Re: Feature request: exec self for NOMMU.

From: Vadim Lobanov <vlobanov@speakeasy.net>
To: Rob Landley <rob@landley.net>
Cc: ray-gmail@madrabbit.org, linux-kernel@vger.kernel.org,
	David McCullough <david_mccullough@au.securecomputing.com>
Subject: Re: Feature request: exec self for NOMMU.
Date: Tue, 26 Dec 2006 22:08:36 -0800	[thread overview]
Message-ID: <1167199716.5616.3.camel@localhost.localdomain> (raw)
In-Reply-To: <200612270051.52690.rob@landley.net>

On Wed, 2006-12-27 at 00:51 -0500, Rob Landley wrote:
> On Wednesday 27 December 2006 12:13 am, Ray Lee wrote:
> > How about openning an fd to yourself at the beginning of execution, then
> > calling fexecve later?
> 
> I haven't got a man page for fexecve.  Does libc have it?

It's implemented inside glibc, and uses /proc to execve() the file that
the fd points to. Here's the code from
sysdeps/unix/sysv/linux/fexecve.c:

fexecve (fd, argv, envp)
     int fd;
     char *const argv[];
     char *const envp[];
{
  ...
  /* We use the /proc filesystem to get the information.  If it is not
     mounted we fail.  */
  char buf[sizeof "/proc/self/fd/" + sizeof (int) * 3];
  __snprintf (buf, sizeof (buf), "/proc/self/fd/%d", fd);

  /* We do not need the return value.  */
  __execve (buf, argv, envp);
  ...
}