), and linking to a dynamic library
+    // involves just passing the right -l flag.
+
+    let formats = sess.dependency_formats.borrow();
+    let data = formats.get(&crate_type).unwrap();
+
+    // Invoke get_used_crates to ensure that we get a topological sorting of
+    // crates.
+    let deps = &codegen_results.crate_info.used_crates_dynamic;
+
+    // There's a few internal crates in the standard library (aka libcore and
+    // libstd) which actually have a circular dependence upon one another. This
+    // currently arises through "weak lang items" where libcore requires things
+    // like `rust_begin_unwind` but libstd ends up defining it. To get this
+    // circular dependence to work correctly in all situations we'll need to be
+    // sure to correctly apply the `--start-group` and `--end-group` options to
+    // GNU linkers, otherwise if we don't use any other symbol from the standard
+    // library it'll get discarded and the whole application won't link.
+    //
+    // In this loop we're calculating the `group_end`, after which crate to
+    // pass `--end-group` and `group_start`, before which crate to pass
+    // `--start-group`. We currently do this by passing `--end-group` after
+    // the first crate (when iterating backwards) that requires a lang item
+    // defined somewhere else. Once that's set then when we've defined all the
+    // necessary lang items we'll pass `--start-group`.
+    //
+    // Note that this isn't amazing logic for now but it should do the trick
+    // for the current implementation of the standard library.
+    let mut group_end = None;
+    let mut group_start = None;
+    let mut end_with = FxHashSet::default();
+    let info = &codegen_results.crate_info;
+    for &(cnum, _) in deps.iter().rev() {
+        if let Some(missing) = info.missing_lang_items.get(&cnum) {
+            end_with.extend(missing.iter().cloned());
+            if end_with.len() > 0 && group_end.is_none() {
+                group_end = Some(cnum);
+            }
+        }
+        end_with.retain(|item| info.lang_item_to_crate.get(item) != Some(&cnum));
+        if end_with.len() == 0 && group_end.is_some() {
+            group_start = Some(cnum);
+            break
+        }
+    }
+
+    // If we didn't end up filling in all lang items from upstream crates then
+    // we'll be filling it in with our crate. This probably means we're the
+    // standard library itself, so skip this for now.
+    if group_end.is_some() && group_start.is_none() {
+        group_end = None;
+    }
+
+    let mut compiler_builtins = None;
+
+    for &(cnum, _) in deps.iter() {
+        if group_start == Some(cnum) {
+            cmd.group_start();
+        }
+
+        // We may not pass all crates through to the linker. Some crates may
+        // appear statically in an existing dylib, meaning we'll pick up all the
+        // symbols from the dylib.
+        let src = &codegen_results.crate_info.used_crate_source[&cnum];
+        match data[cnum.as_usize() - 1] {
+            _ if codegen_results.crate_info.profiler_runtime == Some(cnum) => {
+                add_static_crate::<B>(cmd, sess, codegen_results, tmpdir, crate_type, cnum);
+            }
+            _ if codegen_results.crate_info.sanitizer_runtime == Some(cnum) => {
+                link_sanitizer_runtime::<B>(cmd, sess, codegen_results, tmpdir, cnum);
+            }
+            // compiler-builtins are always placed last to ensure that they're
+            // linked correctly.
+            _ if codegen_results.crate_info.compiler_builtins == Some(cnum) => {
+                assert!(compiler_builtins.is_none());
+                compiler_builtins = Some(cnum);
+            }
+            Linkage::NotLinked |
+            Linkage::IncludedFromDylib => {}
+            Linkage::Static => {
+                add_static_crate::<B>(cmd, sess, codegen_results, tmpdir, crate_type, cnum);
+            }
+            Linkage::Dynamic => {
+                add_dynamic_crate(cmd, sess, &src.dylib.as_ref().unwrap().0)
+            }
+        }
+
+        if group_end == Some(cnum) {
+            cmd.group_end();
+        }
+    }
+
+    // compiler-builtins are always placed last to ensure that they're
+    // linked correctly.
