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Re: Disabling TLS address caching to help QEMU on GNU/Linux

From: Thomas Huth
Subject: Re: Disabling TLS address caching to help QEMU on GNU/Linux
Date: Wed, 21 Jul 2021 09:22:24 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0

On 20/07/2021 16.52, Florian Weimer wrote:
Currently, the GNU/Linux ABI does not really specify whether the thread
pointer (the address of the TCB) may change at a function boundary.
One important piece of software for GNU is QEMU (not just for GNU/Linux,
Hurd development also benefits from virtualization).  QEMU uses stackful
coroutines extensively.  There are some hard-to-change code areas where
resumption happens across threads unfortunately.  These increasingly
cause problems with more inlining, inter-procedural analysis, and a
general push towards LTO (which is also needed for some security
hardening features).

Thanks a lot for your mail, Florian!

As a context for those who read about this for the very first time: We're currently facing the problem that the coroutines in QEMU fail when compiling QEMU with -flto on a non-x86 architecture, see:


Should the GNU toolchain offer something to help out the QEMU

I guess that would be extremely helpful...


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