Re: How to use ld options correctly for --whole-archive in automake and libtool

[Thomas Jahns]

Hello Andy,

On Mar 4, 2015, at 20:05 , Andy Falanga (afalanga) wrote:
> The team I work with has a project which is a C++ shared library  
> which is exposed in two different manners.  The first is a  
> traditional C++ library and the second is it's exposed, through  
> Boost.python, as a module.  I found some great references for how to  
> make this happen.  However, I've run into a problem: wrapping, in  
> their entirety, the libraries used in making the python module.  In  
> brief, the code is laid out thusly:
>
> Main  (has a Makefile.am and configure.ac files)
>  |
>  |-Shared
>  |    |
>  |    |- HwMgmt  (Makefile.am, makes libhwmgmt.a and libhwmgmt.so)
>  |    |- Misc    (Makefile.am, likewise for libmisc)
>  |
>  |-sata  (Makefile.am, produces libsatacpp.so and sata.so)
>  |   |
>  |   |-satacpp   (sources for the C++ API for SATA lib)
>  |   |
>  |   |-sata      (sources wrapping satacpp in boost.python)
>
>
> Since we distribute this in both a C++ and a python API, I decided  
> to simply use the autotools as they are intended to distribute the  
> whole thing.  However, there is a problem.  When I build the whole  
> thing, from "Main", the libraries which are built for sata.so (thy  
> python module) aren't yet built.  So, they've got to be included, or  
> linked, when we build sata.so.
>
> These aren't simply convenience libraries.  So, for example, using  
> "noinst_LTLIBRARIES = libhwmgmt.la" isn't acceptable.  However, the  
> *.a files made must be entirely included into the python module.  In  
> our former, home-baked, makefile arrangement, we just built them up  
> and included them as follows:
>
> gcc ... -Wl,--whole-archive /path/to/first.a, /path/to/second.a - 
> Wl,--no-whole-archive
>
> I'm trying to reproduce this using the automake tools.  I have this  
> in the Makefile.am located in sata:
>
> lib_LTLIBRARIES = satacpp.la
> satacpp_la_SOURCES = ...
>
> pyexec_LTLIBRAIRES = sata.la
> sata_la_LDFLAGS = -module
> sata_la_LIBADD = -Wl,--whole-archive ../Shared/HwMgmt/.libs/ 
> libhwmgmt.a ../Shared/Misc/.libs/libmisc.a .libs/libsata.a -Wl,--no- 
> whole-archive -lz -lrt
>
> As I'm sure no one here will be surprised, this causes automake to  
> fail because, "linker flags such as '-Wl,--whole-archive' belong in  
> sata_la_LDFLAGS."  However, when I place this there, I find that  
> Makefile.in and the final Makefile have things where I expect them,  
> but when make runs, the libraries I've specified to be included as  
> "whole-archive" are not listed between this option.  Instead, they  
> are listed earlier and *nothing is listed* between -Wl,--whole- 
> archive -Wl,--no-whole-archive.  I assume that libtool is doing this  
> for me.
>
> I'm using automake version 1.11.1, autoconf 2.63.
>
> Any help is greatly appreciated.


This is, from my point of view not so much an automake issue but a  
libtool problem: libtool for some reason I don't know decided to make - 
Wl, be the prefix for options to be passed to libtool when it's also  
the prefix for gcc and various other compilers (which serve as link  
editor frontend) for options to pass to the linker and then decides  
later to pass this on to the linker program (CC/CXX/whatever). These  
"options" are then re-ordered with respect to non-options (like  
your .a files) which makes it difficult to pass them in the correct  
position. You might be able to work around this with judicious use of  
extra -Wl, prefixes like this:

sata_la_LIBADD = -Wl,-Wl,,--whole-archive,../Shared/HwMgmt/.libs/ 
libhwmgmt.a,../Shared/Misc/.libs/libmisc.a,.libs/libsata.a,-Wl,,--no- 
whole-archive -lz -lrt

But what exactly is the problem with using e.g. ../Shared/HwMgmt/ 
libhwmgmt.la? That sata.so will then require libhwmgmt.so? libtool  
should be able to set sata.so's rpath such that libhwmgmt.so will be  
found at runtime.

Regards, Thomas

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