+    // We must always link the `compiler_builtins` crate statically. Even if it
+    // was already "included" in a dylib (e.g., `libstd` when `-C prefer-dynamic`
+    // is used)
+    if let Some(cnum) = compiler_builtins {
+        add_static_crate::<B>(cmd, sess, codegen_results, tmpdir, crate_type, cnum);
+    }
+
+    // Converts a library file-stem into a cc -l argument
+    fn unlib<'a>(config: &config::Config, stem: &'a str) -> &'a str {
+        if stem.starts_with("lib") && !config.target.options.is_like_windows {
+            &stem[3..]
+        } else {
+            stem
+        }
+    }
+
+    // We must link the sanitizer runtime using -Wl,--whole-archive but since
+    // it's packed in a .rlib, it contains stuff that are not objects that will
+    // make the linker error. So we must remove those bits from the .rlib before
+    // linking it.
+    fn link_sanitizer_runtime<'a, B: ArchiveBuilder<'a>>(cmd: &mut dyn Linker,
+                              sess: &'a Session,
+                              codegen_results: &CodegenResults,
+                              tmpdir: &Path,
+                              cnum: CrateNum) {
+        let src = &codegen_results.crate_info.used_crate_source[&cnum];
+        let cratepath = &src.rlib.as_ref().unwrap().0;
+
+        if sess.target.target.options.is_like_osx {
+            // On Apple platforms, the sanitizer is always built as a dylib, and
+            // LLVM will link to `@rpath/*.dylib`, so we need to specify an
+            // rpath to the library as well (the rpath should be absolute, see
+            // PR #41352 for details).
+            //
+            // FIXME: Remove this logic into librustc_*san once Cargo supports it
+            let rpath = cratepath.parent().unwrap();
+            let rpath = rpath.to_str().expect("non-utf8 component in path");
+            cmd.args(&["-Wl,-rpath".into(), "-Xlinker".into(), rpath.into()]);
+        }
+
+        let dst = tmpdir.join(cratepath.file_name().unwrap());
+        let mut archive = <B as ArchiveBuilder>::new(sess, &dst, Some(cratepath));
+        archive.update_symbols();
+
+        for f in archive.src_files() {
+            if f.ends_with(RLIB_BYTECODE_EXTENSION) || f == METADATA_FILENAME {
+                archive.remove_file(&f);
+            }
+        }
+
+        archive.build();
+
+        cmd.link_whole_rlib(&dst);
+    }
+
+    // Adds the static "rlib" versions of all crates to the command line.
+    // There's a bit of magic which happens here specifically related to LTO and
+    // dynamic libraries. Specifically:
+    //
+    // * For LTO, we remove upstream object files.
+    // * For dylibs we remove metadata and bytecode from upstream rlibs
+    //
+    // When performing LTO, almost(*) all of the bytecode from the upstream
+    // libraries has already been included in our object file output. As a
+    // result we need to remove the object files in the upstream libraries so
+    // the linker doesn't try to include them twice (or whine about duplicate
+    // symbols). We must continue to include the rest of the rlib, however, as
+    // it may contain static native libraries which must be linked in.
+    //
+    // (*) Crates marked with `#![no_builtins]` don't participate in LTO and
+    // their bytecode wasn't included. The object files in those libraries must
+    // still be passed to the linker.
+    //
+    // When making a dynamic library, linkers by default don't include any
+    // object files in an archive if they're not necessary to resolve the link.
+    // We basically want to convert the archive (rlib) to a dylib, though, so we
+    // *do* want everything included in the output, regardless of whether the
+    // linker thinks it's needed or not. As a result we must use the
+    // --whole-archive option (or the platform equivalent). When using this
+    // option the linker will fail if there are non-objects in the archive (such
+    // as our own metadata and/or bytecode). All in all, for rlibs to be
+    // entirely included in dylibs, we need to remove all non-object files.
+    //
+    // Note, however, that if we're not doing LTO or we're not producing a dylib
+    // (aka we're making an executable), we can just pass the rlib blindly to
+    // the linker (fast) because it's fine if it's not actually included as
+    // we're at the end of the dependency chain.
+    fn add_static_crate<'a, B: ArchiveBuilder<'a>>(cmd: &mut dyn Linker,
+                        sess: &'a Session,
+                        codegen_results: &CodegenResults,
+                        tmpdir: &Path,
+                        crate_type: config::CrateType,
+                        cnum: CrateNum) {
+        let src = &codegen_results.crate_info.used_crate_source[&cnum];
+        let cratepath = &src.rlib.as_ref().unwrap().0;
+
+        // See the comment above in `link_staticlib` and `link_rlib` for why if
+        // there's a static library that's not relevant we skip all object
+        // files.
