linux-kernel - Re: frv build failure in mainline kernel

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Date:   Tue, 16 May 2017 10:21:30 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     David Howells <dhowells@...hat.com>
Cc:     Matthias Kaehlcke <mka@...omium.org>,
        Sudip Mukherjee <sudipm.mukherjee@...il.com>,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: frv build failure in mainline kernel

On Tue, May 16, 2017 at 05:04:32PM +0100, David Howells wrote:
> Guenter Roeck <linux@...ck-us.net> wrote:
> 
> > Turns out not here because ____cacheline_aligned_in_smp includes
> > __page_aligned_data which also declares the section, at least on x86.
> 
> If there's any sort of section specification, that should suffice, I think.
> The problem might come that jiffies and jiffies_64 don't coincide at the same
> address because FRV is BE not LE.
> 
> It ought to be possible to make jiffies 64-bit on FRV since it has double-word
> instructions that can load/store aligned 64-bit values atomically to/from a
> register pair.  That might require some compiler magic, though.  I'll have to
> try and work out if that's possible.
> 
I tried:

diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
index 36872fbb815d..26d0655c4422 100644
--- a/include/linux/jiffies.h
+++ b/include/linux/jiffies.h
@@ -64,13 +64,15 @@ extern int register_refined_jiffies(long clock_tick_rate);
 /* TICK_USEC is the time between ticks in usec assuming fake USER_HZ */
 #define TICK_USEC ((1000000UL + USER_HZ/2) / USER_HZ)
 
+#define __jiffy_data  __attribute__((section(".data")))
+
 /*
  * The 64-bit value is not atomic - you MUST NOT read it
  * without sampling the sequence number in jiffies_lock.
  * get_jiffies_64() will do this for you as appropriate.
  */
-extern u64 __cacheline_aligned_in_smp jiffies_64;
-extern unsigned long volatile __cacheline_aligned_in_smp jiffies;
+extern u64 __cacheline_aligned_in_smp __jiffy_data jiffies_64;
+extern unsigned long volatile __cacheline_aligned_in_smp __jiffy_data jiffies;

This is what I get when building defconfig:

  CC      arch/x86/kernel/asm-offsets.s
In file included from ./include/linux/ktime.h:25:0,
                 from ./include/linux/rcupdate.h:46,
                 from ./include/linux/srcu.h:33,
                 from ./include/linux/notifier.h:15,
                 from ./include/linux/memory_hotplug.h:6,
                 from ./include/linux/mmzone.h:757,
                 from ./include/linux/gfp.h:5,
                 from ./include/linux/slab.h:14,
                 from ./include/linux/crypto.h:24,
                 from arch/x86/kernel/asm-offsets.c:8:
./include/linux/jiffies.h:74:52: error: section of ‘jiffies_64’ conflicts with previous declaration
 extern u64 __cacheline_aligned_in_smp __jiffy_data jiffies_64;
                                                    ^
./include/linux/jiffies.h:75:71: error: section of ‘jiffies’ conflicts with previous declaration
 extern unsigned long volatile __cacheline_aligned_in_smp __jiffy_data jiffies;
                                                                       ^
Kbuild:56: recipe for target 'arch/x86/kernel/asm-offsets.s' failed
make[1]: *** [arch/x86/kernel/asm-offsets.s] Error 1
Makefile:1061: recipe for target 'prepare0' failed
make: *** [prepare0] Error 2

Guenter