linux-kernel - Re: [PATCH] kbuild: avoid regex RS for POSIX awk

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Date:   Wed, 8 Jun 2022 19:11:59 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     David Laight <David.Laight@...lab.com>
Cc:     Kevin Locke <kevin@...inlocke.name>,
        "linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kbuild: avoid regex RS for POSIX awk

On Wed, Jun 8, 2022 at 4:43 PM David Laight <David.Laight@...lab.com> wrote:
>
> From: Kevin Locke
> > Sent: 07 June 2022 03:43
> >
> > In 22f26f21774f8 awk was added to deduplicate *.mod files.
>
> Can't this be done with gmake's $(sort) function?
>
> $(sort list)
>
>     Sorts the words of list in lexical order, removing duplicate words.
>     The output is a list of words separated by single spaces.


$(sort ...) does two things,
  - sort the list alphabetically
  - deduplicate the elements in the list

I want to do only deduplication
without changing the order.




>
> ...
> >  # To make this rule robust against "Argument list too long" error,
> >  # ensure to add $(obj)/ prefix by a shell command.
> > -cmd_mod = echo $(call real-search, $*.o, .o, -objs -y -m) | \
> > -     $(AWK) -v RS='( |\n)' '!x[$$0]++ { print("$(obj)/"$$0) }' > $@
> > +cmd_mod = printf '%s\n' $(call real-search, $*.o, .o, -objs -y -m) | \
> > +     $(AWK) '!x[$$0]++ { print("$(obj)/"$$0) }' > $@
>
> I think the above only works because 'printf' is (usually) a
> shell builtin - so the kernel's argv[] limit doesn't apply.
> So the comment isn't really right.

Is there any difference if 'printf' were not built-in?



Right, for bash and dash, yes, 'printf' is built-in,
and we do not need to be worried about
"Argument list too long", but
I am not sure if we are able to cover all the systems.



> But I think:
>
> cmd_mod = $(addprefix $(obj)/,$(sort $(call real-search, $*.o, .o, -objs -y -m))) >$@
>
> will have the required effect.


I think 'echo' is missing here.
As I noted above, I do not want to change the order.



> Without forking and execing multiple processes.
>
>         David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
>


-- 
Best Regards
Masahiro Yamada