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Debug StackOverflow errors

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A StackOverflowException is thrown when the execution stack overflows because it contains too many nested method calls.

For example, suppose you have an app as follows:

using System;

namespace temp
{
    class Program
    {
        static void Main(string[] args)
        {
            Main(args); // Oops, this recursion won't stop.
        }
    }
}

The Main method will continuously call itself until there is no more stack space. Once there is no more stack space, execution cannot continue and so it will throw a StackOverflowException.

> dotnet run
Stack overflow.

Note

On .NET 5 and later, the callstack is output to the console.

Note

This article describes how to debug a stack overflow with lldb. If you are running on Windows, we suggest debugging the app with Visual Studio or Visual Studio Code.

Example

  1. Run the app with it configured to collect a dump on crash

    > export DOTNET_DbgEnableMiniDump=1
> dotnet run
Stack overflow.
Writing minidump with heap to file /tmp/coredump.6412
Written 58191872 bytes (14207 pages) to core file

    Note

    .NET 6 standardizes on the prefix DOTNET_ instead of COMPlus_ for environment variables that configure .NET run-time behavior. However, the COMPlus_ prefix will continue to work. If you're using a previous version of the .NET runtime, you should still use the COMPlus_ prefix for environment variables.

  2. Install the SOS extension using dotnet-sos

    dotnet-sos install

  3. Debug the dump in lldb to see the failing stack

    lldb --core /temp/coredump.6412
(lldb) bt
...
    frame #261930: 0x00007f59b40900cc
    frame #261931: 0x00007f59b40900cc
    frame #261932: 0x00007f59b40900cc
    frame #261933: 0x00007f59b40900cc
    frame #261934: 0x00007f59b40900cc
    frame #261935: 0x00007f5a2d4a080f libcoreclr.so`CallDescrWorkerInternal at unixasmmacrosamd64.inc:867
    frame #261936: 0x00007f5a2d3cc4c3 libcoreclr.so`MethodDescCallSite::CallTargetWorker(unsigned long const*, unsigned long*, int) at callhelpers.cpp:70
    frame #261937: 0x00007f5a2d3cc468 libcoreclr.so`MethodDescCallSite::CallTargetWorker(this=<unavailable>, pArguments=0x00007ffe8222e7b0, pReturnValue=0x0000000000000000, cbReturnValue=0) at callhelpers.cpp:604
    frame #261938: 0x00007f5a2d4b6182 libcoreclr.so`RunMain(MethodDesc*, short, int*, PtrArray**) [inlined] MethodDescCallSite::Call(this=<unavailable>, pArguments=<unavailable>) at callhelpers.h:468
...

  4. The top frame 0x00007f59b40900cc is repeated several times. Use the SOS ip2md command to figure out what method is located at the 0x00007f59b40900cc address

    (lldb) ip2md 0x00007f59b40900cc
MethodDesc:   00007f59b413ffa8
Method Name:          temp.Program.Main(System.String[])
Class:                00007f59b4181d40
MethodTable:          00007f59b4190020
mdToken:              0000000006000001
Module:               00007f59b413dbf8
IsJitted:             yes
Current CodeAddr:     00007f59b40900a0
Version History:
  ILCodeVersion:      0000000000000000
  ReJIT ID:           0
  IL Addr:            0000000000000000
     CodeAddr:           00007f59b40900a0  (MinOptJitted)
     NativeCodeVersion:  0000000000000000
Source file:  /temp/Program.cs @ 9

  5. Go look at the indicated method temp.Program.Main(System.String[]) and source "/temp/Program.cs @ 9" to see if you can figure out what you did wrong. If it still wasn't clear you could add logging in that area of the code.

See Also