Re: One year since last libtool release

[Bob Friesenhahn]

On Wed, 4 Nov 2009, Ralf Wildenhues wrote:
> * Bob Friesenhahn wrote on Wed, Nov 04, 2009 at 06:25:26PM CET:
> > We should fix the libltdl performance problem (attempting to dlopen
> > a .a file due to the preloader) before making a release.  This is
> > something I am pretty interested in (it causes a HUGE performance
> > hit) so I will be looking into a fix eventually if no one else gets
> > to it first.
>
> Will you please write a testcase for this issue first thing you do?  If
> Autotest is too complicated, then just any kind of small reproducible
> example, but we *need* a test case, and you are in the best position to
> write it.

I am not sure how one would test for this in an automated fashion 
since the only effect is a performance reduction.  It requires 
system-dependent tools in order to watch the system calls and see what 
is actually going on.

> From what I have observed, the minimal run-time for a program which 
loads and unloads two modules differs by a factor of 5-6X between 
loading via the .so files, or loading via the .la files.  This means 
that the actual timing difference must be far larger.  These slow-down 
factors are observed under Solaris and FreeBSD, but are likely less 
under Linux since Linux glibc seems to cache and filter dlopen 
requests.  I am not sure what fraction of the time is wasted due to 
passing dlopen requests for .a archive files to dlopen, but it is 
surely large since this is done for all the dependency libraries (e.g. 
libc) as well.

Besides performance, there may be minor security implications since an 
illicit .a can be inserted anywhere the system searches for libraries, 
including in LD_LIBRARY_PATH.

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