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Link XML formatting reference

Understand how to format a link.xml file, including supported XML elements and attributes and examples of their usage.
Read time 8 minutesLast updated 12 days ago
This reference provides information on the correct formatting of 
link.xml
files, including valid XML elements and attributes and usage examples.
Note
Unity's 
link.xml
format is based on the ILLink (Intermediate Language Linker) Descriptor format used by the .NET linker. For an authoritative reference on that format, refer to the documentation in the dotnet/runtime repository.

Supported XML elements

The following XML elements are supported in link.xml files:

Element

Description

<linker></linker>
Must be used in all 
link.xml
files as the outermost element enclosing all other elements.
<assembly></assembly>
Declare code preservation annotations specific to an assembly.
<type></type>
Declare code preservation annotations specific to a type.
<field></field>
Declare code preservation annotations specific to a field.
<method></method>
Declare code preservation annotations specific to a method.
<property></property>
Declare code preservation annotations specific to a property.
<event></event>
Declare code preservation annotations specific to an event.
For example usages of all these elements, refer to Usage examples.

Supported XML attributes

Attribute

Description

accessors
Apply to a 
<property>
element to specify which of the property's accessor methods to preserve.
feature
Exclude preservations for features that aren't supported based on the settings for the current build. For more information and a usage example, refer to Feature exclusions.
fullname
Identify a code element by it's fully qualified name. Use 
fullname
whenever 
name
alone could be ambiguous.
ignoreIfMissing
Apply to an 
<assembly>
element to declare preservations for an assembly that doesn't exist during all Player builds. For example usage, refer to Ignore a missing assembly.
ignoreIfUnreferenced
Apply to an 
<assembly>
element to preserve the entities in an assembly only if at least one of its members is referenced by another assembly. For example usage, refer to Ignore an unreferenced assembly.
name
Identify a code element by name only, without the parent assembly as a prefix. If the assembly name has already been specified with 
fullname
in a parent XML element, child XML elements can identify the code element by 
name
alone.
preserve
Specify the level of code elements to preserve from stripping. Valid values are as follows:
  • all
    : Preserve the entire element and all its members.
  • fields
    : Preserve the type and all its fields, but not methods.
  • methods
    : Preserve the type and all its methods, but not fields.
  • nothing
    : Preserve the type's existence/metadata but none of its members.
signature
Identify a code element by its signature. A method signature consists of the return type, name, and parameters. A field, property, or event signature consists of the type and name. For example usage, refer to Usage examples.
windowsruntime
Must be added to the 
<assembly>
element in the 
link.xml
file whenever you define preservations for a Windows Runtime Metadata (.winmd) assembly. For example usage, refer to Windows Runtime Metadata assembly.
For example usages of all these attributes, refer to Usage examples.

Usage examples

The following examples demonstrate valid usage of the supported XML elements and attributes.

Different ways to declare the root types of an assembly

The following examples illustrate the different ways that you can declare the root types of a project's assemblies using a 
link.xml
file:
<linker>  <!--Preserve types and members in an assembly-->  <assembly fullname="AssemblyName">    <!--Preserve an entire type-->    <type fullname="Namespace.TypeName" preserve="all"/>    <!--No "preserve" attribute and no members specified means preserve all members-->    <type fullname="Namespace.TypeName"/>    <!--Preserve all fields on a type-->    <type fullname="Namespace.TypeName" preserve="fields"/>    <!--Preserve all methods on a type-->    <type fullname="Namespace.TypeName" preserve="methods"/>    <!--Preserve the type only-->    <type fullname="Namespace.TypeName" preserve="nothing"/>    <!--Preserving only specific members of a type-->    <type fullname="Namespace.TypeName">              <!--Fields-->      <field signature="System.Int32 FieldName" />      <!--Preserve a field by name rather than signature-->      <field name="FieldName" />            <!--Methods-->      <method signature="System.Void MethodName()" />      <!--Preserve a method with parameters-->      <method signature="System.Void MethodName(System.Int32,System.String)" />      <!--Preserve a method by name rather than signature-->      <method name="MethodName" />      <!--Properties-->      <!--Preserve a property, its backing field (if present),           getter, and setter methods-->      <property signature="System.Int32 PropertyName" />      <property signature="System.Int32 PropertyName" accessors="all" />      <!--Preserve a property, its backing field (if present), and getter method-->      <property signature="System.Int32 PropertyName" accessors="get" />      <!--Preserve a property, its backing field (if present), and setter method-->      <property signature="System.Int32 PropertyName" accessors="set" />      <!--Preserve a property by name rather than signature-->      <property name="PropertyName" />      <!--Events-->      <!--Preserve an event, its backing field (if present), add, and remove methods-->      <event signature="System.EventHandler EventName" />      <!--Preserve an event by name rather than signature-->      <event name="EventName" />    </type>  </assembly></linker>

