Re: [PATCH 2/2] x86/asm/entry/32: Remove unnecessary optimization in stub32_clone

From: Josh Triplett <josh@joshtriplett.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>,
	Denys Vlasenko <dvlasenk@redhat.com>,
	Ingo Molnar <mingo@kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
	Oleg Nesterov <oleg@redhat.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Alexei Starovoitov <ast@plumgrid.com>,
	Will Drewry <wad@chromium.org>, Kees Cook <keescook@chromium.org>,
	X86 ML <x86@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] x86/asm/entry/32: Remove unnecessary optimization in stub32_clone
Date: Wed, 22 Apr 2015 13:12:41 -0700	[thread overview]
Message-ID: <20150422201241.GA954@jtriplet-mobl1> (raw)
In-Reply-To: <CA+55aFxTmMSUbtQCP_ob-n4c2oGKWtGeQ8A165hVmt8-dHJrxA@mail.gmail.com>

On Wed, Apr 22, 2015 at 11:22:02AM -0700, Linus Torvalds wrote:
> On Wed, Apr 22, 2015 at 10:10 AM, Josh Triplett <josh@joshtriplett.org> wrote:
> >
> > I do think my two-patch HAVE_COPY_THREAD_TLS series should go in fixing
> > this
> 
> Ugh, I absolutely detesrt that patch.
> 
> Don't make random crazy function signatures that depend on some config
> option. That's just evil. The patch is a mess of #ifdef's and should
> be shot in the head and staked with a silver stake to  make sure it
> never re-appears.
> 
> Either:
> 
>  (a) make the change for every architecture
> 
>  (b) have side-by-side interfaces. With different names!

...that's exactly what I did.  They're called copy_thread and
copy_thread_tls; I very intentionally did not conditionally change the
signature of copy_thread, for exactly that reason.  Those functions are
implemented in architecture-specific code, so the config option just
specifies which of the two functions the architecture provides.

*sys_clone* has different function signatures based on config options,
but I didn't touch that other than fixing the type of the tls argument.
That's historical baggage that we can't throw away without breaking
userspace.

- Josh Triplett