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ndessart mannequin opened this issue Feb 14, 2020 · 4 comments
Open

variadic function call broken on armhf when passing a float argument #83813

ndessart mannequin opened this issue Feb 14, 2020 · 4 comments
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3.7 (EOL) end of life 3.8 (EOL) end of life 3.9 only security fixes 3.10 only security fixes 3.11 only security fixes topic-ctypes

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@ndessart
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Mannequin

ndessart mannequin commented Feb 14, 2020

BPO 39632
Nosy @FFY00, @ndessart
PRs
  • bpo-39632: Fix ctypes variadic function call convention #18560
    		•
    Files
  • ctypes_variadic_function_tests.diff: Reproduce this issue with ctypes unit tests on an armhf target.
    		•

    Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

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    GitHub fields:

    assignee = None
closed_at = None
created_at = <Date 2020-02-14.10:03:28.170>
labels = ['3.8', '3.9', '3.10', '3.11', 'ctypes', '3.7']
title = 'variadic function call broken on armhf when passing a float argument'
updated_at = <Date 2021-07-23.09:26:19.255>
user = 'https://github.com/ndessart'

    bugs.python.org fields:

    activity = <Date 2021-07-23.09:26:19.255>
actor = 'Nicolas Dessart'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['ctypes']
creation = <Date 2020-02-14.10:03:28.170>
creator = 'Nicolas Dessart'
dependencies = []
files = ['48896']
hgrepos = []
issue_num = 39632
keywords = ['patch']
message_count = 4.0
messages = ['361992', '362307', '398026', '398040']
nosy_count = 2.0
nosy_names = ['FFY00', 'Nicolas Dessart']
pr_nums = ['18560']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue39632'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9', 'Python 3.10', 'Python 3.11']
    @ndessart
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    ndessart mannequin commented Feb 14, 2020

    On armhf and for variadic functions (and contrary to non-variadic functions), the VFP co-processor registers are not used for float argument parameter passing. This specificity is apparently completely disregarded by ctypes which always uses ffi_prep_cif to prepare the parameter passing of a function while it should most probably use ffi_prep_cif_var for variadic functions.

    As such variadic function call with float arguments through ctypes
    is currently broken on armhf targets.

    I think that ctypes API should be updated to let the user specify if a function is variadic.

    I've attached a patch to the ctypes unit tests that I'm using to reproduce this bug.

    pi@raspberrypi:~/code/cpython $ ./python -m test test_ctypes    
0:00:00 load avg: 0.00 Run tests sequentially
0:00:00 load avg: 0.00 [1/1] test_ctypes
_testfunc_d_bhilfd_var got 2 3 4 -1242230680 -0.000000 -0.000000
test test_ctypes failed -- Traceback (most recent call last):
  File "/home/pi/code/cpython/Lib/ctypes/test/test_functions.py", line 146, in test_doubleresult_var
    self.assertEqual(result, 21)
AssertionError: -7.086855952261741e-44 != 21

    test_ctypes failed

    == Tests result: FAILURE ==

    1 test failed:
    test_ctypes

    Total duration: 3.8 sec
    Tests result: FAILURE

    @ndessart ndessart mannequin added 3.9 only security fixes topic-ctypes 3.7 (EOL) end of life 3.8 (EOL) end of life labels Feb 14, 2020
    @ndessart
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    ndessart mannequin commented Feb 20, 2020

    As I said in the associated PR, the build is failing on macOS because ctypes uses an obsolete libffi version bundled into Modules/_ctypes/libffi_osx for this platform. This old version of libffi is missing ffi_prep_cif_var.

    There is an open issue that propose to remove the bundled libffi for OSX.
    https://bugs.python.org/issue28491

    @FFY00
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    FFY00 commented Jul 23, 2021

    bpo-28491 is now resolved, so the PR should be unblocked. Would you mind rebasing it on main to retrigger the CI?

    @ndessart
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    ndessart mannequin commented Jul 23, 2021

    I've just rebased this PR but the CI builds failed (for unrelated reasons?).

    That being said I think that this particular issue should mostly be resolved by bpo-41100 and PR-22855 in particular. My PR 18560 still brings the support for Ellipsis/... inside ctypes function arguments type list. This is nice because it allows ctypes to automatically perform the necessary type promotions even if a variadic function is called without extra arguments.

    Since I've rebased my PR on top of bpo-41100 PRs, I had to resolve a few conflicts but didn't tried to limit the diff to the minimum (PR 18560 may be simplified).

    https://bugs.python.org/issue41100
    #22855

    @ndessart ndessart mannequin added 3.10 only security fixes 3.11 only security fixes labels Jul 23, 2021
    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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