Query about cplusplus in linkage.h

[rocky]

Hi, Baruch

Thanks for URL: http://kernelnewbies.org/FAQ/asmlinkage


Only two arch overide asmlinkage definitions in include/linux/linkage.h
1:arch/x86/include/asm/linkage.h
2:arch/ia64/include/asm/linkage.h
that's what the above URL say about parameter passing using STACK or REGISTER;

while I must admit  _cplusplus is  a total different story;


BR
rocky


At 2010-11-23 13:46:43，"Baruch Siach" <baruch at tkos.co.il> wrote:

>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 at 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
>
>-- 
>                                                     ~. .~   Tk Open Systems
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>   - baruch at tkos.co.il - tel: +972.2.679.5364, http://www.tkos.co.il -
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