Re: 2.6.39-rc6-mmotm0506 and -next - __kfree_rcu breaks third-party kernel code

[Valdis . Kletnieks]

On Mon, 09 May 2011 09:17:57 PDT, Randy Dunlap said:

> I'd be happy to see a simple fix, but we don't generally support building
> external modules without using the kernel kbuild infrastructure AFAIK --
> and when I add a Makefile along with your kernconf.c file, it builds successfully
> on mmotm-2011-0506-1639.

And in fact the module *does* use the Makefile stuff for the actual build - it
was just the installer's "am I looking at a sane 2.6 tree" sanity check that
bombed. So I go looking for what special sauce the Makefile adds to make it
work, and....

OK, *now* I'm confused.  The magic sauce appears to be "-Os". Adding that makes
the compile work.  And for no obvious reason - there's something in there that
causes indigestion, but only if the optimizer isn't invoked.

*WTF*?

 LANG=C ./kern.sh 
cat > /tmp/kernconf.c <<EOF
#include <linux/version.h>
#include <linux/utsname.h>
EOF
+ cat

kern="/lib/modules/2.6.39-rc6-mmotm0506/"
+ kern=/lib/modules/2.6.39-rc6-mmotm0506/
cc -D__KERNEL__ -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/4.6.0/include -I${kern}/build/include -I$kern/arch/x86/include/generated -include ${kern}/build/include/generated/autoconf.h -I${kern}/build/arch/x86/include -I${kern}/include/generated -Os -c /tmp/kernconf.c
+ cc -D__KERNEL__ -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/4.6.0/include -I/lib/modules/2.6.39-rc6-mmotm0506//build/include -I/lib/modules/2.6.39-rc6-mmotm0506//arch/x86/include/generated -include /lib/modules/2.6.39-rc6-mmotm0506//build/include/generated/autoconf.h -I/lib/modules/2.6.39-rc6-mmotm0506//build/arch/x86/include -I/lib/modules/2.6.39-rc6-mmotm0506//include/generated -Os -c /tmp/kernconf.c
cc -D__KERNEL__ -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/4.6.0/include -I${kern}/build/include -I$kern/arch/x86/include/generated -include ${kern}/build/include/generated/autoconf.h -I${kern}/build/arch/x86/include -I${kern}/include/generated -c /tmp/kernconf.c
+ cc -D__KERNEL__ -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/4.6.0/include -I/lib/modules/2.6.39-rc6-mmotm0506//build/include -I/lib/modules/2.6.39-rc6-mmotm0506//arch/x86/include/generated -include /lib/modules/2.6.39-rc6-mmotm0506//build/include/generated/autoconf.h -I/lib/modules/2.6.39-rc6-mmotm0506//build/arch/x86/include -I/lib/modules/2.6.39-rc6-mmotm0506//include/generated -c /tmp/kernconf.c
In file included from /lib/modules/2.6.39-rc6-mmotm0506//build/include/linux/sem.h:81:0,
                 from /lib/modules/2.6.39-rc6-mmotm0506//build/include/linux/sched.h:72,
                 from /lib/modules/2.6.39-rc6-mmotm0506//build/include/linux/utsname.h:35,
                 from /tmp/kernconf.c:2:
/lib/modules/2.6.39-rc6-mmotm0506//build/include/linux/rcupdate.h: In function '__kfree_rcu':
/lib/modules/2.6.39-rc6-mmotm0506//build/include/linux/rcupdate.h:822:2: error: size of unnamed array is negative

rm /tmp/kernconf.c
+ rm /tmp/kernconf.c

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