Autotools Makefile cannot find sources

Question

I am trying to use autotools in my Yocto project. Working with another user I was able to get bitbake to recognize my autogen.sh, configure.ac and Makefile.am. I am now getting the error

make: *** No rule to make target 'main.c', needed by 'main.o'.  Stop.

My tree is as follows:

.
├── files
│   ├── MAIN_Application
│   │   ├── autogen.sh
│   │   ├── configure.ac
│   │   ├── include
│   │   │   ├── main.h
│   │   │   ├── scheduler.h
│   │   │   └── utilities
│   │   │       └── time_conversions.h
│   │   ├── Makefile.am
│   │   ├── project.yml
│   │   └── src
│   │       ├── main.c
│   │       ├── Makefile.am
│   │       ├── scheduler.c
│   │       └── utilities
|   |           ├── Makefile.am
│   │           └── time_conversions.c
│   └── services
│       └── mainapplication.service
└── mainapplication_0.0.bb

My makefile.am is as follows:

AUTOMAKE_OPTIONS = foreign

CFLAGS = -Wall -pedantic -O2
include_HEADERS = main.h

bin_PROGRAMS = MAIN_Application
MAIN_Application_SOURCES = main.c

I believe I need to add my other source files. What I am not sure is how to do so. Do I add them with MAIN_Application_SOURCES or do I need to add a Makefile.am in each subdirectory?

Edit: Adding link to previous question. Edit 2: I have added a makefile.am to each directory. In MAIN_Application I have:

AUTOMAKE_OPTIONS = foreign
SUBDIRS = src
    

In src I have:

AUTOMAKE_OPTIONS = foreign
bin_PROGRAMS = MAIN_Application
EVCC_Application_SOURCES = main.c scheduler.c time_conversions.c

This gives a new error:

| Making all in src
| /bin/bash: line 20: cd: src: No such file or directory
| make: *** [Makefile:332: all-recursive] Error 1
| ERROR: oe_runmake failed
            

Edit 3: If I remove my src and include folders, place everything into one folder (top level) it all works. This is ugly and I hate it.

.
├── files
│   ├── MAIN_Application
│   │   ├── autogen.sh
│   │   ├── configure.ac
│   │   ├── main.c
│   │   ├── main.h
│   │   ├── Makefile.am
│   │   ├── project.yml
│   │   ├── scheduler.c
│   │   ├── scheduler.h
│   │   ├── time_conversions.c
│   │   └── time_conversions.h
│   └── services
│       └── mainapplication.service
└── mainapplication_0.0.bb

There has to be a way around this.

Edit 4: I am attempting to move all of my code into a src directory and use SUBDIR in my makefile.am

.
├── files
│   ├── MAIN_Application
│   │   ├── autogen.sh
│   │   ├── configure.ac
│   │   ├── include
│   │   ├── Makefile.am
│   │   ├── project.yml
│   │   ├── src
│   │   │   ├── main.c
│   │   │   ├── main.h
│   │   │   ├── Makefile.am
│   │   │   ├── scheduler.c
│   │   │   ├── scheduler.h
│   │   │   ├── time_conversions.c
│   │   │   └── time_conversions.h
│   │   └── test
│   │       ├── test_scheduler.c
│   │       └── test_time_conversions.c
│   └── services
│       └── mainapplication.service
└── mainapplication_0.0.bb

This leads to the same error of src no such file or directory.

Answer 1

I believe I need to add my other source files. What I am not sure is how to do so.

There is more than one way to do it, but one way or another, yes, you do need to tell Automake about all the sources involved. Depending on how you do it, you might need more than to just designate the sources.

Do I add them with MAIN_Application_SOURCES or do I need to add a Makefile.am in each subdirectory?

For the project as depicted in the question, you can, and probably should, add them to MAIN_Application_SOURCES in the top-level Makefile.am. In that case, you probably do not need any other Makefile.am files. You should provide paths relative to the directory containing the Makefile.am, so something like:

MAIN_Application_SOURCES = \
  src/main.c \
  src/scheduler.c \
  src/utilities/time_conversions.c

(It's not necessary to use the one-per-line format above, but I find that a lot easier to read and maintain than putting multiple filenames on one line.) In this case, you probably also want to add subdir-objects to your AUTOMAKE_OPTIONS:

AUTOMAKE_OPTIONS = foreign subdir-objects

You need more Makefile.am files only if you want more Makefiles to be generated, which ordinarily would be associated with recursive make.

Furthermore, to be useful, a Makefile.am must define at least one target to be built, and I see only one natural target in the whole project (MAIN_Application). You could introduce so-called "convenience libraries" to serve as targets for subdirectory makes, but I do not favor this approach, nor, for that matter, most uses of recursive make.

---

Additionally, this ...

include_HEADERS = main.h

... does not mean what you probably think it means. It says that file main.h (in, or to be generated in, the current directory) should be installed to $(includedir) by make install. It says nothing whatever about main.h's relationship to other targets. Still working on the assumption of a single top-level Makefile.am, I think what you want here is altogether different:

AM_CPPFLAGS = -I$(srcdir)/include

That will cause what appears to be an appropriate -I option to be provided to the compiler.

Supposing that you do not require support for make dist, and you do not actually want to install your header files as part of make install, you do not need to explicitly designate individual header files to Automake.

Answer 2

The issue is with configure.ac! This is my new folder structure

.
├── files
│   ├── MAIN_Application
│   │   ├── autogen.sh
│   │   ├── configure.ac
│   │   ├── include
│   │   │   ├── main.h
│   │   │   ├── scheduler.h
│   │   │   └── utilities
│   │   │       └── time_conversions.h
│   │   ├── Makefile.am
│   │   ├── project.yml
│   │   ├── src
│   │   │   ├── main.c
│   │   │   ├── Makefile.am
│   │   │   ├── scheduler.c
│   │   │   └── utilities
│   │   │       └── time_conversions.c
│   │   └── test
│   │       ├── test_scheduler.c
│   │       └── test_time_conversions.c
│   └── services
│       └── mainapplication.service
└── mainapplication_0.0.bb

My top level Makefile.am contains:

AUTOMAKE_OPTIONS = foreign
SUBDIRS =  src

My Makefile.am in src contains

AUTOMAKE_OPTIONS = foreign
bin_PROGRAMS = MAIN_Application
MAIN_Application_SOURCES = main.c scheduler.c time_conversions.c

Obviously these did not change from my question above. In my configure.ac I added one item to AC_CONFIG_FILES. This line changed from

AC_CONFIG_FILES([Makefile])

to

AC_CONFIG_FILES([Makefile src/Makefile])

Anytime you use a subdirectory like this you need to tell autotools about it. I solved this by searching for similar projects on GitHub and I found this.

In this project they have a top level makefile, as well as a makefile in each subdirectory containing source files. In their configure.ac they also give a path to each makefile!