diff --git a/src/main/java/com/google/devtools/build/docgen/RuleDocumentationAttribute.java b/src/main/java/com/google/devtools/build/docgen/RuleDocumentationAttribute.java
index 0d6f5d6..c68dae2 100644
--- a/src/main/java/com/google/devtools/build/docgen/RuleDocumentationAttribute.java
+++ b/src/main/java/com/google/devtools/build/docgen/RuleDocumentationAttribute.java
@@ -45,6 +45,8 @@
       .put(Type.TRISTATE, "Integer")
       .put(Type.LABEL, "<a href=\"build-ref.html#labels\">Label</a>")
       .put(Type.LABEL_LIST, "List of <a href=\"build-ref.html#labels\">labels</a>")
+      .put(Type.LABEL_DICT_UNARY,
+          "Dictionary mapping strings to <a href=\"build-ref.html#labels\">labels</a>")
       .put(Type.LABEL_LIST_DICT,
           "Dictionary mapping strings to lists of <a href=\"build-ref.html#labels\">labels</a>")
       .put(Type.NODEP_LABEL, "<a href=\"build-ref.html#name\">Name</a>")
diff --git a/src/main/java/com/google/devtools/build/lib/packages/PackageSerializer.java b/src/main/java/com/google/devtools/build/lib/packages/PackageSerializer.java
index 75067b7..16b318cb 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/PackageSerializer.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/PackageSerializer.java
@@ -19,6 +19,7 @@
 import static com.google.devtools.build.lib.packages.Type.INTEGER;
 import static com.google.devtools.build.lib.packages.Type.INTEGER_LIST;
 import static com.google.devtools.build.lib.packages.Type.LABEL;
+import static com.google.devtools.build.lib.packages.Type.LABEL_DICT_UNARY;
 import static com.google.devtools.build.lib.packages.Type.LABEL_LIST;
 import static com.google.devtools.build.lib.packages.Type.LABEL_LIST_DICT;
 import static com.google.devtools.build.lib.packages.Type.LICENSE;
@@ -252,6 +253,17 @@
           attrPb.addStringListDictValue(entry);
         }
       }
+    } else if (type == LABEL_DICT_UNARY) {
+      for (Object value : values) {
+        Map<String, Label> dict = (Map<String, Label>) value;
+        for (Map.Entry<String, Label> dictEntry : dict.entrySet()) {
+          Build.LabelDictUnaryEntry entry = Build.LabelDictUnaryEntry.newBuilder()
+              .setKey(dictEntry.getKey())
+              .setValue(dictEntry.getValue().toString())
+              .build();
+          attrPb.addLabelDictUnaryValue(entry);
+        }
+      }
     } else if (type == LABEL_LIST_DICT) {
       for (Object value : values) {
         Map<String, List<Label>> dict = (Map<String, List<Label>>) value;
diff --git a/src/main/java/com/google/devtools/build/lib/packages/ProtoUtils.java b/src/main/java/com/google/devtools/build/lib/packages/ProtoUtils.java
index 7b6eaf1..653e283 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/ProtoUtils.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/ProtoUtils.java
@@ -20,6 +20,7 @@
 import static com.google.devtools.build.lib.packages.Type.INTEGER;
 import static com.google.devtools.build.lib.packages.Type.INTEGER_LIST;
 import static com.google.devtools.build.lib.packages.Type.LABEL;
+import static com.google.devtools.build.lib.packages.Type.LABEL_DICT_UNARY;
 import static com.google.devtools.build.lib.packages.Type.LABEL_LIST;
 import static com.google.devtools.build.lib.packages.Type.LABEL_LIST_DICT;
 import static com.google.devtools.build.lib.packages.Type.LICENSE;
@@ -65,6 +66,7 @@
           .put(LICENSE, Discriminator.LICENSE)
           .put(STRING_DICT, Discriminator.STRING_DICT)
           .put(FILESET_ENTRY_LIST, Discriminator.FILESET_ENTRY_LIST)
+          .put(LABEL_DICT_UNARY, Discriminator.LABEL_DICT_UNARY)
           .put(LABEL_LIST_DICT, Discriminator.LABEL_LIST_DICT)
           .put(STRING_LIST_DICT, Discriminator.STRING_LIST_DICT)
           .put(BOOLEAN, Discriminator.BOOLEAN)
diff --git a/src/main/java/com/google/devtools/build/lib/packages/Type.java b/src/main/java/com/google/devtools/build/lib/packages/Type.java
index b1ca03e..9619162 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/Type.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/Type.java
@@ -336,6 +336,11 @@
       DictType.create(STRING, LABEL_LIST);
 
