Disabling TLS address caching to help QEMU on GNU/Linux

[Thomas Huth]

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:

  https://bugzilla.redhat.com/show_bug.cgi?id=1952483#c6

> Should the GNU toolchain offer something to help out the QEMU
> developers?

I guess that would be extremely helpful...

  Thomas