Commit 5ca54036ca

Andrew Kelley <andrew@ziglang.org>
2024-10-18 09:23:35
move linker input file parsing to the compilation pipeline
1 parent 2dcfa72
src/link/Elf/relocatable.zig
@@ -2,26 +2,10 @@ pub fn flushStaticLib(elf_file: *Elf, comp: *Compilation, module_obj_path: ?Path
     const gpa = comp.gpa;
     const diags = &comp.link_diags;
 
-    for (comp.link_inputs) |link_input| switch (link_input) {
-        .object => |obj| parseObjectStaticLibReportingFailure(elf_file, obj.path),
-        .archive => |obj| parseArchiveStaticLibReportingFailure(elf_file, obj.path),
-        .dso_exact => unreachable,
-        .res => unreachable,
-        .dso => unreachable,
-    };
-
-    for (comp.c_object_table.keys()) |key| {
-        parseObjectStaticLibReportingFailure(elf_file, key.status.success.object_path);
-    }
-
     if (module_obj_path) |path| {
         parseObjectStaticLibReportingFailure(elf_file, path);
     }
 
-    if (comp.include_compiler_rt) {
-        parseObjectStaticLibReportingFailure(elf_file, comp.compiler_rt_obj.?.full_object_path);
-    }
-
     if (diags.hasErrors()) return error.FlushFailure;
 
     // First, we flush relocatable object file generated with our backends.
@@ -153,17 +137,6 @@ pub fn flushStaticLib(elf_file: *Elf, comp: *Compilation, module_obj_path: ?Path
 pub fn flushObject(elf_file: *Elf, comp: *Compilation, module_obj_path: ?Path) link.File.FlushError!void {
     const diags = &comp.link_diags;
 
-    for (comp.link_inputs) |link_input| {
-        elf_file.parseInputReportingFailure(link_input);
-    }
-
-    // This is a set of object files emitted by clang in a single `build-exe` invocation.
-    // For instance, the implicit `a.o` as compiled by `zig build-exe a.c` will end up
-    // in this set.
-    for (comp.c_object_table.keys()) |key| {
-        elf_file.openParseObjectReportingFailure(key.status.success.object_path);
-    }
-
     if (module_obj_path) |path| elf_file.openParseObjectReportingFailure(path);
 
     if (diags.hasErrors()) return error.FlushFailure;
@@ -223,14 +196,6 @@ fn parseObjectStaticLibReportingFailure(elf_file: *Elf, path: Path) void {
     };
 }
 
-fn parseArchiveStaticLibReportingFailure(elf_file: *Elf, path: Path) void {
-    const diags = &elf_file.base.comp.link_diags;
-    parseArchiveStaticLib(elf_file, path) catch |err| switch (err) {
-        error.LinkFailure => return,
-        else => |e| diags.addParseError(path, "parsing static library failed: {s}", .{@errorName(e)}),
-    };
-}
-
 fn parseObjectStaticLib(elf_file: *Elf, path: Path) Elf.ParseError!void {
     const gpa = elf_file.base.comp.gpa;
     const file_handles = &elf_file.file_handles;
@@ -253,27 +218,6 @@ fn parseObjectStaticLib(elf_file: *Elf, path: Path) Elf.ParseError!void {
     try object.parseAr(path, elf_file);
 }
 
-fn parseArchiveStaticLib(elf_file: *Elf, path: Path) Elf.ParseError!void {
-    const gpa = elf_file.base.comp.gpa;
-    const diags = &elf_file.base.comp.link_diags;
-    const file_handles = &elf_file.file_handles;
-
-    const handle = try path.root_dir.handle.openFile(path.sub_path, .{});
-    const fh = try Elf.addFileHandle(gpa, file_handles, handle);
-
-    var archive = try Archive.parse(gpa, diags, file_handles, path, fh);
-    defer archive.deinit(gpa);
-
-    for (archive.objects) |extracted| {
-        const index: File.Index = @intCast(try elf_file.files.addOne(gpa));
-        elf_file.files.set(index, .{ .object = extracted });
-        const object = &elf_file.files.items(.data)[index].object;
-        object.index = index;
-        try object.parseAr(path, elf_file);
-        try elf_file.objects.append(gpa, index);
-    }
-}
-
 fn claimUnresolved(elf_file: *Elf) void {
     if (elf_file.zigObjectPtr()) |zig_object| {
         zig_object.claimUnresolvedRelocatable(elf_file);
src/link/Elf.zig
@@ -35,8 +35,7 @@ ptr_width: PtrWidth,
 llvm_object: ?LlvmObject.Ptr = null,
 
 /// A list of all input files.
-/// Index of each input file also encodes the priority or precedence of one input file
-/// over another.
+/// First index is a special "null file". Order is otherwise not observed.
 files: std.MultiArrayList(File.Entry) = .{},
 /// Long-lived list of all file descriptors.
 /// We store them globally rather than per actual File so that we can re-use
@@ -350,6 +349,9 @@ pub fn createEmpty(
         return self;
     }
 
+    // --verbose-link
+    if (comp.verbose_link) try self.dumpArgv(comp);
+
     const is_obj = output_mode == .Obj;
     const is_obj_or_ar = is_obj or (output_mode == .Lib and link_mode == .static);
 
@@ -750,6 +752,22 @@ pub fn allocateChunk(self: *Elf, args: struct {
     return res;
 }
 
+pub fn loadInput(self: *Elf, input: link.Input) !void {
+    const gpa = self.base.comp.gpa;
+    const diags = &self.base.comp.link_diags;
+    const target = self.getTarget();
+    const debug_fmt_strip = self.base.comp.config.debug_format == .strip;
+    const default_sym_version = self.default_sym_version;
+
+    switch (input) {
+        .res => unreachable,
+        .dso_exact => @panic("TODO"),
+        .object => |obj| try parseObject(self, obj),
+        .archive => |obj| try parseArchive(gpa, diags, &self.file_handles, &self.files, &self.first_eflags, target, debug_fmt_strip, default_sym_version, &self.objects, obj),
+        .dso => |dso| try parseDso(gpa, diags, dso, &self.shared_objects, &self.files, target),
+    }
+}
+
 pub fn flush(self: *Elf, arena: Allocator, tid: Zcu.PerThread.Id, prog_node: std.Progress.Node) link.File.FlushError!void {
     const use_lld = build_options.have_llvm and self.base.comp.config.use_lld;
     if (use_lld) {
@@ -775,8 +793,6 @@ pub fn flushModule(self: *Elf, arena: Allocator, tid: Zcu.PerThread.Id, prog_nod
     const sub_prog_node = prog_node.start("ELF Flush", 0);
     defer sub_prog_node.end();
 
-    const target = self.getTarget();
-    const link_mode = comp.config.link_mode;
     const directory = self.base.emit.root_dir; // Just an alias to make it shorter to type.
     const module_obj_path: ?Path = if (self.base.zcu_object_sub_path) |path| .{
         .root_dir = directory,
@@ -786,9 +802,6 @@ pub fn flushModule(self: *Elf, arena: Allocator, tid: Zcu.PerThread.Id, prog_nod
             path,
     } else null;
 
-    // --verbose-link
-    if (comp.verbose_link) try self.dumpArgv(comp);
-
     if (self.zigObjectPtr()) |zig_object| try zig_object.flush(self, tid);
 
     switch (comp.config.output_mode) {
@@ -800,124 +813,8 @@ pub fn flushModule(self: *Elf, arena: Allocator, tid: Zcu.PerThread.Id, prog_nod
         .Exe => {},
     }
 
