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174 lines
10 KiB
Markdown
174 lines
10 KiB
Markdown
# Adding a Configuration Option
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Configuration options are also called "parameters" in the source. Let's take a look at an existing parameter `gdb-workaround-stop-event` defined in `pwndbg/gdblib/events.py`.
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```python
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DISABLED = "disabled"
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DISABLED_DEADLOCK = "disabled-deadlock"
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ENABLED = "enabled"
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gdb_workaround_stop_event = config.add_param(
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"gdb-workaround-stop-event",
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DISABLED,
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"asynchronous stop events to improve 'commands' functionality",
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help_docstring=f"""
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Note that this may cause unexpected behavior with pwndbg or gdb.execute.
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Values explained:
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+ `{DISABLED}` - Disable the workaround (default).
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+ `{DISABLED_DEADLOCK}` - Disable only deadlock detection; deadlocks may still occur.
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+ `{ENABLED}` - Enable asynchronous stop events; gdb.execute may behave unexpectedly (asynchronously).
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""",
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param_class=pwndbg.lib.config.PARAM_ENUM,
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enum_sequence=[DISABLED, DISABLED_DEADLOCK, ENABLED],
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)
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```
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To understand it, let's also look at the signature of the `Config.add_param` function defined in `pwndbg.lib.config.py`:
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```python
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def add_param(
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self,
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name: str,
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default: Any,
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set_show_doc: str,
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*,
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help_docstring: str = "",
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param_class: int | None = None,
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enum_sequence: Sequence[str] | None = None,
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scope: Scope = Scope.config,
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) -> Parameter:
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# ...
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```
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So, the first argument specifies the name by which the parameter will be used inside the debugger. The second argument specifies the default value of the parameter.
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## set_show_doc
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The third argument is a very brief description of what the parameter is for. The argument is called `set_show_doc` due to how it is used in GDB.
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```text
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pwndbg> set gdb-workaround-stop-event enabled
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Set asynchronous stop events to improve 'commands' functionality to 'enabled'.
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|------------------------------------------------------------|
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```
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```text
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pwndbg> show gdb-workaround-stop-event
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Asynchronous stop events to improve 'commands' functionality is 'enabled'. [...]
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|-----------------------------------------------------------|
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```
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It is therefore recommended to use a noun phrase rather than describe an action. However, it sometimes may be necessary to break this rule to retain the brevity of the description.
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The `set_show_doc` argument should be short because it is displayed with the `config` family of commands.
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```text
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pwndbg> config
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Name Documentation Value (Default)
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----------------------------------------------------------------------------------------------------------------------------
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ai-anthropic-api-key Anthropic API key ''
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ai-history-size maximum number of questions and answers to keep in the prompt 3
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ai-max-tokens the maximum number of tokens to return in the response 100
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ai-model the name of the large language model to query 'gpt-3.5-turbo'
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ai-ollama-endpoint Ollama API endpoint ''
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ai-openai-api-key OpenAI API key ''
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ai-show-usage whether to show how many tokens are used with each OpenAI API call off
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ai-stack-depth rows of stack context to include in the prompt for the ai command 16
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ai-temperature the temperature specification for the LLM query 0
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attachp-resolution-method how to determine the process to attach when multiple candidates exists 'ask'
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auto-explore-auxv stack exploration for AUXV information; it may be really slow 'warn'
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auto-explore-pages whether to try to infer page permissions when memory maps are missing 'warn'
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auto-explore-stack stack exploration; it may be really slow 'warn'
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auto-save-search automatically pass --save to "search" command off
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bn-autosync whether to automatically run bn-sync every step off
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```
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Because of the various contexts in which a parameter can be show, the first letter of the `set_show_doc` string should be lowercase (unless the first word is a name or an abbreviation) and there should be no punctuation at the end. This way, pwndbg and gdb can more easily modify the string to fit it into these contexts.
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## help_docstring
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While `help_docstring` is not mandatory, it is highly recommended to use it. Put a detailed explanation of what the parameter does here, and explain any caveats. This string does not have a size limit and is shown with the following command in GDB:
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```text
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pwndbg> help set gdb-workaround-stop-event
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Set asynchronous stop events to improve 'commands' functionality.
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Note that this may cause unexpected behavior with pwndbg or gdb.execute.
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Values explained:
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+ `disabled` - Disable the workaround (default).
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+ `disabled-deadlock` - Disable only deadlock detection; deadlocks may still occur.
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+ `enabled` - Enable asynchronous stop events; gdb.execute may behave unexpectedly (asynchronously).
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Default: 'disabled'
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Valid values: 'disabled', 'disabled-deadlock', 'enabled'
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```
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Note that the last two lines are automatically generated by pwndbg.
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!!! note
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There is currently no way to display this string nor the `set_show_doc` string in LLDB.