+        let native_libs = &codegen_results.crate_info.native_libraries[&cnum];
+        let skip_native = native_libs.iter().any(|lib| {
+            lib.kind == NativeLibraryKind::NativeStatic && !relevant_lib(sess, lib)
+        });
+
+        if (!are_upstream_rust_objects_already_included(sess) ||
+            ignored_for_lto(sess, &codegen_results.crate_info, cnum)) &&
+           crate_type != config::CrateType::Dylib &&
+           !skip_native {
+            cmd.link_rlib(&fix_windows_verbatim_for_gcc(cratepath));
+            return
+        }
+
+        let dst = tmpdir.join(cratepath.file_name().unwrap());
+        let name = cratepath.file_name().unwrap().to_str().unwrap();
+        let name = &name[3..name.len() - 5]; // chop off lib/.rlib
+
+        time_ext(sess.time_extended(), Some(sess), &format!("altering {}.rlib", name), || {
+            let mut archive = <B as ArchiveBuilder>::new(sess, &dst, Some(cratepath));
+            archive.update_symbols();
+
+            let mut any_objects = false;
+            for f in archive.src_files() {
+                if f.ends_with(RLIB_BYTECODE_EXTENSION) || f == METADATA_FILENAME {
+                    archive.remove_file(&f);
+                    continue
+                }
+
+                let canonical = f.replace("-", "_");
+                let canonical_name = name.replace("-", "_");
+
+                // Look for `.rcgu.o` at the end of the filename to conclude
+                // that this is a Rust-related object file.
+                fn looks_like_rust(s: &str) -> bool {
+                    let path = Path::new(s);
+                    let ext = path.extension().and_then(|s| s.to_str());
+                    if ext != Some(OutputType::Object.extension()) {
+                        return false
+                    }
+                    let ext2 = path.file_stem()
+                        .and_then(|s| Path::new(s).extension())
+                        .and_then(|s| s.to_str());
+                    ext2 == Some(RUST_CGU_EXT)
+                }
+
+                let is_rust_object =
+                    canonical.starts_with(&canonical_name) &&
+                    looks_like_rust(&f);
+
+                // If we've been requested to skip all native object files
+                // (those not generated by the rust compiler) then we can skip
+                // this file. See above for why we may want to do this.
+                let skip_because_cfg_say_so = skip_native && !is_rust_object;
+
+                // If we're performing LTO and this is a rust-generated object
+                // file, then we don't need the object file as it's part of the
+                // LTO module. Note that `#![no_builtins]` is excluded from LTO,
+                // though, so we let that object file slide.
+                let skip_because_lto = are_upstream_rust_objects_already_included(sess) &&
+                    is_rust_object &&
+                    (sess.target.target.options.no_builtins ||
+                     !codegen_results.crate_info.is_no_builtins.contains(&cnum));
+
+                if skip_because_cfg_say_so || skip_because_lto {
+                    archive.remove_file(&f);
+                } else {
+                    any_objects = true;
+                }
+            }
+
+            if !any_objects {
+                return
+            }
+            archive.build();
+
+            // If we're creating a dylib, then we need to include the
+            // whole of each object in our archive into that artifact. This is
+            // because a `dylib` can be reused as an intermediate artifact.
+            //
+            // Note, though, that we don't want to include the whole of a
+            // compiler-builtins crate (e.g., compiler-rt) because it'll get
+            // repeatedly linked anyway.
+            if crate_type == config::CrateType::Dylib &&
+                codegen_results.crate_info.compiler_builtins != Some(cnum) {
+                cmd.link_whole_rlib(&fix_windows_verbatim_for_gcc(&dst));
+            } else {
+                cmd.link_rlib(&fix_windows_verbatim_for_gcc(&dst));
+            }
+        });
+    }
+
+    // Same thing as above, but for dynamic crates instead of static crates.
