Index: cfe/trunk/lib/Tooling/Tooling.cpp
===================================================================
--- cfe/trunk/lib/Tooling/Tooling.cpp
+++ cfe/trunk/lib/Tooling/Tooling.cpp
@@ -338,17 +338,22 @@
   ArgsAdjuster = nullptr;
 }
 
+static void injectResourceDir(CommandLineArguments &Args, const char *Argv0,
+                              void *MainAddr) {
+  // Allow users to override the resource dir.
+  for (StringRef Arg : Args)
+    if (Arg.startswith("-resource-dir"))
+      return;
+
+  // If there's no override in place add our resource dir.
+  Args.push_back("-resource-dir=" +
+                 CompilerInvocation::GetResourcesPath(Argv0, MainAddr));
+}
+
 int ClangTool::run(ToolAction *Action) {
   // Exists solely for the purpose of lookup of the resource path.
   // This just needs to be some symbol in the binary.
   static int StaticSymbol;
-  // The driver detects the builtin header path based on the path of the
-  // executable.
-  // FIXME: On linux, GetMainExecutable is independent of the value of the
-  // first argument, thus allowing ClangTool and runToolOnCode to just
-  // pass in made-up names here. Make sure this works on other platforms.
-  std::string MainExecutable =
-      llvm::sys::fs::getMainExecutable("clang_tool", &StaticSymbol);
 
   llvm::SmallString<128> InitialDirectory;
   if (std::error_code EC = llvm::sys::fs::current_path(InitialDirectory))
@@ -413,7 +418,17 @@
       if (ArgsAdjuster)
         CommandLine = ArgsAdjuster(CommandLine, CompileCommand.Filename);
       assert(!CommandLine.empty());
-      CommandLine[0] = MainExecutable;
+
+      // Add the resource dir based on the binary of this tool. argv[0] in the
+      // compilation database may refer to a different compiler and we want to
+      // pick up the very same standard library that compiler is using. The
+      // builtin headers in the resource dir need to match the exact clang
+      // version the tool is using.
+      // FIXME: On linux, GetMainExecutable is independent of the value of the
+      // first argument, thus allowing ClangTool and runToolOnCode to just
+      // pass in made-up names here. Make sure this works on other platforms.
+      injectResourceDir(CommandLine, "clang_tool", &StaticSymbol);
+
       // FIXME: We need a callback mechanism for the tool writer to output a
       // customized message for each file.
       DEBUG({ llvm::dbgs() << "Processing: " << File << ".\n"; });
Index: cfe/trunk/test/Tooling/clang-check-builtin-headers.cpp
===================================================================
--- cfe/trunk/test/Tooling/clang-check-builtin-headers.cpp
+++ cfe/trunk/test/Tooling/clang-check-builtin-headers.cpp
@@ -4,9 +4,11 @@
 // RUN: echo '[{"directory":".","command":"/random/tool -c %t/test.cpp","file":"%t/test.cpp"}]' | sed -e 's/\\/\//g' > %t/compile_commands.json
 // RUN: cp "%s" "%t/test.cpp"
 // RUN: not clang-check -p "%t" "%t/test.cpp" 2>&1|FileCheck %s
+// RUN: not clang-check -p "%t" "%t/test.cpp" -extra-arg=-resource-dir=foo 2>&1|FileCheck %s -check-prefix=CHECK-NOHDR
 // FIXME: Make the above easier.
 
 #include <stddef.h>
 
 // CHECK: C++ requires
+// CHECK-NOHDR: fatal error: 'stddef.h' file not
 invalid;