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Date: Wed, 21 Feb 2018 16:38:25 +0900
From: Masahiro Yamada <>
To: Ulf Magnusson <>
Cc: Sam Ravnborg <>,
        Linux Kbuild mailing list <>,
        Linus Torvalds <>,
        Greg Kroah-Hartman <>,
        Arnd Bergmann <>, Kees Cook <>,
        Randy Dunlap <>,
        Michal Marek <>,
        Peter Oberparleiter <>,, Jonathan Corbet <>,, Linux-sh list <>,
        X86 ML <>, Thomas Gleixner <>,
        Rich Felker <>, Jeff Dike <>,
        "H. Peter Anvin" <>,,
        Yoshinori Sato <>,
        Benjamin Herrenschmidt <>,, Paul Mackerras <>,,
        Ingo Molnar <>,
        "David S. Miller" <>,
        Michael Ellerman <>,
        "open list:DOCUMENTATION" <>,
        Linux Kernel Mailing List <>,
        Richard Weinberger <>, Emese Revfy <>
Subject: Re: [PATCH 00/23] kconfig: move compiler capability tests to Kconfig

2018-02-20 0:18 GMT+09:00 Ulf Magnusson <>:

>> I'm not happy that we in one context can reference CONFIG variables
>> directly, but inside the $(call ...) and $(shell ...) needs the $ prefix.
>> But I could not come up with something un-ambigious where this could be avoided.
> I think we should be careful about allowing references to config
> symbols. It mixes up the parsing and evaluation phases, since $() is
> expanded during parsing (which I consider a feature and think is
> needed to retain sanity).
> Patch 06/23 removes the last existing instance of symbol references in
> strings by getting rid of 'option env'. That's an improvement to me.
> We shouldn't add it back.

This is really important design decision,
so I'd like to hear a little more from experts.

For example, x86 allows users to choose sub-arch, either 'i386' or 'x86_64'.

If the user toggles CONFIG_64BIT,
the bi-arch compiler will work in a slightly different mode
(at least, back-end parts)

So, my question is, is there a case,

$(cc-option, -m32 -foo) is y, but
$(cc-option, -m64 -foo) is n  ?
(or vice versa)

If the answer is yes, $(cc-option -foo) would have to be re-calculated
every time CONFIG_64BIT is toggled.

This is what I'd like to avoid, though.

Best Regards
Masahiro Yamada

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