Rollup merge of rust-lang#93901 - petrochenkov:linkmod, r=wesleywiser

Stabilize native library modifier syntax and the `whole-archive` modifier specifically

Stabilization report: rust-lang#93901 (comment)

cc rust-lang#81490

Author: Dylan-DPC

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -387,13 +387,6 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
         if attr.has_name(sym::link) {
             for nested_meta in attr.meta_item_list().unwrap_or_default() {
                 if nested_meta.has_name(sym::modifiers) {
-                    gate_feature_post!(
-                        self,
-                        native_link_modifiers,
-                        nested_meta.span(),
-                        "native link modifiers are experimental"
-                    );
-
                     if let Some(modifiers) = nested_meta.value_str() {
                         for modifier in modifiers.as_str().split(',') {
                             if let Some(modifier) = modifier.strip_prefix(&['+', '-']) {
@@ -412,7 +405,6 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                                 gate_modifier!(
                                     "bundle" => native_link_modifiers_bundle
                                     "verbatim" => native_link_modifiers_verbatim
-                                    "whole-archive" => native_link_modifiers_whole_archive
                                     "as-needed" => native_link_modifiers_as_needed
                                 );
                             }

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -1844,7 +1844,7 @@ fn linker_with_args<'a, B: ArchiveBuilder<'a>>(
     // This change is somewhat breaking in practice due to local static libraries being linked
     // as whole-archive (#85144), so removing whole-archive may be a pre-requisite.
     if sess.opts.debugging_opts.link_native_libraries {
-        add_local_native_libraries(cmd, sess, codegen_results);
+        add_local_native_libraries(cmd, sess, codegen_results, crate_type);
     }
 
     // Upstream rust libraries and their nobundle static libraries
@@ -2016,6 +2016,16 @@ fn add_order_independent_options(
     add_rpath_args(cmd, sess, codegen_results, out_filename);
 }
 
+// A dylib may reexport symbols from the linked rlib or native static library.
+// Even if some symbol is reexported it's still not necessarily counted as used and may be
+// dropped, at least with `ld`-like ELF linkers. So we have to link some rlibs and static
+// libraries as whole-archive to avoid losing reexported symbols.
+// FIXME: Find a way to mark reexported symbols as used and avoid this use of whole-archive.
+fn default_to_whole_archive(sess: &Session, crate_type: CrateType, cmd: &dyn Linker) -> bool {
+    crate_type == CrateType::Dylib
+        && !(sess.target.limit_rdylib_exports && cmd.exported_symbol_means_used_symbol())
+}
+
 /// # Native library linking
 ///
 /// User-supplied library search paths (-L on the command line). These are the same paths used to
@@ -2029,6 +2039,7 @@ fn add_local_native_libraries(
     cmd: &mut dyn Linker,
     sess: &Session,
     codegen_results: &CodegenResults,
+    crate_type: CrateType,
 ) {
     let filesearch = sess.target_filesearch(PathKind::All);
     for search_path in filesearch.search_paths() {
@@ -2046,14 +2057,18 @@ fn add_local_native_libraries(
         codegen_results.crate_info.used_libraries.iter().filter(|l| relevant_lib(sess, l));
 
     let search_path = OnceCell::new();
-    let mut last = (NativeLibKind::Unspecified, None);
+    let mut last = (None, NativeLibKind::Unspecified, None);
     for lib in relevant_libs {
         let Some(name) = lib.name else {
             continue;
         };
 
         // Skip if this library is the same as the last.
-        last = if (lib.kind, lib.name) == last { continue } else { (lib.kind, lib.name) };
+        last = if (lib.name, lib.kind, lib.verbatim) == last {
+            continue;
+        } else {
+            (lib.name, lib.kind, lib.verbatim)
+        };
 
         let verbatim = lib.verbatim.unwrap_or(false);
         match lib.kind {
@@ -2064,15 +2079,19 @@ fn add_local_native_libraries(
             NativeLibKind::Framework { as_needed } => {
                 cmd.link_framework(name, as_needed.unwrap_or(true))
             }
-            NativeLibKind::Static { bundle: None | Some(true), .. }
-            | NativeLibKind::Static { whole_archive: Some(true), .. } => {
-                cmd.link_whole_staticlib(
-                    name,
-                    verbatim,
-                    &search_path.get_or_init(|| archive_search_paths(sess)),
-                );
+            NativeLibKind::Static { whole_archive, .. } => {
+                if whole_archive == Some(true)
+                    || (whole_archive == None && default_to_whole_archive(sess, crate_type, cmd))
+                {
+                    cmd.link_whole_staticlib(
+                        name,
+                        verbatim,
+                        &search_path.get_or_init(|| archive_search_paths(sess)),
+                    );
+                } else {
+                    cmd.link_staticlib(name, verbatim)
+                }
             }
-            NativeLibKind::Static { .. } => cmd.link_staticlib(name, verbatim),
             NativeLibKind::RawDylib => {
                 // FIXME(#58713): Proper handling for raw dylibs.
                 bug!("raw_dylib feature not yet implemented");
@@ -2197,34 +2216,37 @@ fn add_upstream_rust_crates<'a, B: ArchiveBuilder<'a>>(
                 // external build system already has the native dependencies defined, and it
                 // will provide them to the linker itself.
                 if sess.opts.debugging_opts.link_native_libraries {
-                    let mut last = None;
+                    let mut last = (None, NativeLibKind::Unspecified, None);
                     for lib in &codegen_results.crate_info.native_libraries[&cnum] {
+                        let Some(name) = lib.name else {
+                            continue;
+                        };
                         if !relevant_lib(sess, lib) {
-                            // Skip libraries if they are disabled by `#[link(cfg=...)]`
                             continue;
                         }
 
                         // Skip if this library is the same as the last.
-                        if last == lib.name {
+                        last = if (lib.name, lib.kind, lib.verbatim) == last {
                             continue;
-                        }
-
-                        if let Some(static_lib_name) = lib.name {
-                            if let NativeLibKind::Static { bundle: Some(false), whole_archive } =
-                                lib.kind
+                        } else {
+                            (lib.name, lib.kind, lib.verbatim)
+                        };
+
+                        if let NativeLibKind::Static { bundle: Some(false), whole_archive } =
+                            lib.kind
+                        {
+                            let verbatim = lib.verbatim.unwrap_or(false);
+                            if whole_archive == Some(true)
+                                || (whole_archive == None
+                                    && default_to_whole_archive(sess, crate_type, cmd))
                             {
-                                let verbatim = lib.verbatim.unwrap_or(false);
-                                if whole_archive == Some(true) {
-                                    cmd.link_whole_staticlib(
-                                        static_lib_name,
-                                        verbatim,
-                                        search_path.get_or_init(|| archive_search_paths(sess)),
-                                    );
-                                } else {
-                                    cmd.link_staticlib(static_lib_name, verbatim);
-                                }
-
-                                last = lib.name;
+                                cmd.link_whole_staticlib(
+                                    name,
+                                    verbatim,
+                                    search_path.get_or_init(|| archive_search_paths(sess)),
+                                );
+                            } else {
+                                cmd.link_staticlib(name, verbatim);
                             }
                         }
                     }
@@ -2282,15 +2304,10 @@ fn add_upstream_rust_crates<'a, B: ArchiveBuilder<'a>>(
         let cratepath = &src.rlib.as_ref().unwrap().0;
 
         let mut link_upstream = |path: &Path| {
-            // 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.
+            // We don't want to include the whole compiler-builtins crate (e.g., compiler-rt)
+            // regardless of the default because it'll get repeatedly linked anyway.
             let path = fix_windows_verbatim_for_gcc(path);
-            if crate_type == CrateType::Dylib
+            if default_to_whole_archive(sess, crate_type, cmd)
                 && codegen_results.crate_info.compiler_builtins != Some(cnum)
             {
                 cmd.link_whole_rlib(&path);
@@ -2401,7 +2418,7 @@ fn add_upstream_native_libraries(
     sess: &Session,
     codegen_results: &CodegenResults,
 ) {
-    let mut last = (NativeLibKind::Unspecified, None);
+    let mut last = (None, NativeLibKind::Unspecified, None);
     for &cnum in &codegen_results.crate_info.used_crates {
         for lib in codegen_results.crate_info.native_libraries[&cnum].iter() {
             let Some(name) = lib.name else {
@@ -2412,7 +2429,11 @@ fn add_upstream_native_libraries(
             }
 
