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Message-Id: <201307051738.35930.arnd@arndb.de>
Date: Fri, 5 Jul 2013 17:38:35 +0200
From: Arnd Bergmann <arnd@...db.de>
To: linux-arch@...r.kernel.org
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
Chen Gang <gang.chen@...anux.com>,
"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
"Russell King - ARM Linux" <linux@....linux.org.uk>
Subject: [PATCH, re-send] Always trap on BUG()
I've run some size analyis using the ARM 'multi_v7_defconfig'
and gcc-4.8, using various definitions for BUG() and BUG_ON(), to
see how big the size improvement actually gets
1. Baseline: normal bug plus CONFIG_BUG_VERBOSE
text data bss dec hex filename
3743196 224396 206812 4174404 3fb244 vmlinux-bugverbose
2. disabling CONFIG_BUG_VERBOSE, saving 0.6%
3716920 224380 206812 4148112 3f4b90 vmlinux-nobugverbose
3. #define BUG() panic(__func__), #define BUG_ON(c) if(c) BUG(), saving 1.0%
3701076 224384 206812 4132272 3f0db0 vmlinux-bug-panicfunc
3. #define BUG() panic(__func__), #define BUG_ON(c) if(c) BUG(), saving 1.5%
3678884 224400 206812 4110096 3eb710 vmlinux-bug-panic
4. #define BUG() unreachable(), saving 2.1%
3652636 224384 206812 4083832 3e5078 vmlinux-bug-unreachable
5. as 4, plus #define BUG_ON(c) if(c) unreachable(), saving 2.2%
3651108 224380 206812 4082300 3e4a7c vmlinux-bugon-unreachable
6. #define BUG() do{}while(0), saving 2.1%
3654264 224380 206812 4085456 3e56d0 vmlinux-nobug
7. as 6, plus #define BUG_ON if(0 && (c)) unreachable, saving 2.2%
3648392 223996 206748 4079136 3e3e20 vmlinux-no-bugon
8. my patch below, saving 1.8%
3666532 224380 206812 4097724 3e86bc obj-tmp/vmlinux
The gain of doing unreachable and letting the code run off whereever
is minimal compared to the current state of doing nothing, but it
avoids the warnings.
Same test using x86_defconfig:
1. CONFIG_BUG=y, CONFIG_BUGVERBOSE=n
10797859 1395648 1175552 13369059 cbfee3 vmlinux-x86-bug
2. CONFIG_BUG=n, saves 1.0%
10658553 1395584 1175552 13229689 c9de79 vmlinux-x86-nobug
3. with my patch, saves 0.8%
10684186 1395584 1175552 13255322 ca429a vmlinux-x86-archbug
Getting 1-2% savings in kernel size seems absolutely worth keeping the
option, but 0.2-0.4% left for getting reproducible behavior also seems
worthwhile. The result in the patch below.
This basically loses any of the BUG() reporting, but leaves the
logic to trap and kill the task in place when CONFIG_BUG is disabled.
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Cc: linux-arch@...r.kernel.org
Cc: Chen Gang <gang.chen@...anux.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Russell King - ARM Linux <linux@....linux.org.uk>
diff --git a/arch/arm/include/asm/bug.h b/arch/arm/include/asm/bug.h
index 7af5c6c..4a5b85d 100644
--- a/arch/arm/include/asm/bug.h
+++ b/arch/arm/include/asm/bug.h
@@ -3,8 +3,6 @@
#include <linux/linkage.h>
-#ifdef CONFIG_BUG
-
/*
* Use a suitable undefined instruction to use for ARM/Thumb2 bug handling.
* We need to be careful not to conflict with those used by other modules and
@@ -54,7 +52,6 @@ do { \
#endif /* CONFIG_DEBUG_BUGVERBOSE */
#define HAVE_ARCH_BUG
-#endif /* CONFIG_BUG */
#include <asm-generic/bug.h>
diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index 2f03ff0..ba38ebb 100644
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -1,7 +1,6 @@
#ifndef _ASM_X86_BUG_H
#define _ASM_X86_BUG_H
-#ifdef CONFIG_BUG
#define HAVE_ARCH_BUG
#ifdef CONFIG_DEBUG_BUGVERBOSE
@@ -33,8 +32,6 @@ do { \
} while (0)
#endif
-#endif /* !CONFIG_BUG */
-
#include <asm-generic/bug.h>
#endif /* _ASM_X86_BUG_H */
diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index 7d10f96..bbd2872 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -112,12 +112,13 @@ extern void warn_slowpath_null(const char *file, const int line);
#endif
#ifndef HAVE_ARCH_BUG_ON
-#define BUG_ON(condition) do { if (condition) ; } while(0)
+#define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while(0)
#endif
#ifndef HAVE_ARCH_WARN_ON
#define WARN_ON(condition) ({ \
int __ret_warn_on = !!(condition); \
+ (void)__ret_warn_on; \
unlikely(__ret_warn_on); \
})
#endif
@@ -125,6 +126,8 @@ extern void warn_slowpath_null(const char *file, const int line);
#ifndef WARN
#define WARN(condition, format...) ({ \
int __ret_warn_on = !!(condition); \
+ if (0 && (__ret_warn_on)) \
+ printk(format); \
unlikely(__ret_warn_on); \
})
#endif
--
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