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[3.11] gh-97786: Fix compiler warnings in pytime.c (GH-101826) (#102062)

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gh-97786: Fix compiler warnings in pytime.c (GH-101826)

Fixes compiler warnings in pytime.c.
(cherry picked from commit b1b375e267)

Co-authored-by: Mark Dickinson <dickinsm@gmail.com>
Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>
This commit is contained in:
Miss Islington (bot) 2023-02-22 11:11:59 -08:00 • committed by GitHub
parent edbde8feb7
commit ddb65c47b1
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2 changed files with 31 additions and 6 deletions
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2
Misc/NEWS.d/next/Library/2023-02-11-13-23-29.gh-issue-97786.QjvQ1B.rst Normal file
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@ -0,0 +1,2 @@
Fix potential undefined behaviour in corner cases of floating-point-to-time
conversions.

35
Python/pytime.c
View file

@ -1,5 +1,4 @@
#include "Python.h"
#include "pycore_pymath.h" // _Py_InIntegralTypeRange()
#ifdef MS_WINDOWS
# include <winsock2.h> // struct timeval
#endif
@ -41,6 +40,14 @@
# error "unsupported time_t size"
#endif
#if PY_TIME_T_MAX + PY_TIME_T_MIN != -1
# error "time_t is not a two's complement integer type"
#endif
#if _PyTime_MIN + _PyTime_MAX != -1
# error "_PyTime_t is not a two's complement integer type"
#endif
static void
pytime_time_t_overflow(void)
@ -294,7 +301,21 @@ pytime_double_to_denominator(double d, time_t *sec, long *numerator,
}
assert(0.0 <= floatpart && floatpart < denominator);
if (!_Py_InIntegralTypeRange(time_t, intpart)) {
/*
Conversion of an out-of-range value to time_t gives undefined behaviour
(C99 §6.3.1.4p1), so we must guard against it. However, checking that
`intpart` is in range is delicate: the obvious expression `intpart <=
PY_TIME_T_MAX` will first convert the value `PY_TIME_T_MAX` to a double,
potentially changing its value and leading to us failing to catch some
UB-inducing values. The code below works correctly under the mild
assumption that time_t is a two's complement integer type with no trap
representation, and that `PY_TIME_T_MIN` is within the representable
range of a C double.
Note: we want the `if` condition below to be true for NaNs; therefore,
resist any temptation to simplify by applying De Morgan's laws.
*/
if (!((double)PY_TIME_T_MIN <= intpart && intpart < -(double)PY_TIME_T_MIN)) {
pytime_time_t_overflow();
return -1;
}
@ -349,7 +370,8 @@ _PyTime_ObjectToTime_t(PyObject *obj, time_t *sec, _PyTime_round_t round)
d = pytime_round(d, round);
(void)modf(d, &intpart);
if (!_Py_InIntegralTypeRange(time_t, intpart)) {
/* See comments in pytime_double_to_denominator */
if (!((double)PY_TIME_T_MIN <= intpart && intpart < -(double)PY_TIME_T_MIN)) {
pytime_time_t_overflow();
return -1;
}
@ -507,8 +529,9 @@ pytime_from_double(_PyTime_t *tp, double value, _PyTime_round_t round,
d *= (double)unit_to_ns;
d = pytime_round(d, round);
if (!_Py_InIntegralTypeRange(_PyTime_t, d)) {
pytime_overflow();
/* See comments in pytime_double_to_denominator */
if (!((double)_PyTime_MIN <= d && d < -(double)_PyTime_MIN)) {
pytime_time_t_overflow();
return -1;
}
_PyTime_t ns = (_PyTime_t)d;
@ -902,7 +925,7 @@ py_get_system_clock(_PyTime_t *tp, _Py_clock_info_t *info, int raise_exc)
info->monotonic = 0;
info->adjustable = 1;
if (clock_getres(CLOCK_REALTIME, &res) == 0) {
info->resolution = res.tv_sec + res.tv_nsec * 1e-9;
info->resolution = (double)res.tv_sec + (double)res.tv_nsec * 1e-9;
}
else {
info->resolution = 1e-9;