kernel-hardening - Re: [PATCH 00/23] kconfig: move compiler capability tests to Kconfig

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Message-ID: <CAK7LNAQH0WD3A3T97gce0xmZpMy0zWxTO2StfNWaDbiqjQg8gg@mail.gmail.com>
Date: Wed, 21 Feb 2018 16:38:25 +0900
From: Masahiro Yamada <yamada.masahiro@...ionext.com>
To: Ulf Magnusson <ulfalizer@...il.com>
Cc: Sam Ravnborg <sam@...nborg.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>, Kees Cook <keescook@...omium.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Peter Oberparleiter <oberpar@...ux.vnet.ibm.com>,
        kernel-hardening@...ts.openwall.com, Jonathan Corbet <corbet@....net>,
        sparclinux@...r.kernel.org, Linux-sh list <linux-sh@...r.kernel.org>,
        X86 ML <x86@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
        Rich Felker <dalias@...c.org>, Jeff Dike <jdike@...toit.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        user-mode-linux-devel@...ts.sourceforge.net,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        linuxppc-dev@...ts.ozlabs.org, Paul Mackerras <paulus@...ba.org>,
        user-mode-linux-user@...ts.sourceforge.net,
        Ingo Molnar <mingo@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Michael Ellerman <mpe@...erman.id.au>,
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        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Richard Weinberger <richard@....at>, Emese Revfy <re.emese@...il.com>
Subject: Re: [PATCH 00/23] kconfig: move compiler capability tests to Kconfig

2018-02-20 0:18 GMT+09:00 Ulf Magnusson <ulfalizer@...il.com>:

>>
>> 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'.

https://github.com/torvalds/linux/blob/v4.16-rc2/arch/x86/Kconfig#L4



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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