-    const csu = try comp.getCrtPaths(arena);
-
-    // csu prelude
-    if (csu.crt0) |path| openParseObjectReportingFailure(self, path);
-    if (csu.crti) |path| openParseObjectReportingFailure(self, path);
-    if (csu.crtbegin) |path| openParseObjectReportingFailure(self, path);
-
-    // objects and archives
-    for (comp.link_inputs) |link_input| switch (link_input) {
-        .object, .archive => parseInputReportingFailure(self, link_input),
-        .dso_exact => @panic("TODO"),
-        .dso => continue, // handled below
-        .res => unreachable,
-    };
-
-    // This is a set of object files emitted by clang in a single `build-exe` invocation.
-    // For instance, the implicit `a.o` as compiled by `zig build-exe a.c` will end up
-    // in this set.
-    for (comp.c_object_table.keys()) |key| {
-        openParseObjectReportingFailure(self, key.status.success.object_path);
-    }
-
     if (module_obj_path) |path| openParseObjectReportingFailure(self, path);
 
-    if (comp.config.any_sanitize_thread)
-        openParseArchiveReportingFailure(self, comp.tsan_lib.?.full_object_path);
-
-    if (comp.config.any_fuzz)
-        openParseArchiveReportingFailure(self, comp.fuzzer_lib.?.full_object_path);
-
-    // libc
-    if (!comp.skip_linker_dependencies and !comp.config.link_libc) {
-        if (comp.libc_static_lib) |lib|
-            openParseArchiveReportingFailure(self, lib.full_object_path);
-    }
-
-    // dynamic libraries
-    for (comp.link_inputs) |link_input| switch (link_input) {
-        .object, .archive, .dso_exact => continue, // handled above
-        .dso => parseInputReportingFailure(self, link_input),
-        .res => unreachable,
-    };
-
-    // libc++ dep
-    if (comp.config.link_libcpp) {
-        openParseArchiveReportingFailure(self, comp.libcxxabi_static_lib.?.full_object_path);
-        openParseArchiveReportingFailure(self, comp.libcxx_static_lib.?.full_object_path);
-    }
-
-    // libunwind dep
-    if (comp.config.link_libunwind) {
-        openParseArchiveReportingFailure(self, comp.libunwind_static_lib.?.full_object_path);
-    }
-
-    // libc dep
-    diags.flags.missing_libc = false;
-    if (comp.config.link_libc) {
-        if (comp.libc_installation) |lc| {
-            const flags = target_util.libcFullLinkFlags(target);
-
-            for (flags) |flag| {
-                assert(mem.startsWith(u8, flag, "-l"));
-                const lib_name = flag["-l".len..];
-                const suffix = switch (comp.config.link_mode) {
-                    .static => target.staticLibSuffix(),
-                    .dynamic => target.dynamicLibSuffix(),
-                };
-                const lib_path = try std.fmt.allocPrint(arena, "{s}/lib{s}{s}", .{
-                    lc.crt_dir.?, lib_name, suffix,
-                });
-                const resolved_path = Path.initCwd(lib_path);
-                switch (comp.config.link_mode) {
-                    .static => openParseArchiveReportingFailure(self, resolved_path),
-                    .dynamic => openParseDsoReportingFailure(self, resolved_path),
-                }
-            }
-        } else if (target.isGnuLibC()) {
-            for (glibc.libs) |lib| {
-                if (lib.removed_in) |rem_in| {
-                    if (target.os.version_range.linux.glibc.order(rem_in) != .lt) continue;
-                }
-
-                const lib_path = Path.initCwd(try std.fmt.allocPrint(arena, "{s}{c}lib{s}.so.{d}", .{
-                    comp.glibc_so_files.?.dir_path, fs.path.sep, lib.name, lib.sover,
-                }));
-                openParseDsoReportingFailure(self, lib_path);
-            }
-            const crt_file_path = try comp.get_libc_crt_file(arena, "libc_nonshared.a");
-            openParseArchiveReportingFailure(self, crt_file_path);
-        } else if (target.isMusl()) {
-            const path = try comp.get_libc_crt_file(arena, switch (link_mode) {
-                .static => "libc.a",
-                .dynamic => "libc.so",
-            });
-            switch (link_mode) {
-                .static => openParseArchiveReportingFailure(self, path),
-                .dynamic => openParseDsoReportingFailure(self, path),
-            }
-        } else {
-            diags.flags.missing_libc = true;
-        }
-    }
-
-    // Finally, as the last input objects we add compiler_rt and CSU postlude (if any).
-
-    // compiler-rt. Since compiler_rt exports symbols like `memset`, it needs
-    // to be after the shared libraries, so they are picked up from the shared
-    // libraries, not libcompiler_rt.
-    if (comp.compiler_rt_lib) |crt_file| {
-        openParseArchiveReportingFailure(self, crt_file.full_object_path);
-    } else if (comp.compiler_rt_obj) |crt_file| {
-        openParseObjectReportingFailure(self, crt_file.full_object_path);
-    }
-
-    // csu postlude
-    if (csu.crtend) |path| openParseObjectReportingFailure(self, path);
-    if (csu.crtn) |path| openParseObjectReportingFailure(self, path);
-
     if (diags.hasErrors()) return error.FlushFailure;
 
     // If we haven't already, create a linker-generated input file comprising of
@@ -1087,7 +984,17 @@ fn dumpArgv(self: *Elf, comp: *Compilation) !void {
         }
     } else null;
 
-    const csu = try comp.getCrtPaths(arena);
+    const crt_basenames = std.zig.LibCInstallation.CrtBasenames.get(.{
+        .target = target,
+        .link_libc = comp.config.link_libc,
+        .output_mode = comp.config.output_mode,
+        .link_mode = link_mode,
+        .pie = comp.config.pie,
+    });
+    const crt_paths: std.zig.LibCInstallation.CrtPaths = if (comp.libc_installation) |lci|
+        try lci.resolveCrtPaths(arena, crt_basenames, target)
+    else
+        .{};
     const compiler_rt_path: ?[]const u8 = blk: {
         if (comp.compiler_rt_lib) |x| break :blk try x.full_object_path.toString(arena);
         if (comp.compiler_rt_obj) |x| break :blk try x.full_object_path.toString(arena);
@@ -1204,10 +1111,9 @@ fn dumpArgv(self: *Elf, comp: *Compilation) !void {
             try argv.append("-s");
         }
 
-        // csu prelude
-        if (csu.crt0) |path| try argv.append(try path.toString(arena));
-        if (csu.crti) |path| try argv.append(try path.toString(arena));
-        if (csu.crtbegin) |path| try argv.append(try path.toString(arena));
+        if (crt_paths.crt0) |path| try argv.append(try path.toString(arena));
+        if (crt_paths.crti) |path| try argv.append(try path.toString(arena));
+        if (crt_paths.crtbegin) |path| try argv.append(try path.toString(arena));
 
         if (comp.config.link_libc) {
             if (self.base.comp.libc_installation) |libc_installation| {
@@ -1339,9 +1245,8 @@ fn dumpArgv(self: *Elf, comp: *Compilation) !void {
             try argv.append(p);
         }
 
-        // crt postlude
-        if (csu.crtend) |path| try argv.append(try path.toString(arena));
-        if (csu.crtn) |path| try argv.append(try path.toString(arena));
+        if (crt_paths.crtend) |path| try argv.append(try path.toString(arena));
+        if (crt_paths.crtn) |path| try argv.append(try path.toString(arena));
     }
 
     Compilation.dump_argv(argv.items);
@@ -1361,20 +1266,6 @@ pub const ParseError = error{
     UnknownFileType,
 } || fs.Dir.AccessError || fs.File.SeekError || fs.File.OpenError || fs.File.ReadError;
 
-pub fn parseInputReportingFailure(self: *Elf, input: link.Input) void {
-    const gpa = self.base.comp.gpa;
-    const diags = &self.base.comp.link_diags;
-    const target = self.getTarget();
-
-    switch (input) {
-        .res => unreachable,
-        .dso_exact => unreachable,
-        .object => |obj| parseObjectReportingFailure(self, obj),
-        .archive => |obj| parseArchiveReportingFailure(self, obj),
-        .dso => |dso| parseDsoReportingFailure(gpa, diags, dso, &self.shared_objects, &self.files, target),
-    }
-}
-
 pub fn openParseObjectReportingFailure(self: *Elf, path: Path) void {
     const diags = &self.base.comp.link_diags;
     const obj = link.openObject(path, false, false) catch |err| {
@@ -1385,7 +1276,7 @@ pub fn openParseObjectReportingFailure(self: *Elf, path: Path) void {
     self.parseObjectReportingFailure(obj);
 }
 
