Re: [RFC 0/2] tls: add macros for coroutine-safe TLS variables

[Richard Henderson]

On 10/26/21 9:34 AM, Stefan Hajnoczi wrote:
> On Tue, Oct 26, 2021 at 08:10:16AM -0700, Richard Henderson wrote:
> > On 10/26/21 6:22 AM, Stefan Hajnoczi wrote:
> > > If "safe" TLS variables are opt-in then we'll likely have obscure bugs
> > > when code changes to access a TLS variable that was previously never
> > > accessed from a coroutine. There is no compiler error and no way to
> > > detect this. When it happens debugging it is painful.
> >
> > Co-routines are never used in user-only builds.
>
> If developers have the choice of using __thread then bugs can slip
> through.

Huh?  How.  No, really.

> Are you concerned about performance, the awkwardness of calling
> getters/setters, or something else for qemu-user?

Awkwardness first, performance second.

I'll also note that coroutines never run on vcpu threads, only io threads.  So I'll resist 
any use of these interfaces in TCG as well.


r~