Tarballs set as order-only prerequisites, not needed for build calls

Until now, the tarballs were the first normal prerequisite of the
software. As a result if their date changed, the whole software would be
re-built. However, for tarballs specifically, we actually check their
contents with a checksum, so their date is irrelevant (if its newer than
the built program, but has the same checksum, there is no need to re-build
the software).

Also, calling the tarball name as an argument to the building process (for
example `gbuild') was redundant. It is now automatically found from the
list of order-only prerequisites within `gbuild' and `cbuild' (similar to
how it was previously found in the `pybuild' for Python building).

A `README.md' file has also been placed in `reproduce/software/make' to
help describe the shared properties of the software building
Makefiles. This will hopefully grow much larger in the future.

1 files changed, 33 insertions, 0 deletions

diff --git a/reproduce/software/make/README.md b/reproduce/software/make/README.md
new file mode 100644
index 0000000..4eaefce
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+++ b/reproduce/software/make/README.md
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+Software building instructions
+==============================
+
+This directory contains Makefiles that are called by the high-level
+`reproduce/software/bash/configure.sh' script. The main target for the
+installation of each software is a simple plain text file that contains the
+name of the software and its version (which is put in the paper in the
+end). Once built, these plain-text files are all put in the proper
+sub-directory under `$(BDIR)/software/installed/version-info' (where
+`$(BDIR)' is the top-level build-directory specified by the user).
+
+Besides being directly used in the paper, these simple plain text files
+also act as prerequisites for higher-level software that depend on
+lower-level ones.
+
+Note on prerequisites
+---------------------
+
+Tarballs are order-only prerequsites (after a `|') because we already
+check their contents with the checksums, so their date is irrelevant: a
+tarball with a different content must have a new/different name, thus it
+will not exist, so it will be created, even when its order-only.q
+
+Binary programs (that don't install any libraries to be linked/used at
+compile time can also be order-only prerequisites, because usually they
+don't affect the compilation of the programs that depend on them, they
+are only used at run-time or by the low-level build instructions of the
+software. Ofcourse, if a program's version affects the build of a
+higher-level program, then it shouldn't be order-only.
+
+Libraries or Python modules that are used at compile time must be normal
+prerequisites (not order-only), because they are used during the building
+of the program.
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