[gdb] Allow gdb.Value to take a Buffer plus a Type

[timo]

Support for this was introduced in a commit in 2019, which I think means it's been available since gdb 9.1

Commit that introduced the feature: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=fe07eca59d0544eb6c56c3559da9ceece23cae6e

If the type value passed is None or there is no second argument, it falls back to its "convert value from python" logic which tries a few things (bool, long, float, unicode string, gdb.Value, gdb.LazyString).

If instead the type is passed and is not None, it will always go through the buffer protocol, which interestingly means that you can't pass a gdb.Value nor a gdb.LazyString to the variant of the constructor with a type.

(gdb) python-interactive
>>> val = gdb.Value(99)
>>> t = gdb.lookup_type("uint64_t")
>>> t
<gdb.Type code=TYPE_CODE_TYPEDEF name=uint64_t>
>>> gdb.Value(val, t)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
    gdb.Value(val, t)
    ~~~~~~~~~^^^^^^^^
TypeError: Object must support the python buffer protocol.
>>> argv = gdb.selected_frame().read_var("argv")
>>> argv
<gdb.Value object at 0x7f4721a789b0>
>>> argv[0].lazy_string()
<gdb.LazyString object at 0x7f47235be3a0>
>>> ls = argv[0].lazy_string()
>>> gdb.Value(ls, t)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
    gdb.Value(ls, t)
    ~~~~~~~~~^^^^^^^
TypeError: Object must support the python buffer protocol.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[timo]

Thanks!