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

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Date:	Sat, 6 Aug 2016 02:16:42 +1000
From:	Nicholas Piggin <npiggin@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linuxppc-dev@...ts.ozlabs.org,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	"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>,
	Guenter Roeck <linux@...ck-us.net>
Subject: Re: powerpc allyesconfig / allmodconfig linux-next next-20160729 -
 next-20160729 build failures

On Fri, 05 Aug 2016 18:01:13 +0200
Arnd Bergmann <arnd@...db.de> wrote:

> On Friday, August 5, 2016 10:26:25 PM CEST Nicholas Piggin wrote:
> > On Fri, 05 Aug 2016 12:17:27 +0200
> > Arnd Bergmann <arnd@...db.de> wrote:  
> 
> > > and I also get link errors for the .text.fixup section
> > > for any users of __put_user() in really large kernels:
> > > net/batman-adv/batman-adv.o:(.text.fixup+0x4): relocation truncated to fit: R_ARM_JUMP24 against `.text.batadv_log_read'  
> > 
> > This may be fixed by fixing the linker script to bring in the new
> > sections properly (see new patchset).
> > 
> > If not, then if you can combine the sections rather than have them
> > consecutive in the output, e.g.,:
> > 
> >     *(.text .text.fixup)
> > 
> > Rather than
> > 
> >     *(.text)            
> >     *(.text.fixup)
> > 
> > Then the linker has more freedom to rearrange them. I realize it's
> > not that simple with ARM's .text.fixup, but maybe that helps you
> > get it to work.  
> 
> This did the trick:
> 
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 0ec807d69f18..7a3ad269fa23 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -433,7 +433,7 @@
>   * during second ld run in second ld pass when generating System.map */
>  #define TEXT_TEXT							\
>  		ALIGN_FUNCTION();					\
> -		*(.text.hot .text .text.fixup .text.unlikely)		\
> +		*(.text.hot .text .text.* .text.fixup .text.unlikely)	\
>  		*(.ref.text)						\
>  	MEM_KEEP(init.text)						\
>  	MEM_KEEP(exit.text)						\
> 
> 
> It also got much faster again, the link time for an allyesconfig
> kernel is now 18 minutes instead of 10 hours, but it's still
> much worse than the 2 minutes I had earlier or the four minutes
> with the previous patch.

Are you using the patches I just sent? Either way, you also need
to do the same for data and bss sections as you are using
-fdata-sections too.

I've found virtually no build time regression on powerpc or x86
when those are taken care of properly (x86 numbers I sent are typo,
it's not 5m20, it's 5m02).

Thanks,
Nick