Openwall GNU/*/Linux - a small security-enhanced Linux distro for servers
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Date: Wed, 31 Jul 2019 10:30:26 +0200
From: Florian Weimer <>
To: Rich Felker <>
Subject: Re: vdso clock_gettime and time64

* Rich Felker:

> One looming thing that folks probably aren't going to like about
> switching to 64-bit time_t is losing the vdso clock_gettime on old
> kernels. Instead of a function call in userspace, you get *two*
> syscalls, the first (time64) one failing, every time you call
> clock_gettime. Of course the problem goes away immediately if you have
> a time64-capable kernel providing the time64 vdso function.
> Is this a problem, and if so, what can be done about it?

Some users notice fairly quickly if the vDSO fast path is gone and file
bug reports.  (This can happen for various reasons, e.g. buggy kernels
detecting CPU cycle counter drift when there is actually none.)  I don't
know to what extent this matters to legacy architectures.


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