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When writing this explanation, it is important to take into account how it will be displayed [in the documentation](https://pwndbg.re/pwndbg/dev/configuration/) after being parsed as markdown. See what `gdb-workaround-stop-event` looks like here: https://pwndbg.re/pwndbg/dev/configuration/config/#gdb-workaround-stop-event . If there wasn't an empty line between `Values explained:` and ``+ `disabled`..`` the list wouldn't have rendered properly.
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## param_class
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This argument describes the type of the parameter. It will be used by GDB to perform input validation when the parameter is being set so it is important to set this to the correct value. The possible values are defined in `pwndbg.lib.config`, use the most restrictive one that fits:
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```python
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# Boolean value. True or False, same as in Python.
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PARAM_BOOLEAN = 0
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# Boolean value, or 'auto'.
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PARAM_AUTO_BOOLEAN = 1
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# Signed integer value. Disallows zero.
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PARAM_INTEGER = 2
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# Signed integer value.
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PARAM_ZINTEGER = 3
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# Unsigned integer value. Disallows zero.
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PARAM_UINTEGER = 4
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# Unsigned integer value.
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PARAM_ZUINTEGER = 5
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# Unlimited ZUINTEGER.
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PARAM_ZUINTEGER_UNLIMITED = 6
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# String value. Accepts escape sequences.
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PARAM_STRING = 7
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# String value, accepts only one of a number of possible values, specified at
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# parameter creation.
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PARAM_ENUM = 8
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# String value corresponding to the name of a file, if present.
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PARAM_OPTIONAL_FILENAME = 9
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```
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For more information (for instance about what `None` or `"unlimited"` mean) see https://sourceware.org/gdb/current/onlinedocs/gdb.html/Parameters-In-Python.html .
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### enum_sequence
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If the `param_class` is set to `pwndbg.lib.config.PARAM_ENUM` then the `enum_sequence` argument must be supplied as well. It should constitute an array of legal values. GDB and (our) LLDB (driver) won't allow setting the parameter to any other value. The legal values will be automatically displayed at the end of `help_docstring` as previously shown.
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If it isn't immediately obvious what the enum values do, explain them in `help_docstring` using same format that `gdb-workaround-stop-event` uses.
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## scope
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The `scope` argument has the default value of `pwndbg.lib.config.Scope.config` and is used to group parameters. The legal values are:
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```python
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class Scope(Enum):
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# If you want to add another scope here, don't forget to add
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# a command which prints it!
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config = 1
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theme = 2
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heap = 3
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```
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The parameters of each scope are printed using a different command. The `config` scope is printed with [`config`](https://pwndbg.re/pwndbg/dev/commands/pwndbg/config/), the `heap` scope is printed with [`heap-config`](https://pwndbg.re/pwndbg/dev/commands/pwndbg/heap-config/) and the `theme` scope is printed with [`theme`](https://pwndbg.re/pwndbg/dev/commands/pwndbg/theme/). The `config` and `theme` scopes also have corresponding [`configfile`](https://pwndbg.re/pwndbg/dev/commands/pwndbg/configfile/) and [`themefile`](https://pwndbg.re/pwndbg/dev/commands/pwndbg/themefile/) commands which export the values of all the parameters from those scopes.
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### The `theme` scope
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You should never directly pass this scope to `pwndbg.config.add_param`. Instead use the `pwndbg.color.theme.add_param` and `pwndbg.color.theme.add_color_param` wrapper commands like this:
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```python
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# pwndbg/aglib/nearpc.py
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nearpc_branch_marker = pwndbg.color.theme.add_param(
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"nearpc-branch-marker", " ↓", "branch marker line for nearpc command"
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)
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```
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```python
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# pwndbg/color/context.py
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config_highlight_color = theme.add_color_param(
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"highlight-color", "green,bold", "color added to highlights like source/pc"
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)
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```
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## Using the parameter in code
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Usually when a parameter is defined its value is also set to a variable, for instance `gdb_workaround_stop_event = ...` in the initial example. This isn't necessary, as all registered parameters are available as `pwndbg.config.<parameter_name_except_with_underscores>` so in our example, we could also access the `gdb-workaround-stop-event` parameter as `pwndbg.config.gdb_workaround_stop_event`.
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That being said, defining the variable can reduce code verbosity:
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```python
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# pwndbg/aglib/godbg.py
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line_width = pwndbg.config.add_param(
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"go-dump-line-width", 80, "the soft line width for go-dump pretty printing"
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)
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```
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Since the variable is scoped to the `godbg.py` file, its name can be short, and we don't have to write `pwndbg.config.go_dump_line_width` every time.
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### Using color parameters
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Note that the `theme.add_color_param()` function returns a `ColorParameter` object instead of a `Parameter`. The parameter should be used via its `color_function()` method:
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```python
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# pwndbg/aglib/godbg.py
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def fmt_debug(self, val: str, default: str = "") -> str:
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if self.debug:
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return debug_color.color_function(val)
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else:
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return default
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```
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Though you will also see `generateColorFunction(debug_color)(val)` being used in the code to the same effect. |