LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
* [PATCH v3] ARM: Use generic BUG() handler
@ 2011-04-06 23:18 Simon Glass
  2011-04-07  5:35 ` Stephen Boyd
  2011-04-07 17:57 ` Stephen Boyd
  0 siblings, 2 replies; 5+ messages in thread
From: Simon Glass @ 2011-04-06 23:18 UTC (permalink / raw)
  To: linux-arm-kernel
  Cc: Russell King, Tony Lindgren, Nicolas Pitre, Catalin Marinas,
	Joe Perches, Laurent Pinchart, Alexander Shishkin, Phil Carmody,
	Rabin Vincent, linux-kernel, Omar Ramirez Luna, Stephen Boyd,
	Dave Martin, Simon Glass, Simon Glass

From: Simon Glass <sjg@google.com>

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).
Use ARM_EXIT_KEEP() so that some architectures can dump exit text at link time
thanks to Stephen Boyd <sboyd@codeaurora.org> (although since we always
define GENERIC_BUG this might be academic.)
Rebase to linux-2.6.git master.

Change-Id: I07d77c832e816f5ad2390e25f466ddf750adecf4

Signed-off-by: Simon Glass <sjg@chromium.org>
---
 arch/arm/Kconfig              |    4 +++
 arch/arm/include/asm/bug.h    |   55 ++++++++++++++++++++++++++++++++++------
 arch/arm/kernel/traps.c       |   23 +++++++++++++++++
 arch/arm/kernel/vmlinux.lds.S |    3 +-
 4 files changed, 75 insertions(+), 10 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 5b9f78b..7d7df40 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -207,6 +207,10 @@ config ARM_PATCH_PHYS_VIRT_16BIT
 	def_bool y
 	depends on ARM_PATCH_PHYS_VIRT && ARCH_MSM
 
+config GENERIC_BUG
+	def_bool y
+	depends on BUG
+
 source "init/Kconfig"
 
 source "kernel/Kconfig.freezer"
diff --git a/arch/arm/include/asm/bug.h b/arch/arm/include/asm/bug.h
index 4d88425..2914724 100644
--- a/arch/arm/include/asm/bug.h
+++ b/arch/arm/include/asm/bug.h
@@ -3,21 +3,58 @@
 
 
 #ifdef CONFIG_BUG
-#ifdef CONFIG_DEBUG_BUGVERBOSE
-extern void __bug(const char *file, int line) __attribute__((noreturn));
-
-/* give file/line information */
-#define BUG()		__bug(__FILE__, __LINE__)
 
+/*
+ * 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
 
-/* this just causes an oops */
-#define BUG()		do { *(int *)0 = 0; } while (1)
 
-#endif
+#define BUG() _BUG(__FILE__, __LINE__, BUG_INSTR_VALUE)
+#define _BUG(file, line, value) __BUG(file, line, value)
+
+#ifdef CONFIG_DEBUG_BUGVERBOSE
+
+/*
+ * 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.
+ */
+
+#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\", 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)
+
+#else  /* not CONFIG_DEBUG_BUGVERBOSE */
+
+#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>
 
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index f0000e1..25dc8dc 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -21,6 +21,7 @@
 #include <linux/kdebug.h>
 #include <linux/module.h>
 #include <linux/kexec.h>
+#include <linux/bug.h>
 #include <linux/delay.h>
 #include <linux/init.h>
 #include <linux/sched.h>
@@ -271,6 +272,8 @@ void die(const char *str, struct pt_regs *regs, int err)
 	spin_lock_irq(&die_lock);
 	console_verbose();
 	bust_spinlocks(1);
+	if (!user_mode(regs))
+		report_bug(regs->ARM_pc, regs);
 	ret = __die(str, err, thread, regs);
 
 	if (regs && kexec_should_crash(thread->task))
@@ -302,6 +305,26 @@ void arm_notify_die(const char *str, struct pt_regs *regs,
 	}
 }
 
+#ifdef CONFIG_GENERIC_BUG
+
+int is_valid_bugaddr(unsigned long pc)
+{
+#ifdef CONFIG_THUMB2_KERNEL
+	unsigned short bkpt;
+#else
+	unsigned long bkpt;
+#endif
+
+	if (pc < PAGE_OFFSET)
+		return 0;
+	if (probe_kernel_address((unsigned *)pc, bkpt))
+		return 0;
+
+	return bkpt == BUG_INSTR_VALUE;
+}
+
+#endif
+
 static LIST_HEAD(undef_hook);
 static DEFINE_SPINLOCK(undef_lock);
 
diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
index b4348e6..81d4efe 100644
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -21,7 +21,8 @@
 #define ARM_CPU_KEEP(x)
 #endif
 
