ARM: 7017/1: Use generic BUG() handler

ARM uses its own BUG() handler which makes its output slightly different
from other archtectures.

One of the problems is that the ARM implementation doesn't report the
function
with the BUG() in it, but always reports the PC being in __bug(). The
generic
implementation doesn't have this problem.

Currently we get something like:

kernel BUG at fs/proc/breakme.c:35!
Unable to handle kernel NULL pointer dereference at virtual address
00000000
...
PC is at __bug+0x20/0x2c

With this patch it displays:

kernel BUG at fs/proc/breakme.c:35!
Internal error: Oops - undefined instruction: 0 [#1] PREEMPT SMP
...
PC is at write_breakme+0xd0/0x1b4

This implementation uses an undefined instruction to implement BUG, and
sets up
a bug table containing the relevant information. Many versions of gcc do
not
support %c properly for ARM (inserting a # when they shouldn't) so we
work
around this using distasteful macro magic.

v1: Initial version to replace existing ARM BUG() implementation with
something
more similar to other architectures.

v2: Add Thumb support, remove backtrace whitespace output changes.
Change to
use macros instead of requiring the asm %d flag to work (thanks to
Dave Martin <dave.martin@linaro.org>)

v3: Remove old BUG() implementation in favor of this one.
Remove the Backtrace: message (will submit this separately).
Rebase to linux-2.6.git master.

v4: Allow BUGS in modules (these were not reported correctly in v3)
(thanks to Stephen Boyd <sboyd@codeaurora.org> for suggesting that.)
Remove __bug() as this is no longer needed.

v5: Add %progbits as the section flags.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Tested-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
(cherry picked from commit 87e040b6456fd3416a1f6831c1eedaef5c0a94ff)

Change-Id: Ic7692288dff6e4a15c732eb030295bd196a87fb4
Signed-off-by: Manoj Chourasia <mchourasia@nvidia.com>
Reviewed-on: http://git-master/r/117356
Reviewed-by: Automatic_Commit_Validation_User
Tested-by: Vishal Singh <vissingh@nvidia.com>
Reviewed-by: Sandeep Trasi <strasi@nvidia.com>
(cherry picked from commit 6708ffd0b44f4d09d8fe745471641545655091fb)
Reviewed-on: http://git-master/r/119328
Reviewed-by: Bob Johnston <bjohnston@nvidia.com>
Reviewed-by: Varun Wadekar <vwadekar@nvidia.com>

1 files changed, 62 insertions, 8 deletions

diff --git a/arch/arm/include/asm/bug.h b/arch/arm/include/asm/bug.h
index 4d88425a4169..6b7f60c9b944 100644
--- a/arch/arm/include/asm/bug.h
+++ b/arch/arm/include/asm/bug.h
@@ -1,23 +1,77 @@
+/*
+ * arch/arm/include/asm/bug.h
+ *
+ * Copyright (c) 2012, NVIDIA CORPORATION.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
 #ifndef _ASMARM_BUG_H
 #define _ASMARM_BUG_H
 
 
 #ifdef CONFIG_BUG
+
+/*
+ * Use a suitable undefined instruction to use for ARM/Thumb2 bug handling.
+ * We need to be careful not to conflict with those used by other modules and
+ * the register_undef_hook() system.
+ */
+#ifdef CONFIG_THUMB2_KERNEL
+#define BUG_INSTR_VALUE 0xde02
+#define BUG_INSTR_TYPE ".hword "
+#else
+#define BUG_INSTR_VALUE 0xe7f001f2
+#define BUG_INSTR_TYPE ".word "
+#endif
+
+
+#define BUG() _BUG(__FILE__, __LINE__, BUG_INSTR_VALUE)
+#define _BUG(file, line, value) __BUG(file, line, value)
+
 #ifdef CONFIG_DEBUG_BUGVERBOSE
-extern void __bug(const char *file, int line) __attribute__((noreturn));
 
-/* give file/line information */
-#define BUG()		__bug(__FILE__, __LINE__)
+/*
+ * The extra indirection is to ensure that the __FILE__ string comes through
+ * OK. Many version of gcc do not support the asm %c parameter which would be
+ * preferable to this unpleasantness. We use mergeable string sections to
+ * avoid multiple copies of the string appearing in the kernel image.
+ */
 
-#else
+#define __BUG(__file, __line, __value)				\
+do {								\
+	BUILD_BUG_ON(sizeof(struct bug_entry) != 12);		\
+	asm volatile("1:\t" BUG_INSTR_TYPE #__value "\n"	\
+		".pushsection .rodata.str, \"aMS\", %progbits, 1\n" \
+		"2:\t.asciz " #__file "\n" 			\
+		".popsection\n" 				\
+		".pushsection __bug_table,\"a\"\n"		\
+		"3:\t.word 1b, 2b\n"				\
+		"\t.hword " #__line ", 0\n"			\
+		".popsection");					\
+	unreachable();						\
+} while (0)
 
-/* this just causes an oops */
-#define BUG()		do { *(int *)0 = 0; } while (1)
+#else  /* not CONFIG_DEBUG_BUGVERBOSE */
 
-#endif
+#define __BUG(__file, __line, __value)				\
+do {								\
+	asm volatile(BUG_INSTR_TYPE #__value);			\
+	unreachable();						\
+} while (0)
+#endif  /* CONFIG_DEBUG_BUGVERBOSE */
 
 #define HAVE_ARCH_BUG
-#endif
+#endif  /* CONFIG_BUG */
 
 #include <asm-generic/bug.h>