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Linker Analyzer

Linker analyzer is a command line tool to analyze dependencies, which were recorded during linker processing, and led linker to mark an item to keep it in the resulting linked assembly.

It works on an oriented graph of dependencies, which are collected and dumped during the linker run. The vertices of this graph are the items of interest like assemblies, types, methods, fields, linker steps, etc. The edges represent the dependencies.

How to dump dependencies

The linker analyzer needs a linker dependencies file as an input. It can be retrieved by enabling dependencies dumping during linking of a Xamarin.Android, Xamarin.iOS, or .NET SDK style project.

For Xamarin.Android and Xamarin.iOS, that can be done on the command line by setting LinkerDumpDependencies property to true and building the project. (make sure the LinkAssemblies task is called, it might require cleaning the project sometimes) Usually it is enough to build the project like this:

msbuild /p:LinkerDumpDependencies=true /p:Configuration=Release YourAppProject.csproj

For .NET SDK style projects, you will want to use _TrimmerDumpDependencies instead:

msbuild /p:_TrimmerDumpDependencies=true /p:Configuration=Release YourAppProject.csproj

After a successful build, there will be a linker-dependencies.xml.gz file created, containing the information for the analyzer.

How to use the analyzer

Let say you would like to know, why a type, Android.App.Activity for example, was marked by the linker. So run the analyzer like this:

illinkanalyzer -t Android.App.Activity linker-dependencies.xml.gz

Output:

Loading dependency tree from: linker-dependencies.xml.gz

--- Type dependencies: 'Android.App.Activity' -----------------------

--- TypeDef:Android.App.Activity dependencies -----------------------
Dependency #1
	TypeDef:Android.App.Activity
	| TypeDef:XA.App.MainActivity [2 deps]
	| Assembly:XA.App, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null [3 deps]
	| Other:Mono.Linker.Steps.ResolveFromAssemblyStep

The output contains dependencies string(s), starting with the type and continuing with the item of interest, which depends on the type. The dependency could be a result of multiple reasons. For example, the type was referenced from a method, or the type was listed in the linker XML descriptor file.

In our example there is only one dependency string called Dependency #1. It shows us that the type Android.App.Activity was marked during processing of type XA.App.MainActivity by the linker. In this case because the MainActivity type is based on the Activity type and thus the linker marked it and kept it in the linked assembly. We can also see that there are 2 dependencies for the MainActivity class. Note that in the string (above) we see only 1st dependency of the 2, the dependency on the assembly XA.App. And finally the assembly vertex depends on the ResolveFromAssemblyStep vertex. So we see that the assembly was processed in the ResolveFromAssembly linker step.

Now we might want to see the MainActivity dependencies. That could be done by the following analyzer run:

illinkanalyzer -r TypeDef:XA.App.MainActivity linker-dependencies.xml.gz

Output:

Loading dependency tree from: linker-dependencies.xml.gz

--- Raw dependencies: 'TypeDef:XA.App.MainActivity' -----------------

--- TypeDef:XA.App.MainActivity dependencies ------------------------
Dependency #1
	TypeDef:XA.App.MainActivity
	| Assembly:XA.App, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null [3 deps]
	| Other:Mono.Linker.Steps.ResolveFromAssemblyStep
Dependency #2
	TypeDef:XA.App.MainActivity
	| TypeDef:XA.App.MainActivity/<>c__DisplayClass1_0 [2 deps]
	| TypeDef:XA.App.MainActivity [2 deps]
	| Assembly:XA.App, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null [3 deps]
	| Other:Mono.Linker.Steps.ResolveFromAssemblyStep

Known issues

Sometimes the linker processing is not straight forward and the marking is postponed, like processing of some of the methods. They are queued to be processed later. In such case the dependencies are "interrupted" and the dependecy string for the method usually shows just dependency on the Mark step.

Command line help

Usage:

	illinkanalyzer [Options] <linker-dependency-file.xml.gz>

Options:

  -a, --alldeps              show all dependencies
  -h, --help                 show this message and exit.
  -r, --rawdeps=VALUE        show raw vertex dependencies. Raw vertex VALUE is
                               in the raw format written by linker to the
                               dependency XML file. VALUE can be regular
                               expression
      --roots                show root dependencies.
      --stat                 show statistic of loaded dependencies.
      --tree                 reduce the dependency graph to the tree.
      --types                show all types dependencies.
  -t, --typedeps=VALUE       show type dependencies. The VALUE can be regular
                               expression
  -f, --flat                 show all dependencies per vertex and their distance
  -v, --verbose              be more verbose. Enables stat and roots options.