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pylibfdt: fix get_mem_rsv for newer Python versions #128

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blmaier
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@blmaier blmaier commented Mar 18, 2024

The test for get_mem_rsv fails on newer versions of Python with the following error.

Traceback (most recent call last):
File "/__w/dtc/dtc/tests/pylibfdt_tests.py", line 421, in testReserveMap
self.assertEqual([ 0xdeadbeef00000000, 0x100000],
AssertionError: Lists differ: [16045690981097406464, 1048576] != [0, 16045690981097406464, 1048576]

First differing element 0:
16045690981097406464
0

Second list contains 1 additional elements.
First extra element 2:
1048576

  • [16045690981097406464, 1048576]
  • [0, 16045690981097406464, 1048576]
    ? +++

It appears this is because the PyTuple_GET_SIZE() function that was used to build the fdt_get_mem_rsv() return value has changed. It now is returning a non-zero value when it's passed an integer, which causes the SWIG wrapper to append the returned arguments to the return error rather then ignore them.

This is valid behavior per Python's documentation, which says it will "Return the size of the tuple p, which must be non-NULL and point to a tuple; no error checking is performed"[1]. As passing an integer is not a tuple, its return value is undefined.

Fix this issue on older and newer versions by avoiding PyTuple_GET_SIZE() entirely. Always append the arguments to the list, and instead use the wrapper python function to check the first argument and then splice the last two arguments as the return value.

[1] https://docs.python.org/3/c-api/tuple.html#c.PyTuple_GET_SIZE

The test for get_mem_rsv fails on newer versions of Python with the
following error.

> Traceback (most recent call last):
>   File "/__w/dtc/dtc/tests/pylibfdt_tests.py", line 421, in testReserveMap
>     self.assertEqual([ 0xdeadbeef00000000, 0x100000],
> AssertionError: Lists differ: [16045690981097406464, 1048576] != [0, 16045690981097406464, 1048576]
>
> First differing element 0:
> 16045690981097406464
> 0
>
> Second list contains 1 additional elements.
> First extra element 2:
> 1048576
>
> - [16045690981097406464, 1048576]
> + [0, 16045690981097406464, 1048576]
> ?  +++

It appears this is because the PyTuple_GET_SIZE() function that was used
to build the fdt_get_mem_rsv() return value has changed. It now is
returning a non-zero value when it's passed an integer, which causes the
SWIG wrapper to append the returned arguments to the return error rather
then ignore them.

This is valid behaviour per Python's documentation, which says it will
"Return the size of the tuple p, which must be non-NULL and point to a
tuple; no error checking is performed"[1]. As passing an integer is not
a tuple, its return value is undefined.

Fix this issue on older and newer versions by avoiding
PyTuple_GET_SIZE() entirely. Always append the arguments to the list,
and instead use the wrapper python function to check the first argument
and then splice the last two arguments as the return value.

[1] https://docs.python.org/3/c-api/tuple.html#c.PyTuple_GET_SIZE

Signed-off-by: Brandon Maier <brandon.maier@collins.com>
@blmaier
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blmaier commented Mar 18, 2024

Note that the Alpine test failed on the most recent run. This is unrelated to these changes, but is an intermittent failure due to missing Meson dependencies. See this PR for fix #129

@dgibson
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dgibson commented Mar 19, 2024

Thanks so much for this long overdue fix. Merged.

@dgibson dgibson closed this Mar 19, 2024
@blmaier blmaier deleted the master-pylibfdt-fix-get-mem-rsv-for-newer-python branch March 20, 2024 18:46
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2 participants