[PATCH] ARM: head-common.S: Clear lr before jumping to start_kernel()

From: Geert Uytterhoeven
Date: Tue Oct 03 2017 - 11:23:13 EST

If CONFIG_DEBUG_LOCK_ALLOC=y, the kernel log is spammed with a few
hundred identical messages:

unwind: Unknown symbol address c0800300
unwind: Index not found c0800300

c0800300 is the return address from the last subroutine call (to
__memzero()) in __mmap_switched(). Apparently having this address in
the link register confuses the unwinder.

To fix this, reset the link register to zero before jumping to

Fixes: 9520b1a1b5f7a348 ("ARM: head-common.S: speed up startup code")
Suggested-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
Commit 9520b1a1b5f7a348 is in arm/for-next.

arch/arm/kernel/head-common.S | 1 +
1 file changed, 1 insertion(+)

diff --git a/arch/arm/kernel/head-common.S b/arch/arm/kernel/head-common.S
index a25027b87a6024b9..21dde771a7dd8d14 100644
--- a/arch/arm/kernel/head-common.S
+++ b/arch/arm/kernel/head-common.S
@@ -114,6 +114,7 @@ __mmap_switched:
str r8, [r2] @ Save atags pointer
cmp r3, #0
strne r10, [r3] @ Save control register values
+ mov lr, #0
b start_kernel