+    fn add_dynamic_crate(cmd: &mut dyn Linker, sess: &Session, cratepath: &Path) {
+        // Just need to tell the linker about where the library lives and
+        // what its name is
+        let parent = cratepath.parent();
+        if let Some(dir) = parent {
+            cmd.include_path(&fix_windows_verbatim_for_gcc(dir));
+        }
+        let filestem = cratepath.file_stem().unwrap().to_str().unwrap();
+        cmd.link_rust_dylib(&unlib(&sess.target, filestem),
+                            parent.unwrap_or(Path::new("")));
+    }
+}
+
 // Link in all of our upstream crates' native dependencies. Remember that
 // all of these upstream native dependencies are all non-static
 // dependencies. We've got two cases then:
@@ -577,3 +1659,12 @@ pub fn are_upstream_rust_objects_already_included(sess: &Session) -> bool {
         config::Lto::ThinLocal => false,
     }
 }
+
+fn is_pic(sess: &Session) -> bool {
+    let reloc_model_arg = match sess.opts.cg.relocation_model {
+        Some(ref s) => &s[..],
+        None => &sess.target.target.options.relocation_model[..],
+    };
+
+    reloc_model_arg == "pic"
+}
diff --git a/src/librustc_codegen_ssa/back/mod.rs b/src/librustc_codegen_ssa/back/mod.rs
index 888108408fb..a16d099ee3e 100644
--- a/src/librustc_codegen_ssa/back/mod.rs
+++ b/src/librustc_codegen_ssa/back/mod.rs
@@ -5,3 +5,5 @@ pub mod link;
 pub mod command;
 pub mod symbol_export;
 pub mod archive;
+pub mod rpath;
+pub mod wasm;
diff --git a/src/librustc_codegen_ssa/back/rpath.rs b/src/librustc_codegen_ssa/back/rpath.rs
new file mode 100644
index 00000000000..2b7abcb52be
--- /dev/null
+++ b/src/librustc_codegen_ssa/back/rpath.rs
@@ -0,0 +1,270 @@
+use rustc_data_structures::fx::FxHashSet;
+use std::env;
+use std::path::{Path, PathBuf};
+use std::fs;
+
+use rustc::hir::def_id::CrateNum;
+use rustc::middle::cstore::LibSource;
+
+pub struct RPathConfig<'a> {
+    pub used_crates: &'a [(CrateNum, LibSource)],
+    pub out_filename: PathBuf,
+    pub is_like_osx: bool,
+    pub has_rpath: bool,
+    pub linker_is_gnu: bool,
+    pub get_install_prefix_lib_path: &'a mut dyn FnMut() -> PathBuf,
+}
+
+pub fn get_rpath_flags(config: &mut RPathConfig<'_>) -> Vec<String> {
+    // No rpath on windows
+    if !config.has_rpath {
+        return Vec::new();
+    }
+
+    debug!("preparing the RPATH!");
+
+    let libs = config.used_crates.clone();
+    let libs = libs.iter().filter_map(|&(_, ref l)| l.option()).collect::<Vec<_>>();
+    let rpaths = get_rpaths(config, &libs);
+    let mut flags = rpaths_to_flags(&rpaths);
+
+    // Use DT_RUNPATH instead of DT_RPATH if available
+    if config.linker_is_gnu {
+        flags.push("-Wl,--enable-new-dtags".to_owned());
+    }
+
+    flags
+}
+
+fn rpaths_to_flags(rpaths: &[String]) -> Vec<String> {
+    let mut ret = Vec::with_capacity(rpaths.len()); // the minimum needed capacity
+
+    for rpath in rpaths {
+        if rpath.contains(',') {
+            ret.push("-Wl,-rpath".into());
+            ret.push("-Xlinker".into());
+            ret.push(rpath.clone());
+        } else {
+            ret.push(format!("-Wl,-rpath,{}", &(*rpath)));
+        }
+    }
+
+    ret
+}
+
+fn get_rpaths(config: &mut RPathConfig<'_>, libs: &[PathBuf]) -> Vec<String> {
+    debug!("output: {:?}", config.out_filename.display());
+    debug!("libs:");
+    for libpath in libs {
+        debug!("    {:?}", libpath.display());
+    }
+
+    // Use relative paths to the libraries. Binaries can be moved
+    // as long as they maintain the relative relationship to the
+    // crates they depend on.
+    let rel_rpaths = get_rpaths_relative_to_output(config, libs);
+
+    // And a final backup rpath to the global library location.
