linux-kernel - Re: [PATCH v2] kbuild: strip whitespace in cmd_record

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Message-ID: <4f13ecb6-9aa8-5037-a18e-150c026254c2@redhat.com>
Date:   Thu, 28 Mar 2019 09:36:16 -0400
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nicholas Piggin <npiggin@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v2] kbuild: strip whitespace in cmd_record_mcount
 findstring

On 3/28/19 8:57 AM, Masahiro Yamada wrote:
> Hi Joe,
> 
> OK, confirmed.
 >
 > [ ... snip .... ]
> 
> First, I was wondering why I could not reproduce this issue.
> Then, I found the reason was I was using the latest GNU Make
> compiled from the git source tree.
> 
> I found the following commit:
> 
> commit b90fabc8d6f34fb37d428dc0fb1b8b1951a9fbed
> Author: Paul Smith <psmith@....org>
> Date:   Sat May 27 20:07:30 2017 -0400
> 
>      * NEWS: Do not insert a space during '+=' if the value is empty.
> 
>      * doc/make.texi (Appending): Document this behavior.
>      * variable.c (do_variable_definition): Only add a space if the variable
>      value is not empty.
>      * tests/scripts/variables/flavors: Test this behavior.
> 
> diff --git a/NEWS b/NEWS
> index e60644a..6e2c5c6 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -29,6 +29,12 @@
> http://sv.gnu.org/bugs/index.php?group=make&report_id=111&fix_release_id=108&set
>     This was claimed to be fixed in 3.81, but wasn't, for some reason.
>     To detect this change search for 'nocomment' in the .FEATURES variable.
> 
> +* WARNING: Backward-incompatibility!
> +  Previously appending using '+=' to an empty variable would result in a value
> +  starting with a space.  Now the initial space is only added if the variable
> +  already contains some value.  Similarly, appending an empty string does not
> +  add a trailing space.
> +
>   * The previous limit of 63 jobs under -jN on MS-Windows is now
>     increased to 4095.  That limit includes the subprocess started by
>     the $(shell) function.
> 
> Applied to linux-kbuild/fixes with additional comments.
> 
> [Additional info by masahiro.yamada:
> This issue only happens in the released versions of GNU Make.
> CC_FLAGS_FTRACE will not contain the trailing space if you use
> the latest GNU Make, which contains commit b90fabc8d6f3
> ("* NEWS: Do not insert a space during '+=' if the value is empty.")
> ]
Wow, this one gets even more specific.  I had gone down the rabbit hole 
on this one, I didn't care to learn how or why that extra space got 
there :)  Now we know, thanks for running that down and adding the note 
about GNU Make.

-- Joe