Here are variables that can be used to declare how a program or library
is to be built.
In the list below, we refer to the program or library as
In your Makefile.am you would replace this with the
canonicalized name of your program (see Other Automake variables).
This list refers to programs, but in general the same rules apply for
both static and dynamic
libraries; the documentation below notes situations where programs and
This variable, if it exists, lists all the source files that are
compiled to build the program. These files are added to the
distribution by default. When building the program, Automake will cause
each source file to be compiled to a single .o file (or
.lo when using libtool). Normally these object files are named
after the source file, but other factors can change this. If a file in
_SOURCES variable has an unrecognized extension, Automake
will do one of two things with it. If a suffix rule exists for turning
files with the unrecognized extension into .o files, then
automake will treat this file as it will any other source file
(see Support for Other Languages). Otherwise, the file will be
ignored as though it were a header file.
nodist_ can be used to control
whether files listed in a
_SOURCES variable are distributed.
dist_ is redundant, as sources are distributed by default, but it
can be specified for clarity if desired.
It is possible to have both
nodist_ variants of
_SOURCES variable at once; this lets you easily
distribute some files and not others, for instance:
nodist_foo_SOURCES = nodist.c dist_foo_SOURCES = dist-me.c
The output file (on Unix systems, the .o file) will be put into the subdirectory named after the source file. For instance file.c will compiled to file.o, while sub/dir/file.c will be compiled to sub/dir/file.o.
Automake needs to know the list of files you intend to compile
(For one thing, this is the only way Automake has of
knowing what sort of language support a given Makefile.in
This means that, for example, you can’t put a
configure substitution like ‘@my_sources@’ into a ‘_SOURCES’
variable. If you intend to conditionally compile source files and use
configure to substitute the appropriate object names into, e.g.,
_LDADD (see below), then you should list the corresponding source
files in the
This variable also supports
nodist_EXTRA_program_SOURCES would list extra
sources that may need to be built, but should not be distributed.
A static library is created by default by invoking ‘$(AR)
$(ARFLAGS)’ followed by the name of the library and then the objects
being put into the library. You can override this by setting the
_AR variable. This is usually used with C++; some C++
compilers require a special invocation in order to instantiate all the
templates that should go into a library. For instance, the SGI C++
compiler likes this variable set like so:
libfoo_a_AR = $(CXX) -ar -o
Extra objects can be added to a library using the
variable. For instance, this should be used for objects determined by
configure (see Libraries).
In the case of libtool libraries,
program_LIBADD can also
to other libtool libraries.
Extra objects (*.$(OBJEXT)) and libraries (*.a,
*.la) can be added to a program by listing them in the
_LDADD variable. For instance, this should be used for objects
configure (see Linking).
_LIBADD are inappropriate for passing
program-specific linker flags (except for -l, -L,
-dlopen and -dlpreopen). Use the
for this purpose.
For instance, if your configure.ac uses
could link your program against the X libraries like so:
foo_LDADD = $(X_PRE_LIBS) $(X_LIBS) $(X_EXTRA_LIBS)
We recommend that you use -l and -L only when
referring to third-party libraries, and give the explicit file names
of any library built by your package. Doing so will ensure that
program_DEPENDENCIES (see below) is correctly defined by
This variable is used to pass extra flags to the link step of a program
or a shared library. It overrides the
This variable is used to pass extra options to
It overrides the
These options are output before
option, so they should not be mode-specific options (those belong to
the compiler or linker flags). See Libtool Flags.
It is also occasionally useful to have a target (program or library)
depend on some other file that is not actually part of that target.
This can be done using the
_DEPENDENCIES variable. Each
target depends on the contents of such a variable, but no further
interpretation is done.
Since these dependencies are associated to the link rule used to
create the programs they should normally list files used by the link
command. That is *.$(OBJEXT), *.a, or *.la files
for programs; *.lo and *.la files for Libtool libraries;
and *.$(OBJEXT) files for static libraries. In rare cases you
may need to add other kinds of files such as linker scripts, but
listing a source file in
_DEPENDENCIES is wrong. If
some source file needs to be built before all the components of a
program are built, consider using the
_DEPENDENCIES is not supplied, it is computed by Automake.
The automatically-assigned value is the contents of
_LIBADD, with most configure substitutions, -l, -L,
-dlopen and -dlpreopen options removed. The configure
substitutions that are left in are only ‘$(LIBOBJS)’ and
‘$(ALLOCA)’; these are left because it is known that they will not
cause an invalid value for
_DEPENDENCIES to be generated.
_DEPENDENCIES is more likely used to perform conditional
compilation using an
AC_SUBST variable that contains a list of
objects. See Conditional Sources and Conditional Libtool Sources.
EXTRA_*_DEPENDENCIES variable may be useful for cases where
you merely want to augment the
_DEPENDENCIES variable rather than replacing it.