+    let fallback_rpaths = vec![get_install_prefix_rpath(config)];
+
+    fn log_rpaths(desc: &str, rpaths: &[String]) {
+        debug!("{} rpaths:", desc);
+        for rpath in rpaths {
+            debug!("    {}", *rpath);
+        }
+    }
+
+    log_rpaths("relative", &rel_rpaths);
+    log_rpaths("fallback", &fallback_rpaths);
+
+    let mut rpaths = rel_rpaths;
+    rpaths.extend_from_slice(&fallback_rpaths);
+
+    // Remove duplicates
+    let rpaths = minimize_rpaths(&rpaths);
+
+    rpaths
+}
+
+fn get_rpaths_relative_to_output(config: &mut RPathConfig<'_>,
+                                 libs: &[PathBuf]) -> Vec<String> {
+    libs.iter().map(|a| get_rpath_relative_to_output(config, a)).collect()
+}
+
+fn get_rpath_relative_to_output(config: &mut RPathConfig<'_>, lib: &Path) -> String {
+    // Mac doesn't appear to support $ORIGIN
+    let prefix = if config.is_like_osx {
+        "@loader_path"
+    } else {
+        "$ORIGIN"
+    };
+
+    let cwd = env::current_dir().unwrap();
+    let mut lib = fs::canonicalize(&cwd.join(lib)).unwrap_or_else(|_| cwd.join(lib));
+    lib.pop(); // strip filename
+    let mut output = cwd.join(&config.out_filename);
+    output.pop(); // strip filename
+    let output = fs::canonicalize(&output).unwrap_or(output);
+    let relative = path_relative_from(&lib, &output).unwrap_or_else(||
+        panic!("couldn't create relative path from {:?} to {:?}", output, lib));
+    // FIXME (#9639): This needs to handle non-utf8 paths
+    format!("{}/{}", prefix, relative.to_str().expect("non-utf8 component in path"))
+}
+
+// This routine is adapted from the *old* Path's `path_relative_from`
+// function, which works differently from the new `relative_from` function.
+// In particular, this handles the case on unix where both paths are
+// absolute but with only the root as the common directory.
+fn path_relative_from(path: &Path, base: &Path) -> Option<PathBuf> {
+    use std::path::Component;
+
+    if path.is_absolute() != base.is_absolute() {
+        if path.is_absolute() {
+            Some(PathBuf::from(path))
+        } else {
+            None
+        }
+    } else {
+        let mut ita = path.components();
+        let mut itb = base.components();
+        let mut comps: Vec<Component<'_>> = vec![];
+        loop {
+            match (ita.next(), itb.next()) {
+                (None, None) => break,
+                (Some(a), None) => {
+                    comps.push(a);
+                    comps.extend(ita.by_ref());
+                    break;
+                }
+                (None, _) => comps.push(Component::ParentDir),
+                (Some(a), Some(b)) if comps.is_empty() && a == b => (),
+                (Some(a), Some(b)) if b == Component::CurDir => comps.push(a),
+                (Some(_), Some(b)) if b == Component::ParentDir => return None,
+                (Some(a), Some(_)) => {
+                    comps.push(Component::ParentDir);
+                    comps.extend(itb.map(|_| Component::ParentDir));
+                    comps.push(a);
+                    comps.extend(ita.by_ref());
+                    break;
+                }
+            }
+        }
+        Some(comps.iter().map(|c| c.as_os_str()).collect())
+    }
+}
+
+
+fn get_install_prefix_rpath(config: &mut RPathConfig<'_>) -> String {
+    let path = (config.get_install_prefix_lib_path)();
+    let path = env::current_dir().unwrap().join(&path);
+    // FIXME (#9639): This needs to handle non-utf8 paths
+    path.to_str().expect("non-utf8 component in rpath").to_owned()
+}
+
+fn minimize_rpaths(rpaths: &[String]) -> Vec<String> {
+    let mut set = FxHashSet::default();
+    let mut minimized = Vec::new();
+    for rpath in rpaths {
+        if set.insert(rpath) {
+            minimized.push(rpath.clone());
+        }
+    }
+    minimized
+}
+
+#[cfg(all(unix, test))]
+mod tests {
+    use super::{RPathConfig};
+    use super::{minimize_rpaths, rpaths_to_flags, get_rpath_relative_to_output};
+    use std::path::{Path, PathBuf};
+
+    #[test]
+    fn test_rpaths_to_flags() {
+        let flags = rpaths_to_flags(&[
+            "path1".to_string(),
+            "path2".to_string()
+        ]);
+        assert_eq!(flags,
+                   ["-Wl,-rpath,path1",
+                    "-Wl,-rpath,path2"]);
+    }
+
+    #[test]
+    fn test_minimize1() {
+        let res = minimize_rpaths(&[
