Node:AC_LIBOBJ vs. LIBOBJS, Previous:Hosts and Cross-Compilation, Up:Autoconf 2.13
AC_LIBOBJ vs. LIBOBJSUp 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 (see 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.
At the time this documentation is written, Automake does not rely on
traces yet, but this is planed for a near future. Nevertheless, to
ease the transition, and to guarantee this future Automake release will
be able to use Autoconf 2.53, using LIBOBJS directly will make
autoconf fail. But note that the output, configure,
is correct and fully functional: you have some delay to adjust your
source.
There are 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 $U appended to the
base names. Libtool requires the definition of LTLIBOBJS, which
suffixes are mapped to .lo. Although Autoconf provides them with
means to free the user to do that by herself, by the time of this
writing, none do. Therefore, it is common to see configure.ac
end with:
# This is necessary so that .o files in LIBOBJS are also built via # the ANSI2KNR-filtering rules. LIBOBJS=`echo "$LIBOBJS" | sed 's/\.o /\$U.o /g;s/\.o$/\$U.o/'` LTLIBOBJS=`echo "$LIBOBJS" | sed 's/\.o/\.lo/g'` AC_SUBST(LTLIBOBJS)
First, note that this code is wrong, because .o is not the
only possible extension1! Because the token LIBOBJS is now
forbidden, you will have to replace this snippet with:
# 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)
Unfortunately, autoupdate cannot help here, since... this is
not a macro! Of course, first make sure your release of Automake and/or
Libtool still requires these.