-pub fn parseObjectReportingFailure(self: *Elf, obj: link.Input.Object) void {
+fn parseObjectReportingFailure(self: *Elf, obj: link.Input.Object) void {
     const diags = &self.base.comp.link_diags;
     self.parseObject(obj) catch |err| switch (err) {
         error.LinkFailure => return, // already reported
@@ -1423,33 +1314,6 @@ fn parseObject(self: *Elf, obj: link.Input.Object) ParseError!void {
     try object.parse(gpa, diags, obj.path, handle, first_eflags, target, debug_fmt_strip, default_sym_version);
 }
 
-pub fn openParseArchiveReportingFailure(self: *Elf, path: Path) void {
-    const diags = &self.base.comp.link_diags;
-    const obj = link.openObject(path, false, false) catch |err| {
-        switch (diags.failParse(path, "failed to open archive {}: {s}", .{ path, @errorName(err) })) {
-            error.LinkFailure => return,
-        }
-    };
-    parseArchiveReportingFailure(self, obj);
-}
-
-pub fn parseArchiveReportingFailure(self: *Elf, obj: link.Input.Object) void {
-    const gpa = self.base.comp.gpa;
-    const diags = &self.base.comp.link_diags;
-    const first_eflags = &self.first_eflags;
-    const target = self.base.comp.root_mod.resolved_target.result;
-    const debug_fmt_strip = self.base.comp.config.debug_format == .strip;
-    const default_sym_version = self.default_sym_version;
-    const file_handles = &self.file_handles;
-    const files = &self.files;
-    const objects = &self.objects;
-
-    parseArchive(gpa, diags, file_handles, files, first_eflags, target, debug_fmt_strip, default_sym_version, objects, obj) catch |err| switch (err) {
-        error.LinkFailure => return, // already reported
-        else => |e| diags.addParseError(obj.path, "failed to parse archive: {s}", .{@errorName(e)}),
-    };
-}
-
 fn parseArchive(
     gpa: Allocator,
     diags: *Diags,
@@ -1480,38 +1344,6 @@ fn parseArchive(
     }
 }
 
-fn openParseDsoReportingFailure(self: *Elf, path: Path) void {
-    const diags = &self.base.comp.link_diags;
-    const target = self.getTarget();
-    const dso = link.openDso(path, false, false, false) catch |err| {
-        switch (diags.failParse(path, "failed to open shared object {}: {s}", .{ path, @errorName(err) })) {
-            error.LinkFailure => return,
-        }
-    };
-    const gpa = self.base.comp.gpa;
-    parseDsoReportingFailure(gpa, diags, dso, &self.shared_objects, &self.files, target);
-}
-
-fn parseDsoReportingFailure(
-    gpa: Allocator,
-    diags: *Diags,
-    dso: link.Input.Dso,
-    shared_objects: *std.StringArrayHashMapUnmanaged(File.Index),
-    files: *std.MultiArrayList(File.Entry),
-    target: std.Target,
-) void {
-    parseDso(gpa, diags, dso, shared_objects, files, target) catch |err| switch (err) {
-        error.LinkFailure => return, // already reported
-        error.BadMagic, error.UnexpectedEndOfFile => {
-            var notes = diags.addErrorWithNotes(2) catch return diags.setAllocFailure();
-            notes.addMsg("failed to parse shared object: {s}", .{@errorName(err)}) catch return diags.setAllocFailure();
-            notes.addNote("while parsing {}", .{dso.path}) catch return diags.setAllocFailure();
-            notes.addNote("{s}", .{@as([]const u8, "the file may be a GNU ld script, in which case it is not an ELF file but a text file referencing other libraries to link. In this case, avoid depending on the library, convince your system administrators to refrain from using this kind of file, or pass -fallow-so-scripts to force the compiler to check every shared library in case it is an ld script.")}) catch return diags.setAllocFailure();
-        },
-        else => |e| diags.addParseError(dso.path, "failed to parse shared object: {s}", .{@errorName(e)}),
-    };
-}
-
 fn parseDso(
     gpa: Allocator,
     diags: *Diags,
@@ -1524,7 +1356,6 @@ fn parseDso(
     defer tracy.end();
 
     const handle = dso.file;
-    defer handle.close();
 
     const stat = Stat.fromFs(try handle.stat());
     var header = try SharedObject.parseHeader(gpa, diags, dso.path, handle, stat, target);
src/Compilation.zig
@@ -10,6 +10,7 @@ const Target = std.Target;
 const ThreadPool = std.Thread.Pool;
 const WaitGroup = std.Thread.WaitGroup;
 const ErrorBundle = std.zig.ErrorBundle;
+const Path = Cache.Path;
 
 const Value = @import("Value.zig");
 const Type = @import("Type.zig");
@@ -39,9 +40,9 @@ const Air = @import("Air.zig");
 const Builtin = @import("Builtin.zig");
 const LlvmObject = @import("codegen/llvm.zig").Object;
 const dev = @import("dev.zig");
-pub const Directory = Cache.Directory;
-const Path = Cache.Path;
+const ThreadSafeQueue = @import("ThreadSafeQueue.zig").ThreadSafeQueue;
 
+pub const Directory = Cache.Directory;
 pub const Config = @import("Compilation/Config.zig");
 
 /// General-purpose allocator. Used for both temporary and long-term storage.
@@ -108,6 +109,7 @@ win32_resource_table: if (dev.env.supports(.win32_resource)) std.AutoArrayHashMa
 } = .{},
 
 link_diags: link.Diags,
+link_task_queue: ThreadSafeQueue(link.File.Task) = .empty,
 
 work_queues: [
     len: {
@@ -263,6 +265,9 @@ emit_asm: ?EmitLoc,
 emit_llvm_ir: ?EmitLoc,
 emit_llvm_bc: ?EmitLoc,
 
+work_queue_wait_group: WaitGroup = .{},
+work_queue_progress_node: std.Progress.Node = .none,
+
 llvm_opt_bisect_limit: c_int,
 
