Unexpected behavior of `gdb.PARAM_INTEGER` and `gdb.PARAM_UINTEGER` parameter

[Andrew Burgess]

利承昕 via Gdb <gdb@sourceware.org> writes:

> Hi,
>
> I've noticed that if we use Python API to create a `gdb.PARAM_INTEGER` or
> `gdb.PARAM_UINTEGER` parameter this way:
>
> ```
> $ cat test.py
>
> import gdb
> class ExampleParam(gdb.Parameter):
>     def __init__ (self, name):
>         super(ExampleParam, self).__init__ (name, gdb.COMMAND_DATA,
> gdb.PARAM_INTEGER)
>         self.value = 0
>         self.saved_value = True
>
>     def get_set_string (self):
>         print(self.value)
>         return "Set to %r" % self.value
>
> ExampleParam("example”)
> ```
>
> According to the docs here:
> https://sourceware.org/gdb/onlinedocs/gdb/Parameters-In-Python.html, `0`
> should be interpreted to mean "unlimited", so I expected that when a
> `gdb.PARAM_INTEGER` or `gdb.PARAM_UINTEGER` parameter’s value is
> "unlimited" in GDB, then the value in Python will be interpreted to 0.

You are correct that this area is not well documented.  These parameter
types have always returned None for unlimited, so I don't think we'd
want to consider changing the behaviour at this point.

There is already a related patch on the mailing list that will improve
the documentation of these parameter types:

  https://sourceware.org/pipermail/gdb-patches/2022-October/193253.html

Thanks,
Andrew

>
> But somehow, GDB interprets `None` to mean "unlimited" for that parameter
> we created:
>
> ```
> $ gdb -q -nx -ex 'source test.py’
> (gdb) show example
> The current value of 'example' is "unlimited”.
> (gdb) pi gdb.parameter("example") is None
> True
> (gdb) set example unlimited
> None
> Set to None
> (gdb) pi gdb.parameter("example") is None
> True
> (gdb) show example
> The current value of 'example' is "unlimited".
> (gdb) set example 0
> None
> Set to None
> (gdb) pi gdb.parameter("example") is None
> True
> (gdb) show example
> The current value of 'example' is "unlimited".
> ```
>
> You can notice that GDB set the value of the `example` to `None` instead of
> `0`.
>
> Is this the expected result?
>
> My GDB version is GNU gdb (Ubuntu 12.0.90-0ubuntu1) 12.0.90, and I'm on
> Ubuntu 22.04.1 LTS.
>
> Best Regards,
> Alan Li