# Swift defaults to building with `gold` on Linux because it doesn't build with
# `bfd`; Gentoo no longer supports `gold`, so we have to build with `lld`.
#
# We need to:
# 1. Have the Swift drivers default to linking with `lld` over `gold` (both for)
#    eventual end-user code, but also for the built Swift compiler stages to
#    bootstrap the next stage,
# 2. Have the `SWIFT_USE_LINKER` flag be correctly respected everywhere, and
# 3. Set the right linker flags for `lld` because its behavior for ELF on Linux
#    differs from other platforms, and certain Swift symbols need to not be GC'd
#    out
#
# See https://github.com/swiftlang/swift/pull/69538 (merged to main after 5.10
# branched).

--- a/swift/lib/Driver/UnixToolChains.cpp
+++ b/swift/lib/Driver/UnixToolChains.cpp
@@ -110,34 +110,7 @@ ToolChain::InvocationInfo toolchains::GenericUnix::constructInvocation(
   return II;
 }
 
-std::string toolchains::GenericUnix::getDefaultLinker() const {
-  if (getTriple().isAndroid())
-    return "lld";
-
-  switch (getTriple().getArch()) {
-  case llvm::Triple::arm:
-  case llvm::Triple::aarch64:
-  case llvm::Triple::aarch64_32:
-  case llvm::Triple::armeb:
-  case llvm::Triple::thumb:
-  case llvm::Triple::thumbeb:
-    // BFD linker has issues wrt relocation of the protocol conformance
-    // section on these targets, it also generates COPY relocations for
-    // final executables, as such, unless specified, we default to gold
-    // linker.
-    return "gold";
-  case llvm::Triple::x86:
-  case llvm::Triple::x86_64:
-  case llvm::Triple::ppc64:
-  case llvm::Triple::ppc64le:
-  case llvm::Triple::systemz:
-    // BFD linker has issues wrt relocations against protected symbols.
-    return "gold";
-  default:
-    // Otherwise, use the default BFD linker.
-    return "";
-  }
-}
+std::string toolchains::GenericUnix::getDefaultLinker() const { return "lld"; }
 
 bool toolchains::GenericUnix::addRuntimeRPath(const llvm::Triple &T,
                                               const llvm::opt::ArgList &Args) const {

--- a/swift-driver/Sources/SwiftDriver/Jobs/GenericUnixToolchain+LinkerSupport.swift
+++ b/swift-driver/Sources/SwiftDriver/Jobs/GenericUnixToolchain+LinkerSupport.swift
@@ -17,25 +17,7 @@ import struct TSCBasic.AbsolutePath
 
 extension GenericUnixToolchain {
   private func defaultLinker(for targetTriple: Triple) -> String? {
-    if targetTriple.os == .openbsd || targetTriple.os == .freeBSD ||
-        targetTriple.environment == .android {
-      return "lld"
-    }
-
-    switch targetTriple.arch {
-    case .arm, .aarch64, .armeb, .thumb, .thumbeb:
-      // BFD linker has issues wrt relocation of the protocol conformance
-      // section on these targets, it also generates COPY relocations for
-      // final executables, as such, unless specified, we default to gold
-      // linker.
-      return "gold"
-    case .x86, .x86_64, .ppc64, .ppc64le, .systemz:
-      // BFD linker has issues wrt relocations against protected symbols.
-      return "gold"
-    default:
-      // Otherwise, use the default BFD linker.
-      return ""
-    }
+    "lld"
   }
 
   private func majorArchitectureName(for triple: Triple) -> String {
--- a/swift/cmake/modules/AddPureSwift.cmake
+++ b/swift/cmake/modules/AddPureSwift.cmake
@@ -224,6 +224,10 @@ function(add_pure_swift_host_library name)
     target_link_options(${name} PRIVATE
       "-use-ld=${LLVM_USE_LINKER}"
     )
+  elseif(SWIFT_USE_LINKER)
+    target_link_options(${name} PRIVATE
+      "-use-ld=${SWIFT_USE_LINKER}"
+    )
   endif()

   # Export this target.
@@ -322,6 +326,10 @@ function(add_pure_swift_host_tool name)
     target_link_options(${name} PRIVATE
       "-use-ld=${LLVM_USE_LINKER}"
     )
+  elseif(SWIFT_USE_LINKER)
+    target_link_options(${name} PRIVATE
+      "-use-ld=${SWIFT_USE_LINKER}"
+    )
   endif()

   # Workaround to touch the library and its objects so that we don't
--- a/swift/cmake/modules/AddSwift.cmake
+++ b/swift/cmake/modules/AddSwift.cmake
@@ -629,6 +629,10 @@ function(_add_swift_runtime_link_flags target relpath_to_lib_dir bootstrapping)
         endif()
       endif()
     endif()
+
+    if(SWIFT_HOST_VARIANT_SDK MATCHES "LINUX|ANDROID|OPENBSD|FREEBSD" AND SWIFT_USE_LINKER STREQUAL "lld")
+      target_link_options(${target} PRIVATE "LINKER:-z,nostart-stop-gc")
+    endif()
   endif()

   set_property(TARGET ${target} PROPERTY BUILD_WITH_INSTALL_RPATH YES)
--- a/swift/tools/libStaticMirror/CMakeLists.txt
+++ b/swift/tools/libStaticMirror/CMakeLists.txt
@@ -29,6 +29,10 @@ add_llvm_symbol_exports(libStaticMirror ${LLVM_EXPORTED_SYMBOL_FILE})
 # Adds -dead_strip option
 add_link_opts(libStaticMirror)

+if(SWIFT_HOST_VARIANT_SDK MATCHES "LINUX|ANDROID|OPENBSD|FREEBSD" AND SWIFT_USE_LINKER STREQUAL "lld")
+  target_link_options(libStaticMirror PRIVATE "LINKER:-z,nostart-stop-gc")
+endif()
+
 add_dependencies(static-mirror-lib libStaticMirror)
 swift_install_in_component(TARGETS libStaticMirror
   ARCHIVE DESTINATION "lib${LLVM_LIBDIR_SUFFIX}/swift/${SWIFT_SDK_${SWIFT_HOST_VARIANT_SDK}_LIB_SUBDIR}" COMPONENT static-mirror-lib
--- a/swift/tools/libSwiftScan/CMakeLists.txt
+++ b/swift/tools/libSwiftScan/CMakeLists.txt
@@ -67,6 +67,10 @@ add_llvm_symbol_exports(libSwiftScan ${LLVM_EXPORTED_SYMBOL_FILE})
 # Adds -dead_strip option
 add_link_opts(libSwiftScan)

+if(SWIFT_HOST_VARIANT_SDK MATCHES "LINUX|ANDROID|OPENBSD|FREEBSD" AND SWIFT_USE_LINKER STREQUAL "lld")
+  target_link_options(libSwiftScan PRIVATE "LINKER:-z,nostart-stop-gc")
+endif()
+
 add_dependencies(compiler libSwiftScan)