   /**
+   * The type of a dictionary of {@linkplain #LABEL labels}.
+   */
+  public static final DictType<String, Label> LABEL_DICT_UNARY = DictType.create(STRING, LABEL);
+
+  /**
    * The type of a list of {@linkplain #FILESET_ENTRY FilesetEntries}.
    */
   public static final ListType<FilesetEntry> FILESET_ENTRY_LIST = ListType.create(FILESET_ENTRY);
@@ -1003,7 +1008,7 @@
    * Returns whether the specified type is a label type or not.
    */
   public static boolean isLabelType(Type<?> type) {
-    return type == LABEL || type == LABEL_LIST
+    return type == LABEL || type == LABEL_LIST || type == LABEL_DICT_UNARY
         || type == NODEP_LABEL || type == NODEP_LABEL_LIST
         || type == LABEL_LIST_DICT || type == FILESET_ENTRY_LIST;
   }
diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CcToolchainSuite.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CcToolchainSuite.java
new file mode 100644
index 0000000..17d14fe
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CcToolchainSuite.java
@@ -0,0 +1,39 @@
+// Copyright 2015 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package com.google.devtools.build.lib.rules.cpp;
+
+import com.google.devtools.build.lib.actions.Artifact;
+import com.google.devtools.build.lib.analysis.ConfiguredTarget;
+import com.google.devtools.build.lib.analysis.RuleConfiguredTargetBuilder;
+import com.google.devtools.build.lib.analysis.RuleContext;
+import com.google.devtools.build.lib.collect.nestedset.NestedSetBuilder;
+import com.google.devtools.build.lib.collect.nestedset.Order;
+import com.google.devtools.build.lib.rules.RuleConfiguredTargetFactory;
+
+/**
+ * Implementation of the {@code cc_toolchain_suite} rule.
+ *
+ * <p>This is currently a no-op because the logic that transforms this rule into something that can
+ * be understood by the {@code cc_*} rules is in
+ * {@link com.google.devtools.build.lib.rules.cpp.CppConfigurationLoader}.
+ */
+public class CcToolchainSuite implements RuleConfiguredTargetFactory {
+
+  @Override
+  public ConfiguredTarget create(RuleContext ruleContext) throws InterruptedException {
+    return new RuleConfiguredTargetBuilder(ruleContext)
+        .setFilesToBuild(NestedSetBuilder.<Artifact>emptySet(Order.STABLE_ORDER))
+        .build();
+  }
+}
diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CcToolchainSuiteRule.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CcToolchainSuiteRule.java
new file mode 100644
index 0000000..9bc59c9
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CcToolchainSuiteRule.java
@@ -0,0 +1,50 @@
+// Copyright 2015 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package com.google.devtools.build.lib.rules.cpp;
+
+import static com.google.devtools.build.lib.packages.Attribute.attr;
+
+import com.google.devtools.build.lib.analysis.BaseRuleClasses;
+import com.google.devtools.build.lib.analysis.RuleDefinition;
+import com.google.devtools.build.lib.analysis.RuleDefinitionEnvironment;
+import com.google.devtools.build.lib.packages.RuleClass;
+import com.google.devtools.build.lib.packages.RuleClass.Builder;
+import com.google.devtools.build.lib.packages.Type;
+
+/**
+ * Definition of the {@code cc_toolchain_sute} rule.
+ */
+public final class CcToolchainSuiteRule implements RuleDefinition {
+
+  @Override
+  public RuleClass build(Builder builder, RuleDefinitionEnvironment environment) {
+    return builder
+        .setUndocumented()
+        .add(attr("toolchains", Type.LABEL_DICT_UNARY)
+            .mandatory()
+            .nonconfigurable("Used during configuration creation"))
+        .add(attr("proto", Type.STRING)
+            .nonconfigurable("Used during configuration creation"))
+        .build();
+  }
+
+  @Override
+  public Metadata getMetadata() {
+    return RuleDefinition.Metadata.builder()
+        .name("cc_toolchain_suite")
+        .ancestors(BaseRuleClasses.BaseRule.class)
+        .factoryClass(CcToolchainSuite.class)
+        .build();
+  }
+}
diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppConfigurationLoader.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppConfigurationLoader.java
index bf26f63..9d4818e 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppConfigurationLoader.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppConfigurationLoader.java
@@ -28,8 +28,10 @@
 import com.google.devtools.build.lib.packages.NoSuchPackageException;
 import com.google.devtools.build.lib.packages.NoSuchTargetException;
 import com.google.devtools.build.lib.packages.NoSuchThingException;
+import com.google.devtools.build.lib.packages.NonconfigurableAttributeMapper;
 import com.google.devtools.build.lib.packages.Rule;
 import com.google.devtools.build.lib.packages.Target;
+import com.google.devtools.build.lib.packages.Type;
 import com.google.devtools.build.lib.syntax.Label;
 import com.google.devtools.build.lib.syntax.Label.SyntaxException;
 import com.google.devtools.build.lib.vfs.Path;
@@ -108,13 +110,14 @@
     if (directories == null) {
       return null;
     }
-    Label crosstoolTop = RedirectChaser.followRedirects(env,
+    Label crosstoolTopLabel = RedirectChaser.followRedirects(env,
         options.get(CppOptions.class).crosstoolTop, "crosstool_top");
-    if (crosstoolTop == null) {
+    if (crosstoolTopLabel == null) {
       return null;
     }
+
     CrosstoolConfigurationLoader.CrosstoolFile file =
-        CrosstoolConfigurationLoader.readCrosstool(env, crosstoolTop);
+        CrosstoolConfigurationLoader.readCrosstool(env, crosstoolTopLabel);
     if (file == null) {
       return null;
     }
@@ -150,12 +153,33 @@
     }
 
