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[PATCH] MIPS: Make BUG() __noreturn.

To: linux-mips <linux-mips@linux-mips.org>
Subject: [PATCH] MIPS: Make BUG() __noreturn.
From: David Daney <ddaney@caviumnetworks.com>
Date: Thu, 20 Nov 2008 17:26:36 -0800
Cc: linux-kernel@vger.kernel.org
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
User-agent: Thunderbird 2.0.0.16 (X11/20080723)
MIPS: Make BUG() __noreturn.

Often we do things like put BUG() in the default clause of a case
statement.  Since it was not declared __noreturn, this could sometimes
lead to bogus compiler warnings that variables were used
uninitialized.

There is a small problem in that we have to put a magic while(1); loop to
fool GCC into really thinking it is noreturn.  This makes the new
BUG() function 3 instructions long instead of just 1, but I think it
is worth it as it is now unnecessary to do extra work to silence the
'used uninitialized' warnings.

I also re-wrote BUG_ON so that if it is given a constant condition, it
just does BUG() instead of loading a constant value in to a register
and testing it.


Signed-off-by: David Daney <ddaney@caviumnetworks.com>
---
arch/mips/include/asm/bug.h |   29 ++++++++++++++++++++---------
1 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/arch/mips/include/asm/bug.h b/arch/mips/include/asm/bug.h
index 7eb63de..08ea468 100644
--- a/arch/mips/include/asm/bug.h
+++ b/arch/mips/include/asm/bug.h
@@ -7,20 +7,31 @@

#include <asm/break.h>

-#define BUG()                                                          \
-do {                                                                   \
-       __asm__ __volatile__("break %0" : : "i" (BRK_BUG));         \
-} while (0)
+static inline void __noreturn BUG(void)
+{
+       __asm__ __volatile__("break %0" : : "i" (BRK_BUG));
+       /* Fool GCC into thinking the function doesn't return. */
+       while (1)
+               ;
+}

#define HAVE_ARCH_BUG

#if (_MIPS_ISA > _MIPS_ISA_MIPS1)

-#define BUG_ON(condition)                                              \
-do {                                                                   \
-       __asm__ __volatile__("tne $0, %0, %1"                         \
-                            : : "r" (condition), "i" (BRK_BUG));   \
-} while (0)
+static inline void  __BUG_ON(unsigned long condition)
+{
+       if (__builtin_constant_p(condition)) {
+               if (condition)
+                       BUG();
+               else
+                       return;
+       }
+       __asm__ __volatile__("tne $0, %0, %1"
+                            : : "r" (condition), "i" (BRK_BUG));
+}
+
+#define BUG_ON(C) __BUG_ON((unsigned long)(C))

#define HAVE_ARCH_BUG_ON


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