Libtool and Support for Shared Libraries
gnb at fastmail.fm
Tue May 15 18:13:34 EDT 2012
On Tue, May 15, 2012, at 11:52 PM, Дилян Палаузов wrote:
> >>>>> Also, I notice that libcom_err.la is 'noinst'. How do you expect that cyrus executable will be able to find this code at runtime on a platform which has shared libraries but no system com_err library?
> >>>> When the compilation of the internal com_err is requested, the files
> >>>> from libcom_err.la are compiled with -fPIC and statically linked in
> >>>> libimap and libsieve.
> >>> Two questions -
> >>> 1) is this happening by accident because we're currently adding -fPIC to
> >>> the global CFLAGS via @PERL_CCLDFLAGS@ ?
> >> According to my understanding, -fPIC is added, so that the compiled .o
> >> files, can be inserted in a shared library and this is independent from
> >> @PERL_CCLDFLAGS at .
> > Ah. I was under the impression that libtool+automake would build two
> > different .o files, one with -fPIC for shared libraries and one without
> > for static libraries and executables.
> For installable libraries, this is true, because both static and shared
> libraries are installed. For noinst_ (convenience) libraries, this is
> also true (but I do not know why libtool builds .o files twice and I do
> not know, if the files that are supposed to be built without -fPIC are
> build in fact with @PERL_CCLDFLAGS@).
I think there are, or used to be :(, platforms on which you could not
mix -fPIC and not-fPIC code arbitrarily. In particular, you couldn't
build -fPIC code into a fully static executable. In any case, -fPIC is
marginally less efficient than non-fPIC code on most platforms (except
MIPS where all code is -fPIC).
I think we should stop using @PERL_CCLDFLAGS@ now, as the .so's
generated from the Perl build will be able to use the new shared
libraries. Probably we will need to disable those Perl modules in
configure.ac if --disable-shared is given though.
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