linux-kernel - Re: linux-next: build failure after merge of the final tree

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Message-Id: <20120706102151.fd4f769cf2aa3f753ad178bf@canb.auug.org.au>
Date:	Fri, 6 Jul 2012 10:21:51 +1000
From:	Stephen Rothwell <sfr@...b.auug.org.au>
To:	Alan Modra <amodra@...il.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	linuxppc-dev@...ts.ozlabs.org, linux-next@...r.kernel.org,
	linux-kernel@...r.kernel.org, tony@...eyournoodle.com
Subject: Re: linux-next: build failure after merge of the final tree

Hi Alan,

On Thu, 5 Jul 2012 19:13:48 +0930 Alan Modra <amodra@...il.com> wrote:
>
> On Thu, Jul 05, 2012 at 06:33:45PM +1000, Stephen Rothwell wrote:
> > powerpc64-linux-ld: drivers/built-in.o: In function `.gpiochip_is_requested':
> > (.text+0x4): sibling call optimization to `_savegpr0_29' does not allow automatic multiple TOCs; recompile with -mminimal-toc or -fno-optimize-sibling-calls, or make `_savegpr0_29' extern
> > 
> > I got more than 60000 of these messages before I killed the link. :-(  I
> > am not sure what has changed to do this, but it may have been masked for
> > the past few releases due to other linking problems.
> 
> Let me guess.  You're using bleeding edge gcc but not binutils.

powerpc-linux-gcc (GCC) 4.6.3
GNU ld (GNU Binutils) 2.22

both built from upstream sources (by Tony).

> a) Recent gcc has fixed prologue and epilogue generation which now
>    properly makes use of out-of-line register save and restore
>    functions when compiling with -Os.
> b) Recent ld doesn't emit out-of-line save/restore function for ld -r,
>    but yours does.  You need my 2012-06-22 patch.
> c) Kernel uses ld -r for packaging.
> 
> (b) and (c) together mean you get a definition for _savegpr0_29 munged
> together with other functions.  That's bad.  If _savegpr0_29 wasn't
> emitted until the final link stage then it would be in a code section
> containing just save/restore functions.  ld will analyse that section
> and notice the absense of toc relocations; functions therein don't
> use the toc and can thus be called from any toc group without needing
> a toc adjusting stub.  In your case _savegpr0_29 is in a section that
> has toc relocations (from normal compiled code), so ld decides that
> any function in that section must have a proper value for the toc
> register.  But calls to _savegpr0_29 don't have a following nop to
> overwrite with a toc restore insn, hence the ld error.
> 
> Score another black mark for ld -r.

OK, the new toolchain may be the problem.  I changed from:

powerpc-linux-gcc (GCC) 4.6.0
GNU ld (GNU Binutils) 2.21

on June 20 and the current errors may have been masked an early bailout
after getting theses errors:

powerpc64-linux-ld: arch/powerpc/net/built-in.o: In function `bpf_slow_path_word':
(.text+0x90): sibling call optimization to `skb_copy_bits' does not allow automatic multiple TOCs; recompile with -mminimal-toc or -fno-optimize-sibling-calls, or make `skb_copy_bits' extern

which have now been fixed.  So would a simple patch that puts the
_savegpr etc functions in their own section (defined how?) fix this for
us?

-- 
Cheers,
Stephen Rothwell                    sfr@...b.auug.org.au

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