Theme Logo in wordpress

Add the following code in your functions.php file

add_theme_support( 'custom-logo' );

For adding arguments follow the code

add_theme_support( 'custom-logo', array(
 'height'      => 100,
 'width'       => 400,
 'flex-height' => true,
 'flex-width'  => true,
 'header-text' => array( 'site-title', 'site-description' ),
) );

For getting the url

$custom_logo_id = get_theme_mod( 'custom_logo' );
$image = wp_get_attachment_image_src( $custom_logo_id , 'full' );
echo $image[0];