System Call Wrapper of 'open'

UNIX for Advanced & Expert Users
1

When the programmer use 'open' function, the process is like below.
"open -> system call wrapper of open in Glibc -> syscall_open in kernel"

I found the wrapper of open, but there is no implementation like 'int $80'.

int
__open (file, oflag)
     const char *file;
     int oflag;
{
  int mode;

  if (file == NULL)
    {
      __set_errno (EINVAL);
      return -1;
    }

  if (oflag & O_CREAT)
    {
      va_list arg;
      va_start(arg, oflag);
      mode = va_arg(arg, int);
      va_end(arg);
    }

  __set_errno (ENOSYS);
  return -1;
}

Please let me know where the wrapper of open is.

2

This looks to me like you found a stub that's intended for someone to fill in for a specific system, given that no matter what you do to call it, it will return -1 and set errno. That said, I'm not sure why they would do all the other stuff just to return -1.

You need to be looking in a different place, I think.

3

Are you referring to syscall in Linux?

You need to read this page, then download the kernel source if you want.

http://tldp.org/HOWTO/Implement-Sys-Call-Linux-2.6-i386/x50.html

4

Perhaps the following will help you. Assuming you are using a 32-bit X86 2.6 Linux kernel .....

0x80 is the value of the software interrupt (INT) which performs the transfer to kernel mode via system_call(). See ../arch/x84/kernel/entry_32.S for the system_call() source.

The syscall interface for open() is defined in ../include/linux/syscalls.h

asmlinkage long sys_open(const char __user *filename, int flags, int mode);

The system call number for open is defined in ../arch/include/asm/unistd_32.h

#define __NR_open 5