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

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Message-ID: <s5h7fl6a7lg.wl-tiwai@suse.de>
Date:	Wed, 25 Nov 2015 07:58:19 +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: Re: LTO build errors (Re: linux-next: clean up the kbuild tree?)

On Wed, 25 Nov 2015 05:33:44 +0100,
Andi Kleen wrote:
> 
> 
> Hi Takashi,
> 
> On Tue, Nov 24, 2015 at 05:33:36PM +0100, Takashi Iwai wrote:
> >   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:
> 
> I hit the same issue, will send a patch. The other symbol is typically some
> random correct symbol because gcc detects the conflict on a pair of symbols.
> 
> The problem is that placing const correctly is too difficult, the correct line
> would be 
> 
> static const char *const rapl_domain_names[NR_RAPL_DOMAINS] __initconst = {

Ah, so I should have ignored the relation with __setup_* but
concentrate on the line.  LTO goes much deeper than a human being can
look through :)

Yes, such an error is often overseen.  A quick grep shows the
following:

arch/arc/plat-axs10x/axs10x.c:463:static const char *axs101_compat[] __initconst = {
arch/arc/plat-axs10x/axs10x.c:477:static const char *axs103_compat[] __initconst = {
arch/arc/plat-sim/platform.c:22:static const char *simulation_compat[] __initconst = {
arch/arm/mach-imx/mach-imx6ul.c:87:static const char *imx6ul_dt_compat[] __initconst = {
arch/arm/mach-shmobile/setup-r8a7793.c:22:static const char *r8a7793_boards_compat_dt[] __initconst = {
arch/x86/kernel/cpu/perf_event_intel_rapl.c:66:static const char *rapl_domain_names[NR_RAPL_DOMAINS] __initconst = {
drivers/clk/pistachio/clk.h:40:#define PNAME(x) static const char *x[] __initconst

> > `__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)
> 
> This needs
> 
> https://git.kernel.org/cgit/linux/kernel/git/ak/linux-misc.git/commit/?h=lto-4.0&id=d826425f7a9d935d521989bd0a871b76fb4c59e2

OK, noted.


> > /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'
> 
> 
> That's new, but can be fixed by adding __visible or asmlinkage to these symbols
> I guess it's from the recent entry* restructuring.
> 
> I'll do an updated tree later.
> 
> Everything that's called from assembler in C needs to be marked like this. It's
> fairly mechanic.

OK, thanks for the information!


Takashi
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