debug.txt For Vim version 9.0. Last change: 2019 May 07
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):
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:
You can check out different places in the stack trace with:
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"
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.
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.
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.
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:
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.
3.5 Obtaining Microsoft Debugging Tools
The Debugging Tools for Windows (including WinDbg) can be downloaded from
This includes the WinDbg debugger.
Visual C++ 2005 Express Edition can be downloaded for free from: