These instructions will lead you through debugging CoreCLR on Windows and Linux. They will be expanded to support macOS when we have good instructions for that.
Debugging CoreCLR on Windows
- Perform a build of the repo.
- Open solution <reporoot>\bin\obj\Windows_NT.<platform>.<configuration>\CoreCLR.sln in Visual Studio. <platform> and <configuration> are based on type of build you did. By default they are 'x64' and 'Debug'.
- Right click the INSTALL project and choose ‘Set as StartUp Project’
- Bring up the properties page for the INSTALL project
- Select Configuration Properties->Debugging from the left side tree control
- Set Command=
- This points to the folder where the built runtime binaries are present.
- Set Command Arguments=
<managed app you wish to run>(e.g. HelloWorld.exe)
- Set Working Directory=
- This points to the folder containing CoreCLR binaries.
- Press F11 to start debugging at wmain in corerun (or set a breakpoint in source and press F5 to run to it)
- As an example, set a breakpoint for the EEStartup function in ceemain.cpp to break into CoreCLR startup.
Steps 1-8 only need to be done once, and then (9) can be repeated whenever you want to start debugging. The above can be done with Visual Studio 2013.
Using SOS with windbg or cdb on Windows
If you know the path of the
sos.dll for the version of your runtime, load it like
.load c:\path\to\sos\sos.dll. Use can use the
lm command to find the path of the "coreclr.dll" module.
.loadby sos coreclr should also work.
For more information on SOS commands click here.
Debugging CoreCLR on OS X
To use lldb on OS X, you first need to build it and the SOS plugin on the machine you intend to use it. See the instructions in building lldb. The rest of instructions on how to use lldb for Linux on are the same.
Debugging CoreCLR on Linux
Only lldb is supported by the SOS plugin. gdb can be used to debug the coreclr code but with no SOS support. Visual Studio 2015 RTM remote debugging isn't currently supported.
- Perform a build of the coreclr repo.
- Install the corefx managed assemblies to the binaries directory.
- cd to build's binaries:
- Start lldb (the version the plugin was built with, currently 3.9):
lldb-3.9 corerun HelloWorld.exe linux
- Now at the lldb command prompt, load SOS plugin:
plugin load libsosplugin.so
- Launch program:
process launch -s
- To stop annoying breaks on SIGUSR1/SIGUSR2 signals used by the runtime run:
process handle -s false SIGUSR1 SIGUSR2
- Get to a point where coreclr is initialized by setting a breakpoint (i.e.
breakpoint set -n LoadLibraryExWand then
process continue) or stepping into the runtime.
- Run a SOS command like
sos VerifyHeap. The command name is case sensitive.
You can combine steps 4-8 and pass everything on the lldb command line:
lldb-3.9 -o "plugin load libsosplugin.so" -o "process launch -s" -o "process handle -s false SIGUSR1 SIGUSR2" -o "breakpoint set -n LoadLibraryExW" corerun HelloWorld.exe linux
For .NET Core version 1.x and 2.0.x, libsosplugin.so is built for and will only work with version 3.6 of lldb. For .NET Core 2.1, the plugin is built for 3.9 lldb and will work with 3.8 and 3.9 lldb.
This is the full list of commands currently supported by SOS. lldb is case-sensitive unlike windbg.
Type "soshelp <functionname>" for detailed info on that function. Object Inspection Examining code and stacks ----------------------------- ----------------------------- DumpObj (dumpobj) Threads (clrthreads) DumpArray ThreadState DumpStackObjects (dso) IP2MD (ip2md) DumpHeap (dumpheap) u (clru) DumpVC DumpStack (dumpstack) GCRoot (gcroot) EEStack (eestack) PrintException (pe) ClrStack (clrstack) GCInfo EHInfo bpmd (bpmd) Examining CLR data structures Diagnostic Utilities ----------------------------- ----------------------------- DumpDomain VerifyHeap EEHeap (eeheap) FindAppDomain Name2EE (name2ee) DumpLog (dumplog) DumpMT (dumpmt) CreateDump (createdump) DumpClass (dumpclass) DumpMD (dumpmd) Token2EE DumpModule (dumpmodule) DumpAssembly DumpRuntimeTypes DumpIL (dumpil) DumpSig DumpSigElem Examining the GC history Other ----------------------------- ----------------------------- HistInit (histinit) FAQ HistRoot (histroot) Help (soshelp) HistObj (histobj) HistObjFind (histobjfind) HistClear (histclear)
By default you can reach all the SOS commands by using: sos [command_name] However the common commands have been aliased so that you don't need the SOS prefix:
bpmd -> sos bpmd clrstack -> sos ClrStack clrthreads -> sos Threads clru -> sos U createdump -> sos CreateDump dso -> sos DumpStackObjects dumpclass -> sos DumpClass dumpheap -> sos DumpHeap dumpil -> sos DumpIL dumplog -> sos DumpLog dumpmd -> sos DumpMD dumpmodule -> sos DumpModule dumpmt -> sos DumpMT dumpobj -> sos DumpObj dumpstack -> sos DumpStack eeheap -> sos EEHeap eestack -> sos EEStack gcroot -> sos GCRoot histinit -> sos HistInit histroot -> sos HistRoot histobj -> sos HistObj histobjfind -> sos HistObjFind histclear -> sos HistClear ip2md -> sos IP2MD name2ee -> sos Name2EE pe -> sos PrintException soshelp -> sos Help
Debugging core dumps with lldb
It is also possible to debug .NET Core crash dumps using lldb and SOS. In order to do this, you need all of the following:
- The crash dump file. We have a service called "Dumpling" which collects, uploads, and archives crash dump files during all of our CI jobs and official builds.
