Re: Using LS/LE (was: [PATCH v4 2/4] man/man5/tunables.conf: Document system-wide tunables config)

[Alejandro Colomar <alx@kernel.org>]

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> Date: 2026-08-29 10:53:02+0200
> From: Alejandro Colomar <alx@kernel.org>
>
> > Date: 2026-08-29 10:45:34+0200
> > From: Alejandro Colomar <alx@kernel.org>
> >
> > > Date: 2026-08-29 10:42:14+0200
> > > From: Alejandro Colomar <alx@kernel.org>
> > >
> > > Hi Larry,
> > > 
> > > > Date: 2026-08-28 22:50:50-0400
> > > > From: Larry Kollar <larry.kollar@icloud.com>
> > > >
> > > > 
> > > > Alejandro Colomar <alx@kernel.org> wrote:
> > > > 
> > > > > I believe that a set of makefiles that would handle all of the targets
> > > > > of a project like groff wouldn't take much more than that.  It might be
> > > > > a few hundred kB.  If it's well organized, it can be maintainable.
> > > > > 
> > > > > Because the makefile language is so simple, bugs are easy to spot and
> > > > > fix, compared to autotools (possibly automake, but I can't distinguish
> > > > > them enough).
> > > > 
> > > > I don’t know. Can a Makefile check for the presence of certain libraries
> > > > or other apps and fail gracefully (by which I mean exiting with a message
> > > > like “You need app X, plus libraries Y and Z, installed to successfully
> > > > compile this.”)? That’s one of the things that “makes" me appreciate taking
> > > > that extra step of typing `.configure` before make.
> > > 
> > > Yes, it can.  Here's a trivial test for that:
> > > 
> > > 	alx@devuan:~/tmp/testlib$ cat Makefile 
> > > 	HAS_LIBFOO := $(shell find /usr/include/foo.h >/dev/null && echo yes || echo no)
> 
> You can also trivially test with gcc(1) instead of find(1):
> 
> 	$ echo '#include <foo.h>' | gcc -x c -E >/dev/null 2>&1 && echo yes || echo no
> 	no
> 
> If you put that expression within $(shell ...), you can use it similarly.

Of course, I had some typos there.

Here's a fully working example:

	alx@devuan:~/tmp/testlib$ cat Makefile 
	CC ::= cc

	HAS_STDLIB ::= \
		$(shell \
			echo '#include <stdlib.h>' \
			| $(CC) -x c - -E >/dev/null \
			&& echo yes \
			|| echo no; \
		)

	HAS_LIBFOO ::= \
		$(shell \
			echo '#include <foo.h>' \
			| $(CC) -x c - -E >/dev/null \
			&& echo yes \
			|| echo no; \
		)

	ifeq ($(HAS_STDLIB),no)
	  $(error You need <stdlib.h> installed to successfully compile this)
	endif
	ifeq ($(HAS_LIBFOO),no)
	  $(error You need library FOO installed to successfully compile this)
	endif

	all:
		echo Done
	alx@devuan:~/tmp/testlib$ make
	<stdin>:1:10: fatal error: foo.h: No such file or directory
	compilation terminated.
	Makefile:23: *** You need library FOO installed to successfully compile this.  Stop.


Cheers,
Alex

> 
> 
> Cheers,
> alex
> 
> > > 
> > > 	ifeq ($(HAS_LIBFOO),no)
> > > 	  $(error You need library FOO installed to successfully compile this.)
> > 
> > Oh, I didn't need the period here...
> > 
> > > 	endif
> > > 
> > > 	all:
> > > 		echo Done
> > > 	alx@devuan:~/tmp/testlib$ make
> > > 	find: ‘/usr/include/foo.h’: No such file or directory
> > > 	Makefile:4: *** You need library FOO installed to successfully compile this..  Stop.
> > 
> > ... make(1) already appended one here.
> > 
> > :)
> > 
> > > 
> > > You may of course write more complex tests if you need.  Anything that
> > > you can do with a shell script, you can do it with a Makefile.
> > > 
> > > That said, I personally prefer to fail compilation due to missing header
> > > files.  It's simpler, and there's not much difference.  After all, if
> > > compilation fails for <foo.h>, it's trivial to run
> > > 
> > > 	$ apt-file find /include/foo.h
> > > 
> > > But if you want the test, you can have it.
> > > 
> > > 
> > > Have a lovely day!
> > > Alex
> > > 
> > > -- 
> > > <https://www.alejandro-colomar.es>
> > 
> > 
> > 
> > -- 
> > <https://www.alejandro-colomar.es>
> 
> 
> 
> -- 
> <https://www.alejandro-colomar.es>



-- 
<https://www.alejandro-colomar.es>

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