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Date: Mon, 25 Jan 2021 20:48:18 +0100
From: Florian Weimer <>
To: Markus Wichmann <>
Subject: Re: insufficient checking in

* Markus Wichmann:

> Adding a getpid vDSO call would require adding the code itself, adding
> the PID to the vvar page (isn't that shared among all processes?), and
> adding support for finding the vDSO function into the libcs. All of that
> for rather dubious performance benefits (or can you name a program that
> was not fast enough because getpid() ran too slowly?)

There's some discussion about this in the context of extensible rseq
support, including userspace donating thread-local data for kernel use
(“KTLS”).  Reliable PID/TID/UID caching in userspace and sigprocmask
with a userspace fastpath are potential applications.

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