neovim/runtime/doc/dev_tools.txt

*dev_tools.txt*          Nvim


                            NVIM REFERENCE MANUAL


Tools and techniques for developing Nvim                        *dev-tools*

The following advice is helpful when working on or debugging issues with Nvim
itself. See also |debug.txt| for advice that applies to Vim.

                                  Type |gO| to see the table of contents.

==============================================================================
Backtraces                                            *dev-tools-backtrace*

LINUX

Core dumps are disabled by default on Ubuntu, CentOS and others.
To enable core dumps:
>bash
    ulimit -c unlimited
<
On systemd-based systems getting a backtrace is as easy as:
>bash
    coredumpctl -1 gdb
<
`coredumpctl` is an optional tool, so you may need to install it:
>bash
    sudo apt install systemd-coredump
<

The full backtrace is most useful; please send us the `backtrace.txt` file
when reporting a bug related to a crash:
>bash
    2>&1 coredumpctl -1 gdb | tee -a backtrace.txt
    (gdb) thread apply all bt full
<

On systems without `coredumpctl`, you may find a `core` dump file appearing
in the current directory or in other locations. On Linux systems where
`apport` is installed (such as Ubuntu), the directory where core dump files
are saved can be `/var/lib/apport/coredump` or elsewhere, depending on the
system configuration (see `/proc/sys/kernel/core_pattern`). See also:
https://stackoverflow.com/a/18368068

To get a backtrace from the `./core` dump file:
>bash
    gdb build/bin/nvim ./core 2>&1 | tee backtrace.txt
    (gdb) thread apply all bt full
<

MACOS

If `nvim` crashes, you can see the backtrace in `Console.app` (under "Crash
Reports" or "User Diagnostic Reports" for older macOS versions).
>bash
    open -a Console
<
You may also want to enable core dumps on macOS. To do this, first make sure
the `/cores/` directory exists and is writable:
>bash
    sudo mkdir /cores
    sudo chown root:admin /cores
    sudo chmod 1775 /cores
<
Then set the core size limit to `unlimited`:
>bash
    ulimit -c unlimited
<
Note that this is done per shell process. If you want to make this the default
for all shells, add the above line to your shell's init file (e.g. `~/.bashrc`
or similar).

You can then open the core file in `lldb`:
>bash
    lldb -c /cores/core.12345
<
Apple's documentation archive has some other useful information
https://developer.apple.com/library/archive/technotes/tn2124/_index.html#//apple_ref/doc/uid/DTS10003391-CH1-SECCOREDUMPS,
but note that some of the things on this page are out of date (such as enabling
core dumps with `/etc/launchd.conf`).

==============================================================================
Gdb                                                          *dev-tools-gdb*

USING GDB TO STEP THROUGH FUNCTIONAL TESTS

Use `TEST_TAG` to run tests matching busted tags (of the form `#foo` e.g.
`it("test #foo ...", ...)`):
>bash
    GDB=1 TEST_TAG=foo make functionaltest
<
Then, in another terminal:
>bash
    gdb build/bin/nvim
    (gdb) target remote localhost:7777

-- See `nvim_argv` in https://github.com/neovim/neovim/blob/master/test/functional/testnvim.lua.

USING LLDB TO STEP THROUGH UNIT TESTS

>
    lldb .deps/usr/bin/luajit -- .deps/usr/bin/busted --lpath="./build/?.lua" test/unit/
<
USING GDB

To attach to a running `nvim` process with a pid of 1234 (Tip: the pid of a
running Nvim instance can be obtained by calling |getpid()|), for instance:
>bash
    gdb -tui -p 1234 build/bin/nvim
<
The `gdb` interactive prompt will appear. At any time you can:

- `break foo` to set a breakpoint on the `foo()` function
- `n` to step over the next statement
    - `<Enter>` to repeat the last command
- `s` to step into the next statement
- `c` to continue
- `finish` to step out of the current function
- `p zub` to print the value of `zub`
- `bt` to see a backtrace (callstack) from the current location
- `CTRL-x CTRL-a` or `tui enable` to show a TUI view of the source file in the
  current debugging context. This can be extremely useful as it avoids the
  need for a gdb "frontend".
- `<up>` and `<down>` to scroll the source file view

GDB REVERSE DEBUGGING

- `set record full insn-number-max unlimited`
- `continue` for a bit (at least until `main()` is executed
- `record`
- provoke the bug, then use `revert-next`, `reverse-step`, etc. to rewind the
  debugger

USING GDBSERVER

You may want to connect multiple `gdb` clients to the same running `nvim`
process, or you may want to connect to a remote `nvim` process with a local
`gdb`. Using `gdbserver`, you can attach to a single process and control it
from multiple `gdb` clients.

Open a terminal and start `gdbserver` attached to `nvim` like this:
>bash
    gdbserver :6666 build/bin/nvim 2> gdbserver.log
<
`gdbserver` is now listening on port 6666. You then need to attach to this
debugging session in another terminal:
>bash
    gdb build/bin/nvim
<
Once you've entered `gdb`, you need to attach to the remote session:
>
    (gdb) target remote localhost:6666
<
In case gdbserver puts the TUI as a background process, the TUI can become
unable to read input from pty (and receives SIGTTIN signal) and/or output data
(SIGTTOU signal). To force the TUI as the foreground process, you can add
>c
    signal (SIGTTOU, SIG_IGN);
    if (!tcsetpgrp(data->input.in_fd, getpid())) {
        perror("tcsetpgrp failed");
    }
<
to `tui.c:terminfo_start`.

USING GDBSERVER IN TMUX

Consider using a custom makefile
https://github.com/neovim/neovim/blob/master/BUILD.md#custom-makefile to
quickly start debugging sessions using the `gdbserver` method mentioned above.
This example `local.mk` will create the debugging session when you type `make
debug`.
>make
    .PHONY: dbg-start dbg-attach debug build

    build:
        @$(MAKE) nvim

    dbg-start: build
        @tmux new-window -n 'dbg-neovim' 'gdbserver :6666 ./build/bin/nvim -D'

    dbg-attach:
        @tmux new-window -n 'dbg-cgdb' 'cgdb -x gdb_start.sh ./build/bin/nvim'

    debug: dbg-start dbg-attach
<
Here `gdb_start.sh` includes `gdb` commands to be called when the debugger
starts. It needs to attach to the server started by the `dbg-start` rule. For
example:
>
    (gdb) target remote localhost:6666
    (gdb) br main
<

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