 file_system_inputs: ?*std.ArrayListUnmanaged(u8),
@@ -358,9 +363,6 @@ const Job = union(enum) {
     /// After analysis, a `codegen_func` job will be queued.
     /// These must be separate jobs to ensure any needed type resolution occurs *before* codegen.
     analyze_func: InternPool.Index,
-    /// The source file containing the Decl has been updated, and so the
-    /// Decl may need its line number information updated in the debug info.
-    update_line_number: void, // TODO
     /// The main source file for the module needs to be analyzed.
     analyze_mod: *Package.Module,
     /// Fully resolve the given `struct` or `union` type.
@@ -374,6 +376,7 @@ const Job = union(enum) {
     musl_crt_file: musl.CrtFile,
     /// one of the mingw-w64 static objects
     mingw_crt_file: mingw.CrtFile,
+
     /// libunwind.a, usually needed when linking libc
     libunwind: void,
     libcxx: void,
@@ -1769,68 +1772,107 @@ pub fn create(gpa: Allocator, arena: Allocator, options: CreateOptions) !*Compil
         }
         // If we need to build glibc for the target, add work items for it.
         // We go through the work queue so that building can be done in parallel.
-        if (comp.wantBuildGLibCFromSource()) {
-            if (!std.zig.target.canBuildLibC(target)) return error.LibCUnavailable;
+        // If linking against host libc installation, instead queue up jobs
+        // for loading those files in the linker.
+        if (comp.config.link_libc and is_exe_or_dyn_lib and target.ofmt != .c) {
+            if (comp.libc_installation) |lci| {
+                const basenames = LibCInstallation.CrtBasenames.get(.{
+                    .target = target,
+                    .link_libc = comp.config.link_libc,
+                    .output_mode = comp.config.output_mode,
+                    .link_mode = comp.config.link_mode,
+                    .pie = comp.config.pie,
+                });
+                const paths = try lci.resolveCrtPaths(arena, basenames, target);
+
+                const fields = @typeInfo(@TypeOf(paths)).@"struct".fields;
+                try comp.link_task_queue.shared.ensureUnusedCapacity(gpa, fields.len);
+                inline for (fields) |field| {
+                    if (@field(paths, field.name)) |path| {
+                        comp.link_task_queue.shared.appendAssumeCapacity(.{ .load_object = path });
+                    }
+                }
+
+                const flags = target_util.libcFullLinkFlags(target);
+                try comp.link_task_queue.shared.ensureUnusedCapacity(gpa, flags.len);
+                for (flags) |flag| {
+                    assert(mem.startsWith(u8, flag, "-l"));
+                    const lib_name = flag["-l".len..];
+                    const suffix = switch (comp.config.link_mode) {
+                        .static => target.staticLibSuffix(),
+                        .dynamic => target.dynamicLibSuffix(),
+                    };
+                    const sep = std.fs.path.sep_str;
+                    const lib_path = try std.fmt.allocPrint(arena, "{s}" ++ sep ++ "lib{s}{s}", .{
+                        lci.crt_dir.?, lib_name, suffix,
+                    });
+                    const resolved_path = Path.initCwd(lib_path);
+                    comp.link_task_queue.shared.appendAssumeCapacity(switch (comp.config.link_mode) {
+                        .static => .{ .load_archive = resolved_path },
+                        .dynamic => .{ .load_dso = resolved_path },
+                    });
+                }
+            } else if (target.isMusl() and !target.isWasm()) {
+                if (!std.zig.target.canBuildLibC(target)) return error.LibCUnavailable;
 
-            if (glibc.needsCrtiCrtn(target)) {
+                if (musl.needsCrtiCrtn(target)) {
+                    try comp.queueJobs(&[_]Job{
+                        .{ .musl_crt_file = .crti_o },
+                        .{ .musl_crt_file = .crtn_o },
+                    });
+                }
                 try comp.queueJobs(&[_]Job{
-                    .{ .glibc_crt_file = .crti_o },
-                    .{ .glibc_crt_file = .crtn_o },
+                    .{ .musl_crt_file = .crt1_o },
+                    .{ .musl_crt_file = .scrt1_o },
+                    .{ .musl_crt_file = .rcrt1_o },
+                    switch (comp.config.link_mode) {
+                        .static => .{ .musl_crt_file = .libc_a },
+                        .dynamic => .{ .musl_crt_file = .libc_so },
+                    },
                 });
-            }
-            try comp.queueJobs(&[_]Job{
-                .{ .glibc_crt_file = .scrt1_o },
-                .{ .glibc_crt_file = .libc_nonshared_a },
-                .{ .glibc_shared_objects = {} },
-            });
-        }
-        if (comp.wantBuildMuslFromSource()) {
-            if (!std.zig.target.canBuildLibC(target)) return error.LibCUnavailable;
+            } else if (target.isGnuLibC()) {
+                if (!std.zig.target.canBuildLibC(target)) return error.LibCUnavailable;
 
-            if (musl.needsCrtiCrtn(target)) {
+                if (glibc.needsCrtiCrtn(target)) {
+                    try comp.queueJobs(&[_]Job{
+                        .{ .glibc_crt_file = .crti_o },
+                        .{ .glibc_crt_file = .crtn_o },
+                    });
+                }
                 try comp.queueJobs(&[_]Job{
-                    .{ .musl_crt_file = .crti_o },
-                    .{ .musl_crt_file = .crtn_o },
+                    .{ .glibc_crt_file = .scrt1_o },
+                    .{ .glibc_crt_file = .libc_nonshared_a },
+                    .{ .glibc_shared_objects = {} },
                 });
-            }
-            try comp.queueJobs(&[_]Job{
-                .{ .musl_crt_file = .crt1_o },
-                .{ .musl_crt_file = .scrt1_o },
-                .{ .musl_crt_file = .rcrt1_o },
-                switch (comp.config.link_mode) {
-                    .static => .{ .musl_crt_file = .libc_a },
-                    .dynamic => .{ .musl_crt_file = .libc_so },
-                },
-            });
-        }
+            } else if (target.isWasm() and target.os.tag == .wasi) {
+                if (!std.zig.target.canBuildLibC(target)) return error.LibCUnavailable;
 
-        if (comp.wantBuildWasiLibcFromSource()) {
-            if (!std.zig.target.canBuildLibC(target)) return error.LibCUnavailable;
+                for (comp.wasi_emulated_libs) |crt_file| {
+                    try comp.queueJob(.{
+                        .wasi_libc_crt_file = crt_file,
+                    });
+                }
+                try comp.queueJobs(&[_]Job{
+                    .{ .wasi_libc_crt_file = wasi_libc.execModelCrtFile(comp.config.wasi_exec_model) },
+                    .{ .wasi_libc_crt_file = .libc_a },
+                });
+            } else if (target.isMinGW()) {
+                if (!std.zig.target.canBuildLibC(target)) return error.LibCUnavailable;
 
-            for (comp.wasi_emulated_libs) |crt_file| {
-                try comp.queueJob(.{
-                    .wasi_libc_crt_file = crt_file,
+                const crt_job: Job = .{ .mingw_crt_file = if (is_dyn_lib) .dllcrt2_o else .crt2_o };
+                try comp.queueJobs(&.{
+                    .{ .mingw_crt_file = .mingw32_lib },
+                    crt_job,
                 });
+
+                // When linking mingw-w64 there are some import libs we always need.
+                try comp.windows_libs.ensureUnusedCapacity(gpa, mingw.always_link_libs.len);
+                for (mingw.always_link_libs) |name| comp.windows_libs.putAssumeCapacity(name, {});
+            } else {
+                return error.LibCUnavailable;
             }
-            try comp.queueJobs(&[_]Job{
-                .{ .wasi_libc_crt_file = wasi_libc.execModelCrtFile(comp.config.wasi_exec_model) },
-                .{ .wasi_libc_crt_file = .libc_a },
-            });
         }
 
-        if (comp.wantBuildMinGWFromSource()) {
-            if (!std.zig.target.canBuildLibC(target)) return error.LibCUnavailable;
-
-            const crt_job: Job = .{ .mingw_crt_file = if (is_dyn_lib) .dllcrt2_o else .crt2_o };
-            try comp.queueJobs(&.{
-                .{ .mingw_crt_file = .mingw32_lib },
-                crt_job,
-            });
-
-            // When linking mingw-w64 there are some import libs we always need.
-            try comp.windows_libs.ensureUnusedCapacity(gpa, mingw.always_link_libs.len);
-            for (mingw.always_link_libs) |name| comp.windows_libs.putAssumeCapacity(name, {});
-        }
         // Generate Windows import libs.
         if (target.os.tag == .windows) {
             const count = comp.windows_libs.count();
@@ -1885,12 +1927,16 @@ pub fn create(gpa: Allocator, arena: Allocator, options: CreateOptions) !*Compil
         {
             try comp.queueJob(.{ .zig_libc = {} });
         }
+
+        try comp.link_task_queue.shared.append(gpa, .load_explicitly_provided);
     }
 
     return comp;
 }
 
 pub fn destroy(comp: *Compilation) void {
+    const gpa = comp.gpa;
+
     if (comp.bin_file) |lf| lf.destroy();
     if (comp.zcu) |zcu| zcu.deinit();
     comp.cache_use.deinit();
@@ -1901,7 +1947,6 @@ pub fn destroy(comp: *Compilation) void {
     comp.astgen_work_queue.deinit();
     comp.embed_file_work_queue.deinit();
 
-    const gpa = comp.gpa;
     comp.windows_libs.deinit(gpa);
 
     {
@@ -3446,6 +3491,9 @@ pub fn performAllTheWork(
     comp: *Compilation,
     main_progress_node: std.Progress.Node,
 ) JobError!void {
+    comp.work_queue_progress_node = main_progress_node;
+    defer comp.work_queue_progress_node = .none;
+
     defer if (comp.zcu) |zcu| {
         zcu.sema_prog_node.end();
         zcu.sema_prog_node = std.Progress.Node.none;
@@ -3467,12 +3515,20 @@ fn performAllTheWorkInner(
     // (at least for now) single-threaded main work queue. However, C object compilation
     // only needs to be finished by the end of this function.
 