             // Skip if this library is the same as the last.
-            last = if (lib.kind, lib.name) == last { continue } else { (lib.kind, lib.name) };
+            last = if (lib.name, lib.kind, lib.verbatim) == last {
+                continue;
+            } else {
+                (lib.name, lib.kind, lib.verbatim)
+            };
 
             let verbatim = lib.verbatim.unwrap_or(false);
             match lib.kind {

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -186,6 +186,9 @@ pub trait Linker {
     fn no_crt_objects(&mut self);
     fn no_default_libraries(&mut self);
     fn export_symbols(&mut self, tmpdir: &Path, crate_type: CrateType, symbols: &[String]);
+    fn exported_symbol_means_used_symbol(&self) -> bool {
+        true
+    }
     fn subsystem(&mut self, subsystem: &str);
     fn group_start(&mut self);
     fn group_end(&mut self);
@@ -724,6 +727,10 @@ impl<'a> Linker for GccLinker<'a> {
         }
     }
 
+    fn exported_symbol_means_used_symbol(&self) -> bool {
+        self.sess.target.is_like_windows || self.sess.target.is_like_osx
+    }
+
     fn subsystem(&mut self, subsystem: &str) {
         self.linker_arg("--subsystem");
         self.linker_arg(&subsystem);
@@ -1471,6 +1478,10 @@ impl<'a> Linker for L4Bender<'a> {
         return;
     }
 
+    fn exported_symbol_means_used_symbol(&self) -> bool {
+        false
+    }
+
     fn subsystem(&mut self, subsystem: &str) {
         self.cmd.arg(&format!("--subsystem {}", subsystem));
     }

compiler/rustc_feature/src/accepted.rs

@@ -215,6 +215,10 @@ declare_features! (
     /// Allows patterns with concurrent by-move and by-ref bindings.
     /// For example, you can write `Foo(a, ref b)` where `a` is by-move and `b` is by-ref.
     (accepted, move_ref_pattern, "1.49.0", Some(68354), None),
+    /// Allows specifying modifiers in the link attribute: `#[link(modifiers = "...")]`
+    (accepted, native_link_modifiers, "1.61.0", Some(81490), None),
+    /// Allows specifying the whole-archive link modifier
+    (accepted, native_link_modifiers_whole_archive, "1.61.0", Some(81490), None),
     /// Allows using `#![no_std]`.
     (accepted, no_std, "1.6.0", None, None),
     /// Allows defining identifiers beyond ASCII.

compiler/rustc_feature/src/active.rs

@@ -446,16 +446,12 @@ declare_features! (
     (active, must_not_suspend, "1.57.0", Some(83310), None),
     /// Allows using `#[naked]` on functions.
     (active, naked_functions, "1.9.0", Some(32408), None),
-    /// Allows specifying modifiers in the link attribute: `#[link(modifiers = "...")]`
-    (active, native_link_modifiers, "1.53.0", Some(81490), None),
     /// Allows specifying the as-needed link modifier
     (active, native_link_modifiers_as_needed, "1.53.0", Some(81490), None),
     /// Allows specifying the bundle link modifier
     (active, native_link_modifiers_bundle, "1.53.0", Some(81490), None),
     /// Allows specifying the verbatim link modifier
     (active, native_link_modifiers_verbatim, "1.53.0", Some(81490), None),
-    /// Allows specifying the whole-archive link modifier
-    (active, native_link_modifiers_whole_archive, "1.53.0", Some(81490), None),
     /// Allow negative trait implementations.
     (active, negative_impls, "1.44.0", Some(68318), None),
     /// Allows the `!` type. Does not imply 'exhaustive_patterns' (below) any more.

compiler/rustc_llvm/src/lib.rs

@@ -1,5 +1,5 @@
 #![feature(nll)]
-#![feature(native_link_modifiers)]
+#![cfg_attr(bootstrap, feature(native_link_modifiers))]
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 
 // NOTE: This crate only exists to allow linking on mingw targets.

