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GeezerVison is showing github.com — gh-99845: Clean up _PyObject_VAR_SIZE() usage by vstinner · Pull Request #99847 · python/cpython

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@vstinner

@vstinner vstinner commented Nov 28, 2022 •
edited by bedevere-bot
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  • code_sizeof() now uses unsigned type to compute the result.
  • Fix _PyObject_ComputedDictPointer(): cast _PyObject_VAR_SIZE() to Py_ssize_t, rather than long.
  • Clarify that _PyObject_VAR_SIZE() uses an unsigned type (size_t).
  • Issue: PEP 670: Convert _PyObject_SIZE() and _PyObject_VAR_SIZE() macros to functions #99845

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@vstinner
gh-99845: Clean up _PyObject_VAR_SIZE() usage
3ec8130 
* code_sizeof() now uses unsigned type to compute the result.
* Fix _PyObject_ComputedDictPointer(): cast _PyObject_VAR_SIZE() to
  Py_ssize_t, rather than long.
* Clarify that _PyObject_VAR_SIZE() uses an unsigned type (size_t).
@vstinner vstinner added the skip news label Nov 28, 2022
@vstinner
vstinner requested review from markshannon and pablogsal as code owners November 28, 2022 16:43
@bedevere-bot bedevere-bot mentioned this pull request Nov 28, 2022
PEP 670: Convert _PyObject_SIZE() and _PyObject_VAR_SIZE() macros to functions #99845
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@bedevere-bot bedevere-bot added the awaiting core review label Nov 28, 2022
@vstinner
vstinner merged commit 74d5f61 into python:main Nov 29, 2022
@vstinner
vstinner deleted the sizeof_var branch November 29, 2022 11:15
@bedevere-bot bedevere-bot removed the awaiting core review label Nov 29, 2022
serhiy-storchaka
serhiy-storchaka reviewed Nov 30, 2022
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Comment thread Objects/object.c
}
size_t size = _PyObject_VAR_SIZE(tp, tsize);
assert(size <= (size_t)PY_SSIZE_T_MAX);
dictoffset += (Py_ssize_t)size;

@serhiy-storchaka serhiy-storchaka Nov 30, 2022

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It should be backported.

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@vstinner

vstinner commented Dec 1, 2022

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The dictoffset code was different in 2001 when the cast was added: commit 6d483d3

Change:

-               dictoffset += size;
+               dictoffset += (long)size;

Code:

PyObject **
_PyObject_GetDictPtr(PyObject *obj)
{
        long dictoffset;
        ...
        if (dictoffset < 0) {
                size_t size;
                _PyObject_VAR_SIZE(size, tp, ((PyVarObject *)obj)->ob_size);
                dictoffset += (long)size;
                assert(dictoffset > 0);
                assert(dictoffset % SIZEOF_VOID_P == 0);
        }
        ...
}

The dictoffset type was changed in 2006 by commit 725507b without updating the cast, forgotten in the enhancement.

My change, replace (long) cast with (Py_ssize_t) only impact 64-bit Windows. On other platforms, long and Py_ssize_t should be the same type (either 32-bit or 64-bit signed integer, int32_t or int64_t).
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@vstinner

vstinner commented Dec 1, 2022

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I created PR #99922 to backport the cast fix to Python 3.11 (and 3.10).
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@serhiy-storchaka serhiy-storchaka serhiy-storchaka left review comments
@pablogsal pablogsal Awaiting requested review from pablogsal pablogsal is a code owner
@markshannon markshannon Awaiting requested review from markshannon markshannon is a code owner

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@vstinner @serhiy-storchaka @bedevere-bot
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