A confusion about invoking my syscall

[Matthias Brugger]

On 06/19/2012 06:32 AM, 王哲 wrote:
>
>
> 2012/6/19 Jeff Haran <jharan at bytemobile.com <mailto:jharan at bytemobile.com>>
>
>     __ __
>
>     __ __
>
>     *From:*kernelnewbies-bounces at kernelnewbies.org
>     <mailto:kernelnewbies-bounces at kernelnewbies.org>
>     [mailto:kernelnewbies-bounces at kernelnewbies.org
>     <mailto:kernelnewbies-bounces at kernelnewbies.org>] *On Behalf Of *??
>     *Sent:* Monday, June 18, 2012 6:40 PM
>     *To:* kernelnewbies
>     *Subject:* A confusion about invoking my syscall____
>
>     __ __
>
>     Hello everyone:
>
>               I append a simple syscall in kernel. and the function is
>     as follows:
>
>        asmlinkage  long sys_mysyscall(long data)
>       {
>                printk("This is my syscall!\n");
>                return data;
>        }
>
>     and i test it sucessfully in user space . and the test program:
>
>         #include <linux/unistd.h>
>         #include <syscall.h>
>         #include <sys/types.h>
>         #include <stdio.h>
>
>
>
>         int main(void)
>         {
>         long n = 0,m = 0,pid1,pid2;
>         n = syscall(345,190);// #define __NR_mysyscall          345
>         printf("n = %ld\n",n);
>         pid1 = syscall(SYS_getpid);  //getpid
>         printf("pid = %ld\n",pid1);
>         pid2 = syscall(20);  //getpid
>         printf("pid = %ld\n",pid2);
>         return 0;
>        }
>     and the result:
>     n = 190
>     pid = 4097
>     pid = 4097
>
>     but if the test program is:
>     #include <linux/unistd.h>
>     #include <syscall.h>
>     #include <sys/types.h>
>     #include <stdio.h>
>
>
>
>     int main(void)
>     {
>       long n = 0,m = 0,pid1,pid2;
>       n = syscall(345,190);// #define __NR_mysyscall          345
>       printf("n = %ld\n",n);
>       m = syscall(SYS_mysyscall,190);
>       printf("m = %ld\n",m);
>       pid1 = syscall(SYS_getpid);  //getpid
>       printf("pid = %ld\n",pid1);
>       pid2 = syscall(20);  //getpid
>       printf("pid = %ld\n",pid2);
>       return 0;
>     }
>     and the result:
>     wanny at wanny-C-Notebook-XXXX:~/syscall/src$ gcc test1.c
>     test1.c: In function ‘main’:
>     test1.c:13:14: error: ‘SYS_mysyscall’ undeclared (first use in this
>     function)
>     test1.c:13:14: note: each undeclared identifier is reported only
>     once for each function it appears in
>
>
>     why i can't invoke my syscall with "SYS_mysyscall"?
>
>     Thanks in advance!
>
>     Because it appears you never defined the symbol SYS_mysyscall.____
>
>     __ I think so,but where shoud i defne the __symbol SYS_mysyscall ?
>
>        and where is the symbol SYS_getpid defined?

Not sure, but I think the syscalls should be defined in syscall.h which 
is included by your program. I suppose that this file is part of libc, 
so there won't be your syscall definition in there.
The easiest way would be to define the syscall by yourself.

Remember that adding a syscall to the linux kernel is a bad idea.

Regards,
Matthias

>
>     Jeff Haran
>     ____
>
>
>
>
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