     Label ccToolchainLabel;
+    Target crosstoolTop;
+
     try {
-      ccToolchainLabel = crosstoolTop.getRelative("cc-compiler-" + toolchain.getTargetCpu());
-    } catch (Label.SyntaxException e) {
-      throw new InvalidConfigurationException(String.format(
-          "'%s' is not a valid CPU. It should only consist of characters valid in labels",
-          toolchain.getTargetCpu()));
+      crosstoolTop = env.getTarget(crosstoolTopLabel);
+    } catch (NoSuchThingException e) {
+      throw new IllegalStateException(e);  // Should have been found out during redirect chasing
+    }
+
+    if (crosstoolTop instanceof Rule
+        && ((Rule) crosstoolTop).getRuleClass().equals("cc_toolchain_suite")) {
+      Rule ccToolchainSuite = (Rule) crosstoolTop;
+      ccToolchainLabel = NonconfigurableAttributeMapper.of(ccToolchainSuite)
+          .get("toolchains", Type.LABEL_DICT_UNARY)
+          .get(toolchain.getTargetCpu());
+      if (ccToolchainLabel == null) {
+        throw new InvalidConfigurationException(String.format(
+            "cc_toolchain_suite '%s' does not contain a toolchain for CPU '%s'",
+            crosstoolTopLabel, toolchain.getTargetCpu()));
+      }
+    } else {
+      try {
+        ccToolchainLabel = crosstoolTopLabel.getRelative("cc-compiler-" + toolchain.getTargetCpu());
+      } catch (Label.SyntaxException e) {
+        throw new InvalidConfigurationException(String.format(
+            "'%s' is not a valid CPU. It should only consist of characters valid in labels",
+            toolchain.getTargetCpu()));
+      }
     }
 
     Target ccToolchain;
@@ -176,6 +200,6 @@
     }
 
     return new CppConfigurationParameters(toolchain, file.getMd5(), options,
-        fdoZip, directories.getExecRoot(), crosstoolTop, ccToolchainLabel);
+        fdoZip, directories.getExecRoot(), crosstoolTopLabel, ccToolchainLabel);
   }
 }
diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CrosstoolConfigurationLoader.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CrosstoolConfigurationLoader.java
index a113f5f..e595758 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CrosstoolConfigurationLoader.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CrosstoolConfigurationLoader.java
@@ -14,24 +14,30 @@
 
 package com.google.devtools.build.lib.rules.cpp;
 
