linux-kernel - Re: [PATCHv2 1/2] clone: Support passing tls argument via C rather than pt

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Message-ID: <20150512213843.GV21418@twins.programming.kicks-ass.net>
Date:	Tue, 12 May 2015 23:38:43 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Josh Triplett <josh@...htriplett.org>,
	Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
	x86@...nel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCHv2 1/2] clone: Support passing tls argument via C rather
 than pt_regs magic

On Tue, May 12, 2015 at 02:22:50PM -0700, Andrew Morton wrote:
> On Mon, 11 May 2015 12:29:19 -0700 Josh Triplett <josh@...htriplett.org> wrote:
> 
> > Introduce a new CONFIG_HAVE_COPY_THREAD_TLS for architectures to opt
> > into, and a new copy_thread_tls that accepts the tls parameter as an
> > additional unsigned long (syscall-argument-sized) argument.
> > Change sys_clone's tls argument to an unsigned long (which does
> > not change the ABI), and pass that down to copy_thread_tls.
> > 
> > Architectures that don't opt into copy_thread_tls will continue to
> > ignore the C argument to sys_clone in favor of the pt_regs captured at
> > kernel entry, and thus will be unable to introduce new versions of the
> > clone syscall.
> 
> What happens quite frequently is that we do something for x86 with the
> expectation that other architectures will follow along, but this
> doesn't happen.  The arch maintainers simply didn't know about it or
> nobody nags them.  Nothing happens and inconsistencies hang around for
> years.  eg, http://lkml.iu.edu/hypermail/linux/kernel/1504.2/04993.html
> 
> I'm thinking we should find a way to do this better.  One way might be
> to maintain a Documentation/arch-todo which identifies each item, has a
> little list of what-to-do instructions and perhaps a list of the
> not-yet-done architectures.  Basically a way for everyone to
> communicate at the arch maintainers.

If only there was a linux-arch list to which arch maintainers should
subscribe... oh wait :-)
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