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).
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.

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>

2 files changed, 23 insertions, 11 deletions

diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index bc9f9da782c..74969248c37 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 bf977f8514f..7b2541efd9f 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)