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From:   Masahiro Yamada <yamada.masahiro@socionext.com>
Date:   Fri, 9 Feb 2018 02:11:55 +0900
Message-ID: <CAK7LNAQewHbO-xUGHjhwn1YQUQpEV+gbvwm89VH+keYN6kp35w@mail.gmail.com>
Subject: Re: [PATCH 6/6] s390: introduce execute-trampolines for branches
To:     Kees Cook <keescook@chromium.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Martin Schwidefsky <schwidefsky@de.ibm.com>,
        David Woodhouse <dwmw2@infradead.org>,
        Pavel Machek <pavel@ucw.cz>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-s390 <linux-s390@vger.kernel.org>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Cornelia Huck <cohuck@redhat.com>,
        David Hildenbrand <david@redhat.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jon Masters <jcm@redhat.com>,
        Marcus Meissner <meissner@suse.de>,
        Jiri Kosina <jkosina@suse.cz>,
        Dominik Brodowski <linux@dominikbrodowski.net>,
        Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
        Ulf Magnusson <ulfalizer@gmail.com>
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2018-02-08 9:57 GMT+09:00 Kees Cook <keescook@chromium.org>:
> On Thu, Feb 8, 2018 at 10:44 AM, Masahiro Yamada
> <yamada.masahiro@socionext.com> wrote:
>> 2018-02-08 2:55 GMT+09:00 Linus Torvalds <torvalds@linux-foundation.org>:
>>> What I would really want - and this is entirely unrelated to this
>>> particular case - is to have those damn compiler option tests as part
>>> of the config phase in general. We now have about a million of these
>>> crazy things, where we have config options that simply depend on which
>>> compiler we have, and we have no sane way to show them at
>>> configuration time.
>>>
>>> Though Andrew's tree I got yet another ugly hack
>>> (CONFIG_CC_STACKPROTECTOR_AUTO) that handles just _one_ special case
>>> by turning it into a special magic Kconfig entry in the main Makefile.
>>> See commit 44c6dc940b19 ("Makefile: introduce
>>> CONFIG_CC_STACKPROTECTOR_AUTO"). I wasn't sure if I really wanted it,
>>> and honestly, I'm still thinking of just reverting it, because it's
>>> _so_ ugly and _so_ wrong.
>>>
>>> What we need is an extension to the Kconfig language itself so that we can do
>>>
>>>    config CC_HAS_RETPOLINE
>>>         cc_option "-mindirect-branch=thunk -mindirect-branch-table"
>>>
>>> or something. And then we can make sane _conditional_ dependencies at
>>> Kconfig time, and our makefiles would be much cleaner too when you
>>> could just do
>>>
>>>      cflags-$(USE_RETPOLINE) += -mfunction-return=thunk -mindirect-branch-table
>>>
>>> because the validity of the C compiler flag has been tested when configuring.
>>>
>>> And then we could add that warning at configure time (or just disable
>>> the option there thanks to "depends on CC_HAS_xyz" logic).
>>>
>>> All our compiler option handling right now is just nasty nasty nasty crud.
>>>
>>> Adding more people in the hopes that somebody gets motivated.. I've
>>> talked about this before, so far we haven't made any progress.
>>
>>
>> Sorry for slow progress.
>>
>> I agreed this before, and still motivated.
>> (because I also motivated to remove kbuild cache.
>> This turned out not so clever as I first thought)
>>
>> I was trying to do this, but in this development cycle
>> I spent most of my time to flush out lots of piled up Kconfig patches.
>> Sorry.
>>
>> Unless somebody is working, I will.

I sent the first draft.

For people interested, I pushed the series in the following too.

git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git
kconfig-opt-shell-rfc


-- 
Best Regards
Masahiro Yamada