-#if defined(CONFIG_SMP_ON_UP) && !defined(CONFIG_DEBUG_SPINLOCK)
+#if (defined(CONFIG_SMP_ON_UP) && !defined(CONFIG_DEBUG_SPINLOCK)) || \
+	defined(CONFIG_GENERIC_BUG)
 #define ARM_EXIT_KEEP(x)	x
 #else
 #define ARM_EXIT_KEEP(x)
-- 
1.7.3.1


^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH v3] ARM: Use generic BUG() handler
  2011-04-06 23:18 [PATCH v3] ARM: Use generic BUG() handler Simon Glass
@ 2011-04-07  5:35 ` Stephen Boyd
  2011-04-07 16:49   ` Simon Glass
  2011-04-07 17:57 ` Stephen Boyd
  1 sibling, 1 reply; 5+ messages in thread
From: Stephen Boyd @ 2011-04-07  5:35 UTC (permalink / raw)
  To: Simon Glass
  Cc: linux-arm-kernel, Russell King, Tony Lindgren, Nicolas Pitre,
	Catalin Marinas, Joe Perches, Laurent Pinchart,
	Alexander Shishkin, Phil Carmody, Rabin Vincent, linux-kernel,
	Omar Ramirez Luna, Dave Martin, Simon Glass

On 4/6/2011 4:18 PM, Simon Glass wrote:
> v3: Remove old BUG() implementation in favor of this one.
> Remove the Backtrace: message (will submit this separately).
> Use ARM_EXIT_KEEP() so that some architectures can dump exit text at link time
> thanks to Stephen Boyd <sboyd@codeaurora.org> (although since we always
> define GENERIC_BUG this might be academic.)

Its not entirely academic because CONFIG_BUG=n and CONFIG_SMP_ON_UP=n
would allow us to remove the exit text. This could be huge for people
who want to cram kernel's onto space constrained devices.

> Rebase to linux-2.6.git master.
>
> Change-Id: I07d77c832e816f5ad2390e25f466ddf750adecf4

Don't forget to remove these before submitting to the patch tracker (and
sending to the list).

> diff --git a/arch/arm/include/asm/bug.h b/arch/arm/include/asm/bug.h
> index 4d88425..2914724 100644
> --- a/arch/arm/include/asm/bug.h
> +++ b/arch/arm/include/asm/bug.h
> @@ -3,21 +3,58 @@
>  
>  
>  #ifdef CONFIG_BUG
> -#ifdef CONFIG_DEBUG_BUGVERBOSE
> -extern void __bug(const char *file, int line) __attribute__((noreturn));
> -
> -/* give file/line information */
> -#define BUG()		__bug(__FILE__, __LINE__)

Does anybody reference __bug() anymore? If not you can remove that too.

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH v3] ARM: Use generic BUG() handler
  2011-04-07  5:35 ` Stephen Boyd
@ 2011-04-07 16:49   ` Simon Glass
  0 siblings, 0 replies; 5+ messages in thread
From: Simon Glass @ 2011-04-07 16:49 UTC (permalink / raw)
  To: Stephen Boyd
  Cc: linux-arm-kernel, Russell King, Tony Lindgren, Nicolas Pitre,
	Catalin Marinas, Joe Perches, Laurent Pinchart,
	Alexander Shishkin, Phil Carmody, Rabin Vincent, linux-kernel,
	Omar Ramirez Luna, Dave Martin

On Wed, Apr 6, 2011 at 10:35 PM, Stephen Boyd <sboyd@codeaurora.org> wrote:
> On 4/6/2011 4:18 PM, Simon Glass wrote:
>> v3: Remove old BUG() implementation in favor of this one.
>> Remove the Backtrace: message (will submit this separately).
>> Use ARM_EXIT_KEEP() so that some architectures can dump exit text at link time
>> thanks to Stephen Boyd <sboyd@codeaurora.org> (although since we always
>> define GENERIC_BUG this might be academic.)
>
> Its not entirely academic because CONFIG_BUG=n and CONFIG_SMP_ON_UP=n
> would allow us to remove the exit text. This could be huge for people
> who want to cram kernel's onto space constrained devices.

OK I see. On my kernel this is 8KB but every little helps and no point
it having it in there if it isn't needed.

