Disabling TLS address caching to help QEMU on GNU/Linux

[Michael Matz]

Hello,

On Thu, 22 Jul 2021, Richard Biener via Gcc wrote:

> But how does TLS usage transfer between threads?  On the gimple level 
> the TLS pointer is not visible and thus we'd happily CSE its address:

Yes.  All take-address operations then need to be encoded explicitely with 
a non-CSE-able internal function (or so):

  &x --> __ifn_get_tls_addr(&x);

(&x in the argument just so that it's clear that it doesn't access the 
value at x and to get the current effects of address-taken marking of 
ADDR_EXPR).

(Or of course, ADDR_EXPR could be taken as unstable when applied to TLS 
decls).

Quite a big hammer IMHO.


Ciao,
Michael.