[kernel] powerpc/powernv: Fix clobbered MSR

[Michael Ellerman]

On Thu, 2017-03-02 at 06:41:24 UTC, Alexey Kardashevskiy wrote:
> If CONFIG_DEBUG_INFO_SPLIT is not set but CONFIG_DEBUG_INFO is,
> the kernel makefile just adds "-g" and the scripts/gcc-goto.sh test for
> the "asm goto ("" :::: entry)" support succedes and adds
> -DCC_HAVE_ASM_GOTO to KBUILD_CFLAGS/KBUILD_AFLAGS. This effectively
> makes OPAL_BRANCH() a noop (or something similar).
> 
> With CONFIG_DEBUG_INFO_SPLIT=y, the makefile adds "-gsplit-dwarf" which
> somehow makes the scripts/gcc-goto.sh test fail and not have
> CC_HAVE_ASM_GOTO defined so the alternative OPAL_BRANCH() is used
> and this particular chunk clobbers r12 where the parenting code -
> OPAL_CALL() - stores MSR; as the result, the kernel oops'es right after
> early_setup() because of broken MSR.
> 
> This replaces r12 with r11 which is overwritten right after
> OPAL_BRANCH(opal_tracepoint_entry) anyway.
> 
> I used gcc 5.4.1 20161205 built from sha1 ffadbf3ae29.
> 
> Fixes: ab9bad0ead9a ("powerpc/powernv: Remove separate entry for OPAL real mode calls")
> Suggested-by: Paul Mackerras <paulus at samba.org>
> Signed-off-by: Alexey Kardashevskiy <aik at ozlabs.ru>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/2a9c4f40ab2c281f95d41577ff0f7f

cheers