[avahi] Re: [fwd] acx_pthread fixes for GCC shared/pthread inconsistency

Sjoerd Simons sjoerd at luon.net
Sat May 27 12:55:46 PDT 2006

I've included the Avahi mailing list in my reply. To give the avahi people some
context.  When i made the acx_pthread patch for avahi, i also proposed it
upstream. Now apparently it's the ``wrong'' solution. Below is the mail from the
acx_pthread author about it. 

Steven, thanks for your reply. Avahi does actually use libtool, but still it
fails to build on debian mips without the change to acx_pthread.. If i
understand you correctly this is a bug in libtool then (or avahi's use of it) ?

On Sat, May 27, 2006 at 02:49:35PM -0400, Steven G. Johnson wrote:
> On Sat, 27 May 2006, Steven G. Johnson wrote:
> >This is a bug in the ekg package, which doesn't follow the documentation 
> >for ACX_PTHREAD.  The documentation clearly states that PTHREAD_CFLAGS 
> >must be used for *both* compiling and linking.
> Sorry, I had misread the first few lines in the Debian thread.  They did 
> include -pthread when linking.  I have now looked into it more closely, 
> and I see what they are doing.  However, I still would like you to revert 
> the patch.
> The problem is that they were not linking an executable, but creating a 
> shared library with an inter-library dependency.  This is not the problem 
> that ACX_PTHREAD solves, and is inherently non-portable.  (Although it 
> happens to work in some cases.)
> ACX_PTHREAD figures out how to link a *program* that needs pthreads.
> Creating a shared library is a whole different beast, and the proper way 
> to do this portably is to use GNU libtool.  Otherwise, to do it right you 
> would have to duplicate large parts of libtool in ACX_PTHREAD, which is 
> not reasonable.  The proposed patch doesn't attempt this, and instead only 
> tries to solve the problem for gcc on certain platforms.
> (In fact, it's not even *possible* to create shared libraries with 
> inter-library dependencies on some platforms.)
> Unfortunately, the authors of the ekg program were not using libtool, and 
> instead of doing the right thing they hacked acx_pthread instead.  This is 
> fine for their purpose (getting it to run on Debian), but should not go 
> into the official acx_pthread macro.
> In summary, please revert the patch.  People wanting to build shared 
> libraries need to hack on libtool, not acx_pthread.
> Steven

When you know absolutely nothing about the topic, make your forecast by
asking a carefully selected probability sample of 300 others who don't
know the answer either.
		-- Edgar R. Fiedler

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