Fix SHM driver on x64 Windows

[pziezio]

Hi all,
there is a bug in the SHM driver (ntp-4.2.8p18) that makes it impossible to run on Windows x64 platform.

In refclock_smh.c, line 185:
shmid = CreateFileMapping ((HANDLE)0xffffffff, psec, PAGE_READWRITE,

(HANDLE)0xffffffff is not equal to (-1) on x64 platform.

According to MSDN (https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createfilemappinga#parameters),
it should pass INVALID_HANDLE_VALUE (-1) as a first parameter for this specific use case.

I'm using this driver to provide time from the GPS receiver. For the moment I'm using custom build with this bug corrected and everything works correctly.

[hart-NTP]

Thanks for catching this. refclock_shm.c is not built on Windows by default, and I'm not aware of programs which provide the shared memory for it to use. Is the GPS tool you're using open source?

[hart-NTP]

I've opened a bug report in our primary bug tracker

https://bugs.ntp.org/show_bug.cgi?id=4007

@pziezio if you don't already have a bugs.ntp.org account, I suggest setting one up so you can add yourself as a watcher to that bug report. Thanks again for your report.

[pziezio]

I've already reported this over 2 years ago:
https://bugs.ntp.org/show_bug.cgi?id=3867

But no one replied, hence the report here.

[pziezio]

Thanks for catching this. refclock_shm.c is not built on Windows by default, and I'm not aware of programs which provide the shared memory for it to use. Is the GPS tool you're using open source?

No, unfortunately this is custom software and is not released to the public.

[hart-NTP]

I've resolved 4007 as a duplicate of 3867. I apologize for the lack of attention to your report in 2023. We should get this fixed in 4.2.8p19, along with some minor cleanup to avoid the need to use FormatMessage() in refclock_shm.c and to include the driver in Windows ntpd by default.