Anyone tried building smbsh on Linux lately?

David Collier-Brown davecb at
Sat Mar 23 07:49:01 GMT 2002

Steve Langasek wrote:
> On Fri, Mar 22, 2002 at 12:25:40PM -0500, David Collier-Brown wrote:
> >   A colleague (Fred Weigel) just prototyped an interposer
> > library on Linux 2.2 using LD_PRELOAD, which worked
> > happily, substantially the same as on Solaris.
> >   In addition, dlsym(RTLD_NEXT,...) seems to be
> > supported.
> >   Any other things necessary for smbsh on Linux?
> On Linux, that sounds to me like it's everything that's needed.  As a
> general-purpose rewrite of smbsh that works on multiple platforms, I
> would guess that there needs to be something in the configure script to
> figure out the path to the appropriate C library.

	As long as you're not doing your dlsyms in a vendor-
	specific _init function, you can use the RTLD_NEXT
	option to dlsym.  
	Failing that, use syscall and don't call the libraries at all.

	From the (Solaris) man page, 

      void *dlsym(void *handle, const char *name);

      The dlsym() function allows a process to obtain the  address
      of  a  symbol  defined within a shared object or executable.
      The handle argument is either the value returned from a call
      to  dlopen()  or  one  of  the special handles RTLD_DEFAULT,
      RTLD_NEXT, or RTLD_SELF. The name argument is  the  symbol's
      name as a character string.

      In  the  case  of  a  handle  returned  from  dlopen(),  the
      corresponding  shared object must not have been closed using
      dlclose(). The dlsym() function searches for the named  sym-
      bol  in  all shared objects loaded automatically as a result
      of loading the object referenced by handle. See dlopen(3DL).

      In the case of  the  special  handle  RTLD_DEFAULT,  dlsym()
      searches for the named symbol starting with the first object
      loaded and proceeding through the  list  of  initial  loaded
      objects,  and  any global objects obtained with dlopen(3DL),
      until a match is found.  This  search  follows  the  default
      model employed to relocate all objects within the process.
	[And finds the interceptor you just wrote (:-(]

      In  the  case  of  the  special  handle  RTLD_NEXT,  dlsym()
      searches  for  the  named  symbol  in  the objects that were
      loaded following the object from which the dlsym()  call  is
      being made. [Ie, the underlying symbol, in libc and so
	forth.  This does require the 

	[and RTLD_SELF searches in the current .so]
David Collier-Brown,           | Always do right. This will gratify 
Performance & Engineering      | some people and astonish the rest.
Americas Customer Engineering, |                      -- Mark Twain
(905) 415-2849                 | davecb at

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