1 | #ifndef Py_PYFPE_H |
2 | #define Py_PYFPE_H |
3 | #ifdef __cplusplus |
4 | extern "C" { |
5 | #endif |
6 | /* |
7 | --------------------------------------------------------------------- |
8 | / Copyright (c) 1996. \ |
9 | | The Regents of the University of California. | |
10 | | All rights reserved. | |
11 | | | |
12 | | Permission to use, copy, modify, and distribute this software for | |
13 | | any purpose without fee is hereby granted, provided that this en- | |
14 | | tire notice is included in all copies of any software which is or | |
15 | | includes a copy or modification of this software and in all | |
16 | | copies of the supporting documentation for such software. | |
17 | | | |
18 | | This work was produced at the University of California, Lawrence | |
19 | | Livermore National Laboratory under contract no. W-7405-ENG-48 | |
20 | | between the U.S. Department of Energy and The Regents of the | |
21 | | University of California for the operation of UC LLNL. | |
22 | | | |
23 | | DISCLAIMER | |
24 | | | |
25 | | This software was prepared as an account of work sponsored by an | |
26 | | agency of the United States Government. Neither the United States | |
27 | | Government nor the University of California nor any of their em- | |
28 | | ployees, makes any warranty, express or implied, or assumes any | |
29 | | liability or responsibility for the accuracy, completeness, or | |
30 | | usefulness of any information, apparatus, product, or process | |
31 | | disclosed, or represents that its use would not infringe | |
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33 | | cial products, process, or service by trade name, trademark, | |
34 | | manufacturer, or otherwise, does not necessarily constitute or | |
35 | | imply its endorsement, recommendation, or favoring by the United | |
36 | | States Government or the University of California. The views and | |
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39 | | of California, and shall not be used for advertising or product | |
40 | \ endorsement purposes. / |
41 | --------------------------------------------------------------------- |
42 | */ |
43 | |
44 | /* |
45 | * Define macros for handling SIGFPE. |
46 | * Lee Busby, LLNL, November, 1996 |
47 | * busby1@llnl.gov |
48 | * |
49 | ********************************************* |
50 | * Overview of the system for handling SIGFPE: |
51 | * |
52 | * This file (Include/pyfpe.h) defines a couple of "wrapper" macros for |
53 | * insertion into your Python C code of choice. Their proper use is |
54 | * discussed below. The file Python/pyfpe.c defines a pair of global |
55 | * variables PyFPE_jbuf and PyFPE_counter which are used by the signal |
56 | * handler for SIGFPE to decide if a particular exception was protected |
57 | * by the macros. The signal handler itself, and code for enabling the |
58 | * generation of SIGFPE in the first place, is in a (new) Python module |
59 | * named fpectl. This module is standard in every respect. It can be loaded |
60 | * either statically or dynamically as you choose, and like any other |
61 | * Python module, has no effect until you import it. |
62 | * |
63 | * In the general case, there are three steps toward handling SIGFPE in any |
64 | * Python code: |
65 | * |
66 | * 1) Add the *_PROTECT macros to your C code as required to protect |
67 | * dangerous floating point sections. |
68 | * |
69 | * 2) Turn on the inclusion of the code by adding the ``--with-fpectl'' |
70 | * flag at the time you run configure. If the fpectl or other modules |
71 | * which use the *_PROTECT macros are to be dynamically loaded, be |
72 | * sure they are compiled with WANT_SIGFPE_HANDLER defined. |
73 | * |
74 | * 3) When python is built and running, import fpectl, and execute |
75 | * fpectl.turnon_sigfpe(). This sets up the signal handler and enables |
76 | * generation of SIGFPE whenever an exception occurs. From this point |
77 | * on, any properly trapped SIGFPE should result in the Python |
78 | * FloatingPointError exception. |
79 | * |
80 | * Step 1 has been done already for the Python kernel code, and should be |
81 | * done soon for the NumPy array package. Step 2 is usually done once at |
82 | * python install time. Python's behavior with respect to SIGFPE is not |
83 | * changed unless you also do step 3. Thus you can control this new |