-    var work_queue_wait_group: WaitGroup = .{};
+    const work_queue_wait_group = &comp.work_queue_wait_group;
+
+    work_queue_wait_group.reset();
     defer work_queue_wait_group.wait();
 
+    if (comp.bin_file) |lf| {
+        if (try comp.link_task_queue.enqueue(comp.gpa, &.{.load_explicitly_provided})) {
+            comp.thread_pool.spawnWg(work_queue_wait_group, link.File.flushTaskQueue, .{ lf, main_progress_node });
+        }
+    }
+
     if (comp.docs_emit != null) {
         dev.check(.docs_emit);
-        comp.thread_pool.spawnWg(&work_queue_wait_group, workerDocsCopy, .{comp});
+        comp.thread_pool.spawnWg(work_queue_wait_group, workerDocsCopy, .{comp});
         work_queue_wait_group.spawnManager(workerDocsWasm, .{ comp, main_progress_node });
     }
 
@@ -3538,21 +3594,32 @@ fn performAllTheWorkInner(
         }
 
         while (comp.c_object_work_queue.readItem()) |c_object| {
-            comp.thread_pool.spawnWg(&work_queue_wait_group, workerUpdateCObject, .{
+            comp.thread_pool.spawnWg(work_queue_wait_group, workerUpdateCObject, .{
                 comp, c_object, main_progress_node,
             });
         }
 
         while (comp.win32_resource_work_queue.readItem()) |win32_resource| {
-            comp.thread_pool.spawnWg(&work_queue_wait_group, workerUpdateWin32Resource, .{
+            comp.thread_pool.spawnWg(work_queue_wait_group, workerUpdateWin32Resource, .{
                 comp, win32_resource, main_progress_node,
             });
         }
     }
 
-    if (comp.job_queued_compiler_rt_lib) work_queue_wait_group.spawnManager(buildRt, .{ comp, "compiler_rt.zig", .compiler_rt, .Lib, &comp.compiler_rt_lib, main_progress_node });
-    if (comp.job_queued_compiler_rt_obj) work_queue_wait_group.spawnManager(buildRt, .{ comp, "compiler_rt.zig", .compiler_rt, .Obj, &comp.compiler_rt_obj, main_progress_node });
-    if (comp.job_queued_fuzzer_lib) work_queue_wait_group.spawnManager(buildRt, .{ comp, "fuzzer.zig", .libfuzzer, .Lib, &comp.fuzzer_lib, main_progress_node });
+    if (comp.job_queued_compiler_rt_lib) {
+        comp.job_queued_compiler_rt_lib = false;
+        work_queue_wait_group.spawnManager(buildRt, .{ comp, "compiler_rt.zig", .compiler_rt, .Lib, &comp.compiler_rt_lib, main_progress_node });
+    }
+
+    if (comp.job_queued_compiler_rt_obj) {
+        comp.job_queued_compiler_rt_obj = false;
+        work_queue_wait_group.spawnManager(buildRt, .{ comp, "compiler_rt.zig", .compiler_rt, .Obj, &comp.compiler_rt_obj, main_progress_node });
+    }
+
+    if (comp.job_queued_fuzzer_lib) {
+        comp.job_queued_fuzzer_lib = false;
+        work_queue_wait_group.spawnManager(buildRt, .{ comp, "fuzzer.zig", .libfuzzer, .Lib, &comp.fuzzer_lib, main_progress_node });
+    }
 
     if (comp.zcu) |zcu| {
         const pt: Zcu.PerThread = .{ .zcu = zcu, .tid = .main };
@@ -3570,7 +3637,7 @@ fn performAllTheWorkInner(
 
     if (!InternPool.single_threaded) {
         comp.codegen_work.done = false; // may be `true` from a prior update
-        comp.thread_pool.spawnWgId(&work_queue_wait_group, codegenThread, .{comp});
+        comp.thread_pool.spawnWgId(work_queue_wait_group, codegenThread, .{comp});
     }
     defer if (!InternPool.single_threaded) {
         {
@@ -3679,31 +3746,6 @@ fn processOneJob(tid: usize, comp: *Compilation, job: Job, prog_node: std.Progre
                 error.AnalysisFail => return,
             };
         },
-        .update_line_number => |decl_index| {
-            const named_frame = tracy.namedFrame("update_line_number");
-            defer named_frame.end();
-
-            if (true) @panic("TODO: update_line_number");
-
-            const gpa = comp.gpa;
-            const pt: Zcu.PerThread = .{ .zcu = comp.zcu.?, .tid = @enumFromInt(tid) };
-            const decl = pt.zcu.declPtr(decl_index);
-            const lf = comp.bin_file.?;
-            lf.updateDeclLineNumber(pt, decl_index) catch |err| {
-                try pt.zcu.failed_analysis.ensureUnusedCapacity(gpa, 1);
-                pt.zcu.failed_analysis.putAssumeCapacityNoClobber(
-                    InternPool.AnalUnit.wrap(.{ .decl = decl_index }),
-                    try Zcu.ErrorMsg.create(
-                        gpa,
-                        decl.navSrcLoc(pt.zcu),
-                        "unable to update line number: {s}",
-                        .{@errorName(err)},
-                    ),
-                );
-                decl.analysis = .codegen_failure;
-                try pt.zcu.retryable_failures.append(gpa, InternPool.AnalUnit.wrap(.{ .decl = decl_index }));
-            };
-        },
         .analyze_mod => |mod| {
             const named_frame = tracy.namedFrame("analyze_mod");
             defer named_frame.end();
@@ -4920,7 +4962,9 @@ fn updateCObject(comp: *Compilation, c_object: *CObject, c_obj_prog_node: std.Pr
         // the contents were the same, we hit the cache but the manifest is dirty and we need to update
         // it to prevent doing a full file content comparison the next time around.
         man.writeManifest() catch |err| {
-            log.warn("failed to write cache manifest when compiling '{s}': {s}", .{ c_object.src.src_path, @errorName(err) });
+            log.warn("failed to write cache manifest when compiling '{s}': {s}", .{
+                c_object.src.src_path, @errorName(err),
+            });
         };
     }
 
@@ -4935,6 +4979,8 @@ fn updateCObject(comp: *Compilation, c_object: *CObject, c_obj_prog_node: std.Pr
             .lock = man.toOwnedLock(),
         },
     };
+
+    comp.enqueueLinkTasks(&.{.{ .load_object = c_object.status.success.object_path }});
 }
 
 fn updateWin32Resource(comp: *Compilation, win32_resource: *Win32Resource, win32_resource_prog_node: std.Progress.Node) !void {
@@ -6058,35 +6104,6 @@ fn crtFilePath(crt_files: *std.StringHashMapUnmanaged(CrtFile), basename: []cons
     return crt_file.full_object_path;
 }
 