>> Rebase to linux-2.6.git master.
>>
>> Change-Id: I07d77c832e816f5ad2390e25f466ddf750adecf4
>
> Don't forget to remove these before submitting to the patch tracker (and
> sending to the list).

OK thanks.

>> diff --git a/arch/arm/include/asm/bug.h b/arch/arm/include/asm/bug.h
>> index 4d88425..2914724 100644
>> --- a/arch/arm/include/asm/bug.h
>> +++ b/arch/arm/include/asm/bug.h
>> @@ -3,21 +3,58 @@
>>
>>
>>  #ifdef CONFIG_BUG
>> -#ifdef CONFIG_DEBUG_BUGVERBOSE
>> -extern void __bug(const char *file, int line) __attribute__((noreturn));
>> -
>> -/* give file/line information */
>> -#define BUG()                __bug(__FILE__, __LINE__)
>
> Does anybody reference __bug() anymore? If not you can remove that too.

No one is using it now, I will do this.

Regards,
Simon

^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH v3] ARM: Use generic BUG() handler
  2011-04-06 23:18 [PATCH v3] ARM: Use generic BUG() handler Simon Glass
  2011-04-07  5:35 ` Stephen Boyd
@ 2011-04-07 17:57 ` Stephen Boyd
  2011-04-14 23:02   ` Simon Glass
  1 sibling, 1 reply; 5+ messages in thread
From: Stephen Boyd @ 2011-04-07 17:57 UTC (permalink / raw)
  To: Simon Glass
  Cc: linux-arm-kernel, Russell King, Tony Lindgren, Nicolas Pitre,
	Catalin Marinas, Joe Perches, Laurent Pinchart,
	Alexander Shishkin, Phil Carmody, Rabin Vincent, linux-kernel,
	Omar Ramirez Luna, Dave Martin, Simon Glass

On 04/06/2011 04:18 PM, Simon Glass wrote:
> From: Simon Glass <sjg@google.com>
>
> ARM uses its own BUG() handler which makes its output slightly different
> from other archtectures.
>
[snip]
>
> Signed-off-by: Simon Glass <sjg@chromium.org>
> ---
>  arch/arm/Kconfig              |    4 +++
>  arch/arm/include/asm/bug.h    |   55 ++++++++++++++++++++++++++++++++++------
>  arch/arm/kernel/traps.c       |   23 +++++++++++++++++
>  arch/arm/kernel/vmlinux.lds.S |    3 +-
>  4 files changed, 75 insertions(+), 10 deletions(-)

Also, have you tried this with a module? I think you would at least need
to modify arch/arm/kernel/module.c to hook up the module_bug_finalize()
and module_bug_cleanup() stuff.

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH v3] ARM: Use generic BUG() handler
  2011-04-07 17:57 ` Stephen Boyd
@ 2011-04-14 23:02   ` Simon Glass
  0 siblings, 0 replies; 5+ messages in thread
From: Simon Glass @ 2011-04-14 23:02 UTC (permalink / raw)
  To: Stephen Boyd
  Cc: linux-arm-kernel, Russell King, Tony Lindgren, Nicolas Pitre,
	Catalin Marinas, Joe Perches, Laurent Pinchart,
	Alexander Shishkin, Phil Carmody, Rabin Vincent, linux-kernel,
	Omar Ramirez Luna, Dave Martin

On Thu, Apr 7, 2011 at 10:57 AM, Stephen Boyd <sboyd@codeaurora.org> wrote:
> On 04/06/2011 04:18 PM, Simon Glass wrote:
>> From: Simon Glass <sjg@google.com>
>>
>> ARM uses its own BUG() handler which makes its output slightly different
>> from other archtectures.
>>
> [snip]
>>
> Also, have you tried this with a module? I think you would at least need
> to modify arch/arm/kernel/module.c to hook up the module_bug_finalize()
> and module_bug_cleanup() stuff.

Actually this just works, except that I need to allow the PC to be
below PAGE_OFFSET where modules are loaded. This is a benefit of using
generic Linux code.

I have sent a new version of the patch to review.

Regards,
Simon

^ permalink raw reply	[flat|nested] 5+ messages in thread

end of thread, other threads:[~2011-04-14 23:02 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2011-04-06 23:18 [PATCH v3] ARM: Use generic BUG() handler Simon Glass
2011-04-07  5:35 ` Stephen Boyd
2011-04-07 16:49   ` Simon Glass
2011-04-07 17:57 ` Stephen Boyd
2011-04-14 23:02   ` Simon Glass

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).