linux-kernel - Re: [PATCH 2/2] x86/asm/entry/32: Remove unnecessary optimization in stub32

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Date:	Wed, 22 Apr 2015 13:12:41 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>, Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] x86/asm/entry/32: Remove unnecessary optimization in
 stub32_clone

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@...htriplett.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
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