+            "rpath1".to_string(),
+            "rpath2".to_string(),
+            "rpath1".to_string()
+        ]);
+        assert!(res == [
+            "rpath1",
+            "rpath2",
+        ]);
+    }
+
+    #[test]
+    fn test_minimize2() {
+        let res = minimize_rpaths(&[
+            "1a".to_string(),
+            "2".to_string(),
+            "2".to_string(),
+            "1a".to_string(),
+            "4a".to_string(),
+            "1a".to_string(),
+            "2".to_string(),
+            "3".to_string(),
+            "4a".to_string(),
+            "3".to_string()
+        ]);
+        assert!(res == [
+            "1a",
+            "2",
+            "4a",
+            "3",
+        ]);
+    }
+
+    #[test]
+    fn test_rpath_relative() {
+        if cfg!(target_os = "macos") {
+            let config = &mut RPathConfig {
+                used_crates: Vec::new(),
+                has_rpath: true,
+                is_like_osx: true,
+                linker_is_gnu: false,
+                out_filename: PathBuf::from("bin/rustc"),
+                get_install_prefix_lib_path: &mut || panic!(),
+            };
+            let res = get_rpath_relative_to_output(config,
+                                                   Path::new("lib/libstd.so"));
+            assert_eq!(res, "@loader_path/../lib");
+        } else {
+            let config = &mut RPathConfig {
+                used_crates: Vec::new(),
+                out_filename: PathBuf::from("bin/rustc"),
+                get_install_prefix_lib_path: &mut || panic!(),
+                has_rpath: true,
+                is_like_osx: false,
+                linker_is_gnu: true,
+            };
+            let res = get_rpath_relative_to_output(config,
+                                                   Path::new("lib/libstd.so"));
+            assert_eq!(res, "$ORIGIN/../lib");
+        }
+    }
+
+    #[test]
+    fn test_xlinker() {
+        let args = rpaths_to_flags(&[
+            "a/normal/path".to_string(),
+            "a,comma,path".to_string()
+        ]);
+
+        assert_eq!(args, vec![
+            "-Wl,-rpath,a/normal/path".to_string(),
+            "-Wl,-rpath".to_string(),
+            "-Xlinker".to_string(),
+            "a,comma,path".to_string()
+        ]);
+    }
+}
diff --git a/src/librustc_codegen_ssa/back/wasm.rs b/src/librustc_codegen_ssa/back/wasm.rs
new file mode 100644
index 00000000000..f90bb89fbe8
--- /dev/null
+++ b/src/librustc_codegen_ssa/back/wasm.rs
@@ -0,0 +1,191 @@
+use std::fs;
+use std::path::Path;
+use std::str;
+
+use serialize::leb128;
+
+// https://webassembly.github.io/spec/core/binary/modules.html#binary-importsec
+const WASM_CUSTOM_SECTION_ID: u8 = 0;
+
+/// Adds or augment the existing `producers` section to encode information about
+/// the Rust compiler used to produce the wasm file.
+pub fn add_producer_section(
+    path: &Path,
+    rust_version: &str,
+    rustc_version: &str,
+) {
+    struct Field<'a> {
+        name: &'a str,
+        values: Vec<FieldValue<'a>>,
+    }
+
+    #[derive(Copy, Clone)]
+    struct FieldValue<'a> {
+        name: &'a str,
+        version: &'a str,
+    }
+
+    let wasm = fs::read(path).expect("failed to read wasm output");
+    let mut ret = WasmEncoder::new();
+    ret.data.extend(&wasm[..8]);
+
+    // skip the 8 byte wasm/version header
+    let rustc_value = FieldValue {
+        name: "rustc",
+        version: rustc_version,
+    };
+    let rust_value = FieldValue {
+        name: "Rust",
+        version: rust_version,
+    };
+    let mut fields = Vec::new();
+    let mut wrote_rustc = false;
+    let mut wrote_rust = false;
+
+    // Move all sections from the original wasm file to our output, skipping
+    // everything except the producers section
+    for (id, raw) in WasmSections(WasmDecoder::new(&wasm[8..])) {
+        if id != WASM_CUSTOM_SECTION_ID {
+            ret.byte(id);
+            ret.bytes(raw);
+            continue
+        }
+        let mut decoder = WasmDecoder::new(raw);
+        if decoder.str() != "producers" {
+            ret.byte(id);
+            ret.bytes(raw);
+            continue
+        }
+
+        // Read off the producers section into our fields outside the loop,
+        // we'll re-encode the producers section when we're done (to handle an
+        // entirely missing producers section as well).
