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From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Thu, 21 Jan 2021 04:41:13 +0900
Message-ID: <CAK7LNAQhsiaumkLF21zTkpOHCpQyCzxdrGX=897Bsc8w=aMapw@mail.gmail.com>
Subject: Re: [PATCH v5] modules: introduce the MODULE_SCMVERSION config
To:     Will McVicker <willmcvicker@google.com>
Cc:     Jessica Yu <jeyu@kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Christoph Hellwig <hch@infradead.org>,
        Saravana Kannan <saravanak@google.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        "Cc: Android Kernel" <kernel-team@android.com>
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On Wed, Jan 20, 2021 at 9:19 AM Will McVicker <willmcvicker@google.com> wrote:
>
> Hi Masahiro,
>
> After testing your suggestions for module_srcpath, I remembered why I
> needed this:
>
> +ifneq ($(realpath $(srctree)/$(KBUILD_EXTMOD) 2>/dev/null),)
> +       module_srcpath := $(srctree)/$(KBUILD_EXTMOD)
> +else
> +       module_srcpath := $(KBUILD_EXTMOD)
> +endif
>
> Basically KBUILD_EXTMOD actually has two uses when defined as a relative path:
>
> (1) defines the path to the external module's source relative to $(srctree)
> (2) defines the path to the external module's build artifacts relative
> to $(objtree)
>
> Since setlocalversion is run from $(objtree), we need to use
> $(srctree)/$(KBUILD_EXTMOD) when it's a relative path. Just to note,
> if I do just use KBUILD_EXTMOD, then the script setlocalversion fails
> to find the srctree and returns an empty string.
>
> Please correct me if I'm wrong. I messed around with this by adding
> many prints to Makefile.modpost and setlocalversion to make sure
> everything was defined as expected.


Hmm, you are right.

I did not know the current Kbuild works like that.

But, I do not want to uglify the code
just for supporting this rare use-case.


Rather, I want to apply this
https://lore.kernel.org/patchwork/patch/1368277/


and, still want to see as simple code as the following:


--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -66,6 +66,7 @@ ifeq ($(KBUILD_EXTMOD),)

 input-symdump := vmlinux.symvers
 output-symdump := Module.symvers
+module-srcpath := $(srctree)

 else

@@ -82,9 +83,20 @@ MODPOST += -e

 input-symdump := Module.symvers $(KBUILD_EXTRA_SYMBOLS)
 output-symdump := $(KBUILD_EXTMOD)/Module.symvers
+module-srcpath := $(KBUILD_EXTMOD)

 endif


-- 
Best Regards
Masahiro Yamada