This variable is used to pass extra flags to the link step of a program
or a shared library.
+@item maude_DEPENDENCIES
+It is also occasionally useful to have a program depend on some other
+target which is not actually part of that program. This can be done
+using the @samp{_DEPENDENCIES} variable. Each program depends on the
+contents of such a variable, but no further interpretation is done.
+
+If @samp{_DEPENDENCIES} is not supplied, it is computed by Automake.
+The automatically-assigned value is the contents of @samp{_LDADD} or
+@samp{_LIBADD}, with most configure substitutions, @samp{-l}, @samp{-L},
+@samp{-dlopen} and @samp{-dlpreopen} options removed. The configure
+substitutions that are left in are only @samp{$(LIBOBJS)} and
+@samp{$(ALLOCA)}; these are left because it is known that they will not
+cause an invalid value for @samp{_DEPENDENCIES} to be generated.
+
@item maude_LINK
You can override the linker on a per-program basis. By default the
linker is chosen according to the languages used by the program. For
@itemx maude_OBJCFLAGS
@itemx maude_RFLAGS
@itemx maude_YFLAGS
+@cindex per-target compilation flags, defined
Automake allows you to set compilation flags on a per-program (or
per-library) basis. A single source file can be included in several
programs, and it will potentially be compiled with different flags for
each program. This works for any language directly supported by
-Automake. The flags are
+Automake. These @dfn{per-target compilation flags} are
@samp{_CCASFLAGS},
@samp{_CFLAGS},
@samp{_CPPFLAGS},
@samp{_RFLAGS}, and
@samp{_YFLAGS}.
-When using a per-program compilation flag, Automake will choose a
+When using a per-target compilation flag, Automake will choose a
different name for the intermediate object files. Ordinarily a file
like @file{sample.c} will be compiled to produce @file{sample.o}.
However, if the program's @samp{_CFLAGS} variable is set, then the
object file will be named, for instance, @file{maude-sample.o}.
+(See also @ref{renamed objects}.)
-In compilations with per-program flags, the ordinary @samp{AM_} form of
+In compilations with per-target flags, the ordinary @samp{AM_} form of
the flags variable is @emph{not} automatically included in the
compilation (however, the user form of the variable @emph{is} included).
So for instance, if you want the hypothetical @file{maude} compilations
@end example
-@item maude_DEPENDENCIES
-It is also occasionally useful to have a program depend on some other
-target which is not actually part of that program. This can be done
-using the @samp{_DEPENDENCIES} variable. Each program depends on the
-contents of such a variable, but no further interpretation is done.
-
-If @samp{_DEPENDENCIES} is not supplied, it is computed by Automake.
-The automatically-assigned value is the contents of @samp{_LDADD} or
-@samp{_LIBADD}, with most configure substitutions, @samp{-l}, @samp{-L},
-@samp{-dlopen} and @samp{-dlpreopen} options removed. The configure
-substitutions that are left in are only @samp{$(LIBOBJS)} and
-@samp{$(ALLOCA)}; these are left because it is known that they will not
-cause an invalid value for @samp{_DEPENDENCIES} to be generated.
-
@item maude_SHORTNAME
On some platforms the allowable file names are very short. In order to
-support these systems and per-program compilation flags at the same
+support these systems and per-target compilation flags at the same
time, Automake allows you to set a ``short name'' which will influence
-how intermediate object files are named. For instance, if you set
-@samp{maude_SHORTNAME} to @samp{m}, then in the above per-program
-compilation flag example the object file would be named
-@file{m-sample.o} rather than @file{maude-sample.o}. This facility is
-rarely needed in practice, and we recommend avoiding it until you find
-it is required.
-@end table
+how intermediate object files are named. For instance, in the following
+example,
+
+@example
+bin_PROGRAMS = maude
+maude_CPPFLAGS = -DSOMEFLAG
+maude_SHORTNAME = m
+maude_SOURCES = sample.c @dots{}
+@end example
+
+@noindent
+the object file would be named @file{m-sample.o} rather than
+@file{maude-sample.o}.
+This facility is rarely needed in practice,
+and we recommend avoiding it until you find it is required.
+@end table
@node LIBOBJS, Program variables, Program and Library Variables, Programs
@section Special handling for LIBOBJS and ALLOCA
* maintainer-mode:: missing and AM_MAINTAINER_MODE
* wildcards:: Why doesn't Automake support wildcards?
* distcleancheck:: Files left in build directory after distclean
+* renamed objects:: Why are object files sometimes renamed?
@end menu
@node CVS, maintainer-mode, FAQ, FAQ
You can get warnings about @code{$(wildcard ...}) constructs using the
@code{-Wportability} flag.
-@node distcleancheck, , wildcards, FAQ
+@node distcleancheck, renamed objects, wildcards, FAQ
@section Files left in build directory after distclean
@cindex distclean, diagnostic
@cindex dependencies and distributed files
complains before you do this. @code{distcleancheck_listfiles} is a
way to @emph{hide} errors, not to fix them. You can always do better.
+@node renamed objects, , distcleancheck, FAQ
+@section Why are object files sometimes renamed?
+
+This happens when per-target compilation flags are used. Object
+files need to be renamed just in case they would clash with object
+files compiled from the same sources, but with different flags.
+Consider the following example.
+
+@example
+bin_PROGRAMS = true false
+true_SOURCES = generic.c
+true_CPPFLAGS = -DEXIT_CODE=0
+false_SOURCES = generic.c
+false_CPPFLAGS = -DEXIT_CODE=1
+@end example
+@noindent
+Obviously the two programs are built from the same source, but it
+would be bad if they shared the same object, because @file{generic.o}
+cannot be built with both @code{-DEXIT_CODE=0} *and*
+@code{-DEXIT_CODE=1}. Therefore @command{automake} outputs rules to
+build two different objects: @file{true-generic.o} and
+@file{false-generic.o}.
+
+@command{automake} doesn't actually look whether sources files are
+shared to decide if it must rename objects. It will just rename all
+objects of a target as soon as it sees per-target compilation flags
+are used.
+
+It's OK to share object files when per-target compilation flags are not
+used. For instance @file{true} and @file{false} will both use
+@file{version.o} in the following example.
+
+@example
+AM_CPPFLAGS = -DVERSION=1.0
+bin_PROGRAMS = true false
+true_SOURCES = true.c version.c
+false_SOURCES = false.c version.c
+@end example
+
+Note that the renaming of objects is also affected by the
+@code{_SHORTNAME} variable (@pxref{Program and Library Variables}).
+
@page
@node Macro and Variable Index, General Index, FAQ, Top
@unnumbered Macro and Variable Index
@c LocalWords: MSG xtrue DBG pathchk CYGWIN afile proglink versioned CVS's
@c LocalWords: wildcards Autoconfiscated subsubheading autotools Meyering
@c LocalWords: ois's wildcard Wportability cartouche vrindex printindex
+@c LocalWords: DSOMEFLAG DVERSION
git://sourceware.org / automake.git / commitdiff