linux-kernel - Re: powerpc allyesconfig / allmodconfig linux-next next-20160729

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Date:	Thu, 04 Aug 2016 17:43:20 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Nicholas Piggin <npiggin@...il.com>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	Nicolas Pitre <nico@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Luis R. Rodriguez" <mcgrof@...nel.org>,
	linux-next@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	linuxppc-dev@...ts.ozlabs.org, Guenter Roeck <linux@...ck-us.net>
Subject: Re: powerpc allyesconfig / allmodconfig linux-next next-20160729 - next-20160729 build failures

On Thursday, August 4, 2016 11:54:18 PM CEST Nicholas Piggin wrote:
> On Thu, 4 Aug 2016 22:31:39 +1000
> Nicholas Piggin <npiggin@...il.com> wrote:
> > On Thu, 04 Aug 2016 14:09:02 +0200
> > Arnd Bergmann <arnd@...db.de> wrote:
> > > Nicolas Pitre has done some related work, adding him to Cc. IIRC we have
> > > actually had multiple implementations of -ffunction-sections/--gc-sections
> > > in the past that people have used in production, but none of them
> > > ever made it upstream.  
> 
> After some googling around it seems lto has been difficult to
> get in and it was agreed this gc-sections should be done first
> anyway (although it may indeed provide a superset of DCE, but
> it's always going to be more costly and complicated). Lto would
> have the same issue with liveness of entry points, which is
> really the only thing you need change in the kernel as far as I
> can see.

Ok, good.

> I didn't really see what problems people were having with it
> though, so maybe it's architecture specific or something I
> haven't run into yet.

I remember trying it a few years ago without success, it's possible
that old binutils versions were more problematic.

I'm happy to test your patches on ARM, with my randconfig builder
I tend to find obscure bugs in corner cases that you might not
normally find with just defconfig/allmodconfig builds.

	Arnd