linux-kernel - [PATCH 4.14 8/8] ARM: 8702/1: head-common.S: Clear lr before jumping to start

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Message-Id: <20200805153507.382671788@linuxfoundation.org>
Date:   Wed,  5 Aug 2020 17:53:34 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Nicolas Pitre <nico@...aro.org>,
        Russell King <rmk+kernel@...linux.org.uk>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: [PATCH 4.14 8/8] ARM: 8702/1: head-common.S: Clear lr before jumping to start_kernel()

From: Geert Uytterhoeven <geert@...ux-m68k.org>

commit 59b6359dd92d18f5dc04b14a4c926fa08ab66f7c upstream.

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
start_kernel().

Fixes: 9520b1a1b5f7a348 ("ARM: head-common.S: speed up startup code")
Suggested-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
Acked-by: Nicolas Pitre <nico@...aro.org>
Signed-off-by: Russell King <rmk+kernel@...linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>

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

--- a/arch/arm/kernel/head-common.S
+++ b/arch/arm/kernel/head-common.S
@@ -101,6 +101,7 @@ __mmap_switched:
 	str	r2, [r6]			@ Save atags pointer
 	cmp	r7, #0
 	strne	r0, [r7]			@ Save control register values
+	mov	lr, #0
 	b	start_kernel
 ENDPROC(__mmap_switched)