+        info!("rewriting existing producers section");
+
+        for _ in 0..decoder.u32() {
+            let name = decoder.str();
+            let mut values = Vec::new();
+            for _ in 0..decoder.u32() {
+                let name = decoder.str();
+                let version = decoder.str();
+                values.push(FieldValue { name, version });
+            }
+
+            if name == "language" {
+                values.push(rust_value);
+                wrote_rust = true;
+            } else if name == "processed-by" {
+                values.push(rustc_value);
+                wrote_rustc = true;
+            }
+            fields.push(Field { name, values });
+        }
+    }
+
+    if !wrote_rust {
+        fields.push(Field {
+            name: "language",
+            values: vec![rust_value],
+        });
+    }
+    if !wrote_rustc {
+        fields.push(Field {
+            name: "processed-by",
+            values: vec![rustc_value],
+        });
+    }
+
+    // Append the producers section to the end of the wasm file.
+    let mut section = WasmEncoder::new();
+    section.str("producers");
+    section.u32(fields.len() as u32);
+    for field in fields {
+        section.str(field.name);
+        section.u32(field.values.len() as u32);
+        for value in field.values {
+            section.str(value.name);
+            section.str(value.version);
+        }
+    }
+    ret.byte(WASM_CUSTOM_SECTION_ID);
+    ret.bytes(&section.data);
+
+    fs::write(path, &ret.data).expect("failed to write wasm output");
+}
+
+struct WasmSections<'a>(WasmDecoder<'a>);
+
+impl<'a> Iterator for WasmSections<'a> {
+    type Item = (u8, &'a [u8]);
+
+    fn next(&mut self) -> Option<(u8, &'a [u8])> {
+        if self.0.data.is_empty() {
+            return None
+        }
+
+        // see https://webassembly.github.io/spec/core/binary/modules.html#sections
+        let id = self.0.byte();
+        let section_len = self.0.u32();
+        info!("new section {} / {} bytes", id, section_len);
+        let section = self.0.skip(section_len as usize);
+        Some((id, section))
+    }
+}
+
+struct WasmDecoder<'a> {
+    data: &'a [u8],
+}
+
+impl<'a> WasmDecoder<'a> {
+    fn new(data: &'a [u8]) -> WasmDecoder<'a> {
+        WasmDecoder { data }
+    }
+
+    fn byte(&mut self) -> u8 {
+        self.skip(1)[0]
+    }
+
+    fn u32(&mut self) -> u32 {
+        let (n, l1) = leb128::read_u32_leb128(self.data);
+        self.data = &self.data[l1..];
+        return n
+    }
+
+    fn skip(&mut self, amt: usize) -> &'a [u8] {
+        let (data, rest) = self.data.split_at(amt);
+        self.data = rest;
+        data
+    }
+
+    fn str(&mut self) -> &'a str {
+        let len = self.u32();
+        str::from_utf8(self.skip(len as usize)).unwrap()
+    }
+}
+
+struct WasmEncoder {
+    data: Vec<u8>,
+}
+
+impl WasmEncoder {
+    fn new() -> WasmEncoder {
+        WasmEncoder { data: Vec::new() }
+    }
+
+    fn u32(&mut self, val: u32) {
+        leb128::write_u32_leb128(&mut self.data, val);
+    }
+
+    fn byte(&mut self, val: u8) {
+        self.data.push(val);
+    }
+
+    fn bytes(&mut self, val: &[u8]) {
+        self.u32(val.len() as u32);
+        self.data.extend_from_slice(val);
+    }
+
+    fn str(&mut self, val: &str) {
+        self.bytes(val.as_bytes())
+    }
+}