linux-kernel - [PATCH 3.2 076/185] avr32: fix out-of-range jump in large kernels

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Message-ID: <lsq.1388282923.893199703@decadent.org.uk>
Date:	Sun, 29 Dec 2013 03:08:43 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Andreas Bießmann" <andreas@...ssmann.de>,
	"Hans-Christian Egtvedt" <egtvedt@...fundet.no>,
	"Haavard Skinnemoen" <hskinnemoen@...il.com>
Subject: [PATCH 3.2 076/185] avr32: fix out-of-range jump in large kernels

3.2.54-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Andreas Bießmann <andreas@...ssmann.de>

commit d617b338bbfdd77e9cbd8e7dc949cee3dd73d575 upstream.

This patch fixes following error (for big kernels):

---8<---
arch/avr32/boot/u-boot/head.o: In function `no_tag_table':
(.init.text+0x44): relocation truncated to fit: R_AVR32_22H_PCREL against symbol `panic' defined in .text.unlikely section in kernel/built-in.o
arch/avr32/kernel/built-in.o: In function `bad_return':
(.ex.text+0x236): relocation truncated to fit: R_AVR32_22H_PCREL against symbol `panic' defined in .text.unlikely section in kernel/built-in.o
--->8---

It comes up when the kernel increases and 'panic()' is too far away to fit in
the +/- 2MiB range. Which in turn issues from the 21-bit displacement in
'br{cond4}' mnemonic which is one of the two ways to do jumps (rjmp has just
10-bit displacement and therefore a way smaller range). This fact was stated
before in 8d29b7b9f81d6b83d869ff054e6c189d6da73f1f.
One solution to solve this is to add a local storage for the symbol address
and just load the $pc with that value.

Signed-off-by: Andreas Bießmann <andreas@...ssmann.de>
Acked-by: Hans-Christian Egtvedt <egtvedt@...fundet.no>
Cc: Haavard Skinnemoen <hskinnemoen@...il.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/avr32/boot/u-boot/head.S    | 5 ++++-
 arch/avr32/kernel/entry-avr32b.S | 3 ++-
 2 files changed, 6 insertions(+), 2 deletions(-)

--- a/arch/avr32/boot/u-boot/head.S
+++ b/arch/avr32/boot/u-boot/head.S
@@ -73,8 +73,11 @@ init_sr:
 	.long	0x007f0000	/* Supervisor mode, everything masked */
 stack_addr:
 	.long	init_thread_union
+panic_addr:
+	.long	panic
 
 no_tag_table:
 	sub	r12, pc, (. - 2f)
-	bral	panic
+	/* branch to panic() which can be far away with that construct */
+	lddpc	pc, panic_addr
 2:	.asciz	"Boot loader didn't provide correct magic number\n"
--- a/arch/avr32/kernel/entry-avr32b.S
+++ b/arch/avr32/kernel/entry-avr32b.S
@@ -399,9 +399,10 @@ handle_critical:
 	/* We should never get here... */
 bad_return:
 	sub	r12, pc, (. - 1f)
-	bral	panic
+	lddpc	pc, 2f
 	.align	2
 1:	.asciz	"Return from critical exception!"
+2:	.long	panic
 
 	.align	1
 do_bus_error_write:

--
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