eryksun added the comment:
> On Windows, the C lib strftime() segfaults with a trailing '%',
> just as it does with unsupported format codes.
No, it doesn't segfault; it invokes the invalid parameter handler (IPH). This
could always be configured for the whole process, but with VC 14 it can also be
configured per thread. I think it was Steve Dower who updated time_strftime to
take advantage of this feature in 3.5, using the new macros
_Py_BEGIN_SUPPRESS_IPH and _Py_END_SUPPRESS_IPH. This allowed removing the
following check that used to be in the code prior to 3.5:
if (outbuf[1]=='\0' ||
!strchr("aAbBcdHIjmMpSUwWxXyYzZ%", outbuf[1]))
{
PyErr_SetString(PyExc_ValueError, "Invalid format string");
Py_DECREF(format);
return NULL;
}
With this change the time module no longer has to make assumptions about what
the CRT considers to be a valid format string in order to avoid invoking the
IPH. However, this also accidentally removed checking whether outbuf[1]=='\0'.
Now, instead of calling the default IPH that terminates the process, Python's
_silent_invalid_parameter_handler gets called, which of course does nothing by
design:
>>> import time
>>> time.strftime('A%')
Breakpoint 0 hit
python35!_silent_invalid_parameter_handler:
00000000`5eadae50 c20000 ret 0
0:000> k8
Child-SP RetAddr Call Site
00000000`002af018 000007fe`e9d8d2ab
python35!_silent_invalid_parameter_handler
00000000`002af020 000007fe`e9d8d2c9 ucrtbase!invalid_parameter+0x103
00000000`002af060 000007fe`e9dafedc ucrtbase!invalid_parameter_noinfo+0x9
00000000`002af0a0 000007fe`e9dac359 ucrtbase!Wcsftime_l+0x168
00000000`002af140 000007fe`e9dac3f5 ucrtbase!Strftime_l+0x155
00000000`002af1d0 00000000`5e9fc785 ucrtbase!strftime+0x15
00000000`002af210 00000000`5ea7d5c2 python35!time_strftime+0x1f5
00000000`002af2b0 00000000`5eaf8fd0 python35!PyCFunction_Call+0x122
----------
nosy: +eryksun
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<http://bugs.python.org/issue24917>
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