linux-kernel - Re: [PATCH] Eliminate thousands of warnings in WARN

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Date:	Thu, 23 Apr 2009 14:23:27 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andi Kleen <andi@...stfloor.org>, arjan@...ux.intel.com,
	linux-kernel@...r.kernel.org, torvalds@...l.org, akpm@...l.org
Subject: Re: [PATCH] Eliminate thousands of warnings in WARN_ON with gcc 3.2 build

On Thu, Apr 23, 2009 at 02:02:19PM +0200, Johannes Weiner wrote:
> > +{
> > +	warn_slowpath_fmt(file, line, "");
> > +}
> > +EXPORT_SYMBOL(warn_slowpath_null);
> 
> That should still emit a warning due to passing in a zero-length
> format string.  Using (const char *){ 0 } as the literal would
> suppress it (on gcc 4.3.3 at least) but I'm not sure if it's worth the
> uglyness...

Hmm, you're right 3.3 generates a warning for that, 3.2 doesn't
But at least it's only a single one, not thousands.
Your trick would make sense. Updated patch attached.

-Andi

---

Eliminate thousands of warnings with gcc 3.2 build v2

When building with gcc 3.2 I get thousands of warnings about passing
a NULL format string to warn_on_slowpath(). Split this case out
into a separate call. This should also shrink the kernel
slightly.

v2: Avoid warning in warn_slowpath_null on newer gccs too (J.Weiner)

Acked-by: Jesper Nilsson <jesper.nilsson@...s.com>
Signed-off-by: Andi Kleen <ak@...ux.intel.com>

---
 include/asm-generic/bug.h |    7 ++++---
 kernel/panic.c            |   12 +++++++++---
 2 files changed, 13 insertions(+), 6 deletions(-)

Index: linux-2.6.30-rc2-ak/include/asm-generic/bug.h
===================================================================
--- linux-2.6.30-rc2-ak.orig/include/asm-generic/bug.h	2009-01-11 20:20:40.000000000 +0100
+++ linux-2.6.30-rc2-ak/include/asm-generic/bug.h	2009-04-22 23:52:48.000000000 +0200
@@ -58,12 +58,13 @@
  */
 #ifndef __WARN
 #ifndef __ASSEMBLY__
-extern void warn_slowpath(const char *file, const int line,
+extern void warn_slowpath_fmt(const char *file, const int line,
 		const char *fmt, ...) __attribute__((format(printf, 3, 4)));
+extern void warn_slowpath_null(const char *file, const int line);
 #define WANT_WARN_ON_SLOWPATH
 #endif
-#define __WARN()		warn_slowpath(__FILE__, __LINE__, NULL)
-#define __WARN_printf(arg...)	warn_slowpath(__FILE__, __LINE__, arg)
+#define __WARN()		warn_slowpath_null(__FILE__, __LINE__)
+#define __WARN_printf(arg...)	warn_slowpath_fmt(__FILE__, __LINE__, arg)
 #else
 #define __WARN_printf(arg...)	do { printk(arg); __WARN(); } while (0)
 #endif
Index: linux-2.6.30-rc2-ak/kernel/panic.c
===================================================================
--- linux-2.6.30-rc2-ak.orig/kernel/panic.c	2009-04-19 19:29:07.000000000 +0200
+++ linux-2.6.30-rc2-ak/kernel/panic.c	2009-04-23 14:17:34.000000000 +0200
@@ -342,7 +342,7 @@
 }
 
 #ifdef WANT_WARN_ON_SLOWPATH
-void warn_slowpath(const char *file, int line, const char *fmt, ...)
+void warn_slowpath_fmt(const char *file, int line, const char *fmt, ...)
 {
 	va_list args;
 	char function[KSYM_SYMBOL_LEN];
@@ -358,7 +358,7 @@
 	if (board)
 		printk(KERN_WARNING "Hardware name: %s\n", board);
 
-	if (fmt) {
+	if (*fmt) {
 		va_start(args, fmt);
 		vprintk(fmt, args);
 		va_end(args);
@@ -369,7 +369,13 @@
 	print_oops_end_marker();
 	add_taint(TAINT_WARN);
 }
-EXPORT_SYMBOL(warn_slowpath);
+EXPORT_SYMBOL(warn_slowpath_fmt);
+
+void warn_slowpath_null(const char *file, int line)
+{
+	warn_slowpath_fmt(file, line, (const char *) { 0 });
+}
+EXPORT_SYMBOL(warn_slowpath_null);
 #endif
 
 #ifdef CONFIG_CC_STACKPROTECTOR


-- 
ak@...ux.intel.com -- Speaking for myself only.
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