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- <h1>The GHC Commentary - Mindboggling Makefiles</h1>
- <p>
- The size and structure of GHC's makefiles makes it quite easy to scream
- out loud - in pain - during the process of tracking down problems in the
- make system or when attempting to alter it. GHC's <a
- href="http://haskell.cs.yale.edu/ghc/docs/latest/building/building-guide.html">Building
- Guide</a> has valuable information on <a
- href="http://haskell.cs.yale.edu/ghc/docs/latest/building/sec-makefile-arch.html">the
- makefile architecture.</a>
-
- <h4>A maze of twisty little passages, all alike</h4>
- <p>
- The <code>fptools/</code> toplevel and the various project directories
- contain not only a <code>Makefile</code> each, but there are
- subdirectories of name <code>mk/</code> at various levels that contain
- rules, targets, and so on specific to a project - or, in the case of the
- toplevel, the default rules for the whole system. Each <code>mk/</code>
- directory contains a file <code>boilerplate.mk</code> that ties the
- various other makefiles together. Files called <code>target.mk</code>,
- <code>paths.mk</code>, and <code>suffix.mk</code> contain make targets,
- definitions of variables containing paths, and suffix rules,
- respectively.
- <p>
- One particularly nasty trick used in this hierarchy of makefiles is the
- way in which the variable <code>$(TOP)</code> is used. AFAIK,
- <code>$(TOP)</code> always points to a directory containing an
- <code>mk/</code> subdirectory; however, it not necessarily points to the
- toplevel <code>fptools/</code> directory. For example, within the GHC
- subtree, <code>$(TOP)</code> points to <code>fptools/ghc/</code>.
- However, some of the makefiles in <code>fptools/ghc/mk/</code> will then
- <em>temporarily</em> redefine <code>$(TOP)</code> to point a level
- higher (i.e., to <code>fptools/</code>) while they are including the
- toplevel boilerplate. After that <code>$(TOP)</code> is redefined to
- whatever value it had before including makefiles from higher up in the
- hierarchy.
-
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-Last modified: Wed Aug 22 16:46:33 GMT Daylight Time 2001
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