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

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Date:   Tue, 16 May 2017 10:58:20 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     David Howells <dhowells@...hat.com>,
        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

El Tue, May 16, 2017 at 10:21:30AM -0700 Guenter Roeck ha dit:

> 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

Thanks for giving it a try!

What would work is this:

diff --git a/arch/frv/include/asm/cache.h b/arch/frv/include/asm/cache.h
index 2797163b8f4f..25bf4e85f582 100644
--- a/arch/frv/include/asm/cache.h
+++ b/arch/frv/include/asm/cache.h
@@ -20,4 +20,6 @@
 #define __cacheline_aligned    __attribute__((aligned(L1_CACHE_BYTES)))
 #define ____cacheline_aligned  __attribute__((aligned(L1_CACHE_BYTES)))
 
+#define __jiffies_arch_xyz     __attribute__((__section__(".data")))
+
 #endif
diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
index 36872fbb815d..8904eb52928d 100644
--- a/include/linux/jiffies.h
+++ b/include/linux/jiffies.h
@@ -70,7 +70,7 @@ extern int register_refined_jiffies(long clock_tick_rate);
  * 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 unsigned long volatile __cacheline_aligned_in_smp __jiffies_arch_xyz jiffies;
 
 #if (BITS_PER_LONG < 64)
 u64 get_jiffies_64(void);


We'd only have to find a halfway decent name for __jiffies_arch_xyz.

Matthias