Is it possible to configure automake to generate a Makefile which, in addition to building the .o files and linked binary, also has targets for %.s? I want to be able to review the compiler output in a text format without having to invoke binutils on the .o files.
Specifically, if I have main.c as a source file, I want to be able to run make main.s. The desired recipe would be the same as that for main.o, but using CC1 := $(CC) -S.
The question is a little XY.
You want to be able make the intermediate assembly file foo.s, where
the source file foo.c is one of the sources in an autotooled project, using
a makefile that is generated by the project's ./configure script. You
assume that to do this you must do something to the automake inputs -
the Makefile.ams? - that will cause ./configure to generate Makefiles
that include assembly targets *.s matching all object targets *.o.
Well you could, but then your project would not be a regular autotooled project as usually distributed, and there is no need to make it irregular to get what you want.
The GCC option -save-temps
exists to let developers see the intermediate files of compilation - the preprocessor
output, the assembly.
$ gcc -c -o foo.o foo.c
outputs foo.o
$ gcc -save-temps -c -o foo.o foo.c
outputs:
foo.o
foo.i # preprocessed source
foo.s # assembly
As I expect you know, GNU Make receives compiler options from the make-variable
CFLAGS, and automake respects this convention, independently of and in addition to any compiler
options prescribed by the project's autotooling. So, if you would otherwise generate
makefiles with:
$ ./configure ...
then, to add -save-temps to the C compiler options, generate makefiles instead
with:
$ ./configure CFLAGS=-save-temps ...
And if you are already using CFLAGS, e.g.
$ ./configure CFLAGS="-g -O0" ...
then append -save-temps:
$ ./configure CFLAGS="-g -O0 -save-temps" ...
Then,
$ make main.o
will make main.o, main.i and main.s up-to-date.
To disable -save-temps, of course, rerun ./configure, removing it from
the CFLAGS.
If the project involves C++ compilation, then CXXFLAGS affects the C++
compiler in the same way that CFLAGS affects the C compiler. Note that
the generated preprocessed C++ sources will be called *.ii, not *.i.
With -save-temps enabled, make clean will not delete the *.i and *.s
files. You may not care, since compilation will always clobber them. If you
do care, you may take advantage of automake's standard phony target clean-local,
which is supported to let an autotooling maintainer extend the behaviour of
clean. Add the following recipe to the Makefile.am of each source directory
in the project:
clean-local:
$(RM) *.i *.ii *.s
Then update the autotooling and regenerate Makefiles:
$ autoreconf
$ ./configure ...
While the COMPILE variable in the generated Makefile.in is technically an internal detail, and this solution relies on the compiler to understand -c -S, adding:
.c.s:
$(COMPILE) -c -S $<
to the Makefile.am has worked for as long as I've been using the autotools. It might also be convenient to add:
clean-local:
rm -f *.s
I find this useful in development to have a look at the assembly output for specific configure and CC, CFLAGS options.
The COMPILE variable will be defined as something like:
COMPILE = $(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(AM_CPPFLAGS) \
$(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS)
Similarly, for C++ source we have:
.cc.s:
$(CXXCOMPILE) -c -S $<
