linux-kernel - LTO build errors (Re: linux-next: clean up the kbuild tree?)

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Date:	Tue, 24 Nov 2015 17:33:36 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Andi Kleen <ak@...ux.intel.com>
Cc:	Michal Marek <mmarek@...e.cz>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: LTO build errors (Re: linux-next: clean up the kbuild tree?)

On Tue, 24 Nov 2015 03:12:31 +0100,
Andi Kleen wrote:
> 
> > > 5.x is better than 4.x but it's still a slower. It's also not incremential.
> > 
> > At the last time I tested with the latest 5.x and stock binutils on
> > openSUSE Tumbleweed, I failed to build, unfortunately.  Partly the
> > detection of gcc version doesn't work for 5.x, and partly something is
> 
> Really? It work for me with gcc 5

I retested now, and it seems like only the binutils, not about gcc
version, indeed.  Sorry for confusion.

> > missing in binutils side, although it's already built with plugin.
> 
> Yes it needs HJ Lu's Linux binutils, not the standard FSF binutils.
> The patch to fix LTO with ld -r was submitted to standard binutils, but they
> didn't want to fix the issue.

I did "make allnoconfig", disabled tracers, gcov, etc, and then
enabled LTO.  With hlj version, the build reaches to the almost end
hitting this:

  LD      vmlinux
arch/x86/kernel/cpu/perf_event_intel_rapl.c:66:20: error: rapl_domain_names causes a section type conflict with __setup_str_set_reset_devices
 static const char *rapl_domain_names[NR_RAPL_DOMAINS] __initconst = {
                    ^
init/main.c:159:19: note: ‘__setup_str_set_reset_devices’ was declared here
 __setup("reset_devices", set_reset_devices);

Hmm...  I see no direct relation, but OK, let's try to get rid of
__initconst.  Now it hits lots of other errors like:

`__sw_hweight32' referenced in section `.text' of /tmp/ccUCMU7n.ltrans13.ltrans.o: defined in discarded section `.text' of lib/built-in.o (symbol from plugin)
`__sw_hweight32' referenced in section `.text' of /tmp/ccUCMU7n.ltrans13.ltrans.o: defined in discarded section `.text' of lib/built-in.o (symbol from plugin)
`__sw_hweight32' referenced in section `.text' of /tmp/ccUCMU7n.ltrans13.ltrans.o: defined in discarded section `.text' of lib/built-in.o (symbol from plugin)
`__sw_hweight32' referenced in section `.text' of /tmp/ccUCMU7n.ltrans13.ltrans.o: defined in discarded section `.text' of lib/built-in.o (symbol from plugin)
/tmp/ccUCMU7n.ltrans21.ltrans.o: In function `do_exit':
<artificial>:(.text+0xfc0): undefined reference to `sys_futex'
/tmp/ccUCMU7n.ltrans22.ltrans.o: In function `_do_fork':
<artificial>:(.text+0x39f7): undefined reference to `ret_from_fork'
<artificial>:(.text+0x4428): undefined reference to `ret_from_kernel_thread'
....

Any hints to solve these?

thanks,

Takashi
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