From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Chen Gang <gang.chen@asianux.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] include/linux/posix_acl.h: need 'return NULL' when BUG(), if neither CONFIG_BUG nor HAVE_ARCH_BUG is defined.
Date: Mon, 20 May 2013 17:31:18 +0100 [thread overview]
Message-ID: <20130520163118.GX18614@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <97dada79-cd78-4799-8f18-ed2bf8eee508@email.android.com>
On Mon, May 20, 2013 at 07:40:24AM -0700, Eric W. Biederman wrote:
> Seriously? The correct fix it would seem is to give a useful default BUG
> definition. Say *NULL.
Absolutely.
The real question is... how is this happening. I've seen it occasionally
in the randconfig builds - though I don't have any logs to hand which
show that in the build system at the moment. So, looking at the files:
arch/arm/include/asm/bug.h:
#ifdef CONFIG_BUG
#define BUG() _BUG(__FILE__, __LINE__, BUG_INSTR_VALUE)
#define _BUG(file, line, value) __BUG(file, line, value)
#ifdef CONFIG_DEBUG_BUGVERBOSE
#define __BUG(__file, __line, __value) \
...
unreachable(); \
...
#else /* not CONFIG_DEBUG_BUGVERBOSE */
#define __BUG(__file, __line, __value) \
...
unreachable(); \
...
#endif /* CONFIG_DEBUG_BUGVERBOSE */
#define HAVE_ARCH_BUG
#endif /* CONFIG_BUG */
#include <asm-generic/bug.h>
So here, whenever we have CONFIG_BUG enabled, we always define a non-empty
BUG() macro to override the generic version. So far so good.
include/asm-generic/bug.h:
#ifdef CONFIG_BUG
... we're providing our own version ...
#else /* !CONFIG_BUG */
#ifndef HAVE_ARCH_BUG
#define BUG() do {} while(0)
#endif
#ifndef HAVE_ARCH_BUG_ON
#define BUG_ON(condition) do { if (condition) ; } while(0)
#endif
So, the generic stuff becomes no-ops which just fall through. Seriously?
Is this really what we want?
So either we need to fix the generic bug.h code, or fix every site which
uses BUG()/BUG_ON().
Note - I'm not saying *NULL as you did, because that isn't guaranteed to
fault on all platforms. NoMMU may allow *NULL to succeed without causing
an exception.
WARNING: multiple messages have this Message-ID (diff)
From: linux@arm.linux.org.uk (Russell King - ARM Linux)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] include/linux/posix_acl.h: need 'return NULL' when BUG(), if neither CONFIG_BUG nor HAVE_ARCH_BUG is defined.
Date: Mon, 20 May 2013 17:31:18 +0100 [thread overview]
Message-ID: <20130520163118.GX18614@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <97dada79-cd78-4799-8f18-ed2bf8eee508@email.android.com>
On Mon, May 20, 2013 at 07:40:24AM -0700, Eric W. Biederman wrote:
> Seriously? The correct fix it would seem is to give a useful default BUG
> definition. Say *NULL.
Absolutely.
The real question is... how is this happening. I've seen it occasionally
in the randconfig builds - though I don't have any logs to hand which
show that in the build system at the moment. So, looking at the files:
arch/arm/include/asm/bug.h:
#ifdef CONFIG_BUG
#define BUG() _BUG(__FILE__, __LINE__, BUG_INSTR_VALUE)
#define _BUG(file, line, value) __BUG(file, line, value)
#ifdef CONFIG_DEBUG_BUGVERBOSE
#define __BUG(__file, __line, __value) \
...
unreachable(); \
...
#else /* not CONFIG_DEBUG_BUGVERBOSE */
#define __BUG(__file, __line, __value) \
...
unreachable(); \
...
#endif /* CONFIG_DEBUG_BUGVERBOSE */
#define HAVE_ARCH_BUG
#endif /* CONFIG_BUG */
#include <asm-generic/bug.h>
So here, whenever we have CONFIG_BUG enabled, we always define a non-empty
BUG() macro to override the generic version. So far so good.
include/asm-generic/bug.h:
#ifdef CONFIG_BUG
... we're providing our own version ...
#else /* !CONFIG_BUG */
#ifndef HAVE_ARCH_BUG
#define BUG() do {} while(0)
#endif
#ifndef HAVE_ARCH_BUG_ON
#define BUG_ON(condition) do { if (condition) ; } while(0)
#endif
So, the generic stuff becomes no-ops which just fall through. Seriously?
Is this really what we want?
So either we need to fix the generic bug.h code, or fix every site which
uses BUG()/BUG_ON().
Note - I'm not saying *NULL as you did, because that isn't guaranteed to
fault on all platforms. NoMMU may allow *NULL to succeed without causing
an exception.
next prev parent reply other threads:[~2013-05-20 16:31 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-05-20 8:16 [PATCH] include/linux/posix_acl.h: need 'return NULL' when BUG(), if neither CONFIG_BUG nor HAVE_ARCH_BUG is defined Chen Gang
2013-05-20 8:16 ` Chen Gang
2013-05-20 14:40 ` Eric W. Biederman
2013-05-20 14:40 ` Eric W. Biederman
2013-05-20 16:31 ` Russell King - ARM Linux [this message]
2013-05-20 16:31 ` Russell King - ARM Linux
2013-05-21 1:51 ` Chen Gang
2013-05-21 1:51 ` Chen Gang
2013-05-21 10:59 ` Russell King - ARM Linux
2013-05-21 10:59 ` Russell King - ARM Linux
2013-05-21 11:16 ` Chen Gang
2013-05-21 11:16 ` Chen Gang
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