diff --git a/site-tools/update-doc-list.php b/site-tools/update-doc-list.php
index f189a64d..5afbd218 100644
--- a/site-tools/update-doc-list.php
+++ b/site-tools/update-doc-list.php
@@ -1,13 +1,114 @@
 <?php
 
-echo "Serializing library info\n";
-
 require_once(dirname(__FILE__) . '/../common/code/boost_libraries.php');
 
 function main() {
+    $args = $_SERVER['argv'];
+    $git_mirror = null;
+
+    switch (count($args)) {
+        case 1: break;
+        case 2: $git_mirror = $args[1]; break;
+        default:
+            echo "Usage: update-doc-list.php [mirror_root]";
+            exit(1);
+    }
+
     $libs = boost_libraries::from_file(dirname(__FILE__) . '/../doc/libraries.xml');
+    if ($git_mirror) {
+        update_from_git($libs, $git_mirror, 'master');
+        update_from_git($libs, $git_mirror, 'develop');
+    }
+
+    echo "Writing to disk\n";
+
     file_put_contents(dirname(__FILE__) . '/../doc/libraries.xml.new', $libs->to_xml());
     file_put_contents(dirname(__FILE__) . '/../generated/libraries.txt', serialize($libs));
 }
 
-main();
\ No newline at end of file
+function update_from_git($libs, $location, $branch) {
+    echo "Updating from {$branch}\n";
+
+    $git_command = "cd '${location}' && git";
+
+    $is_bare = get_bool_from_array(run_process("{$git_command} rev-parse --is-bare-repository"));
+
+    $modules = Array();
+
+    foreach(run_process("{$git_command} config -l --blob ".
+            "\$({$git_command} ls-tree {$branch} .gitmodules | cut -f 1 | cut -f 3 -d ' ')")
+        as $line_number => $line)
+    {
+        if (!$line) continue;
+
+        if (preg_match('@^submodule\.(\w+)\.(\w+)=(.*)$@', trim($line), $matches)) {
+            $modules[$matches[1]][$matches[2]] = $matches[3];
+        }
+        else {
+            throw new RuntimeException("Unsupported config line: {$line}");
+        }
+    }
+
+    $modules_by_path = Array();
+    foreach($modules as $name => $details) {
+        $modules_by_path[$details['path']] = $name;
+    }
+
+    foreach(run_process("{$git_command} ls-tree {$branch} ".implode(' ', array_keys($modules_by_path)))
+        as $line_number => $line)
+    {
+        if (!$line) continue;
+
+        if (preg_match("@^160000 commit ([a-zA-Z0-9]+)\t(.*)$@", $line, $matches)) {
+            $modules[$modules_by_path[$matches[2]]]['hash'] = $matches[1];
+        }
+        else {
+            throw new RuntimeException("Unmatched submodule line: {$line}");
+        }
+    }
+
+    foreach($modules as $name => $module) {
+        $module_location = $is_bare ? "{$location}/{$module['url']}" :
+            "{$location}/{$module['path']}";
+        $module_command = "cd '{$module_location}' && git";
+
+        foreach(run_process("{$module_command} ls-tree {$module['hash']} metadata.xml") as $entry) {
+            $entry = trim($entry);
+            if (preg_match("@^100644 blob ([a-zA-Z0-9]+)\t(.*)$@", $entry, $matches)) {
+                $libs->update(
+                    implode("\n", (run_process("{$module_command} show {$matches[1]}"))),
+                    $branch);
+            }
+        }
+    }
+}
+
+function get_bool_from_array($array) {
+    if (count($array) != 1) throw new RuntimeException("get_bool_from_array: invalid array");
+    switch ($array[0]) {
+        case 'true': return true;
+        case 'false': return false;
+        default: throw new RuntimeException("invalid bool: ${array[0]}");
+    }
+}
+
+class ProcessError extends RuntimeException {
+    public $error_code;
+
+    function __construct($error_code) {
+        $this->error_code = $error_code;
+        parent::__construct("Process failed with status: {$error_code}");
+    }
+}
+
+function run_process($command) {
+    exec($command, $output, $return_var);
+
+    if ($return_var != 0) {
+        throw new ProcessError($return_var);
+    }
+
+    return $output;
+}
+
+main();