compiler/rustc_metadata/src/native_libs.rs

@@ -125,13 +125,18 @@ impl<'tcx> ItemLikeVisitor<'tcx> for Collector<'tcx> {
 
             // Do this outside the above loop so we don't depend on modifiers coming
             // after kinds
-            if let Some(item) = items.iter().find(|item| item.has_name(sym::modifiers)) {
+            let mut modifiers_count = 0;
+            for item in items.iter().filter(|item| item.has_name(sym::modifiers)) {
                 if let Some(modifiers) = item.value_str() {
+                    modifiers_count += 1;
                     let span = item.name_value_literal_span().unwrap();
+                    let mut has_duplicate_modifiers = false;
                     for modifier in modifiers.as_str().split(',') {
                         let (modifier, value) = match modifier.strip_prefix(&['+', '-']) {
                             Some(m) => (m, modifier.starts_with('+')),
                             None => {
+                                // Note: this error also excludes the case with empty modifier
+                                // string, like `modifiers = ""`.
                                 sess.span_err(
                                     span,
                                     "invalid linking modifier syntax, expected '+' or '-' prefix \
@@ -143,6 +148,9 @@ impl<'tcx> ItemLikeVisitor<'tcx> for Collector<'tcx> {
 
                         match (modifier, &mut lib.kind) {
                             ("bundle", NativeLibKind::Static { bundle, .. }) => {
+                                if bundle.is_some() {
+                                    has_duplicate_modifiers = true;
+                                }
                                 *bundle = Some(value);
                             }
                             ("bundle", _) => {
@@ -153,9 +161,17 @@ impl<'tcx> ItemLikeVisitor<'tcx> for Collector<'tcx> {
                                 );
                             }
 
-                            ("verbatim", _) => lib.verbatim = Some(value),
+                            ("verbatim", _) => {
+                                if lib.verbatim.is_some() {
+                                    has_duplicate_modifiers = true;
+                                }
+                                lib.verbatim = Some(value);
+                            }
 
                             ("whole-archive", NativeLibKind::Static { whole_archive, .. }) => {
+                                if whole_archive.is_some() {
+                                    has_duplicate_modifiers = true;
+                                }
                                 *whole_archive = Some(value);
                             }
                             ("whole-archive", _) => {
@@ -168,6 +184,9 @@ impl<'tcx> ItemLikeVisitor<'tcx> for Collector<'tcx> {
 
                             ("as-needed", NativeLibKind::Dylib { as_needed })
                             | ("as-needed", NativeLibKind::Framework { as_needed }) => {
+                                if as_needed.is_some() {
+                                    has_duplicate_modifiers = true;
+                                }
                                 *as_needed = Some(value);
                             }
                             ("as-needed", _) => {
@@ -190,12 +209,22 @@ impl<'tcx> ItemLikeVisitor<'tcx> for Collector<'tcx> {
                             }
                         }
                     }
+                    if has_duplicate_modifiers {
+                        let msg =
+                            "same modifier is used multiple times in a single `modifiers` argument";
+                        sess.span_err(item.span(), msg);
+                    }
                 } else {
                     let msg = "must be of the form `#[link(modifiers = \"...\")]`";
                     sess.span_err(item.span(), msg);
                 }
             }
 
+            if modifiers_count > 1 {
+                let msg = "multiple `modifiers` arguments in a single `#[link]` attribute";
+                sess.span_err(m.span, msg);
+            }
+
             // In general we require #[link(name = "...")] but we allow
             // #[link(wasm_import_module = "...")] without the `name`.
             let requires_name = kind_specified || lib.wasm_import_module.is_none();
@@ -349,6 +378,15 @@ impl Collector<'_> {
                 .drain_filter(|lib| {
                     if let Some(lib_name) = lib.name {
                         if lib_name.as_str() == passed_lib.name {
+                            // FIXME: This whole logic is questionable, whether modifiers are
+                            // involved or not, library reordering and kind overriding without
+                            // explicit `:rename` in particular.
+                            if lib.has_modifiers() || passed_lib.has_modifiers() {
+                                self.tcx.sess.span_err(
+                                    self.tcx.def_span(lib.foreign_module.unwrap()),
+                                    "overriding linking modifiers from command line is not supported"
+                                );
+                            }
                             if passed_lib.kind != NativeLibKind::Unspecified {
                                 lib.kind = passed_lib.kind;
                             }