-fn wantBuildLibCFromSource(comp: Compilation) bool {
-    const is_exe_or_dyn_lib = switch (comp.config.output_mode) {
-        .Obj => false,
-        .Lib => comp.config.link_mode == .dynamic,
-        .Exe => true,
-    };
-    const ofmt = comp.root_mod.resolved_target.result.ofmt;
-    return comp.config.link_libc and is_exe_or_dyn_lib and
-        comp.libc_installation == null and ofmt != .c;
-}
-
-fn wantBuildGLibCFromSource(comp: Compilation) bool {
-    return comp.wantBuildLibCFromSource() and comp.getTarget().isGnuLibC();
-}
-
-fn wantBuildMuslFromSource(comp: Compilation) bool {
-    return comp.wantBuildLibCFromSource() and comp.getTarget().isMusl() and
-        !comp.getTarget().isWasm();
-}
-
-fn wantBuildWasiLibcFromSource(comp: Compilation) bool {
-    return comp.wantBuildLibCFromSource() and comp.getTarget().isWasm() and
-        comp.getTarget().os.tag == .wasi;
-}
-
-fn wantBuildMinGWFromSource(comp: Compilation) bool {
-    return comp.wantBuildLibCFromSource() and comp.getTarget().isMinGW();
-}
-
 fn wantBuildLibUnwindFromSource(comp: *Compilation) bool {
     const is_exe_or_dyn_lib = switch (comp.config.output_mode) {
         .Obj => false,
@@ -6334,9 +6351,11 @@ fn buildOutputFromZig(
 
     try comp.updateSubCompilation(sub_compilation, misc_task_tag, prog_node);
 
-    // Under incremental compilation, `out` may already be populated from a prior update.
-    assert(out.* == null or comp.incremental);
-    out.* = try sub_compilation.toCrtFile();
+    const crt_file = try sub_compilation.toCrtFile();
+    assert(out.* == null);
+    out.* = crt_file;
+
+    comp.enqueueLinkTaskMode(crt_file.full_object_path, output_mode);
 }
 
 pub fn build_crt_file(
@@ -6443,8 +6462,39 @@ pub fn build_crt_file(
 
     try comp.updateSubCompilation(sub_compilation, misc_task_tag, prog_node);
 
-    try comp.crt_files.ensureUnusedCapacity(gpa, 1);
-    comp.crt_files.putAssumeCapacityNoClobber(basename, try sub_compilation.toCrtFile());
+    const crt_file = try sub_compilation.toCrtFile();
+    comp.enqueueLinkTaskMode(crt_file.full_object_path, output_mode);
+
+    {
+        comp.mutex.lock();
+        defer comp.mutex.unlock();
+        try comp.crt_files.ensureUnusedCapacity(gpa, 1);
+        comp.crt_files.putAssumeCapacityNoClobber(basename, crt_file);
+    }
+}
+
+pub fn enqueueLinkTaskMode(comp: *Compilation, path: Path, output_mode: std.builtin.OutputMode) void {
+    comp.enqueueLinkTasks(switch (output_mode) {
+        .Exe => unreachable,
+        .Obj => &.{.{ .load_object = path }},
+        .Lib => &.{.{ .load_archive = path }},
+    });
+}
+
+/// Only valid to call during `update`. Automatically handles queuing up a
+/// linker worker task if there is not already one.
+fn enqueueLinkTasks(comp: *Compilation, tasks: []const link.File.Task) void {
+    const use_lld = build_options.have_llvm and comp.config.use_lld;
+    if (use_lld) return;
+    const target = comp.root_mod.resolved_target.result;
+    if (target.ofmt != .elf) return;
+    if (comp.link_task_queue.enqueue(comp.gpa, tasks) catch |err| switch (err) {
+        error.OutOfMemory => return comp.setAllocFailure(),
+    }) {
+        comp.thread_pool.spawnWg(&comp.work_queue_wait_group, link.File.flushTaskQueue, .{
+            comp.bin_file.?, comp.work_queue_progress_node,
+        });
+    }
 }
 
 pub fn toCrtFile(comp: *Compilation) Allocator.Error!CrtFile {
src/glibc.zig
@@ -1204,14 +1204,12 @@ pub fn buildSharedObjects(comp: *Compilation, prog_node: std.Progress.Node) !voi
     };
 
     assert(comp.glibc_so_files == null);
-    comp.glibc_so_files = BuiltSharedObjects{
+    comp.glibc_so_files = .{
         .lock = man.toOwnedLock(),
         .dir_path = try comp.global_cache_directory.join(comp.gpa, &.{ "o", &digest }),
     };
 }
 
-// zig fmt: on
-
 fn buildSharedLib(
     comp: *Compilation,
     arena: Allocator,
src/libcxx.zig
@@ -355,7 +355,9 @@ pub fn buildLibCXX(comp: *Compilation, prog_node: std.Progress.Node) BuildError!
     };
 
     assert(comp.libcxx_static_lib == null);
-    comp.libcxx_static_lib = try sub_compilation.toCrtFile();
+    const crt_file = try sub_compilation.toCrtFile();
+    comp.libcxx_static_lib = crt_file;
+    comp.enqueueLinkTaskMode(crt_file.full_object_path, output_mode);
 }
 
 pub fn buildLibCXXABI(comp: *Compilation, prog_node: std.Progress.Node) BuildError!void {
@@ -584,7 +586,9 @@ pub fn buildLibCXXABI(comp: *Compilation, prog_node: std.Progress.Node) BuildErr
     };
 
     assert(comp.libcxxabi_static_lib == null);
-    comp.libcxxabi_static_lib = try sub_compilation.toCrtFile();
+    const crt_file = try sub_compilation.toCrtFile();
+    comp.libcxxabi_static_lib = crt_file;
+    comp.enqueueLinkTaskMode(crt_file.full_object_path, output_mode);
 }
 
 pub fn hardeningModeFlag(optimize_mode: std.builtin.OptimizeMode) []const u8 {
src/libtsan.zig
@@ -342,8 +342,10 @@ pub fn buildTsan(comp: *Compilation, prog_node: std.Progress.Node) BuildError!vo
         },
     };
 
+    const crt_file = try sub_compilation.toCrtFile();
+    comp.enqueueLinkTaskMode(crt_file.full_object_path, output_mode);
     assert(comp.tsan_lib == null);
-    comp.tsan_lib = try sub_compilation.toCrtFile();
+    comp.tsan_lib = crt_file;
 }
 
 const tsan_sources = [_][]const u8{
src/libunwind.zig
@@ -199,8 +199,10 @@ pub fn buildStaticLib(comp: *Compilation, prog_node: std.Progress.Node) BuildErr
         },
     };
 
+    const crt_file = try sub_compilation.toCrtFile();
+    comp.enqueueLinkTaskMode(crt_file.full_object_path, output_mode);
     assert(comp.libunwind_static_lib == null);
-    comp.libunwind_static_lib = try sub_compilation.toCrtFile();
+    comp.libunwind_static_lib = crt_file;
 }
 
 const unwind_src_list = [_][]const u8{
src/link.zig
@@ -24,6 +24,7 @@ const LlvmObject = @import("codegen/llvm.zig").Object;
 const lldMain = @import("main.zig").lldMain;
 const Package = @import("Package.zig");
 const dev = @import("dev.zig");
+const ThreadSafeQueue = @import("ThreadSafeQueue.zig").ThreadSafeQueue;
 
 pub const LdScript = @import("link/LdScript.zig");
 
@@ -368,6 +369,9 @@ pub const File = struct {
     lock: ?Cache.Lock = null,
     child_pid: ?std.process.Child.Id = null,
 
+    /// Ensure only 1 simultaneous call to `flushTaskQueue`.
+    task_queue_safety: std.debug.SafetyLock = .{},
+
     pub const OpenOptions = struct {
         symbol_count_hint: u64 = 32,
         program_code_size_hint: u64 = 256 * 1024,
@@ -995,6 +999,86 @@ pub const File = struct {
         }
     }
 
