linux-kernel - Re: [GIT PULL 2/2] Kconfig updates for v5.10-rc1

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Date:   Wed, 2 Dec 2020 10:58:12 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Emese Revfy <re.emese@...il.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL 2/2] Kconfig updates for v5.10-rc1

On Wed, Dec 02, 2020 at 10:03:47PM +0900, Masahiro Yamada wrote:
> On Wed, Dec 2, 2020 at 9:53 PM Masahiro Yamada <masahiroy@...nel.org> wrote:
> >
> > Hi Linus,
> >
> > On Sun, Nov 29, 2020 at 3:28 AM Linus Torvalds
> > <torvalds@...ux-foundation.org> wrote:
> > >
> > > On Fri, Nov 27, 2020 at 11:05 PM Masahiro Yamada <masahiroy@...nel.org> wrote:
> > > >
> > > > As for the cc1plus cost, I got a similar result.
> > > >
> > > > Running scripts/gcc-plugin.sh directly
> > > > took me 0.5 sec, which is a fourth
> > > > of the allmodconfig run-time.
> > > >
> > > > Actually, I did not know this shell script
> > > > was so expensive to run...
> > >
> > > So it turns out that one reason it's so expensive to run is that it
> > > does a *lot* more than it claims to do.
> > >
> > > It says "we need a c++ compiler that supports the designated
> > > initializer GNU extension", but then it actually includes a header
> > > file from hell, rather than just test designated initializers.
> > >
> > > This patch makes the cc1plus overhead go down a lot. That said, I'm
> > > doubtful we really want gcc plugins at all, considering that the only
> > > real users have all apparently migrated to clang builtin functionality
> > > instead.
> > >
> > >         Linus
> >
> >
> > The attached patch looks OK to me.
> >
> > Just a nit:
> > Now that the test code does not include any header,
> > you can also delete
> > "-I $srctree/gcc-plugins -I $gccplugins_dir/include"
> >
> >
> > If you apply it directly, please feel free to add
> >
> > Reviewed-by: Masahiro Yamada <masahiroy@...nel.org>
> 
> 
> BTW, gcc plugins are always compiled with g++.
> 
> Why do we need to compile the following in the first place?
> 
> class test {
> public:
>         int test;
> } test = {
>         .test = 1
> };
> 
> 
> I think any C++ compiler will succeed
> in compiling such simple code.
> 
> 
> 
> So,
> 
> test -e "$gccplugins_dir/include/plugin-version.h"
> 
> looks enough to me.
> 
> 
> 
> What is the intention of this compile test?

Yeah, I'd agree: we're just looking for a g++ and plugin-version.h.

-- 
Kees Cook