[Driver] Allow setting the default linker during build

This change allows setting the default linker used by the Clang
driver when configuring the build.

Differential Revision: https://reviews.llvm.org/D25263

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@289668 91177308-0d34-0410-b5e6-96231b3b80d8

CMakeLists.txt

@@ -198,6 +198,9 @@ set(ENABLE_LINKER_BUILD_ID OFF CACHE BOOL "pass --build-id to ld")
 set(ENABLE_X86_RELAX_RELOCATIONS OFF CACHE BOOL
     "enable x86 relax relocations by default")
 
+set(CLANG_DEFAULT_LINKER "" CACHE STRING
+  "Default linker to use (linker name or absolute path, empty for platform default)")
+
 set(CLANG_DEFAULT_CXX_STDLIB "" CACHE STRING
   "Default C++ stdlib to use (\"libstdc++\" or \"libc++\", empty for platform default")
 if (NOT(CLANG_DEFAULT_CXX_STDLIB STREQUAL "" OR

include/clang/Config/config.h.cmake

@@ -8,6 +8,9 @@
 /* Bug report URL. */
 #define BUG_REPORT_URL "${BUG_REPORT_URL}"
 
+/* Default linker to use. */
+#define CLANG_DEFAULT_LINKER "${CLANG_DEFAULT_LINKER}"
+
 /* Default C++ stdlib to use. */
 #define CLANG_DEFAULT_CXX_STDLIB "${CLANG_DEFAULT_CXX_STDLIB}"
 

include/clang/Driver/ToolChain.h

@@ -105,7 +105,6 @@ class ToolChain {
 
 protected:
   MultilibSet Multilibs;
-  const char *DefaultLinker = "ld";
 
   ToolChain(const Driver &D, const llvm::Triple &T,
             const llvm::opt::ArgList &Args);
@@ -272,6 +271,11 @@ class ToolChain {
     return 0;
   }
 
+  /// GetDefaultLinker - Get the default linker to use.
+  virtual const char *getDefaultLinker() const {
+    return "ld";
+  }
+
   /// GetDefaultRuntimeLibType - Get the default runtime library variant to use.
   virtual RuntimeLibType GetDefaultRuntimeLibType() const {
     return ToolChain::RLT_Libgcc;

lib/Driver/ToolChain.cpp

@@ -351,33 +351,31 @@ std::string ToolChain::GetProgramPath(const char *Name) const {
 }
 
 std::string ToolChain::GetLinkerPath() const {
-  if (Arg *A = Args.getLastArg(options::OPT_fuse_ld_EQ)) {
-    StringRef UseLinker = A->getValue();
-
-    if (llvm::sys::path::is_absolute(UseLinker)) {
-      // If we're passed -fuse-ld= with what looks like an absolute path,
-      // don't attempt to second-guess that.
-      if (llvm::sys::fs::exists(UseLinker))
-        return UseLinker;
-    } else {
-      // If we're passed -fuse-ld= with no argument, or with the argument ld,
-      // then use whatever the default system linker is.
-      if (UseLinker.empty() || UseLinker == "ld")
-        return GetProgramPath("ld");
-
-      llvm::SmallString<8> LinkerName("ld.");
-      LinkerName.append(UseLinker);
-
-      std::string LinkerPath(GetProgramPath(LinkerName.c_str()));
-      if (llvm::sys::fs::exists(LinkerPath))
-        return LinkerPath;
-    }
+  const Arg* A = Args.getLastArg(options::OPT_fuse_ld_EQ);
+  StringRef UseLinker = A ? A->getValue() : CLANG_DEFAULT_LINKER;
+
+  if (llvm::sys::path::is_absolute(UseLinker)) {
+    // If we're passed what looks like an absolute path, don't attempt to
+    // second-guess that.
+    if (llvm::sys::fs::exists(UseLinker))
+      return UseLinker;
+  } else if (UseLinker.empty() || UseLinker == "ld") {
+    // If we're passed -fuse-ld= with no argument, or with the argument ld,
+    // then use whatever the default system linker is.
+    return GetProgramPath(getDefaultLinker());
+  } else {
+    llvm::SmallString<8> LinkerName("ld.");
+    LinkerName.append(UseLinker);
+
+    std::string LinkerPath(GetProgramPath(LinkerName.c_str()));
+    if (llvm::sys::fs::exists(LinkerPath))
+      return LinkerPath;
+  }
 
+  if (A)
     getDriver().Diag(diag::err_drv_invalid_linker_name) << A->getAsString(Args);
-    return "";
-  }
 
-  return GetProgramPath(DefaultLinker);
+  return GetProgramPath(getDefaultLinker());
 }
 
 types::ID ToolChain::LookupTypeForExtension(StringRef Ext) const {

lib/Driver/ToolChains.cpp

@@ -3059,9 +3059,6 @@ MipsLLVMToolChain::MipsLLVMToolChain(const Driver &D,
   LibSuffix = tools::mips::getMipsABILibSuffix(Args, Triple);
   getFilePaths().clear();
   getFilePaths().push_back(computeSysRoot() + "/usr/lib" + LibSuffix);
-
-  // Use LLD by default.
-  DefaultLinker = "lld";
 }
 
 void MipsLLVMToolChain::AddClangSystemIncludeArgs(
@@ -4749,9 +4746,6 @@ Fuchsia::Fuchsia(const Driver &D, const llvm::Triple &Triple,
 
   getFilePaths().push_back(D.SysRoot + "/lib");
   getFilePaths().push_back(D.ResourceDir + "/lib/fuchsia");
-
-  // Use LLD by default.
-  DefaultLinker = "lld";
 }
 
 Tool *Fuchsia::buildAssembler() const {
@@ -5173,9 +5167,6 @@ WebAssembly::WebAssembly(const Driver &D, const llvm::Triple &Triple,
   assert(Triple.isArch32Bit() != Triple.isArch64Bit());
   getFilePaths().push_back(
       getDriver().SysRoot + "/lib" + (Triple.isArch32Bit() ? "32" : "64"));
-
-  // Use LLD by default.
-  DefaultLinker = "lld";
 }
 
 bool WebAssembly::IsMathErrnoDefault() const { return false; }

lib/Driver/ToolChains.h

@@ -961,6 +961,10 @@ class LLVM_LIBRARY_VISIBILITY MipsLLVMToolChain : public Linux {
                                      : RuntimeLibType::RLT_CompilerRT;
   }
 
+  const char *getDefaultLinker() const override {
+    return "lld";
+  }
+
 private:
   Multilib SelectedMultilib;
   std::string LibSuffix;
@@ -1090,6 +1094,10 @@ class LLVM_LIBRARY_VISIBILITY Fuchsia : public Generic_ELF {
   void AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
                            llvm::opt::ArgStringList &CmdArgs) const override;
 
+  const char *getDefaultLinker() const override {
+    return "lld";
+  }
+
 protected:
   Tool *buildAssembler() const override;
   Tool *buildLinker() const override;
@@ -1289,6 +1297,10 @@ class LLVM_LIBRARY_VISIBILITY WebAssembly final : public ToolChain {
       const llvm::opt::ArgList &DriverArgs,
       llvm::opt::ArgStringList &CC1Args) const override;
 
+  const char *getDefaultLinker() const override {
+    return "lld";
+  }
+
   Tool *buildLinker() const override;
 };