+    /// Opens a path as an object file and parses it into the linker.
+    fn openLoadObject(base: *File, path: Path) anyerror!void {
+        const diags = &base.comp.link_diags;
+        const input = try openObjectInput(diags, path);
+        errdefer input.object.file.close();
+        try loadInput(base, input);
+    }
+
+    /// Opens a path as a static library and parses it into the linker.
+    fn openLoadArchive(base: *File, path: Path) anyerror!void {
+        const diags = &base.comp.link_diags;
+        const input = try openArchiveInput(diags, path, false, false);
+        errdefer input.archive.file.close();
+        try loadInput(base, input);
+    }
+
+    /// Opens a path as a shared library and parses it into the linker.
+    /// Handles GNU ld scripts.
+    fn openLoadDso(base: *File, path: Path, query: UnresolvedInput.Query) anyerror!void {
+        const dso = try openDso(path, query.needed, query.weak, query.reexport);
+        errdefer dso.file.close();
+        loadInput(base, .{ .dso = dso }) catch |err| switch (err) {
+            error.BadMagic, error.UnexpectedEndOfFile => {
+                if (base.tag != .elf) return err;
+                try loadGnuLdScript(base, path, query, dso.file);
+                dso.file.close();
+                return;
+            },
+            else => return err,
+        };
+    }
+
+    fn loadGnuLdScript(base: *File, path: Path, parent_query: UnresolvedInput.Query, file: fs.File) anyerror!void {
+        const diags = &base.comp.link_diags;
+        const gpa = base.comp.gpa;
+        const stat = try file.stat();
+        const size = std.math.cast(u32, stat.size) orelse return error.FileTooBig;
+        const buf = try gpa.alloc(u8, size);
+        defer gpa.free(buf);
+        const n = try file.preadAll(buf, 0);
+        if (buf.len != n) return error.UnexpectedEndOfFile;
+        var ld_script = try LdScript.parse(gpa, diags, path, buf);
+        defer ld_script.deinit(gpa);
+        for (ld_script.args) |arg| {
+            const query: UnresolvedInput.Query = .{
+                .needed = arg.needed or parent_query.needed,
+                .weak = parent_query.weak,
+                .reexport = parent_query.reexport,
+                .preferred_mode = parent_query.preferred_mode,
+                .search_strategy = parent_query.search_strategy,
+                .allow_so_scripts = parent_query.allow_so_scripts,
+            };
+            if (mem.startsWith(u8, arg.path, "-l")) {
+                @panic("TODO");
+            } else {
+                if (fs.path.isAbsolute(arg.path)) {
+                    const new_path = Path.initCwd(try gpa.dupe(u8, arg.path));
+                    switch (Compilation.classifyFileExt(arg.path)) {
+                        .shared_library => try openLoadDso(base, new_path, query),
+                        .object => try openLoadObject(base, new_path),
+                        .static_library => try openLoadArchive(base, new_path),
+                        else => diags.addParseError(path, "GNU ld script references file with unrecognized extension: {s}", .{arg.path}),
+                    }
+                } else {
+                    @panic("TODO");
+                }
+            }
+        }
+    }
+
+    pub fn loadInput(base: *File, input: Input) anyerror!void {
+        switch (base.tag) {
+            inline .elf => |tag| {
+                dev.check(tag.devFeature());
+                return @as(*tag.Type(), @fieldParentPtr("base", base)).loadInput(input);
+            },
+            else => {},
+        }
+    }
+
     pub fn linkAsArchive(base: *File, arena: Allocator, tid: Zcu.PerThread.Id, prog_node: std.Progress.Node) FlushError!void {
         dev.check(.lld_linker);
 
@@ -1261,6 +1345,111 @@ pub const File = struct {
     pub const Wasm = @import("link/Wasm.zig");
     pub const NvPtx = @import("link/NvPtx.zig");
     pub const Dwarf = @import("link/Dwarf.zig");
+
+    /// Does all the tasks in the queue. Runs in exactly one separate thread
+    /// from the rest of compilation. All tasks performed here are
+    /// single-threaded with respect to one another.
+    pub fn flushTaskQueue(base: *File, prog_node: std.Progress.Node) void {
+        const comp = base.comp;
+        base.task_queue_safety.lock();
+        defer base.task_queue_safety.unlock();
+        while (comp.link_task_queue.check()) |tasks| {
+            for (tasks) |task| doTask(base, prog_node, task);
+        }
+    }
+
+    pub const Task = union(enum) {
+        /// Loads the objects, shared objects, and archives that are already
+        /// known from the command line.
+        load_explicitly_provided,
+        /// Tells the linker to load an object file by path.
+        load_object: Path,
+        /// Tells the linker to load a static library by path.
+        load_archive: Path,
+        /// Tells the linker to load a shared library, possibly one that is a
+        /// GNU ld script.
+        load_dso: Path,
+        /// Tells the linker to load an input which could be an object file,
+        /// archive, or shared library.
+        load_input: Input,
+    };
+
+    fn doTask(base: *File, parent_prog_node: std.Progress.Node, task: Task) void {
+        const comp = base.comp;
+        switch (task) {
+            .load_explicitly_provided => {
+                const prog_node = parent_prog_node.start("Linker Parse Input", comp.link_inputs.len);
+                defer prog_node.end();
+
+                for (comp.link_inputs) |input| {
+                    const sub_node = prog_node.start(input.taskName(), 0);
+                    defer sub_node.end();
+                    base.loadInput(input) catch |err| switch (err) {
+                        error.LinkFailure => return, // error reported via link_diags
+                        else => |e| {
+                            if (input.path()) |path| {
+                                comp.link_diags.addParseError(path, "failed to parse linker input: {s}", .{@errorName(e)});
+                            } else {
+                                comp.link_diags.addError("failed to {s}: {s}", .{ input.taskName(), @errorName(e) });
+                            }
+                        },
+                    };
+                }
+            },
+            .load_object => |path| {
+                const prog_node = parent_prog_node.start("Linker Parse Object", 0);
+                defer prog_node.end();
+                const sub_node = prog_node.start(path.basename(), 0);
+                defer sub_node.end();
+
+                base.openLoadObject(path) catch |err| switch (err) {
+                    error.LinkFailure => return, // error reported via link_diags
+                    else => |e| comp.link_diags.addParseError(path, "failed to parse object: {s}", .{@errorName(e)}),
+                };
+            },
+            .load_archive => |path| {
+                const prog_node = parent_prog_node.start("Linker Parse Archive", 0);
+                defer prog_node.end();
+                const sub_node = prog_node.start(path.basename(), 0);
+                defer sub_node.end();
+
+                base.openLoadArchive(path) catch |err| switch (err) {
+                    error.LinkFailure => return, // error reported via link_diags
+                    else => |e| comp.link_diags.addParseError(path, "failed to parse archive: {s}", .{@errorName(e)}),
+                };
+            },
+            .load_dso => |path| {
+                const prog_node = parent_prog_node.start("Linker Parse Shared Library", 0);
+                defer prog_node.end();
+                const sub_node = prog_node.start(path.basename(), 0);
+                defer sub_node.end();
+
+                base.openLoadDso(path, .{
+                    .preferred_mode = .dynamic,
+                    .search_strategy = .paths_first,
+                }) catch |err| switch (err) {
+                    error.LinkFailure => return, // error reported via link_diags
+                    else => |e| comp.link_diags.addParseError(path, "failed to parse shared library: {s}", .{@errorName(e)}),
+                };
+            },
+            .load_input => |input| {
+                const prog_node = parent_prog_node.start("Linker Parse Input", 0);
+                defer prog_node.end();
+                const sub_node = prog_node.start(input.taskName(), 0);
+                defer sub_node.end();
+                base.loadInput(input) catch |err| switch (err) {
+                    error.LinkFailure => return, // error reported via link_diags
+                    else => |e| {
+                        if (input.path()) |path| {
+                            comp.link_diags.addParseError(path, "failed to parse linker input: {s}", .{@errorName(e)});
+                        } else {
+                            comp.link_diags.addError("failed to {s}: {s}", .{ input.taskName(), @errorName(e) });
+                        }
+                    },
+                };
+            },
+        }
+    }
 };
 
 pub fn spawnLld(
@@ -1480,6 +1669,14 @@ pub const Input = union(enum) {
             .dso_exact => null,
         };
     }
+
+    pub fn taskName(input: Input) []const u8 {
+        return switch (input) {
+            .object, .archive => |obj| obj.path.basename(),
+            inline .res, .dso => |x| x.path.basename(),
+            .dso_exact => "dso_exact",
+        };
+    }
 };
 
 pub fn hashInputs(man: *Cache.Manifest, link_inputs: []const Input) !void {
src/musl.zig
@@ -19,7 +19,7 @@ pub const CrtFile = enum {
     libc_so,
 };
 
