linux-kernel - Re: [PATCH 7/7] kbuild: doc: document subdir-y syntax

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Date:   Sat, 28 Nov 2020 17:58:44 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        Michal Marek <michal.lkml@...kovi.net>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 7/7] kbuild: doc: document subdir-y syntax

On Tue, Nov 24, 2020 at 3:03 AM Randy Dunlap <rdunlap@...radead.org> wrote:
>
> On 11/22/20 8:54 PM, Masahiro Yamada wrote:
> > There is no explanation about subdir-y.
> >
> > Let's document it.
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> > ---
> >
> >  Documentation/kbuild/makefiles.rst | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> >
> > diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst
> > index 159e470f2616..6332b9ca7942 100644
> > --- a/Documentation/kbuild/makefiles.rst
> > +++ b/Documentation/kbuild/makefiles.rst
> > @@ -319,6 +319,20 @@ more details, with real examples.
> >       that directory specifies obj-y, those objects will be left orphan.
> >       It is very likely a bug of the Makefile or of dependencies in Kconfig.
> >
> > +     Kbuild also supports dedicated syntax, subdir-y and subdir-m, for
> > +     descending into subdirectories. It is a good fit when you know they
> > +     do not contain kernel-space objects at all. A typical usage is to let
> > +     Kbuild descend into subdirectories to build tools.
> > +
> > +     Examples::
> > +
> > +             subdir-$(CONFIG_GCC_PLUGINS) += gcc-plugins
> > +             subdir-$(CONFIG_MODVERSIONS) += genksyms
> > +             subdir-$(CONFIG_SECURITY_SELINUX) += selinux
> > +
> > +     Unlike obj-y/m, subdir-y/m does not need the trailing slash since this
> > +     syntax is always used for directories.
> > +
>
> Just curious:  Is a trailing slash allowed here?  say for consistency?


If you use a trailing slash for the subdir-y syntax,
it will still work.


Only the problem I see is that the build log will look clumsy
due to the double slashes "//".





For example, if you change scripts/Makefile as follows:


diff --git a/scripts/Makefile b/scripts/Makefile
index b5418ec587fb..554534449877 100644
--- a/scripts/Makefile
+++ b/scripts/Makefile
@@ -32,9 +32,9 @@ hostprogs += unifdef
 # The module linker script is preprocessed on demand
 targets += module.lds

-subdir-$(CONFIG_GCC_PLUGINS) += gcc-plugins
-subdir-$(CONFIG_MODVERSIONS) += genksyms
-subdir-$(CONFIG_SECURITY_SELINUX) += selinux
+subdir-$(CONFIG_GCC_PLUGINS) += gcc-plugins/
+subdir-$(CONFIG_MODVERSIONS) += genksyms/
+subdir-$(CONFIG_SECURITY_SELINUX) += selinux/

 # Let clean descend into subdirs
 subdir-        += basic dtc gdb kconfig mod




The build log will look like follows:


masahiro@...ver:~/workspace/linux$ make allmodconfig; make scripts
#
# configuration written to .config
#
  SYNC    include/config/auto.conf
  HOSTCC  scripts/dtc/dtc.o
  HOSTCC  scripts/dtc/flattree.o
  HOSTCC  scripts/dtc/fstree.o
  HOSTCC  scripts/dtc/data.o
  HOSTCC  scripts/dtc/livetree.o
  HOSTCC  scripts/dtc/treesource.o
  HOSTCC  scripts/dtc/srcpos.o
  HOSTCC  scripts/dtc/checks.o
  HOSTCC  scripts/dtc/util.o
  LEX     scripts/dtc/dtc-lexer.lex.c
  YACC    scripts/dtc/dtc-parser.tab.[ch]
  HOSTCC  scripts/dtc/dtc-lexer.lex.o
  HOSTCC  scripts/dtc/dtc-parser.tab.o
  HOSTLD  scripts/dtc/dtc
  HOSTCXX scripts/gcc-plugins//latent_entropy_plugin.so
  GENSEED scripts/gcc-plugins//randomize_layout_seed.h
  HOSTCXX scripts/gcc-plugins//randomize_layout_plugin.so
  HOSTCXX scripts/gcc-plugins//stackleak_plugin.so
  HOSTCC  scripts/genksyms//genksyms.o
  YACC    scripts/genksyms//parse.tab.[ch]
  HOSTCC  scripts/genksyms//parse.tab.o
  LEX     scripts/genksyms//lex.lex.c
  HOSTCC  scripts/genksyms//lex.lex.o
  HOSTLD  scripts/genksyms//genksyms
  HOSTCC  scripts/selinux//genheaders/genheaders
  HOSTCC  scripts/selinux//mdp/mdp
  HOSTCC  scripts/kallsyms
  HOSTCC  scripts/sorttable
  HOSTCC  scripts/asn1_compiler
  HOSTCC  scripts/extract-cert
  HOSTCC  scripts/bin2c
  HOSTCC  scripts/recordmcount
  HOSTCC  scripts/sign-file
  HOSTCC  scripts/insert-sys-cert




I can fix Kbuild to avoid "//", but I do not want to support two ways.

So, I'd recommend not to add the trailing slash to subdir-y.





For the others, thank you for pointing out my typos.




>
> >       It is good practice to use a `CONFIG_` variable when assigning directory
> >       names. This allows kbuild to totally skip the directory if the
> >       corresponding `CONFIG_` option is neither 'y' nor 'm'.
> >
>
> Reviewed-by: Randy Dunlap <rdunlap@...radead.org>
>
> thanks.
>
> --
> ~Randy



--
Best Regards
Masahiro Yamada