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

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Message-ID: <87efldr9np.fsf@concordia.ellerman.id.au>
Date:   Thu, 22 Feb 2018 14:22:02 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Arnd Bergmann <arnd@...db.de>
Cc:     Rich Felker <dalias@...c.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        X86 ML <x86@...nel.org>, Paul Mackerras <paulus@...ba.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        sparclinux <sparclinux@...r.kernel.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Jonathan Corbet <corbet@....net>,
        Richard Weinberger <richard@....at>,
        Linux-sh list <linux-sh@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...hat.com>,
        Emese Revfy <re.emese@...il.com>,
        Kees Cook <keescook@...omium.org>,
        uml-devel <user-mode-linux-devel@...ts.sourceforge.net>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Peter Oberparleiter <oberpar@...ux.vnet.ibm.com>,
        Jeff Dike <jdike@...toit.com>,
        user-mode-linux-user@...ts.sourceforge.net,
        Thomas Gleixner <tglx@...utronix.de>,
        Michal Marek <michal.lkml@...kovi.net>,
        Ulf Magnusson <ulfalizer@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "open list\:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 00/23] kconfig: move compiler capability tests to Kconfig

Masahiro Yamada <yamada.masahiro@...ionext.com> writes:
>
<snip>
>
> (Case 3)
> Compiler flag -foo is sensitive to endian-ness.
>
>
> config CC_NEEDS_BIG_ENDIAN
>           def_bool $(cc-option -mbig-endian) && CPU_BIG_ENDIAN
>
> config CC_NEEDS_LITTLE_ENDIAN
>           def_bool $(cc-option -mlittle-endian) && CPU_LITTLE_ENDIAN
>
> config CC_HAS_FOO
>          bool
>          default $(cc-option -mbig-endian -foo) if CC_NEEDS_BIG_ENDIAN
>          default $(cc-option -mlittle-endian -foo) if CC_NEEDS_LITTLE_ENDIAN
>          default $(cc-option -foo)

We may do something like this on powerpc, where we have 32/64-bit and
big/little endian (on 64-bit) and then some ABI options that we
set/unset depending on endian.

The above looks like it could work though.

cheers