# Vim documentation: debug

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    *debug.txt*	For Vim version 9.2.  Last change: 2026 Feb 14

    		  VIM REFERENCE MANUAL	  by Bram Moolenaar

    Debugging Vim						*debug-vim*

    This is for debugging Vim itself, when it doesn't work properly.
    For debugging Vim scripts, functions, etc. see |debug-scripts|

    1. Location of a crash, using gcc and gdb	|debug-gcc|
    2. Locating memory leaks			|debug-leaks|
    3. Windows Bug Reporting			|debug-win32|

    ==============================================================================

    1. Location of a crash, using gcc and gdb		*debug-gcc* *gdb*

    When Vim crashes in one of the test files, and you are using gcc for
    compilation, here is what you can do to find out exactly where Vim crashes.
    This also applies when using the MingW tools.

    1. Compile Vim with the "-g" option (there is a line in the src/Makefile for
       this, which you can uncomment).  Also make sure "strip" is disabled (do not
       install it, or use the line "STRIP = /bin/true").

    2. Execute these commands (replace "11" with the test that fails):
    	cd testdir
    	gdb ../vim
    	run -u unix.vim -U NONE -s dotest.in test11.in

    3. Check where Vim crashes, gdb should give a message for this.

    4. Get a stack trace from gdb with this command:
    	where
       You can check out different places in the stack trace with:
    	frame 3
       Replace "3" with one of the numbers in the stack trace.

    ==============================================================================

    2. Locating memory leaks			*debug-leaks* *valgrind*

    If you suspect Vim is leaking memory and you are using Linux, the valgrind
    tool is very useful to pinpoint memory leaks.

    First of all, build Vim with EXITFREE defined.  Search for this in MAKEFILE
    and uncomment the line.

    Use this command to start Vim:

    	valgrind --log-file=valgrind.log --leak-check=full ./vim

    Note: Vim will run much slower.  If your .vimrc is big or you have several
    plugins you need to be patient for startup, or run with the "--clean"
    argument.

    There are often a few leaks from libraries, such as getpwuid() and
    XtVaAppCreateShell().  Those are unavoidable.  The number of bytes should be
    very small a Kbyte or less.

    ==============================================================================

    3. Windows Bug Reporting				*debug-win32*

    If the Windows version of Vim crashes in a reproducible manner, you can take
    some steps to provide a useful bug report.

    3.1 GENERIC

    You must obtain the debugger symbols (PDB) file for your executable: gvim.pdb
    for gvim.exe, or vim.pdb for vim.exe.  The PDB should be available from the
    same place that you obtained the executable.  Be sure to use the PDB that
    matches the EXE (same date).

    If you built the executable yourself with the Microsoft Visual C++ compiler,
    then the PDB was built with the EXE.

    If you have Visual Studio, use that instead of the VC Toolkit and WinDbg.

    For other compilers, you should always use the corresponding debugger: gdb
    (see above |debug-gcc|) for the Cygwin and MinGW compilers.

    								*debug-vs2005*
    3.2 Debugging Vim crashes with Visual Studio 2005/Visual C++ 2005 Express

    First launch vim.exe or gvim.exe and then launch Visual Studio.  (If you don't
    have Visual Studio, follow the instructions at |get-ms-debuggers| to obtain a
    free copy of Visual C++ 2005 Express Edition.)

    On the Tools menu, click Attach to Process.  Choose the Vim process.

    In Vim, reproduce the crash.  A dialog will appear in Visual Studio, telling
    you about the unhandled exception in the Vim process.  Click Break to break
    into the process.

    Visual Studio will pop up another dialog, telling you that no symbols are
    loaded and that the source code cannot be displayed.  Click OK.

    Several windows will open.  Right-click in the Call Stack window.  Choose Load
    Symbols.  The Find Symbols dialog will open, looking for (g)vim.pdb.  Navigate
    to the directory where you have the PDB file and click Open.

    At this point, you should have a full call stack with vim function names and
    line numbers.  Double-click one of the lines and the Find Source dialog will
    appear.  Navigate to the directory where the Vim source is (if you have it.)

    If you don't know how to debug this any further, follow the instructions
    at ":help bug-reports".  Paste the call stack into the bug report.

    If you have a non-free version of Visual Studio, you can save a minidump via
    the Debug menu and send it with the bug report.  A minidump is a small file
    (<100KB), which contains information about the state of your process.
    Visual C++ 2005 Express Edition cannot save minidumps and it cannot be
    installed as a just-in-time debugger.  Use WinDbg, |debug-windbg|, if you
    need to save minidumps or you want a just-in-time (postmortem) debugger.

    								*debug-windbg*
    3.3 Debugging Vim crashes with WinDbg

    See |get-ms-debuggers| to obtain a copy of WinDbg.

    As with the Visual Studio IDE, you can attach WinDbg to a running Vim process.
    You can also have your system automatically invoke WinDbg as a postmortem
    debugger.  To set WinDbg as your postmortem debugger, run "windbg -I".

    To attach WinDbg to a running Vim process, launch WinDbg.  On the File menu,
    choose Attach to a Process.  Select the Vim process and click OK.

    At this point, choose Symbol File Path on the File menu, and add the folder
    containing your Vim PDB to the sympath.  If you have Vim source available,
    use Source File Path on the File menu.  You can now open source files in
    WinDbg and set breakpoints, if you like.  Reproduce your crash.  WinDbg should
    open the source file at the point of the crash.  Using the View menu, you can
    examine the call stack, local variables, watch windows, and so on.

    If WinDbg is your postmortem debugger, you do not need to attach WinDbg to
    your Vim process.  Simply reproduce the crash and WinDbg will launch
    automatically.  As above, set the Symbol File Path and the Source File Path.

    To save a minidump, type the following at the WinDbg command line:
            .dump vim.dmp

    							*debug-minidump*
    3.4 Opening a Minidump

    If you have a minidump file, you can open it in Visual Studio or in WinDbg.

    In Visual Studio 2005: on the File menu, choose Open, then Project/Solution.
    Navigate to the .dmp file and open it.  Now press F5 to invoke the debugger.
    Follow the instructions in |debug-vs2005| to set the Symbol File Path.

    In WinDbg: choose Open Crash Dump on the File menu.  Follow the instructions
    in |debug-windbg| to set the Symbol File Path.

    							*get-ms-debuggers*
    3.5 Obtaining Microsoft Debugging Tools

    The Debugging Tools for Windows (including WinDbg) can be downloaded from
        https://learn.microsoft.com/en-us/windows-hardware/drivers/debugger/debugger-download-tools
    This includes the WinDbg debugger.

    Visual C++ 2005 Express Edition can be downloaded for free from:
        https://visualstudio.microsoft.com/

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