Re: A confusion about invoking my syscall

June 20, 2012


      2012/6/20 Jeff Haran <jharan@bytemobile.com>
...
** **
** **
*From:* 王哲 [mailto:wangzhe5004@gmail.com]
*Sent:* Monday, June 18, 2012 9:32 PM
*To:* Jeff Haran
*Cc:* kernelnewbies
*Subject:* Re: A confusion about invoking my syscall****
** **
** **
2012/6/19 Jeff Haran <jharan@bytemobile.com>****
****
****
*From:* kernelnewbies-bounces@kernelnewbies.org [mailto:
kernelnewbies-bounces@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@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? ****
On my system /usr/include/bits/syscall.h, which is being included in your
program because it includes syscall.h.
83 #define SYS_getpid __NR_getpid  ，so SYS_getpid is replaced
by __NR_getpid. and __NR_getpid was defined in the
kernel(arch/x86/include/asm/unistd_32.h). and my syscall was also defined
there.#define SYS_mysyscall __NR_mysyscall, i don't kown why it doesn't
works.
...
****
Jeff Haran****