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

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

[利承昕]

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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.

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

Re: 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