(autoconf.info.gz) AC_LIBOBJ vs LIBOBJS

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 `AC_LIBOBJ' vs. `LIBOBJS'
 -------------------------
 
    Up to Autoconf 2.13, the replacement of functions was triggered via
 the variable `LIBOBJS'.  Since Autoconf 2.50, the macro `AC_LIBOBJ'
 should be used instead ( Generic Functions).  Starting at
 Autoconf 2.53, the use of `LIBOBJS' is an error.
 
    This change is mandated by the unification of the GNU Build System
 components.  In particular, the various fragile techniques used to parse
 a `configure.ac' are all replaced with the use of traces.  As a
 consequence, any action must be traceable, which obsoletes critical
 variable assignments.  Fortunately, `LIBOBJS' was the only problem, and
 it can even be handled gracefully (read, "without your having to change
 something").
 
    There were two typical uses of `LIBOBJS': asking for a replacement
 function, and adjusting `LIBOBJS' for Automake and/or Libtool.
 
 
    As for function replacement, the fix is immediate: use `AC_LIBOBJ'.
 For instance:
 
      LIBOBJS="$LIBOBJS fnmatch.o"
      LIBOBJS="$LIBOBJS malloc.$ac_objext"
 
 should be replaced with:
 
      AC_LIBOBJ([fnmatch])
      AC_LIBOBJ([malloc])
 
 
    When asked for automatic de-ANSI-fication, Automake needs
 `LIBOBJS''ed filenames to have `$U' appended to the base names.
 Libtool requires the definition of `LTLIBOBJS', whose suffixes are
 mapped to `.lo'.  People used to run snippets such as:
 
      # This is necessary so that .o files in LIBOBJS are also built via
      # the ANSI2KNR-filtering rules.
      LIBOBJS=`echo "$LIBOBJS" | sed 's/\.o /\$U.o /g;s/\.o$/\$U.o/'`
      LTLIBOBJS=`echo "$LIBOBJS" | sed 's/\.o/\.lo/g'`
      AC_SUBST(LTLIBOBJS)
 
 Note that this code is _wrong_, because `.o' is not the only possible
 extension(1)!  It should have read:
 
      # This is necessary so that .o files in LIBOBJS are also built via
      # the ANSI2KNR-filtering rules.
      LIB@&t@OBJS=`echo "$LIB@&t@OBJS" |
                   sed 's,\.[[^.]]* ,$U&,g;s,\.[[^.]]*$,$U&,'`
      LTLIBOBJS=`echo "$LIB@&t@OBJS" |
                 sed 's,\.[[^.]]* ,.lo ,g;s,\.[[^.]]*$,.lo,'`
      AC_SUBST(LTLIBOBJS)
 
 
    You no longer have to use this: `AC_OUTPUT' normalizes `LIBOBJS' and
 `LTLIBOBJS' (hence it works with any version of Automake and Libtool).
 Just remove these lines (`autoupdate' cannot handle this task, since
 this is not a macro).
 
    Note that `U' must not be used in your Makefiles.
 
    ---------- Footnotes ----------
 
    (1) Yet another reason why assigning `LIBOBJS' directly is
 discouraged.
 

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