[cfe-dev] Adding -fuse-ld= support to clang

[David Chisnall]

Hi Everyone,

In FreeBSD, we are about to start the process of migrating from (ancient) BFD ld to MCLinker, so we're going to need support for multiple linkers for a while.  It turns out that gcc already has an option to select linkers, so I have attempted to remain compatible in the attached patch.  This adds a -fuse-ld={name} option, which takes a string as an argument.  The toolchains then request a linker and get either ld.{name}, ld-{name}, or {name} as the linker.  

Does anyone have objections to committing this as-is, or would anyone like to recommend a better approach?

David

Index: include/clang/Basic/DiagnosticDriverKinds.td
===================================================================
--- include/clang/Basic/DiagnosticDriverKinds.td	(revision 182184)
+++ include/clang/Basic/DiagnosticDriverKinds.td	(working copy)
@@ -26,6 +26,8 @@
   "unsupported runtime library '%0' for platform '%1'">;
 def err_drv_invalid_stdlib_name : Error<
   "invalid library name in argument '%0'">;
+def err_drv_invalid_linker_name : Error<
+  "invalid linker name in argument '%0'">;
 def err_drv_invalid_opt_with_multiple_archs : Error<
   "option '%0' cannot be used with multiple -arch options">;
 def err_drv_invalid_output_with_multiple_archs : Error<
Index: include/clang/Driver/Options.td
===================================================================
--- include/clang/Driver/Options.td	(revision 182184)
+++ include/clang/Driver/Options.td	(working copy)
@@ -744,6 +744,8 @@
 def fuse_cxa_atexit : Flag<["-"], "fuse-cxa-atexit">, Group<f_Group>;
 def fuse_init_array : Flag<["-"], "fuse-init-array">, Group<f_Group>, Flags<[CC1Option]>,
   HelpText<"Use .init_array instead of .ctors">;
+def fuse_ld_EQ : Joined<["-", "--"], "fuse-ld=">, Group<f_Group>,
+  HelpText<"The linker to use.">;
 def fverbose_asm : Flag<["-"], "fverbose-asm">, Group<f_Group>;
 def fvisibility_EQ : Joined<["-"], "fvisibility=">, Group<f_Group>,
   HelpText<"Set the default symbol visibility for all global declarations">;
Index: include/clang/Driver/ToolChain.h
===================================================================
--- include/clang/Driver/ToolChain.h	(revision 182184)
+++ include/clang/Driver/ToolChain.h	(working copy)
@@ -136,6 +136,9 @@
 
   std::string GetFilePath(const char *Name) const;
   std::string GetProgramPath(const char *Name) const;
+  /// Returns the linker path, respecting the -fuse-ld= argument to determine
+  /// the linker suffix or name.
+  std::string GetLinkerPath() const;
 
   // Platform defaults information
 
Index: lib/Driver/ToolChain.cpp
===================================================================
--- lib/Driver/ToolChain.cpp	(revision 182184)
+++ lib/Driver/ToolChain.cpp	(working copy)
@@ -132,6 +132,36 @@
 
 }
 
+std::string ToolChain::GetLinkerPath() const {
+  if (Arg *A = Args.getLastArg(options::OPT_fuse_ld_EQ)) {
+    StringRef Value = A->getValue();
+    // If we're passed -fuse-ld= with no argument, or with the argument ld,
+    // then use whatever the default system linker is.
+    if (Value.empty() || Value == "ld")
+      return GetFilePath("ld");
+    std::string LinkerName = Value.str();
+    std::string LD("ld.");
+    LD += LinkerName;
+    std::string LinkerPath = GetFilePath(LD.c_str());
+    bool Exists;
+    if (!llvm::sys::fs::exists(LinkerPath, Exists) && Exists)
+      return LinkerPath;
+    LD = std::string("ld-") + LinkerName;
+    LinkerPath = GetFilePath(LD.c_str());
+    if (!llvm::sys::fs::exists(LinkerPath, Exists) && Exists)
+      return LinkerPath;
+    LinkerPath = GetFilePath(LinkerName.c_str());
+    if (!llvm::sys::fs::exists(LinkerPath, Exists) && Exists)
+      return LinkerPath;
+    getDriver().Diag(diag::err_drv_invalid_linker_name)
+      << A->getAsString(Args);
+    // Fall through and run the system linker - we could do a hard error here,
+    // but we may as well try and see if it works.
+  }
+  return GetFilePath("ld");
+}
+
+
 std::string ToolChain::GetProgramPath(const char *Name) const {
   return D.GetProgramPath(Name, *this);
 }
Index: lib/Driver/Tools.cpp
===================================================================
--- lib/Driver/Tools.cpp	(revision 182184)
+++ lib/Driver/Tools.cpp	(working copy)
@@ -5219,8 +5219,7 @@
                               getToolChain().GetFilePath("crtendS.o")));
   }
 