+import static java.nio.charset.StandardCharsets.UTF_8;
+
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Function;
+import com.google.common.cache.Cache;
 import com.google.common.cache.CacheBuilder;
-import com.google.common.cache.CacheLoader;
-import com.google.common.cache.LoadingCache;
 import com.google.common.io.BaseEncoding;
 import com.google.devtools.build.lib.analysis.RedirectChaser;
 import com.google.devtools.build.lib.analysis.config.BuildOptions;
 import com.google.devtools.build.lib.analysis.config.ConfigurationEnvironment;
 import com.google.devtools.build.lib.analysis.config.InvalidConfigurationException;
 import com.google.devtools.build.lib.packages.NoSuchThingException;
+import com.google.devtools.build.lib.packages.NonconfigurableAttributeMapper;
 import com.google.devtools.build.lib.packages.Package;
+import com.google.devtools.build.lib.packages.Rule;
+import com.google.devtools.build.lib.packages.Target;
+import com.google.devtools.build.lib.packages.Type;
 import com.google.devtools.build.lib.syntax.Label;
 import com.google.devtools.build.lib.syntax.Label.SyntaxException;
-import com.google.devtools.build.lib.util.Pair;
+import com.google.devtools.build.lib.util.Fingerprint;
 import com.google.devtools.build.lib.vfs.FileSystemUtils;
 import com.google.devtools.build.lib.vfs.Path;
 import com.google.devtools.build.lib.view.config.crosstool.CrosstoolConfig;
+import com.google.devtools.build.lib.view.config.crosstool.CrosstoolConfig.CrosstoolRelease;
 import com.google.protobuf.TextFormat;
 import com.google.protobuf.TextFormat.ParseException;
 import com.google.protobuf.UninitializedMessageException;
@@ -39,6 +45,7 @@
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.concurrent.Callable;
 import java.util.concurrent.ExecutionException;
 
 import javax.annotation.Nullable;
@@ -46,6 +53,10 @@
 /**
  * A loader that reads Crosstool configuration files and creates CToolchain
  * instances from them.
+ *
+ * <p>Note that this class contains a cache for the text format -> proto objects mapping of
+ * Crosstool protos that is completely independent from Skyframe or anything else. This should be
+ * done in a saner way.
  */
 public class CrosstoolConfigurationLoader {
   private static final String CROSSTOOL_CONFIGURATION_FILENAME = "CROSSTOOL";
@@ -54,53 +65,27 @@
    * Cache for storing result of toReleaseConfiguration function based on path and md5 sum of
    * input file. We can use md5 because result of this function depends only on the file content.
    */
-  private static final LoadingCache<Pair<Path, String>, CrosstoolConfig.CrosstoolRelease> 
-      crosstoolReleaseCache = CacheBuilder.newBuilder().concurrencyLevel(4).maximumSize(100).build(
-        new CacheLoader<Pair<Path, String>, CrosstoolConfig.CrosstoolRelease>() {
-          @Override
-          public CrosstoolConfig.CrosstoolRelease load(Pair<Path, String> key) throws IOException {
-            char[] data = FileSystemUtils.readContentAsLatin1(key.first);
-            return toReleaseConfiguration(key.first.getPathString(), new String(data));
-          }
-        });
-
+  private static final Cache<String, CrosstoolRelease> crosstoolReleaseCache =
+      CacheBuilder.newBuilder().concurrencyLevel(4).maximumSize(100).build();
   /**
    * A class that holds the results of reading a CROSSTOOL file.
    */
   public static class CrosstoolFile {
-    private final Label crosstoolTop;
-    private Path crosstoolPath;
-    private CrosstoolConfig.CrosstoolRelease crosstool;
-    private String md5;
+    private final String location;
+    private final CrosstoolConfig.CrosstoolRelease crosstool;
+    private final String md5;
 
