sh: BUG() handling through trapa vector.

Previously we haven't been doing anything with verbose BUG() reporting,
and we've been relying on the oops path for handling BUG()'s, which is
rather sub-optimal.

This switches BUG handling to use a fixed trapa vector (#0x3e) where we
construct a small bug frame post trapa instruction to get the context
right. This also makes it trivial to wire up a DIE_BUG for the atomic
die chain, which we couldn't really do before.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>

include/asm-sh/bug.h

@@ -1,19 +1,54 @@
 #ifndef __ASM_SH_BUG_H
 #define __ASM_SH_BUG_H
 
-
 #ifdef CONFIG_BUG
-/*
- * Tell the user there is some problem.
- */
-#define BUG() do { \
-	printk("kernel BUG at %s:%d!\n", __FILE__, __LINE__); \
-	*(volatile int *)0 = 0; \
+
+struct bug_frame {
+	unsigned short	opcode;
+	unsigned short	line;
+	const char	*file;
+	const char	*func;
+};
+
+struct pt_regs;
+
+extern void handle_BUG(struct pt_regs *);
+
+#define TRAPA_BUG_OPCODE	0xc33e	/* trapa #0x3e */
+
+#ifdef CONFIG_DEBUG_BUGVERBOSE
+
+#define BUG()						\
+do {							\
+	__asm__ __volatile__ (				\
+		".align	2\n\t"				\
+		".short	%O0\n\t"			\
+		".short	%O1\n\t"			\
+		".long	%O2\n\t"			\
+		".long	%O3\n\t"			\
+		:					\
+		: "n" (TRAPA_BUG_OPCODE),		\
+		  "i" (__LINE__), "X" (__FILE__),	\
+		  "X" (__FUNCTION__));			\
 } while (0)
 
+#else
+
+#define BUG()					\
+do {						\
+	__asm__ __volatile__ (			\
+		".align	2\n\t"			\
+		".short	%O0\n\t"		\
+		:				\
+		: "n" (TRAPA_BUG_OPCODE));	\
+} while (0)
+
+#endif /* CONFIG_DEBUG_BUGVERBOSE */
+
 #define HAVE_ARCH_BUG
-#endif
+
+#endif /* CONFIG_BUG */
 
 #include <asm-generic/bug.h>
 
-#endif
+#endif /* __ASM_SH_BUG_H */