[PATCH v5] ARM: Use generic BUG() handler

Simon Glass
2011-07-29T07:58:50Z

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.

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.

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 | 31 +++++++++++++++-------
arch/arm/kernel/vmlinux.lds.S | 3 +-
4 files changed, 73 insertions(+), 20 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 09ebf0b..4570473 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -216,6 +216,10 @@ config ARM_PATCH_PHYS_VIRT_16BIT
to allow physical memory down to a theoretical minimum of 64K
boundaries.

+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..9abe7a0 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\", %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)
+
+#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 bc9f9da..7496924 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>
@@ -270,6 +271,8 @@ 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))
@@ -301,6 +304,24 @@ 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 (probe_kernel_address((unsigned *)pc, bkpt))
+ return 0;
+
+ return bkpt == BUG_INSTR_VALUE;
+}
+
+#endif
+
static LIST_HEAD(undef_hook);
static DEFINE_SPINLOCK(undef_lock);

@@ -706,16 +727,6 @@ baddataabort(int code, unsigned long instr, struct pt_regs *regs)
arm_notify_die("unknown data abort code", regs, &info, instr, 0);
}

-void __attribute__((noreturn)) __bug(const char *file, int line)
-{
- printk(KERN_CRIT"kernel BUG at %s:%d!\n", file, line);
- *(int *)0 = 0;
-
- /* Avoid "noreturn function does return" */
- for (;;);
-}
-EXPORT_SYMBOL(__bug);
-
void __readwrite_bug(const char *fn)
{
printk("%s called, but not implemented\n", fn);
diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
index bf977f8..7b2541e 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