如何用WinDbg調(diào)試Linux上的.NET程序

作者：一線碼農(nóng)聊技術(shù) 2024-07-26 00:00:12

最新版本 1.2402.24001.0 的WinDbg真的讓人很興奮，可以將自己偽裝成 GDB 來和遠(yuǎn)程的 GDBServer 打通來實現(xiàn)對 Linux 上 .NET程序進(jìn)行調(diào)試，這樣就可以繼續(xù)使用熟悉的WinDbg 命令，在這個版本中我覺得 WinDbg 不再是 WinDbg，而是 XDbg 了。

一、背景

1. 講故事

圖片

簡圖有了，接下來就要付出實踐了。

二、實操 Linux 上 .NET調(diào)試

1. 測試程序

本想在 CentOS7 上安裝 .NET8，不大好裝，這里就用一個現(xiàn)存的 .NETCore 3.1 吧，測試代碼如下：

internal class Program
    {
        static void Main(string[] args)
        {
            while (true)
            {
                Console.WriteLine($"{DateTime.Now},tid={Thread.CurrentThread.ManagedThreadId}");
                Thread.Sleep(1000);
            }
        }
    }

代碼非常簡單，就是1s輸出一條記錄，接下來編譯成x64部署到 Centos7 上。

[root@localhost data]# ls
ConsoleApp7  ConsoleApp7.deps.json  ConsoleApp7.dll  ConsoleApp7.pdb  ConsoleApp7.runtimeconfig.json

2. 安裝GDBServer

在 linux 上安裝 gdbserver 比較簡單，使用 yum 安裝即可 yum install gdb-gdbserver ，輸出如下：

[root@localhost data]# yum install gdb-gdbserver
Loaded plugins: fastestmirror, langpacks
Loading mirror speeds from cached hostfile
 * base: mirror-hk.koddos.net
 * centos-sclo-rh: ftp.sjtu.edu.cn
 * centos-sclo-sclo: ftp.sjtu.edu.cn
 * epel: mirror.hoster.kz
 * extras: ftp.sjtu.edu.cn
 * updates: mirror-hk.koddos.net
Package gdb-gdbserver-7.6.1-120.el7.x86_64 already installed and latest version
Nothing to do
[root@localhost data]# gdbserver –version
Usage: gdbserver [OPTIONS] COMM PROG [ARGS ...]
 gdbserver [OPTIONS] --attach COMM PID
 gdbserver [OPTIONS] --multi COMM

COMM may either be a tty device (for serial debugging), or 
HOST:PORT to listen for a TCP connection.

Options:
  --debug               Enable general debugging output.
  --remote-debug        Enable remote protocol debugging output.
  --version             Display version information and exit.
  --wrapper WRAPPER --  Run WRAPPER to start new programs.
  --once                Exit after the first connection has closed.

安裝好之后，接下來用 gdbserver 來啟動我們的程序，并啟動調(diào)試端口為 1234，參考如下：

[root@localhost data]# gdbserver 192.168.128.130:1234 dotnet ConsoleApp7.dll
Process dotnet created; pid = 3643
Listening on port 1234

3. 使用 windbg 連接

打開Windbg后，選擇 Connect to remote debugger 選項, 在連接字符串中填入 gdb:server=192.168.128.130,port=1234 即可，截圖如下：

