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

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Message-ID: <05f8480125584a9caea029b9c3111ef4@AcuMS.aculab.com>
Date:   Wed, 8 Jun 2022 07:43:45 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Kevin Locke' <kevin@...inlocke.name>,
        Masahiro Yamada <masahiroy@...nel.org>,
        "linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] kbuild: avoid regex RS for POSIX awk

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.

...
>  # 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.

But I think:

cmd_mod = $(addprefix $(obj)/,$(sort $(call real-search, $*.o, .o, -objs -y -m))) >$@

will have the required effect.
Without forking and execing multiple processes.

	David

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