-  const char *Exec =
-    Args.MakeArgString(getToolChain().GetProgramPath("ld"));
+  const char *Exec = Args.MakeArgString(getToolChain().GetLinkerPath());
   C.addCommand(new Command(JA, *this, Exec, CmdArgs));
 }
 
@@ -5361,8 +5360,7 @@
                               getToolChain().GetFilePath("crtendS.o")));
   }
 
-  const char *Exec =
-    Args.MakeArgString(getToolChain().GetProgramPath("ld"));
+  const char *Exec = Args.MakeArgString(getToolChain().GetLinkerPath());
   C.addCommand(new Command(JA, *this, Exec, CmdArgs));
 }
 
@@ -5612,8 +5610,7 @@
 
   addProfileRT(ToolChain, Args, CmdArgs, ToolChain.getTriple());
 
-  const char *Exec =
-    Args.MakeArgString(ToolChain.GetProgramPath("ld"));
+  const char *Exec = Args.MakeArgString(getToolChain().GetLinkerPath());
   C.addCommand(new Command(JA, *this, Exec, CmdArgs));
 }
 
@@ -5762,7 +5759,7 @@
 
   addProfileRT(getToolChain(), Args, CmdArgs, getToolChain().getTriple());
 
-  const char *Exec = Args.MakeArgString(getToolChain().GetProgramPath("ld"));
+  const char *Exec = Args.MakeArgString(getToolChain().GetLinkerPath());
   C.addCommand(new Command(JA, *this, Exec, CmdArgs));
 }
 
@@ -6247,7 +6244,7 @@
          Args.MakeArgString(getToolChain().GetFilePath("crtend.o")));
   }
 
-  const char *Exec = Args.MakeArgString(getToolChain().GetProgramPath("ld"));
+  const char *Exec = Args.MakeArgString(getToolChain().GetLinkerPath());
   C.addCommand(new Command(JA, *this, Exec, CmdArgs));
 }
 
@@ -6430,8 +6427,7 @@
 
   addProfileRT(getToolChain(), Args, CmdArgs, getToolChain().getTriple());
 
-  const char *Exec =
-    Args.MakeArgString(getToolChain().GetProgramPath("ld"));
+  const char *Exec = Args.MakeArgString(getToolChain().GetLinkerPath());
   C.addCommand(new Command(JA, *this, Exec, CmdArgs));
 }
 
Index: test/Driver/fuse_ld.c
===================================================================
--- test/Driver/fuse_ld.c	(revision 0)
+++ test/Driver/fuse_ld.c	(working copy)
@@ -0,0 +1,7 @@
+// RUN: rm -f ld.foo
+// RUN: %clang %s -target i386-unknown-freebsd -fuse-ld=foo -### 2>&1 | FileCheck -check-prefix=MISSING %s
+// RUN: touch ld.foo
+// RUN: %clang %s -B. -target i386-unknown-freebsd -fuse-ld=foo -### 2>&1 | FileCheck -check-prefix=FOUND %s
+
+// CHECK-MISSING: error: invalid linker name in argument '-fuse-ld=foo'
+// CHECK-FOUND: "./ld.foo"