From: Paul Mackerras <paulus@samba.org>
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Message-ID: <16083.60374.284044.751867@nanango.paulus.ozlabs.org>
Date: Wed, 28 May 2003 08:51:02 +1000 (EST)
To: torvalds@transmeta.com
Cc: linux-kernel@vger.kernel.org
Subject: Proposed patch to kernel.h
Sender: linux-kernel-owner@vger.kernel.org
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Lines: 43

Linus,

PowerPC has a conditional trap instruction that I would like to use
for BUG_ON.  I would like to make BUG_ON for ppc look like this:

#define BUG_ON(x) do {						\
	__asm__ __volatile__(					\
		"1:	twnei %0,0\n"				\
		".section __bug_table,\"a\"\n"			\
		"	.long 1b,%1,%2\n"			\
		".previous"					\
		: : "r" (x), "i" (__LINE__), "i" (__FILE__));	\
} while (0)

This avoids a conditional branch and is nice and compact.  (The twnei
instruction takes an exception if the register operand is not equal
to the immediate operand - trap word not equal immediate.)

However, at the moment BUG_ON is unconditionally defined in kernel.h.
The patch below is the simplest way I can see to make it possible for
architectures to supply their own BUG_ON.  Please apply.

Thanks,
Paul.

diff -urN linux-2.5/include/linux/kernel.h pmac-2.5/include/linux/kernel.h
--- linux-2.5/include/linux/kernel.h	2003-05-21 08:27:25.000000000 +1000
+++ pmac-2.5/include/linux/kernel.h	2003-05-26 22:01:54.000000000 +1000
@@ -228,7 +228,9 @@
 	char _f[20-2*sizeof(long)-sizeof(int)];	/* Padding: libc5 uses this.. */
 };
 
+#ifndef BUG_ON
 #define BUG_ON(condition) do { if (unlikely((condition)!=0)) BUG(); } while(0)
+#endif
 #define WARN_ON(condition) do { \
 	if (unlikely((condition)!=0)) { \
 		printk("Badness in %s at %s:%d\n", __FUNCTION__, __FILE__, __LINE__); \
-
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