sh: unwinder: Use a special bug flag for unwinder traps.

This simplifies the unwinder trap handling, dropping the use of the
special trapa vector and simply piggybacking on top of the BUG support. A
new BUGFLAG_UNWINDER is added for flagging the unwinder fault, before
continuing on with regular BUG dispatch.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/include/asm/bug.h

 #ifndef __ASM_SH_BUG_H
 #define __ASM_SH_BUG_H
 
-#define TRAPA_UNWINDER_BUG_OPCODE 0xc33b /* trapa #0x3b */
 #define TRAPA_BUG_OPCODE	0xc33e	/* trapa #0x3e */
+#define BUGFLAG_UNWINDER	(1 << 1)
 
 #ifdef CONFIG_GENERIC_BUG
 #define HAVE_ARCH_BUG
@@ -73,15 +73,16 @@ do {							\
 	unlikely(__ret_warn_on);				\
 })
 
-#define UNWINDER_BUG()						\
+#define UNWINDER_BUG()					\
 do {							\
 	__asm__ __volatile__ (				\
 		"1:\t.short %O0\n"			\
-		_EMIT_BUG_ENTRY		\
+		_EMIT_BUG_ENTRY				\
 		 :					\
-		 : "n" (TRAPA_UNWINDER_BUG_OPCODE),	\
+		 : "n" (TRAPA_BUG_OPCODE),		\
 		   "i" (__FILE__),			\
-		   "i" (__LINE__), "i" (0),		\
+		   "i" (__LINE__),			\
+		   "i" (BUGFLAG_UNWINDER),		\
 		   "i" (sizeof(struct bug_entry)));	\
 } while (0)
 

arch/sh/kernel/debugtraps.S

@@ -19,10 +19,6 @@
 
 #if !defined(CONFIG_SH_STANDARD_BIOS)
 #define sh_bios_handler			debug_trap_handler
-#endif
-
-#if !defined(CONFIG_DWARF_UNWINDER)
-#define unwinder_trap_handler		debug_trap_handler
 #endif
 
 	.data
@@ -39,7 +35,7 @@ ENTRY(debug_trap_table)
 	.long debug_trap_handler	/* 0x38 */
 	.long debug_trap_handler	/* 0x39 */
 	.long debug_trap_handler	/* 0x3a */
-	.long unwinder_trap_handler	/* 0x3b */
+	.long debug_trap_handler	/* 0x3b */
 	.long breakpoint_trap_handler	/* 0x3c */
 	.long singlestep_trap_handler	/* 0x3d */
 	.long bug_trap_handler		/* 0x3e */

arch/sh/kernel/traps.c

@@ -5,18 +5,32 @@
 #include <linux/signal.h>
 #include <linux/sched.h>
 #include <linux/uaccess.h>
+#include <asm/unwinder.h>
 #include <asm/system.h>
 
 #ifdef CONFIG_BUG
 void handle_BUG(struct pt_regs *regs)
 {
+	const struct bug_entry *bug;
+	unsigned long bugaddr = regs->pc;
 	enum bug_trap_type tt;
-	tt = report_bug(regs->pc, regs);
+
+	if (!is_valid_bugaddr(bugaddr))
+		goto invalid;
+
+	bug = find_bug(bugaddr);
+
+	/* Switch unwinders when unwind_stack() is called */
+	if (bug->flags & BUGFLAG_UNWINDER)
+		unwinder_faulted = 1;
+
+	tt = report_bug(bugaddr, regs);
 	if (tt == BUG_TRAP_TYPE_WARN) {
-		regs->pc += instruction_size(regs->pc);
+		regs->pc += instruction_size(bugaddr);
 		return;
 	}
 
+invalid:
 	die("Kernel BUG", regs, TRAPA_BUG_OPCODE & 0xff);
 }
 
@@ -28,8 +42,7 @@ int is_valid_bugaddr(unsigned long addr)
 		return 0;
 	if (probe_kernel_address((insn_size_t *)addr, opcode))
 		return 0;
-
-	if (opcode == TRAPA_BUG_OPCODE || opcode == TRAPA_UNWINDER_BUG_OPCODE)
+	if (opcode == TRAPA_BUG_OPCODE)
 		return 1;
 
 	return 0;

arch/sh/kernel/unwinder.c

@@ -161,25 +161,4 @@ void unwind_stack(struct task_struct *task, struct pt_regs *regs,
 
 	curr_unwinder->dump(task, regs, sp, ops, data);
 }
-
-/*
- * Trap handler for UWINDER_BUG() statements. We must switch to the
- * unwinder with the next highest rating.
- */
-BUILD_TRAP_HANDLER(unwinder)
-{
-	insn_size_t insn;
-	TRAP_HANDLER_DECL;
-
-	/* Rewind */
-	regs->pc -= instruction_size(ctrl_inw(regs->pc - 4));
-	insn = *(insn_size_t *)instruction_pointer(regs);
-
-	/* Switch unwinders when unwind_stack() is called */
-	unwinder_faulted = 1;
-
-#ifdef CONFIG_BUG
-	handle_BUG(regs);
-#endif
-}
 EXPORT_SYMBOL_GPL(unwind_stack);