84 | * facility at compile time, or run time, or both. |
85 | * |
86 | ******************************** |
87 | * Using the macros in your code: |
88 | * |
89 | * static PyObject *foobar(PyObject *self,PyObject *args) |
90 | * { |
91 | * .... |
92 | * PyFPE_START_PROTECT("Error in foobar", return 0) |
93 | * result = dangerous_op(somearg1, somearg2, ...); |
94 | * PyFPE_END_PROTECT(result) |
95 | * .... |
96 | * } |
97 | * |
98 | * If a floating point error occurs in dangerous_op, foobar returns 0 (NULL), |
99 | * after setting the associated value of the FloatingPointError exception to |
100 | * "Error in foobar". ``Dangerous_op'' can be a single operation, or a block |
101 | * of code, function calls, or any combination, so long as no alternate |
102 | * return is possible before the PyFPE_END_PROTECT macro is reached. |
103 | * |
104 | * The macros can only be used in a function context where an error return |
105 | * can be recognized as signaling a Python exception. (Generally, most |
106 | * functions that return a PyObject * will qualify.) |
107 | * |
108 | * Guido's original design suggestion for PyFPE_START_PROTECT and |
109 | * PyFPE_END_PROTECT had them open and close a local block, with a locally |
110 | * defined jmp_buf and jmp_buf pointer. This would allow recursive nesting |
111 | * of the macros. The Ansi C standard makes it clear that such local |
112 | * variables need to be declared with the "volatile" type qualifier to keep |
113 | * setjmp from corrupting their values. Some current implementations seem |
114 | * to be more restrictive. For example, the HPUX man page for setjmp says |
115 | * |
116 | * Upon the return from a setjmp() call caused by a longjmp(), the |
117 | * values of any non-static local variables belonging to the routine |
118 | * from which setjmp() was called are undefined. Code which depends on |
119 | * such values is not guaranteed to be portable. |
120 | * |
121 | * I therefore decided on a more limited form of nesting, using a counter |
122 | * variable (PyFPE_counter) to keep track of any recursion. If an exception |
123 | * occurs in an ``inner'' pair of macros, the return will apparently |
124 | * come from the outermost level. |
125 | * |
126 | */ |
127 | |
128 | #ifdef WANT_SIGFPE_HANDLER |
129 | #include <signal.h> |
130 | #include <setjmp.h> |
131 | #include <math.h> |
132 | extern jmp_buf PyFPE_jbuf; |
133 | extern int PyFPE_counter; |
134 | extern double PyFPE_dummy(void *); |
135 | |
136 | #define PyFPE_START_PROTECT(err_string, leave_stmt) \ |
137 | if (!PyFPE_counter++ && setjmp(PyFPE_jbuf)) { \ |
138 | PyErr_SetString(PyExc_FloatingPointError, err_string); \ |
139 | PyFPE_counter = 0; \ |
140 | leave_stmt; \ |
141 | } |
142 | |
143 | /* |
144 | * This (following) is a heck of a way to decrement a counter. However, |
145 | * unless the macro argument is provided, code optimizers will sometimes move |
146 | * this statement so that it gets executed *before* the unsafe expression |
147 | * which we're trying to protect. That pretty well messes things up, |
148 | * of course. |
149 | * |
150 | * If the expression(s) you're trying to protect don't happen to return a |
151 | * value, you will need to manufacture a dummy result just to preserve the |
152 | * correct ordering of statements. Note that the macro passes the address |
153 | * of its argument (so you need to give it something which is addressable). |
154 | * If your expression returns multiple results, pass the last such result |
155 | * to PyFPE_END_PROTECT. |
156 | * |
157 | * Note that PyFPE_dummy returns a double, which is cast to int. |
158 | * This seeming insanity is to tickle the Floating Point Unit (FPU). |
159 | * If an exception has occurred in a preceding floating point operation, |
160 | * some architectures (notably Intel 80x86) will not deliver the interrupt |
161 | * until the *next* floating point operation. This is painful if you've |
162 | * already decremented PyFPE_counter. |
163 | */ |
164 | #define PyFPE_END_PROTECT(v) PyFPE_counter -= (int)PyFPE_dummy(&(v)); |
165 | |
166 | #else |
167 | |
168 | #define PyFPE_START_PROTECT(err_string, leave_stmt) |
169 | #define PyFPE_END_PROTECT(v) |
170 | |
171 | #endif |
172 | |
173 | #ifdef __cplusplus |
174 | } |
175 | #endif |
176 | #endif /* !Py_PYFPE_H */ |
177 | |