-    CrosstoolFile(Label crosstoolTop) {
-      this.crosstoolTop = crosstoolTop;
-    }
-
-    void setCrosstoolPath(Path crosstoolPath) {
-      this.crosstoolPath = crosstoolPath;
-    }
-
-    void setCrosstool(CrosstoolConfig.CrosstoolRelease crosstool) {
+    CrosstoolFile(String location, CrosstoolConfig.CrosstoolRelease crosstool, String md5) {
+      this.location = location;
       this.crosstool = crosstool;
-    }
-
-    void setMd5(String md5) {
       this.md5 = md5;
     }
 
     /**
-     * Returns the crosstool top as resolved.
+     * Returns a user-friendly location of the CROSSTOOL proto for error messages.
      */
-    public Label getCrosstoolTop() {
-      return crosstoolTop;
-    }
-
-    /**
-     * Returns the absolute path from which the CROSSTOOL file was read.
-     */
-    public Path getCrosstoolPath() {
-      return crosstoolPath;
+    public String getLocation() {
+      return location;
     }
 
     /**
@@ -145,27 +130,115 @@
     }
   }
 
-  private static boolean findCrosstoolConfiguration(
-      ConfigurationEnvironment env,
-      CrosstoolConfigurationLoader.CrosstoolFile file)
+  /**
+   * This class is the in-memory representation of a text-formatted Crosstool proto file.
+   *
+   * <p>This layer of abstraction is here so that we can load these protos either from BUILD files
+   * or from CROSSTOOL files.
+   *
+   * <p>An implementation of this class should override {@link #getContents()} and call
+   * the constructor with the MD5 checksum of what that method will return and a human-readable name
+   * used in error messages.
+   */
+  private abstract static class CrosstoolProto {
+    private final byte[] md5;
+    private final String name;
+
+    private CrosstoolProto(byte[] md5, String name) {
+      this.md5 = md5;
+      this.name = name;
+    }
+
+    /**
+     * The binary MD5 checksum of the proto.
+     */
+    public byte[] getMd5() {
+      return md5;
+    }
+
+    /**
+     * A user-friendly string describing the location of the proto.
+     */
+    public String getName() {
+      return name;
+    }
+
+    /**
+     * The proto itself.
+     */
+    public abstract String getContents() throws IOException;
+  }
+
+  private static CrosstoolProto getCrosstoolProtofromBuildFile(
+      ConfigurationEnvironment env, Label crosstoolTop) {
+    Target target;
+    try {
+      target = env.getTarget(crosstoolTop);
+    } catch (NoSuchThingException e) {
+      throw new IllegalStateException(e);  // Should have beeen evaluated by RedirectChaser
+    }
+
+    if (!(target instanceof Rule)) {
+      return null;
+    }
+
+    Rule rule = (Rule) target;
+    if (!(rule.getRuleClass().equals("cc_toolchain_suite"))
+        || !rule.isAttributeValueExplicitlySpecified("proto")) {
+      return null;
+    }
+
+    final String contents = NonconfigurableAttributeMapper.of(rule).get("proto", Type.STRING);
+    byte[] md5 = new Fingerprint().addBytes(contents.getBytes(UTF_8)).digestAndReset();
+    return new CrosstoolProto(md5, "cc_toolchain_suite rule " + crosstoolTop.toString()) {
+
+      @Override
+      public String getContents() throws IOException {
+        return contents;
+      }
+    };
+  }
+
+  private static CrosstoolProto getCrosstoolProtoFromCrosstoolFile(
+      ConfigurationEnvironment env, Label crosstoolTop)
       throws IOException, InvalidConfigurationException {
-    Label crosstoolTop = file.getCrosstoolTop();
-    Path path = null;
+    final Path path;
     try {
       Package containingPackage = env.getTarget(crosstoolTop.getLocalTargetLabel("BUILD"))
           .getPackage();
       if (containingPackage == null) {
-        return false;
+        return null;
       }
       path = env.getPath(containingPackage, CROSSTOOL_CONFIGURATION_FILENAME);
     } catch (SyntaxException e) {
       throw new InvalidConfigurationException(e);
     } catch (NoSuchThingException e) {
       // Handled later
+      return null;
     }
 
