functions.php

add_action( 'genesis_before_header', 'your_function' );
function your_function() {
if ( get_theme_mod( 'themeslug_logo' ) ) : ?>
    <div class='site-logo'>
        <a href='<?php echo esc_url( home_url( '/' ) ); ?>' title='<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>' rel='home'><img src='<?php echo esc_url( get_theme_mod( 'themeslug_logo' ) ); ?>' alt='<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>'></a>
    </div>
<?php else : ?>
    <hgroup>
        <h1 class='site-title'><a href='<?php echo esc_url( home_url( '/' ) ); ?>' title='<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>' rel='home'><?php bloginfo( 'name' ); ?></a></h1>
        <h2 class='site-description'><?php bloginfo( 'description' ); ?></h2>
    </hgroup>
<?php endif; 
}