Index: clang/lib/Driver/ToolChains/AVR.cpp
===================================================================
--- clang/lib/Driver/ToolChains/AVR.cpp
+++ clang/lib/Driver/ToolChains/AVR.cpp
@@ -297,8 +297,8 @@
 }
 
 const StringRef PossibleAVRLibcLocations[] = {
-    "/usr/avr",
-    "/usr/lib/avr",
+    "/avr",
+    "/lib/avr",
 };
 
 } // end anonymous namespace
@@ -334,10 +334,17 @@
         // No avr-libc found and so no runtime linked.
         D.Diag(diag::warn_drv_avr_libc_not_found);
       } else { // We have enough information to link stdlibs
-        std::string GCCRoot = std::string(GCCInstallation.getInstallPath());
+        std::string GCCRoot(GCCInstallation.getInstallPath());
+        std::string ParentLibPath(GCCInstallation.getParentLibPath());
         std::string LibcRoot = AVRLibcRoot.getValue();
         std::string SubPath = GetMCUSubPath(CPU);
 
+        // Use user specified program path (via --sysroot) as the first choice,
+        // and use GCCInstallation's as an alternative.
+        if (!getDriver().SysRoot.empty())
+          getProgramPaths().push_back(getDriver().SysRoot + "/bin");
+        getProgramPaths().push_back(ParentLibPath + "/../bin");
+
         getFilePaths().push_back(LibcRoot + std::string("/lib/") + SubPath);
         getFilePaths().push_back(GCCRoot + std::string("/") + SubPath);
 
@@ -419,9 +426,14 @@
 
 llvm::Optional<std::string> AVRToolChain::findAVRLibcInstallation() const {
   for (StringRef PossiblePath : PossibleAVRLibcLocations) {
+    // Use user specified avr-libc path (via --sysroot) if available, otherwise
+    // search '/usr'.
+    std::string Path(getDriver().SysRoot.empty() ? "/usr"
+                                                 : getDriver().SysRoot);
+    Path += PossiblePath.str();
     // Return the first avr-libc installation that exists.
-    if (llvm::sys::fs::is_directory(PossiblePath))
-      return Optional<std::string>(std::string(PossiblePath));
+    if (llvm::sys::fs::is_directory(Path))
+      return Optional<std::string>(Path);
   }
 
   return llvm::None;
Index: clang/test/Driver/avr-ld.c
===================================================================
--- /dev/null
+++ clang/test/Driver/avr-ld.c
@@ -0,0 +1,2 @@
+// RUN: %clang -### --target=avr -mmcu=atmega328 --sysroot %S/Inputs/basic_avr_tree %s 2>&1 | FileCheck -check-prefix LINK %s
+// LINK: {{".*ld.*"}} {{.*}} {{"-L.*avr5"}} {{.*}} "-Tdata=0x800100" {{.*}} "-latmega328" "-mavr5"