[PATCH] verbose BUG_ON reporting

[Pekka J Enberg <penberg@cs.Helsinki.FI>]

On Mon, 27 Jun 2005, Andi Kleen wrote:
> It won't work for me because it'll bloat the kernel .text
> considerable. There is a reason why BUG is implemented
> like it is. Compare it.

The assertion codes bloat the kernel all the same. So how about this 
instead?

This patch adds a CONFIG_DEBUG_BUG_ON_VERBOSE that makes BUG_ON report the
evaluated expression in human readable form when the assertion fails.

The size of vmlinux with allyesconfig increases about 100k when the config
option is enabled:

    text    data     bss      dec filename
19333351 6699691 1845604 27878646 vmlinux-2.6.12-git8
19434139 6699691 1845604 27979434 vmlinux-2.6.12-git8-verbose-bug_on

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
---

 include/asm-generic/bug.h |   11 ++++++++++-
 lib/Kconfig.debug         |    7 +++++++
 2 files changed, 17 insertions(+), 1 deletion(-)

Index: 2.6/include/asm-generic/bug.h
===================================================================
--- 2.6.orig/include/asm-generic/bug.h
+++ 2.6/include/asm-generic/bug.h
@@ -12,8 +12,17 @@
 } while (0)
 #endif
 
+#ifdef CONFIG_DEBUG_BUG_ON_VERBOSE
+#define FAIL_BUG_ON(expr_str) do { \
+	printk("BUG_ON(%s) failed.\n", expr_str); \
+	BUG(); \
+} while (0)
+#else
+#define FAIL_BUG_ON(expr_str) BUG()
+#endif
+
 #ifndef HAVE_ARCH_BUG_ON
-#define BUG_ON(condition) do { if (unlikely((condition)!=0)) BUG(); } while(0)
+#define BUG_ON(condition) do { if (unlikely((condition)!=0)) FAIL_BUG_ON(#condition); } while(0)
 #endif
 
 #ifndef HAVE_ARCH_WARN_ON
Index: 2.6/lib/Kconfig.debug
===================================================================
--- 2.6.orig/lib/Kconfig.debug
+++ 2.6/lib/Kconfig.debug
@@ -116,6 +116,13 @@ config DEBUG_BUGVERBOSE
 	  of the BUG call as well as the EIP and oops trace.  This aids
 	  debugging but costs about 70-100K of memory.
 
+config DEBUG_BUG_ON_VERBOSE
+	bool "Verbose BUG_ON() reporting"
+	depends on DEBUG_KERNEL && BUG
+	default false
+	help
+	  Say Y here to make BUG_ON() panics output the evaluated expression.
+
 config DEBUG_INFO
 	bool "Compile the kernel with debug info"
 	depends on DEBUG_KERNEL
-
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