[PATCH] bcache: Fix link errors on ARM

[mpatocka@redhat.com (Mikulas Patocka)]

On Mon, 22 Apr 2013, Rob Herring wrote:

> On 04/22/2013 12:32 PM, Mikulas Patocka wrote:
> > 
> > 
> > On Thu, 18 Apr 2013, Rob Herring wrote:
> > 
> >> Current errors in linux-next for ARM multi-platform randconfig builds.
> >>
> >> Rob
> >>
> >> drivers/built-in.o:drivers/md/dm-cache-target.c:429: more undefined references to `__udivdi3' follow
> >> /var/lib/jenkins/jobs/linux-randconfig/workspace/drivers/md/dm-cache-target.c:429: undefined reference to `__udivdi3'
> >> /var/lib/jenkins/jobs/linux-randconfig/workspace/drivers/md/dm-cache-target.c:429: undefined reference to `__umoddi3'
> >> driversdrivers/md/dm-cache-target.c:429: more undefined references to `__udivdi3' follow
> >> drivers/md/dm-cache-target.c:429: undefined reference to `__udivdi3'
> >> drivers/md/dm-cache-target.c:429: undefined reference to `__umoddi3'
> > 
> > Hi
> > 
> > I tried to cross-compile dm-cache on linux-next for arm and there were no 
> > failures and no references to __udivdi3 and __umoddi3.
> > 
> > Please send the .config file that resulted in these faulures.
> 
> The config is attached. My guess is it might be related to CONFIG_AEABI
> not set. The compiler is "gcc version 4.6.3 (Ubuntu/Linaro
> 4.6.3-1ubuntu5)" which is ubuntu 12.04 arm cross compiler.
> 
> Rob

This is a problem in gcc-4.6. (gcc-4.7 is OK).

---

bcache: Fix link errors on ARM

gcc-4.6 on ARM has some problem, it creates a function block_div.part.8,
it references __udivdi3 and __umoddi3 and it is never called. The
references to __udivdi3 and __umoddi3 cause a link failure.

__always_inline works around the bug.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

Index: linux-2.6/drivers/md/dm-cache-target.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-cache-target.c	2013-05-14 00:03:53.276986022 +0200
+++ linux-2.6/drivers/md/dm-cache-target.c	2013-05-14 00:34:09.128986023 +0200
@@ -425,6 +425,10 @@
 	return cache->sectors_per_block_shift >= 0;
 }
 
+/* gcc on ARM generates spurious references to __udivdi3 and __umoddi3 */
+#if defined(CONFIG_ARM) && __GNUC__ == 4 && __GNUC_MINOR__ <= 6
+__always_inline
+#endif
 static dm_block_t block_div(dm_block_t b, uint32_t n)
 {
 	do_div(b, n);