linux-kernel - Re: [PATCH v2 04/10] um: Turn signals

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Message-ID: <3c4bc989c4f10609eab699b26e8331bc878c2a0a.camel@sipsolutions.net>
Date: Thu, 11 Sep 2025 09:37:58 +0200
From: Benjamin Berg <benjamin@...solutions.net>
To: Tiwei Bie <tiwei.bie@...ux.dev>, johannes@...solutions.net
Cc: richard@....at, anton.ivanov@...bridgegreys.com, arnd@...db.de, 
	linux-um@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	tiwei.btw@...group.com
Subject: Re: [PATCH v2 04/10] um: Turn signals_* into thread-local variables

Hi,

On Thu, 2025-09-11 at 12:34 +0800, Tiwei Bie wrote:
> On Wed, 10 Sep 2025 14:15:28 +0200, Johannes Berg wrote:
> > On Sun, 2025-08-10 at 13:51 +0800, Tiwei Bie wrote:
> > > From: Tiwei Bie <tiwei.btw@...group.com>
> > > 
> > > Turn signals_enabled, signals_pending and signals_active into
> > > thread-local variables. This enables us to control and track
> > > signals independently on each CPU thread. This is a preparation
> > > for adding SMP support.
> > 
> > [...]
> > 
> > > +static __thread int signals_enabled;
> > 
> > How much glibc infrastructure does __thread rely on? More
> > specifically:
> > Some time ago we had a discussion about building UML as a nolibc
> > binary,
> > what would that mean for the __thread usage here?
> 
> We would need to parse TLS data (PT_TLS) from the ELF file ourselves
> and properly set up TLS when creating threads using clone().

I guess right now we cannot use PER_CPU variables in these files.
However, my expectation that this is possible when using nolibc, and
then it should be simple enough to replace the __thread.

Benjamin