vstinner
commented
3 years ago In Python 3.6, there was a WANT_SIGFPE_HANDLER macro defined if Python was built with ./configure --with-fpectl. By default, the macro was not defined. The fpectl module installed a SIGFPE signal handler which uses longjmp(). If the WANT_SIGFPE_HANDLER macro was defined, PyFPE_START_PROTECT() and PyFPE_END_PROTECT() macros used setjmp() to catch SIGFPE.
All of this machinery was removed by bpo-29137 to fix ABI issues:
commit 735ae8d139a673b30b321dc10acfd3d14f0d633b Author: Nathaniel J. Smith \njs@pobox.com\ Date: Fri Jan 5 23:15:34 2018 -0800
bpo-29137: Remove fpectl module (bpo-4789)
This module has never been enabled by default, never worked correctly
on x86-64, and caused ABI problems that caused C extension
compatibility. See bpo-29137 for details/discussion.The PyFPE_START_PROTECT() and PyFPE_END_PROTECT() macros still exist for backward compatibility with Python 3.6 and older. Python/pyfpe.c contains the comment:
/* These variables used to be used when Python was built with --with-fpectl,
- but support for that was dropped in 3.7. We continue to define them,
- though, because they may be referenced by extensions using the stable ABI. */
I'm not convinced that these macros are part of the stable ABI. The PEP-384 doesn't exclude pyfpe.h explicitly, but it's also unclear if it's part of the stable ABI or not. "PyFPE_START_PROTECT" and "PyFPE_END_PROTECT" symbols are not part of the stable ABI at least: they are missing from PC/python3dll.c and Doc/data/stable_abi.dat. Well, these are macros which emitted directly code rather than calling an opaque function. That sounds really bad in term of stable ABI :-(
Python 3.6 macros, when WANT_SIGFPE_HANDLER macro is defined:
---
#include <signal.h>
#include <setjmp.h>
#include <math.h>
extern jmp_buf PyFPE_jbuf;
extern int PyFPE_counter;
extern double PyFPE_dummy(void *);
#define PyFPE_START_PROTECT(err_string, leave_stmt) \
if (!PyFPE_counter++ && setjmp(PyFPE_jbuf)) { \
PyErr_SetString(PyExc_FloatingPointError, err_string); \
PyFPE_counter = 0; \
leave_stmt; \
}
#define PyFPE_END_PROTECT(v) PyFPE_counter -= (int)PyFPE_dummy(&(v));I propose to either deprecate these macros or remove them. These macros are not documented.
In Python 3.6, the PyFPE macros were used in the Python stdlib, by files:
Doc/library/fpectl.rst Include/pyfpe.h Modules/_tkinter.c Modules/clinic/cmathmodule.c.h Modules/cmathmodule.c Modules/fpetestmodule.c Modules/mathmodule.c Objects/complexobject.c Objects/floatobject.c Python/bltinmodule.c Python/pystrtod.c
But it doesn't seem to be used outside Python.
Note: In master, they are not used anywhere, they are only defined by Include/pyfpe.h.
shihai1991
njsmith
da-woods
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: ```python assignee = None closed_at = None created_at =
labels = ['expert-C-API', '3.10']
title = '[C API] Deprecate or remove PyFPE_START_PROTECT() and PyFPE_END_PROTECT()'
updated_at =
user = 'https://github.com/vstinner'
```
bugs.python.org fields:
```python
activity =
actor = 'corona10'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['C API']
creation =
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 43250
keywords = []
message_count = 8.0
messages = ['387213', '387215', '387218', '387219', '387220', '387225', '387461', '387467']
nosy_count = 4.0
nosy_names = ['vstinner', 'njs', 'corona10', 'shihai1991']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue43250'
versions = ['Python 3.10']
```