Declare entire assemblies as roots

The following example shows how you can declare entire assemblies:
<!--Preserve an entire assembly-->  <assembly fullname="AssemblyName" preserve="all"/>  <!--No "preserve" attribute and no types specified means preserve all-->  <assembly fullname="AssemblyName"/>  <!--Fully qualified assembly name-->  <assembly fullname="AssemblyName, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null">    <type fullname="Namespace.Foo" preserve="all"/>  </assembly>  <!--Force an assembly to be processed for roots but don't explicitly preserve anything in particular. Useful when the assembly isn't referenced.-->  <assembly fullname="AssemblyName" preserve="nothing"/>

Preserve nested or generic types

The following example shows how to preserve either nested or generic types:
<!--Examples with generics-->    <type fullname="Namespace.G`1">      <!--Preserve a field with generics in the signature-->      <field signature="System.Collections.Generic.List`1<System.Int32> FieldName" />      <field signature="System.Collections.Generic.List`1<T> FieldName" />      <!--Preserve a method with generics in the signature-->      <method signature="System.Void MethodName(System.Collections.Generic.List`1<System.Int32>)" />      <!--Preserve an event with generics in the signature-->      <event signature="System.EventHandler`1<System.EventArgs> EventName" />    </type>    <!--Preserve a nested type-->    <type fullname="Namespace.H/Nested" preserve="all"/>    <!--Preserve all fields of a type if the type is used.  If the type isn't used, it will be removed-->    <type fullname="Namespace.I" preserve="fields" required="0"/>    <!--Preserve all methods of a type if the type is used. If the type isn't used, it will be removed-->    <type fullname="Namespace.J" preserve="methods" required="0"/>    <!--Preserve all types in a namespace-->    <type fullname="Namespace.SomeNamespace*" preserve="all"/>    <!--Preserve all types with a common prefix in their name-->    <type fullname="Prefix*" preserve="all"/>

Ignore a missing assembly

Use the 
ignoreIfMissing
attribute on the 
<assembly>
element if you need to declare preservations for an assembly that doesn't exist during all Player builds:
<linker>  <assembly fullname="Foo" ignoreIfMissing="1">    <type name="TypeName"/>  </assembly></linker>

Ignore an unreferenced assembly

Use the 
ignoreIfUnreferenced
attribute on the 
<assembly>
element to preserve the entities in an assembly only when at least one type is referenced in another assembly:
<linker>  <assembly fullname="Bar" ignoreIfUnreferenced="1">    <type name="TypeName"/>  </assembly></linker>

Windows Runtime Metadata assembly

You must use the 
windowsruntime
attribute on the 
<assembly>
element whenever you define preservations for a Windows Runtime Metadata (.winmd) assembly:
<linker>  <assembly fullname="Windows" windowsruntime="true">    <type name="TypeName"/> </assembly></linker>

Feature exclusions

The 
mscorlib.xml
file embedded in 
mscorlib.dll
uses this attribute, but you can use it in any 
link.xml
file when appropriate.
At the High stripping level, the Unity linker excludes preservations for features that aren't supported based on the settings for the current build:
  1. remoting
    — Excluded when targeting the IL2CPP scripting backend.
  2. sre
    — Excluded when targeting the IL2CPP scripting backend.
  3. com
    — Excluded when targeting platforms that don't support COM.
For example, the following 
link.xml
file preserves one method of a type on platforms that support COM, and one method on all platforms:
<linker>    <assembly fullname="Foo">        <type fullname="Type1">            <!--Preserve FeatureOne on platforms that support COM-->            <method signature="System.Void FeatureOne()" feature="com"/>            <!--Preserve FeatureTwo on all platforms-->            <method signature="System.Void FeatureTwo()"/>        </type>    </assembly></linker>

Additional resources