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To make sense of the above diagram, use this legend:
- Squares = callstacks
- Ovals = input/output files
- Green = python
- Blue = perl
- Black = raw text
- Purple = CMake
Explaining a bit further, the build of an E3SM case is primarily influenced by the Setup (case.setup, represented by the left side of the diagram) and Build (case.build, represented by the right side of the diagram) case phases. Case.setup will call BuildTools.configure, which processes all the XML stuff in E3SM/cime/config/e3sm/machines/config_compilers.xml and produces a Macros.cmake file. This file contains things like which compilers to use, which compiler flags to use, and which link flags to add. The next key task for setup is building namelists for each active component. As best as I can tell, our builds are not influenced by namelist files, but the buildnml scripts are responsible for calling the build configure scripts ($component/bld/configure) which are still in Perl for all our core components. The build configure scripts are responsible for producing two key input files for the build phase, "Filepath" and "CCSM_cppdefs", which will be placed in $case/Buildconf/${component}conf (e.g. $case/Buildconf/camconf/Filepath). Filepath is list of directories that will be globbed for source files. An interesting feature of our build system is that no repeated file basenames are allowed. For example, if Filepath contains directories A and B and A/foo.f90 and B/foo.f90 both exist, then only A/foo.f90 will be compiled by our build system (assuming A came first in the Filepath list). I believe the original intent of this approach was to allow for custom per-case srcmods. CCSM_cppdefs is a list of c preprocessor directives that will be applied to every compilation of every source file in the component. Both Filepath and CCSM_cppdefs are tweakable by users (users can modify these files in-place and re-run case.build).
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Be sure not to forget to source $case/.env_mach_specific.sh first so that your environment matches the CIME build environment. 'cd $EXEROOT/cmake-bld' . Just find and edit the appropriate link.txt file (will typically be mcmake/cpl/CMakeFiles/e3sm.exe.dir/link.txt, edit, and re-run make).
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