README.cross

Cross-compiling cado-nfs

It is possible to cross-compile cado-nfs. This has been tested only once,
as a mere curiosity check. This appeared to successfully compile. You may
wish to follow the instructions below, but nothing is guaranteed
concerning the results.

The following assumes that:
    - you are building for a system which is called, say, SYSTEM. The
      value of SYSTEM quite possibly *must* follow what is returned from
      the GNU autotools config.guess program, although this has not been
      verified.
    - you have already built or obtained cross-compilers for the C and
      C++ language, which are accessible from within your $PATH as
      SYSTEM-cc, or SYSTEM-gcc, and SYSTEM-c++, or SYSTEM-g++.
    - you have also already built the standard linker utilities such as
      ld, and these are accessible as SYSTEM-ld
    - the include files for SYSTEM-cc can be fetched from the directory
      SYSTEM_ROOT, which serves as a virtual root for the host system.
    - you have already cross-compiled the Gnu MP library into
      SYSTEM_ROOT. Note that the gmp shared libraries must of course
      eventually go to the shared system as well.

In all the example code below, be sure to substitute SYSTEM, SYSTEM-cc,
SYSTEM-c++, and SYSTEM_ROOT with the appropriate values. Also substitute
CADO_NFS_SOURCE_ROOT of course.

For cross-compiling cado, do the following:

    export GF2X_CONFIGURE_EXTRA_FLAGS=--host=SYSTEM
    export PREFIX=SYSTEM_ROOT/usr/local

(of course you may wish to choose another install path on the host
system ; see also README.shared for disabling shared libraries).

Create a file $HOME/SYSTEM-toolchain.cmake, containing the following:

    SET(CMAKE_SYSTEM_NAME Linux)
    SET(CMAKE_SYSTEM_VERSION 1)
    SET(CMAKE_C_COMPILER SYSTEM-cc)
    SET(CMAKE_CXX_COMPILER SYSTEM-c++)
    SET(CMAKE_FIND_ROOT_PATH SYSTEM_ROOT)
    SET(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
    SET(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
    SET(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)

Create a build directory outside of the cado-nfs source tree, and cd to
that directory. From there, do:

    cmake -DCMAKE_TOOLCHAIN_FILE=$HOME/SYSTEM-toolchain.cmake CADO_NFS_SOURCE_ROOT
    make
    make install

Following this, once you copy the files under SYSTEM_ROOT/usr/local to
your target system, you should be able to run cado-nfs.py. Of course,
this assumes that all the *run-time* dependencies of cado-nfs are met
(python3, etc).


Issues with shared libraries (not only system ones, but those cado-nfs
builds and uses itself) are common. To prevent cado-nfs from building
shared libs, see README.shared.