Debugging .net application with windbg, cannot insert breakpoints

Question

I use windbg, to debug a simple c# application, which consits just of empty form like this:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApp2
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }
    }
}

I compile, run this app, attach to it with windbg, then run in windbg:

0:009> .cordll -ve -u -l
Automatically loaded SOS Extension
CLRDLL: Loaded DLL C:\Windows\Microsoft.NET\Framework64\v2.0.50727\mscordacwks.dll
CLR DLL status: Loaded DLL C:\Windows\Microsoft.NET\Framework64\v2.0.50727\mscordacwks.dll

And thein i load SOS extension and verify that its loaded:

0:009> .loadby sos mscorwks
0:009> .chain
Extension DLL search Path:
    C:\Program Files (x86)\Windows Kits\10\Debuggers\x64\WINXP;C:\Program Files (x86)\Windows Kits\10\Debuggers\x64\winext;C:\Program Files (x86)\Windows Kits\10\Debuggers\x64\winext\arcade;C:\Program Files (x86)\Windows Kits\10\Debuggers\x64\pri;C:\Program Files (x86)\Windows Kits\10\Debuggers\x64;C:\Users\username\AppData\Local\Dbg\EngineExtensions;C:\Program Files (x86)\Windows Kits\10\Debuggers\x64;C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\WINDOWS\System32\WindowsPowerShell\v1.0\;C:\Program Files\PuTTY\;C:\Program Files (x86)\Bitvise SSH Client;C:\Program Files\nodejs\;C:\Program Files\Microsoft SQL Server\130\Tools\Binn\;C:\Program Files\Git\cmd;C:\Users\username\AppData\Local\Android\sdk\platform-tools;C:\Program Files (x86)\Nox\bin\;C:\Users\username\AppData\Local\Microsoft\WindowsApps;C:\Users\username\AppData\Roaming\npm;C:\Program Files (x86)\Nmap;C:\Program Files (x86)\mitmproxy\bin
Extension DLL chain:
    C:\Windows\Microsoft.NET\Framework64\v2.0.50727\sos: image 2.0.50727.8794, API 1.0.0, built Tue Jun 20 23:15:41 2017
        [path: C:\Windows\Microsoft.NET\Framework64\v2.0.50727\SOS.dll]
    C:\Windows\Microsoft.NET\Framework64\v2.0.50727\SOS.dll: image 2.0.50727.8794, API 1.0.0, built Tue Jun 20 23:15:41 2017
        [path: C:\Windows\Microsoft.NET\Framework64\v2.0.50727\SOS.dll]
    dbghelp: image 10.0.15063.468, API 10.0.6, built Thu Jan  1 03:00:00 1970
        [path: C:\Program Files (x86)\Windows Kits\10\Debuggers\x64\dbghelp.dll]
    ext: image 10.0.15063.468, API 1.0.0, built Thu Jan  1 03:00:00 1970
        [path: C:\Program Files (x86)\Windows Kits\10\Debuggers\x64\winext\ext.dll]
    exts: image 10.0.15063.468, API 1.0.0, built Thu Jan  1 03:00:00 1970
        [path: C:\Program Files (x86)\Windows Kits\10\Debuggers\x64\WINXP\exts.dll]
    uext: image 10.0.15063.468, API 1.0.0, built Thu Jan  1 03:00:00 1970
        [path: C:\Program Files (x86)\Windows Kits\10\Debuggers\x64\winext\uext.dll]
    ntsdexts: image 10.0.15063.468, API 1.0.0, built Thu Jan  1 03:00:00 1970
        [path: C:\Program Files (x86)\Windows Kits\10\Debuggers\x64\WINXP\ntsdexts.dll]

Then i set the debugging symbols path to the folder where .pdb located, and sources folder.

But when i open the source file and set the breakpoint on a source line, and then continue the process i get error in windbg:

0:009> g
Unable to insert breakpoint 3 at 00000000`008f001a, Win32 error 0n998
    "Invalid access to memory."
bp3 at 00000000`008f001a failed
WaitForEvent failed

I expected it would break, and show me the .net assembler instructions, but it fails all the time. How do you breakpoint the .net application using windbg then?

Answer 1

You can't set breakpoints in .NET using F9 on a source file. Instead you need the SOS !bpmd or SOSEX !mbp command.

The SOS syntax is

!BPMD <module name> <method name>
!BPMD -md <MethodDesc>

and it cannot use line numbers.

The SOSEX syntax is

!sosex.mbp <source file> <line number> [<column number>] [Options]

and can use line numbers if the PDBs are available.

!mbc clears a managed breakpoint. !mbd disables a managed breakpoint and !mbl lists managed breakpoints.

If I remember well, there's a difference: !bpmd only works if the method was already JIT compiled, so that a breakpoint can be set in executable machine code. !mbp can set breakpoints although the method was not JIT-compiled. It will set the breakpoint itself as soon as the method is compiled.