-    // If we can't find a file, fall back to the provided alternative.
     if (path == null || !path.exists()) {
+      return null;
+    }
+
+    return new CrosstoolProto(path.getMD5Digest(), "CROSSTOOL file " + path.getPathString()) {
+      @Override
+      public String getContents() throws IOException {
+        return new String(FileSystemUtils.readContentAsLatin1(path.getInputStream()));
+      }
+    };
+  }
+
+  private static CrosstoolFile findCrosstoolConfiguration(
+      ConfigurationEnvironment env, Label crosstoolTop)
+      throws IOException, InvalidConfigurationException {
+
+    CrosstoolProto crosstoolProto = getCrosstoolProtofromBuildFile(env, crosstoolTop);
+    if (crosstoolProto == null) {
+      crosstoolProto = getCrosstoolProtoFromCrosstoolFile(env, crosstoolTop);
+    }
+
+    if (crosstoolProto == null) {
       throw new InvalidConfigurationException("The crosstool_top you specified was resolved to '" +
           crosstoolTop + "', which does not contain a CROSSTOOL file. " +
           "You can use a crosstool from the depot by specifying its label.");
@@ -173,18 +246,22 @@
       // Do this before we read the data, so if it changes, we get a different MD5 the next time.
       // Alternatively, we could calculate the MD5 of the contents, which we also read, but this
       // is faster if the file comes from a file system with md5 support.
-      file.setCrosstoolPath(path);
-      String md5 = BaseEncoding.base16().lowerCase().encode(path.getMD5Digest());
+      final CrosstoolProto finalProto = crosstoolProto;
+      String md5 = BaseEncoding.base16().lowerCase().encode(finalProto.getMd5());
       CrosstoolConfig.CrosstoolRelease release;
       try {
-        release = crosstoolReleaseCache.get(new Pair<Path, String>(path, md5));
-        file.setCrosstool(release);
-        file.setMd5(md5);
+        release = crosstoolReleaseCache.get(md5, new Callable<CrosstoolRelease>() {
+          @Override
+          public CrosstoolRelease call() throws Exception {
+            return toReleaseConfiguration(finalProto.getName(), finalProto.getContents());
+          }
+        });
       } catch (ExecutionException e) {
         throw new InvalidConfigurationException(e);
       }
+
+      return new CrosstoolFile(finalProto.getName(), release, md5);
     }
-    return true;
   }
 
   /**
@@ -197,11 +274,8 @@
     if (crosstoolTop == null) {
       return null;
     }
-    CrosstoolConfigurationLoader.CrosstoolFile file =
-        new CrosstoolConfigurationLoader.CrosstoolFile(crosstoolTop);
     try {
-      boolean allDependenciesPresent = findCrosstoolConfiguration(env, file);
-      return allDependenciesPresent ? file : null;
+      return findCrosstoolConfiguration(env, crosstoolTop);
     } catch (IOException e) {
       throw new InvalidConfigurationException(e);
     }
diff --git a/src/main/protobuf/build.proto b/src/main/protobuf/build.proto
index a84df42..6780d4d 100644
--- a/src/main/protobuf/build.proto
+++ b/src/main/protobuf/build.proto
@@ -38,6 +38,11 @@
   required string value = 2;
 }
 
+message LabelDictUnaryEntry {
+  required string key = 1;
+  required string value = 2;
+}
+
 message LabelListDictEntry {
   required string key = 1;
   repeated string value = 2;
@@ -112,6 +117,7 @@
     INTEGER_LIST = 16;       // int_list_value
     STRING_DICT_UNARY = 17;  // string_dict_unary_value
     UNKNOWN = 18;            // unknown type, use only for build extensions
+    LABEL_DICT_UNARY = 19;   // label_dict_unary_value
   }
 
   // Values for the TriState field type.
@@ -186,6 +192,9 @@
 
   // If this is a string dict unary, each entry will be stored here.
   repeated StringDictUnaryEntry string_dict_unary_value = 18;
+
+  // If this is a label dict unary, each entry will be stored here.
+  repeated LabelDictUnaryEntry label_dict_unary_value = 19;
 }
 
 // A rule from a BUILD file (e.g., cc_library, java_binary).  The rule class