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From: Nicolas Pitre <nicolas.pitre@linaro.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Nicholas Piggin <npiggin@gmail.com>,
	linux-kbuild@vger.kernel.org, linux-arch@vger.kernel.org,
	Michal Marek <mmarek@suse.com>, Sam Ravnborg <sam@ravnborg.org>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Segher Boessenkool <segher@kernel.crashing.org>,
	Alan Modra <amodra@gmail.com>
Subject: Re: [EXPERIMENTAL] enable thin archives and --gc-sections on ARM
Date: Thu, 11 Aug 2016 17:05:09 -0400 (EDT)	[thread overview]
Message-ID: <alpine.LFD.2.20.1608111648520.17623@knanqh.ubzr> (raw)
In-Reply-To: <7664972.4URQm6Y4Ik@wuerfel>

On Thu, 11 Aug 2016, Arnd Bergmann wrote:

> On Thursday, August 11, 2016 4:01:33 PM CEST Nicolas Pitre wrote:
> > >  #ifdef CONFIG_SMP_ON_UP
> > >       .init.smpalt : {
> > >               __smpalt_begin = .;
> > > -             *(.alt.smp.init)
> > > +             KEEP(*(.alt.smp.init))
> > 
> > Yes unfortunately this needs a KEEP() right now as there is no explicit 
> > references to those entries. But by doing so you force a reference from 
> > those entries to all functions they annotate, preventing those functions 
> > from being discarded if there isn't any reference to that code 
> > otherwise. That's a case that falls into the "missing forward reference" 
> > category in my slides.
> 
> I see. This actually relates to an existing problem with SMP alternatives
> in exit sections, which cause a linker error. I've done a patch for
> this at some point, but didn't feel confident enough to send it out

The only sane way I found to solve this implied a patch to gas, and it 
was accepted upstream. Please see:

http://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=451133cefa

The example given is for .init sections, but that would solve the 
link-time discarding of .exit sections just as well.


Nicolas

  reply	other threads:[~2016-08-11 21:05 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-08-11 10:16 [PATCH 0/6 v2] kbuild changes, thin archives, --gc-sections Nicholas Piggin
2016-08-11 10:16 ` [PATCH 1/6] kbuild: allow architectures to use thin archives instead of ld -r Nicholas Piggin
2016-08-11 10:16 ` [PATCH 2/6] kbuild: allow archs to select link dead code/data elimination Nicholas Piggin
2016-08-11 10:16 ` [PATCH 3/6] kbuild: add arch specific post-link pass Nicholas Piggin
2016-08-16  9:23   ` Michal Marek
2016-08-17  4:43     ` Nicholas Piggin
2016-08-17  9:05       ` Michal Marek
2016-08-17  9:56       ` Sam Ravnborg
2016-08-18  0:17         ` Nicholas Piggin
2016-08-11 10:16 ` [PATCH 4/6] powerpc: switch to using thin archives Nicholas Piggin
2016-08-11 10:16 ` [PATCH 5/6] powerpc/64: use linker dead code elimination Nicholas Piggin
2016-08-11 10:16 ` [PATCH 6/6] powerpc: use the new post-link pass to check relocations Nicholas Piggin
2016-08-11 12:31 ` [PATCH 0/6 v2] kbuild changes, thin archives, --gc-sections Stephen Rothwell
2016-08-11 12:39 ` [PATCH] Xen: remove -fshort-wchar gcc flag Arnd Bergmann
2016-08-11 12:51   ` Jan Beulich
2016-08-11 12:51   ` [Xen-devel] " Jan Beulich
2016-08-11 14:01     ` Arnd Bergmann
2016-08-11 14:06       ` Jan Beulich
2016-08-11 14:06       ` Jan Beulich
2016-08-11 14:01     ` Arnd Bergmann
2016-08-24 17:18   ` [Xen-devel] " David Vrabel
2016-08-24 17:18   ` David Vrabel
2016-08-11 12:39 ` Arnd Bergmann
2016-08-11 13:55 ` [EXPERIMENTAL] enable thin archives and --gc-sections on ARM Arnd Bergmann
2016-08-11 20:01   ` Nicolas Pitre
2016-08-11 20:37     ` Arnd Bergmann
2016-08-11 21:05       ` Nicolas Pitre [this message]
2016-08-23  6:17 ` [PATCH 0/6 v2] kbuild changes, thin archives, --gc-sections Nicholas Piggin

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