圖片

連接好之后，會有一個初始中斷，直接輸入g就好了，輸出如下：

64-bit machine not using 64-bit API

************* Path validation summary **************
Response                         Time (ms)     Location
Deferred                                       SRV*C:\mysymbols*https://msdl.microsoft.com/download/symbols
Symbol search path is: SRV*C:\mysymbols*https://msdl.microsoft.com/download/symbols
Executable search path is: 
Unknown System Version 0 UP Free x64
System Uptime: not available
Process Uptime: not available
Reloading current modules
ModLoad: 00005555`55554000 00005555`555770cd   /usr/share/dotnet/dotnet
ModLoad: 00007fff`f7bbf000 00007fff`f7dda488   /lib64/libpthread.so.0
ModLoad: 00007fff`f79bb000 00007fff`f7bbe130   /lib64/libdl.so.2
ModLoad: 00007fff`f76b3000 00007fff`f79ba420   /lib64/libstdc++.so.6
ModLoad: 00007fff`f73b1000 00007fff`f76b2138   /lib64/libm.so.6
ModLoad: 00007fff`f719b000 00007fff`f73b0400   /lib64/libgcc_s.so.1
ModLoad: 00007fff`f6dcd000 00007fff`f719a200   /lib64/libc.so.6
ModLoad: 00007fff`f7ddb000 00007fff`f7ffe150   /lib64/ld-linux-x86-64.so.2
ModLoad: 00007fff`f7f72000 00007fff`f7fda288   /usr/share/dotnet/host/fxr/6.0.26/libhostfxr.so
ModLoad: 00007fff`f6b7c000 00007fff`f6dcc3b0   /usr/share/dotnet/shared/Microsoft.NETCore.App/3.1.32/libhostpolicy.so
ModLoad: 00007fff`f63e7000 00007fff`f6b7bac8   /usr/share/dotnet/shared/Microsoft.NETCore.App/3.1.32/libcoreclr.so
ModLoad: 00007fff`f61df000 00007fff`f63e6c38   /lib64/librt.so.1
ModLoad: 00007fff`f57d2000 00007fff`f59dd8c0   /lib64/libnuma.so.1
ModLoad: 00007fff`f3142000 00007fff`f3413dac   /usr/share/dotnet/shared/Microsoft.NETCore.App/3.1.32/libclrjit.so
ModLoad: 00007fff`f2f31000 00007fff`f3141468   /usr/share/dotnet/shared/Microsoft.NETCore.App/3.1.32/System.Native.so
ModLoad: 00007fff`f2d26000 00007fff`f2f30488   /usr/share/dotnet/shared/Microsoft.NETCore.App/3.1.32/System.Globalization.Native.so
ModLoad: 00007fff`f29ad000 00007fff`f2d25fe0   /lib64/libicuuc.so.50
ModLoad: 00007fff`f13da000 00007fff`f29ac030   /lib64/libicudata.so.50
ModLoad: 00007fff`f0fdb000 00007fff`f13d9340   /lib64/libicui18n.so.50
...................
ReadVirtual() failed in GetXStateConfiguration() first read attempt (error == 0.)
Unable to load image /lib64/libpthread.so.0, Win32 error 0n2
*** WARNING: Unable to verify timestamp for /lib64/libpthread.so.0
Unable to load image /usr/share/dotnet/shared/Microsoft.NETCore.App/3.1.32/libcoreclr.so, Win32 error 0n2
*** WARNING: Unable to verify timestamp for /usr/share/dotnet/shared/Microsoft.NETCore.App/3.1.32/libcoreclr.so
libpthread_so!_pthread_cond_timedwait+0x132:
00007fff`f7bcade2 4989c6          mov     r14,rax
0:000> g

有些人可能會好奇，為什么 WinDbg 能偽裝成 GDB 來和 GDBServer 來通訊，這其實得益于 WinDbg 是一個宿主，它可以被很多外來的插件無線擴(kuò)容自己的功能，這和 Linux 的分而治之恰恰相反。。。

接下來可以用 .chain 命令觀察插件列表，其中的 GDBServerComposition 和 ELFBinComposition 讓這項功能得到實現(xiàn)。

0:000> .chain
Extension DLL chain:
    GDBServerComposition: image 10.0.27553.1004, API 0.0.0, 
        [path: C:\Program Files\WindowsApps\Microsoft.WinDbg_1.2402.24001.0_x64__8wekyb3d8bbwe\amd64\winext\GDBServerComposition.dll]
    ELFBinComposition: image 10.0.27553.1004, API 0.0.0, 
        [path: C:\Program Files\WindowsApps\Microsoft.WinDbg_1.2402.24001.0_x64__8wekyb3d8bbwe\amd64\winext\ELFBinComposition.dll]
    dbghelp: image 10.0.27553.1004, API 10.0.6, 
        [path: C:\Program Files\WindowsApps\Microsoft.WinDbg_1.2402.24001.0_x64__8wekyb3d8bbwe\amd64\dbghelp.dll]
    uext: image 10.0.27553.1004, API 1.0.0, 
        [path: C:\Program Files\WindowsApps\Microsoft.WinDbg_1.2402.24001.0_x64__8wekyb3d8bbwe\amd64\winext\uext.dll]

接下來就可以做驗證了，研究 coreclr 源碼，你會發(fā)現(xiàn)在 Linux 上 .NET 的 Sleep 函數(shù)是借助于底層的 pthread_cond_timedwait 函數(shù)，Linux并沒有提供類似Windows 的SleepEx這樣的系統(tǒng)調(diào)用，這就比較坑了，參考如下：

PAL_ERROR CPalSynchronizationManager::ThreadNativeWait(
    ThreadNativeWaitData* ptnwdNativeWaitData,
    DWORD dwTimeout,
    ThreadWakeupReason* ptwrWakeupReason,
    DWORD* pdwSignaledObject)
{
 //...
    while (FALSE == ptnwdNativeWaitData->iPred)
    {
        if (INFINITE == dwTimeout)
        {
            iWaitRet = pthread_cond_wait(&ptnwdNativeWaitData->cond,
                &ptnwdNativeWaitData->mutex);
        }
        else
        {
            iWaitRet = pthread_cond_timedwait(&ptnwdNativeWaitData->cond,
                &ptnwdNativeWaitData->mutex,
                &tsAbsTmo);
        }
    }
 //...
}

圖片

不管怎么說，我們用 WinDbg 調(diào)試 Linux 的 .NET 程序算是大功告成了。

三、總結(jié)

現(xiàn)在的 WinDbg 早已今非昔比，全平臺(MacOs,Linux,Windows) 通吃，這也得益于 Windbg 是一個宿主模式的架構(gòu)體系，給 WinDbg 點贊！

責(zé)任編輯：武曉燕來源：一線碼農(nóng)聊技術(shù)