- On Linux, there is an utility called
createdump(see doc) that can be setup to generate core dumps when a managed app throws an unhandled exception or faults.
- To get matching runtime and symbol binaries for the core dump use the symbol downloader CLI extension:
- Install the .NET Core 2.1 SDK.
- Install the symbol downloader extension:
dotnet tool install -g dotnet-symbol. Make sure you are not in any project directory with a NuGet.Config that doesn't include nuget.org as a source.
dotnet symbol coredumpto download the runtime binaries and symbols.
- Check out the coreclr and corefx repositories at the appropriate commit for the appropriate source.
- For further information see: dotnet-symbol.
- lldb version 3.9. The SOS plugin (i.e. libsosplugin.so) provided is now built for lldb 3.9. In order to install lldb 3.9 just run the following commands:
~$ echo "deb http://llvm.org/apt/trusty/ llvm-toolchain-trusty-3.9 main" | sudo tee /etc/apt/sources.list.d/llvm.list ~$ wget -O - http://llvm.org/apt/llvm-snapshot.gpg.key | sudo apt-key add - ~$ sudo apt-get update ~$ sudo apt-get install lldb-3.9
Once you have everything listed above, you are ready to start debugging. You need to specify an extra parameter to lldb in order for it to correctly resolve the symbols for libcoreclr.so. Use a command like this:
lldb-3.9 -O "settings set target.exec-search-paths <runtime-path>" -o "plugin load <path-to-libsosplugin.so>" --core <core-file-path> <host-path>
<runtime-path>: The path containing libcoreclr.so.dbg, as well as the rest of the runtime and framework assemblies.
<core-file-path>: The path to the core dump you are attempting to debug.
<host-path>: The path to the dotnet or corerun executable, potentially in the
<path-to-libsosplugin.so>: The path to libsosplugin.so, should be in the
lldb should start debugging successfully at this point. You should see stacktraces with resolved symbols for libcoreclr.so. At this point, you can run
plugin load <libsosplugin.so-path>, and begin using SOS commands, as above.
lldb-3.9 -O "settings set target.exec-search-paths /home/parallels/Downloads/System.Drawing.Common.Tests/home/helixbot/dotnetbuild/work/2a74cf82-3018-4e08-9e9a-744bb492869e/Payload/shared/Microsoft.NETCore.App/9.9.9/" -o "plugin load /home/parallels/Downloads/System.Drawing.Common.Tests/home/helixbot/dotnetbuild/work/2a74cf82-3018-4e08-9e9a-744bb492869e/Payload/shared/Microsoft.NETCore.App/9.9.9/libsosplugin.so" --core /home/parallels/Downloads/System.Drawing.Common.Tests/home/helixbot/dotnetbuild/work/2a74cf82-3018-4e08-9e9a-744bb492869e/Work/f6414a62-9b41-4144-baed-756321e3e075/Unzip/core /home/parallels/Downloads/System.Drawing.Common.Tests/home/helixbot/dotnetbuild/work/2a74cf82-3018-4e08-9e9a-744bb492869e/Payload/shared/Microsoft.NETCore.App/9.9.9/dotnet
Disabling Managed Attach/Debugging
The "COMPlus_EnableDiagnostics" environment variable can be used to disable managed debugging. This prevents the various OS artifacts used for debugging like the named pipes and semaphores on Linux/MacOS and shared memory on Windows from being created.
Using Visual Studio Code
- Install Visual Studio Code
- Install the C# Extension
- Open the folder containing the source you want to debug in VS Code
- Open the debug window:
ctrl-shift-Dor click on the button on the left
- Click the gear button at the top to create a launch configuration, select
.NET Corefrom the selection dropdown
- In the
.NET Core Launch (console)configuration do the following
- delete the
programto the full path to corerun in the test directory
cwdto the test directory
argsto the command line arguments to pass to the test
- something like:
[ "xunit.console.netcore.exe", "<test>.dll", "-notrait", .... ]
- something like:
- delete the
- Set a breakpoint and launch the debugger, inspecting variables and call stacks will now work