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Subject: [PATCH] x86: remove unneeded endless loop in BUG()
From: Petr Tesarik <ptesarik@suse.cz>
To: Ingo Molnar <mingo@elte.hu>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>, "H. Peter Anvin" <hpa@zytor.com>,
       LKML <linux-kernel@vger.kernel.org>
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Organization: SUSE LINUX
Date: Thu, 19 Feb 2009 19:38:33 +0100
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Since __builtin_trap() will always generate an illegal instruction, we
can replace the explicit asm("ud2") with it.

This way gcc will understand that the function never returns, plus it
won't emit any extra instructions.

Signed-off-by: Petr Tesarik <ptesarik@suse.cz>

diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index d9cf1cd..9b7c50a 100644
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -4,6 +4,13 @@
 #ifdef CONFIG_BUG
 #define HAVE_ARCH_BUG
 
+#define DO_BUG()						\
+do {								\
+	__builtin_trap();					\
+	printk("BUG: failure at %s:%d/%s()!\n", __FILE__, __LINE__, __func__); \
+	panic("BUG!");						\
+} while(0)
+
 #ifdef CONFIG_DEBUG_BUGVERBOSE
 
 #ifdef CONFIG_X86_32
@@ -14,7 +21,7 @@
 
 #define BUG()							\
 do {								\
-	asm volatile("1:\tud2\n"				\
+	asm volatile("1:\n"					\
 		     ".pushsection __bug_table,\"a\"\n"		\
 		     __BUG_C0					\
 		     "\t.word %c1, 0\n"				\
@@ -22,15 +29,11 @@ do {								\
 		     ".popsection"				\
 		     : : "i" (__FILE__), "i" (__LINE__),	\
 		     "i" (sizeof(struct bug_entry)));		\
-	for (;;) ;						\
+	DO_BUG();					\
 } while (0)
 
 #else
-#define BUG()							\
-do {								\
-	asm volatile("ud2");					\
-	for (;;) ;						\
-} while (0)
+#define BUG	DO_BUG
 #endif
 
 #endif /* !CONFIG_BUG */