From: baruch@tkos.co.il (Baruch Siach)
To: linux-arm-kernel@lists.infradead.org
Subject: Query about cplusplus in linkage.h
Date: Tue, 23 Nov 2010 07:46:43 +0200 [thread overview]
Message-ID: <20101123054643.GA6156@jasper.tkos.co.il> (raw)
In-Reply-To: <1c8df545.121ab.12c74028c01.Coremail.bill_carson@126.com>
Hi rocky,
On Mon, Nov 22, 2010 at 10:35:12PM +0800, rocky wrote:
> thanks for you kindly replay;
> I am still lost in this maze, so does extern "C" help user space C++ program to call schedule/printk?
> sys_xxx functions are called through SWI ,not directly called from user space C++ program;
It seems I was wrong. Userspace programs never call these functions directly.
See http://kernelnewbies.org/FAQ/asmlinkage for a better answer.
baruch
> At 2010-11-22 16:30:10?"Baruch Siach" <baruch@tkos.co.il> wrote:
>
> >Hi rocky,
> >
> >On Sat, Nov 20, 2010 at 12:17:02PM +0800, rocky wrote:
> >> I am a little confused about the following definition :
> >>
> >> --------------include/linux/linkage.h-----------
> >> #ifdef __cplusplus
> >> #define CPP_ASMLINKAGE extern "C"
> >> #else
> >> #define CPP_ASMLINKAGE
> >> #endif
> >>
> >> #ifndef asmlinkage
> >> #define asmlinkage CPP_ASMLINKAGE
> >> #endif
> >>
> >> all system call functions are marked with asmlinkage, as well as other kernel function like printk/schedule/do_softirq
> >>
> >>
> >> so every asmlinkage function has extern "C" attribute if cplusplus is defined, which definitely happens when compiling C++ code.
> >>
> >> I dont get it when cplusplus is needed when compiling kernel?
> >
> >It isn't.
> >
> >> Can anyone help me out of this little misunderstanding?
> >
> >Userspace C++ code may include kernel header files. Making the exported
> >function calls extern "C" makes it easier to build such applications.
> >
> >baruch
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- baruch at tkos.co.il - tel: +972.2.679.5364, http://www.tkos.co.il -
next prev parent reply other threads:[~2010-11-23 5:46 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-20 4:17 Query about cplusplus in linkage.h rocky
2010-11-22 8:30 ` Baruch Siach
2010-11-22 15:07 ` rocky
2010-11-23 5:46 ` Baruch Siach [this message]
2010-11-23 6:06 ` rocky
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