linux-kernel - Re: [PATCH v3 3/5] kbuild: add read-file macro

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Date:   Sat, 10 Dec 2022 22:02:48 +0100
From:   Nicolas Schier <nicolas@...sle.eu>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Alexander Lobakin <alexandr.lobakin@...el.com>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH v3 3/5] kbuild: add read-file macro

On Sat, Dec 10, 2022 at 11:10:12PM +0900 Masahiro Yamada wrote:
> On Thu, Dec 8, 2022 at 1:25 AM Alexander Lobakin
> <alexandr.lobakin@...el.com> wrote:
> >
> > From: Alexander Lobakin <alexandr.lobakin@...el.com>
> > Date: Wed, 7 Dec 2022 16:40:44 +0100
> >
> > > From: Masahiro Yamada <masahiroy@...nel.org>
> > > Date: Sun, 27 Nov 2022 07:56:22 +0900
> > >
> > > > Since GNU Make 4.2, $(file ...) supports the read operater '<', which
> > > > is useful to read a file without forking any process. No warning is
> > > > shown even if the input file is missing.
> >
> > [...]
> >
> > > Great stuff. Used it in my upcoming series to simplify things, works
> > > as expected.
> > >
> > > sed-syms = $(subst $(space),\|,$(foreach file,$(sym-files-y),$(call read-file,$(file))))
> > >
> > > The only thing that came to my mind while I was implementing the
> > > oneliner above: maybe add ability to read multiple files? For now,
> > > I used a foreach, could it be somehow incorporated into read-file
> > > already?
> >
> > Oh, nevermind. This one also works:
> >
> > sed-syms = $(subst $(space),\|,$(call read-file,$(sym-files-y)))
> >
> > So I believe read-file works for an arbitrary number of files.
> 
> 
> 
> Really?
> 
> 
> In my understanding, $(call read-file, foo bar) reads a single file "foo bar".
> (a space in the file name).

yes, except for make < 4.2, due to:

read-file = $(shell cat $1 2>/dev/null)