Re: Error reporting should be improved

[Bob Friesenhahn]

This note in the Solaris manual page for dlerror() is interesting:

NOTES
     The messages returned by  dlerror() can reside in  a  static
     buffer that is overwritten on each call to dlerror(). Appli-
     cation code should not write to this buffer.  Programs want-
     ing  to  preserve  an  error  message  should make their own
     copies of that message.

The implementation of lt__set_last_error  is:

  static const char       *last_error     = 0;
  const char *
  lt__set_last_error (const char *errormsg)
  {
    return last_error = errormsg;
  }

so the current implementation is not reliable since the buffer pointed 
to may be updated several times before it is used.  It is also not 
thread safe.  Note that dlerror() may only be invoked once per error 
since calling it a second time returns a null pointer.  The Linux 
manual page recommends invoking dlerror() to clear any existing error 
message before invoking dlsym() (which we are not doing) so a symbol 
which has a valid value of zero will result in picking up some old 
error message.

It is not clear how to make the interface completely thread safe, but 
it is clear that the message needs to be copied immediately to a 
private buffer before returning back to the caller in order to make 
sure that the error returned is due to invoking a libltdl function.

Bob
--
Bob Friesenhahn
address@hidden, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/