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From:   Linus Torvalds <torvalds@linuxfoundation.org>
Date:   Mon, 6 Sep 2021 14:24:39 -0700
Message-ID: <CAHk-=wikLP4KbTUUY_OKL6doyztjqFNKu_Q713vcrkjthc4S0g@mail.gmail.com>
Subject: Re: [GIT PULL v2] Kbuild updates for v5.15-rc1
To:     Jakub Jelinek <jakub@redhat.com>
Cc:     Segher Boessenkool <segher@kernel.crashing.org>,
        Florian Weimer <fweimer@redhat.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        llvm@lists.linux.dev, linux-toolchains@vger.kernel.org
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On Mon, Sep 6, 2021 at 2:08 PM Linus Torvalds
<torvalds@linuxfoundation.org> wrote:
>
> And you think that we're making it harder for compiler people, but
> that's not at all the case.
>
> You really don't want to deal with us saying "you can't do that" when
> you do something that is

That got cut short when I went off to adding the examples of errors
that happen for those intrinsics headers.

But it was supposed to be "when you do something that is not valid in
the kernel".

There are some *very* core header files that the kernel cannot include
from outside. That "stdlib.h" thing already came up in the errors I
quoted.

But I think you'll find that you guys want to include things like
<errno.h> too, and you'll probably add others (<types.h>? things like
that) simply because they always work fine in user space, and you'd
not even notice.

Header file include chains get messy very quickly, and very easily.

I'm pretty sure you guys don't really want to deal with the pain that
is crazy kernel people that have their very bare environment.

So you may *think* you want the kernel to use your header files
"because compiler portability". Instead, you should be very thankful
that we don't, and that you don't have to deal with our mess any more
than you already do.

          Linus