Linux vsyscall deprecated, may still be used in some project apps

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Joined: 28 Jun 14
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Message 79662 - Posted: 18 Jul 2017, 4:51:15 UTC

An alert to Linux hosts... I've updated to a 4.9 kernel (Debian) and discovered that support of the "vsyscall" kernel function is being phased out, i.e. strongly discouraged, but is still "supported" via legacy emulation code with an appropriate kernel compile option. Only some project applications still use "vsyscall." If they do then the kernel will need the CONFIG_LEGACY_VSYSCALL_EMULATE setting. (The other choices are: NATIVE or NONE.) It is likely, but not a sure thing, that distribution kernel images will have that emulation setting. The failure symptom may be a little misleading: computation error, output file absent. There is nothing wrong with the file/directory permissions; rather, the application "seg faults" very early, no output file was ever created, and boincmgr (correctly) reports the output file absent. The "seg fault" results from a vsyscall to a kernel that does not have that capability or an emulation of it. The error is reported in the kern.log and messages. Only limited experience to report:
Asteroids@home (CPU) o.k.; NFS@home (CPU) FAILS; Einstein@home (GPU) o.k.; Einstein@home (CPU) FAILS.
[boinc 7.6.33 / Linux 4.9.30 / GTX 750Ti / AMD 7 1700]
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Message 79677 - Posted: 19 Jul 2017, 1:52:26 UTC

This was brought up some time ago on the Einstein forums. See this thread

I have a couple of Ryzen's doing gravity wave work without any issue at the moment, running Debian Stretch.
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Message 79690 - Posted: 20 Jul 2017, 13:12:54 UTC

This is a problem for projects that use applications that are built using libc 2.13 or earlier. Those don't support the non-vsyscall functions. Those are mainly time() and gettimeofday() that are used in the app.

The solution on the project side is to rebuilt using a libc 2.14 or newer. An ideal build host for this would be Ubuntu 12.04 LTS which has libc 2.15.

The current Debian stretch doesn't have this problem (they enabled vsyscalls again while stretch was still testing) but the next version (buster, now testing) comes with kernel 4.11 which has vsyscalls disabled again.

The solution on the volunteer side is to enable vsyscalls via kernel option "vsyscall=emulate". How to change this differs for each distribution on Debian it is in /etc/default/grub.
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Message boards : Questions and problems : Linux vsyscall deprecated, may still be used in some project apps

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