Merge pull request #1596 from apple/revert-1545-ewilde/linker-selection

Revert "Update Generic Unix linker selection"

Author: etcwilde

Sources/SwiftDriver/Jobs/DarwinToolchain+LinkerSupport.swift

@@ -176,8 +176,8 @@ extension DarwinToolchain {
       }
     }
 
-    if let arg = parsedOptions.getLastArgument(.useLd)?.asSingle {
-      commandLine.appendFlag("-fuse-ld=\(arg)")
+    if let arg = parsedOptions.getLastArgument(.useLd) {
+      commandLine.appendFlag("-fuse-ld=\(arg.asSingle)")
     }
 
     if let arg = parsedOptions.getLastArgument(.ldPath)?.asSingle {

Sources/SwiftDriver/Jobs/GenericUnixToolchain+LinkerSupport.swift

@@ -16,6 +16,29 @@ import func TSCBasic.lookupExecutablePath
 import struct TSCBasic.AbsolutePath
 
 extension GenericUnixToolchain {
+  private func defaultLinker(for targetTriple: Triple) -> String? {
+    if targetTriple.os == .openbsd || targetTriple.os == .freeBSD ||
+         targetTriple.environment == .android ||
+         targetTriple.isFullyStaticLinux {
+      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 ""
+    }
+  }
+
   private func majorArchitectureName(for triple: Triple) -> String {
     // The concept of a "major" arch name only applies to Linux triples
     guard triple.os == .linux else { return triple.archName }
@@ -48,11 +71,35 @@ extension GenericUnixToolchain {
       commandLine.appendFlag("-shared")
       fallthrough
     case .executable:
-      // Select the linker to use.
-      if let arg = parsedOptions.getLastArgument(.useLd)?.asSingle {
-        commandLine.appendFlag("--fuse-ld=\(arg)")
+        // Select the linker to use.
+      var linker: String?
+      if let arg = parsedOptions.getLastArgument(.useLd) {
+        linker = arg.asSingle
       } else if lto != nil {
-        commandLine.appendFlag("--fuse-ld=lld")
+        linker = "lld"
+      } else {
+        linker = defaultLinker(for: targetTriple)
+      }
+
+      if let linker = linker {
+        #if os(Haiku)
+        // For now, passing -fuse-ld on Haiku doesn't work as swiftc doesn't
+        // recognise it. Passing -use-ld= as the argument works fine.
+        commandLine.appendFlag("-use-ld=\(linker)")
+        #else
+        commandLine.appendFlag("-fuse-ld=\(linker)")
+        #endif
+        // Starting with lld 13, Swift stopped working with the lld
+        // --gc-sections implementation for ELF, unless -z nostart-stop-gc is
+        // also passed to lld:
+        //
+        // https://reviews.llvm.org/D96914
+        if linker == "lld" || linker.hasSuffix("ld.lld") {
+          commandLine.appendFlag(.Xlinker)
+          commandLine.appendFlag("-z")
+          commandLine.appendFlag(.Xlinker)
+          commandLine.appendFlag("nostart-stop-gc")
+        }
       }
 
       if let arg = parsedOptions.getLastArgument(.ldPath)?.asSingle {

Sources/SwiftDriver/Jobs/WindowsToolchain+LinkerSupport.swift

@@ -99,8 +99,8 @@ extension WindowsToolchain {
     }
 
     // Select the linker to use.
-    if let arg = parsedOptions.getLastArgument(.useLd)?.asSingle {
-      commandLine.appendFlag("-fuse-ld=\(arg)")
+    if let arg = parsedOptions.getLastArgument(.useLd) {
+      commandLine.appendFlag("-fuse-ld=\(arg.asSingle)")
     } else if lto != nil {
       commandLine.appendFlag("-fuse-ld=lld")
     }

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -2368,11 +2368,20 @@ final class SwiftDriverTests: XCTestCase {
 
     do {
       // The Android NDK only uses the lld linker now
-      var driver = try Driver(args: commonArgs + ["-emit-library", "-target", "aarch64-unknown-linux-android24", "-use-ld=lld"], env: env)
+      var driver = try Driver(args: commonArgs + ["-emit-library", "-target", "aarch64-unknown-linux-android24"], env: env)
       let plannedJobs = try driver.planBuild().removingAutolinkExtractJobs()
       let lastJob = plannedJobs.last!
       XCTAssertTrue(lastJob.tool.name.contains("clang"))
-      XCTAssertTrue(lastJob.commandLine.contains(.flag("--fuse-ld=lld")))
+      XCTAssertTrue(lastJob.commandLine.contains(subsequence: [.flag("-fuse-ld=lld"),
+        .flag("-Xlinker"), .flag("-z"), .flag("-Xlinker"), .flag("nostart-stop-gc")]))
+    }
+
+    do {
+      var driver = try Driver(args: commonArgs + ["-emit-library", "-target", "x86_64-unknown-freebsd"], env: env)
+      let plannedJobs = try driver.planBuild().removingAutolinkExtractJobs()
+      let lastJob = plannedJobs.last!
+      XCTAssertTrue(lastJob.tool.name.contains("clang"))
+      XCTAssertTrue(lastJob.commandLine.contains(.flag("-fuse-ld=lld")))
     }
   }