[PATCH 1/2] Clean up: Makefile.in: Correct the prerequisites

[Michael Witten]

On Tue, 11 Jul 2017 05:08:56 -0000, Michael Witten wrote:

> diff --git a/libtommath/Makefile.in b/libtommath/Makefile.in
> index dbcd2a0..c06187a 100644
> --- a/libtommath/Makefile.in
> +++ b/libtommath/Makefile.in
> @@ -17,7 +17,7 @@ endif
>  ifneq ($V,1)
>  	@echo "   * ${CC} $@"
>  endif
> -	${silent} ${CC} -c ${CFLAGS} $^ -o $@
> +	${silent} ${CC} -c ${CFLAGS} $*.c -o $@
>
>  #default files to install
>  ifndef LIBNAME

The above change is not quite correct; primarily, it breaks
out-of-tree builds (which are already broken, and will be fixed
shortly in another patch that I'll be submitting).

The patch above alters the recipe for all object files (the rule
not shown is `%.o: %.c'); in the original, the automatic variable
`$^' is replaced with all of the prerequisites for the target in
question, but this didn't work, because another part of this patch
tells `make' that some of the prerequisites are header files, and
thus `$^' expands to include those header files as well, which the
compiler doesn't appreciate.

The solution provided here just uses the pattern-matching stem
of the target, provided by the automatic variable `$*', in order
to construct the relevant `*.c' file. Alas, during an out-of-tree
build, the stem is not enough to construct the path to the source
code that needs to be compiled.

In order to benefit from the search-for-prerequisites performed by
`make', it's necessary to use the `$^' automatic variable, so the
real solution to all of the above is just to filter the expansion
of `$^' so that only `*.c' prerequisites are placed on the command
line.

More concretely, the above patch *should* look like this:

  diff --git a/libtommath/Makefile.in b/libtommath/Makefile.in
  index dbcd2a0..c06187a 100644
  --- a/libtommath/Makefile.in
  +++ b/libtommath/Makefile.in
  @@ -17,7 +17,7 @@ endif
   ifneq ($V,1)
   	@echo "   * ${CC} $@"
   endif
  -	${silent} ${CC} -c ${CFLAGS} $^ -o $@
  +	${silent} ${CC} -c ${CFLAGS} $(filter %.c,$^) -o $@
  
   #default files to install
   ifndef LIBNAME

As out-of-tree builds are already broken, there's little value in
updating this particular patch; instead, the above improvement on
this patch will be incorporated in a future patch that I'll submit
soon for the purpose of fixing out-of-tree builds.

Sincerely,
Michael Witten