linux-kernel - Re: [PATCH 7/7] kbuild: link vmlinux just once for CONFIG_TRIM_UNUSED

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Date:   Thu, 15 Mar 2018 14:50:02 -0400 (EDT)
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Jarod Wilson <jarod@...hat.com>,
        Prarit Bhargava <prarit@...hat.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 7/7] kbuild: link vmlinux just once for
 CONFIG_TRIM_UNUSED_KSYMS

On Thu, 15 Mar 2018, Masahiro Yamada wrote:

> I am not familiar with Make internal, but
> I can test it with simple code.
> 
> 
> [Test Makefile]
> A: B
>         cp B A
>         echo $?
> 
> B: C
>         cp C B
>         touch A
> 
> [Result]
> $ rm -rf A B C
> $ touch C
> $ make
> cp C B
> touch A
> cp B A
> echo B
> B
> 
> 
> In the recipe of 'B', 'A' is touched,
> so the dependency 'A: B' has already been met
> before the recipe of 'A' is executed,
> but Make does not notice that fact,
> then tries to update 'A'.
> 
> 
> The situation is the same.
> vmlinux has been updated in the recursed sub-make,
> but it is not noticed.

OK, I agree.


Nicolas