-pub fn buildCrtFile(comp: *Compilation, crt_file: CrtFile, prog_node: std.Progress.Node) !void {
+pub fn buildCrtFile(comp: *Compilation, in_crt_file: CrtFile, prog_node: std.Progress.Node) !void {
     if (!build_options.have_llvm) {
         return error.ZigCompilerNotBuiltWithLLVMExtensions;
     }
@@ -28,7 +28,7 @@ pub fn buildCrtFile(comp: *Compilation, crt_file: CrtFile, prog_node: std.Progre
     defer arena_allocator.deinit();
     const arena = arena_allocator.allocator();
 
-    switch (crt_file) {
+    switch (in_crt_file) {
         .crti_o => {
             var args = std.ArrayList([]const u8).init(arena);
             try addCcArgs(comp, arena, &args, false);
@@ -195,8 +195,9 @@ pub fn buildCrtFile(comp: *Compilation, crt_file: CrtFile, prog_node: std.Progre
         .libc_so => {
             const optimize_mode = comp.compilerRtOptMode();
             const strip = comp.compilerRtStrip();
+            const output_mode: std.builtin.OutputMode = .Lib;
             const config = try Compilation.Config.resolve(.{
-                .output_mode = .Lib,
+                .output_mode = output_mode,
                 .link_mode = .dynamic,
                 .resolved_target = comp.root_mod.resolved_target,
                 .is_test = false,
@@ -276,12 +277,17 @@ pub fn buildCrtFile(comp: *Compilation, crt_file: CrtFile, prog_node: std.Progre
 
             try comp.updateSubCompilation(sub_compilation, .@"musl libc.so", prog_node);
 
-            try comp.crt_files.ensureUnusedCapacity(comp.gpa, 1);
-
             const basename = try comp.gpa.dupe(u8, "libc.so");
             errdefer comp.gpa.free(basename);
 
-            comp.crt_files.putAssumeCapacityNoClobber(basename, try sub_compilation.toCrtFile());
+            const crt_file = try sub_compilation.toCrtFile();
+            comp.enqueueLinkTaskMode(crt_file.full_object_path, output_mode);
+            {
+                comp.mutex.lock();
+                defer comp.mutex.unlock();
+                try comp.crt_files.ensureUnusedCapacity(comp.gpa, 1);
+                comp.crt_files.putAssumeCapacityNoClobber(basename, crt_file);
+            }
         },
     }
 }
src/target.zig
@@ -1,4 +1,6 @@
 const std = @import("std");
+const assert = std.debug.assert;
+
 const Type = @import("Type.zig");
 const AddressSpace = std.builtin.AddressSpace;
 const Alignment = @import("InternPool.zig").Alignment;
@@ -284,40 +286,17 @@ pub fn hasRedZone(target: std.Target) bool {
 pub fn libcFullLinkFlags(target: std.Target) []const []const u8 {
     // The linking order of these is significant and should match the order other
     // c compilers such as gcc or clang use.
-    return switch (target.os.tag) {
-        .netbsd, .openbsd => &[_][]const u8{
-            "-lm",
-            "-lpthread",
-            "-lc",
-            "-lutil",
-        },
-        .solaris, .illumos => &[_][]const u8{
-            "-lm",
-            "-lsocket",
-            "-lnsl",
-            // Solaris releases after 10 merged the threading libraries into libc.
-            "-lc",
-        },
-        .haiku => &[_][]const u8{
-            "-lm",
-            "-lroot",
-            "-lpthread",
-            "-lc",
-            "-lnetwork",
-        },
-        else => if (target.isAndroid() or target.abi.isOpenHarmony()) &[_][]const u8{
-            "-lm",
-            "-lc",
-            "-ldl",
-        } else &[_][]const u8{
-            "-lm",
-            "-lpthread",
-            "-lc",
-            "-ldl",
-            "-lrt",
-            "-lutil",
-        },
+    const result: []const []const u8 = switch (target.os.tag) {
+        .netbsd, .openbsd => &.{ "-lm", "-lpthread", "-lc", "-lutil" },
+        // Solaris releases after 10 merged the threading libraries into libc.
+        .solaris, .illumos => &.{ "-lm", "-lsocket", "-lnsl", "-lc" },
+        .haiku => &.{ "-lm", "-lroot", "-lpthread", "-lc", "-lnetwork" },
+        else => if (target.isAndroid() or target.abi.isOpenHarmony())
+            &.{ "-lm", "-lc", "-ldl" }
+        else
+            &.{ "-lm", "-lpthread", "-lc", "-ldl", "-lrt", "-lutil" },
     };
+    return result;
 }
 
 pub fn clangMightShellOutForAssembly(target: std.Target) bool {
src/ThreadSafeQueue.zig
@@ -0,0 +1,63 @@
+const std = @import("std");
+const assert = std.debug.assert;
+const Allocator = std.mem.Allocator;
+
+pub fn ThreadSafeQueue(comptime T: type) type {
+    return struct {
+        worker_owned: std.ArrayListUnmanaged(T),
+        /// Protected by `mutex`.
+        shared: std.ArrayListUnmanaged(T),
+        mutex: std.Thread.Mutex,
+        state: State,
+
+        const Self = @This();
+
+        pub const State = enum { wait, run };
+
+        pub const empty: Self = .{
+            .worker_owned = .empty,
+            .shared = .empty,
+            .mutex = .{},
+            .state = .wait,
+        };
+
+        pub fn deinit(self: *Self, gpa: Allocator) void {
+            self.worker_owned.deinit(gpa);
+            self.shared.deinit(gpa);
+            self.* = undefined;
+        }
+
+        /// Must be called from the worker thread.
+        pub fn check(self: *Self) ?[]T {
+            assert(self.worker_owned.items.len == 0);
+            {
+                self.mutex.lock();
+                defer self.mutex.unlock();
+                assert(self.state == .run);
+                if (self.shared.items.len == 0) {
+                    self.state = .wait;
+                    return null;
+                }
+                std.mem.swap(std.ArrayListUnmanaged(T), &self.worker_owned, &self.shared);
+            }
+            const result = self.worker_owned.items;
+            self.worker_owned.clearRetainingCapacity();
+            return result;
+        }
+
+        /// Adds items to the queue, returning true if and only if the worker
+        /// thread is waiting. Thread-safe.
+        /// Not safe to call from the worker thread.
+        pub fn enqueue(self: *Self, gpa: Allocator, items: []const T) error{OutOfMemory}!bool {
+            self.mutex.lock();
+            defer self.mutex.unlock();
+            try self.shared.appendSlice(gpa, items);
+            const was_waiting = switch (self.state) {
+                .run => false,
+                .wait => true,
+            };
+            self.state = .run;
+            return was_waiting;
+        }
+    };
+}
CMakeLists.txt
@@ -522,6 +522,7 @@ set(ZIG_STAGE2_SOURCES
     src/Sema.zig
     src/Sema/bitcast.zig
     src/Sema/comptime_ptr_access.zig
+    src/ThreadSafeQueue.zig
     src/Type.zig
     src/Value.zig
     src/Zcu.zig