Compiler Wrapper for Automated Options Generation with pkg-config
pecc is a compiler wrapper utilizing [pkg-config] (https://www.freedesktop.org/wiki/Software/pkg-config/) to automatically generate the correct compiler options on the command line. This is particularly useful when combined with [Environment Module] (http://modules.sourceforge.net/), typicaly available in High-Performance Computing (HPC) and clusters.
An example works much better to clarify the above description. Typically, without the compiler wrapper, a user needs to do something like this:
module load fftw
gcc ${FFTW_DIR}/include my_fft_code.c ${FFTW_DIR}/lib -lfftw3
or, with MPI compiler:
module load fftw
mpicc ${FFTW_DIR}/include my_fft_mpicode.c ${FFTW_DIR}/lib -lfftw3_mpi -lfftw3
This is assuming the environment variable $(FFTW_DIR) is set in the modulefile for FFTW.
With pecc, the above compile and linking lines are much simplified for the user:
module load fftw
pecc my_fft_code.c
pecc my_fft_mpicode.c
because pecc automatically generates the correct compiler options behind the scene.
pecc makes compiler and linking much easier for end-users by shifting the burden to setting up the correct environment to the software installers and system administrators. However, the work needed is relatively simple.
Using our example with FFTW above, the modulefile for FFTW only needs to few more extra environment variables:
prepend-path PE_PKGCONFIG_LIBS fftw
prepend-path PKG_CONFIG_PATH [directory containing fftw.pc]
The file fftw.pc needs to be created during installation. Many software and libraries provide this already, and its content can simply be customized. The file is typically located in ${PACKAGE_DIR}/lib/pkgconfig where $PACKAGE_DIR is the installation directory.
For example, here is the content of fftw.pc that would work with our example above:
prefix=/software/cs400/fftw/3.3.5/centos7.2_gnu5.3.0
includedir=${prefix}/include
libdir=${prefix}/lib
Name: fftw
Description: fftw Library
URL: http://www.fftw.org
Version: 3.3.5
Cflags: -I${includedir}
Libs: -L${libdir} -lfftw3_mpi -lfftw3_omp -lfftw3_threads -lfftw3 -lfftw3f_mpi -lfftw3f_omp -lfftw3f_threads -lfftw3f
Libs.private: -lpthreads
In this file we include both the douple precision,single precision, threading, and MPI libraries in a single link line to make it easier for users. Overlinking is avoided because pecc by default added --as-needed flag to the linker. But of course system administrator can choose how to customize or split the FFTW package into multiple versions (for example, it is conceivable to have separate fftw, fftw-threaded, fftw-mpi modules instead).
PE_CC, PE_CXX, and PE_FORTRAN need to be set to the actual back-end C, C++, and Fortran compilers, respectively. Typically this is the MPI compiler wrappers (e.g. mpicc, mpic++, mpif90 or mpifort) for MPI environment, or just the real compilers (e.g. gcc, g++, or gfortran for the GNU compilers)
PE_ADD_RPATH: Setting this environment variable to 1 or Y will add the -rpath option to the linker for every library locations provided by packages (i.e. modulefiles). This remove the need to re-load the modulefile or set LD_LIBRARY_PATH during runtime.
PE_PRE_FLAGS and PE_POST_FLAGS can be set to insert arbitrary flags at the beginning and at the end of the compile line.