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
instance, a program that includes C++ source code would use the C++
compiler to link. The
_LINK variable must hold the name of a
command that can be passed all the .o file names and libraries
to link against as arguments. Note that the name of the underlying
program is not passed to
_LINK; typically one uses
foo_LINK = $(CCLD) -magic -o $@
_LINK variable is not supplied, it may still be generated
and used by Automake due to the use of per-target link flags such as
_LIBTOOLFLAGS, in cases where
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. These per-target compilation flags are ‘_CCASFLAGS’, ‘_CFLAGS’, ‘_CPPFLAGS’, ‘_CXXFLAGS’, ‘_FFLAGS’, ‘_GCJFLAGS’, ‘_LFLAGS’, ‘_OBJCFLAGS’, ‘_OBJCXXFLAGS’, ‘_RFLAGS’, ‘_UPCFLAGS’, and ‘_YFLAGS’.
When using a per-target compilation flag, Automake will choose a
different name for the intermediate object files. Ordinarily a file
like sample.c will be compiled to produce sample.o.
However, if the program’s
_CFLAGS variable is set, then the
object file will be named, for instance, foo-sample.o. (See
also Renamed Objects).
In compilations with per-target flags, the ordinary ‘AM_’ form of
the flags variable is not automatically included in the
compilation (however, the user form of the variable is included).
So for instance, if you want the hypothetical foo compilations
to also use the value of
AM_CFLAGS, you would need to write:
foo_CFLAGS = … your flags … $(AM_CFLAGS)
See Flag Variables Ordering for more discussion about the interaction between all these variables.
On some platforms the allowable file names are very short. In order to support these systems and per-target compilation flags at the same time, Automake allows you to set a “short name” that will change the naming of intermediate object files. For instance, in the following example,
bin_PROGRAMS = foo foo_CPPFLAGS = -DSOMEFLAG foo_SHORTNAME = f foo_SOURCES = sample.c …
the object file would be named f-sample.o rather than foo-sample.o.
This facility is rarely needed in practice, and we recommend avoiding it until you find it is required.
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.
bin_PROGRAMS = true false true_SOURCES = generic.c true_CPPFLAGS = -DEXIT_CODE=0 false_SOURCES = generic.c false_CPPFLAGS = -DEXIT_CODE=1
Obviously the two programs are built from the same source, but it
would be bad if they shared the same object, because generic.o
cannot be built with both ‘-DEXIT_CODE=0’ and
automake outputs rules to
build two different objects: true-generic.o and
automake doesn’t actually look whether source 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
It’s OK to share object files when per-target compilation flags are not used. For instance, true and false will both use version.o in the following example.
AM_CPPFLAGS = -DVERSION=1.0 bin_PROGRAMS = true false true_SOURCES = true.c version.c false_SOURCES = false.c version.c
Note that the renaming of objects is also affected by the
_SHORTNAME variable (see Program and Library Variables).
One of my source files needs to be compiled with different flags. How do I do?
Automake supports per-program and per-library compilation flags (see Program and Library Variables and Flag Variables Ordering). With this you can define compilation flags that apply to all files compiled for a target. For instance, in
bin_PROGRAMS = foo foo_SOURCES = foo.c foo.h bar.c bar.h main.c foo_CFLAGS = -some -flags
foo-foo.o, foo-bar.o, and foo-main.o will all be
compiled with ‘-some -flags’. (If you wonder about the names of
these object files, see Renamed Objects.) Note that
foo_CFLAGS gives the flags to use when compiling all the C
sources of the program
foo, it has nothing to do with
foo.c or foo-foo.o specifically.
What if foo.c needs to be compiled into foo.o using some specific flags, that none of the other files requires? Obviously per-program flags are not directly applicable here. Something like per-object flags are expected, i.e., flags that would be used only when creating foo-foo.o. Automake does not support that, however this is easy to simulate using a library that contains only that object, and compiling this library with per-library flags.
bin_PROGRAMS = foo foo_SOURCES = bar.c bar.h main.c foo_CFLAGS = -some -flags foo_LDADD = libfoo.a noinst_LIBRARIES = libfoo.a libfoo_a_SOURCES = foo.c foo.h libfoo_a_CFLAGS = -some -other -flags
Here foo-bar.o and foo-main.o will all be compiled with ‘-some -flags’, while libfoo_a-foo.o will be compiled using ‘-some -other -flags’. Eventually, all three objects will be linked to form foo.
This trick can also be achieved using Libtool convenience libraries, for instance ‘noinst_LTLIBRARIES = libfoo.la’ (see Libtool Convenience Libraries).
Another tempting idea to implement per-object flags is to override the
automake would output for these files.
Automake will not define a rule for a target you have defined, so you
could think about defining the ‘foo-foo.o: foo.c’ rule yourself.
We recommend against this, because this is error prone. For instance,
if you add such a rule to the first example, it will break the day you
decide to remove
foo_CFLAGS (because foo.c will then be
compiled as foo.o instead of foo-foo.o, see Renamed Objects). Also in order to support dependency tracking, the two
.o/.obj extensions, and all the other flags variables
involved in a compilation, you will end up modifying a copy of the
rule previously output by
automake for this file. If a new
release of Automake generates a different rule, your copy will need to
be updated by hand.