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From:   Marco Elver <elver@google.com>
Date:   Tue, 1 Dec 2020 21:12:57 +0100
Message-ID: <CANpmjNOfs8Of0Kvp3v7miw5x0Neg5i4egc43bevLV3_rGCNqtA@mail.gmail.com>
Subject: Re: [PATCH] genksyms: Ignore module scoped _Static_assert()
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Joe Perches <joe@perches.com>
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On Tue, 1 Dec 2020 at 21:00, Nick Desaulniers <ndesaulniers@google.com> wrote:
>
> On Tue, Dec 1, 2020 at 7:21 AM Marco Elver <elver@google.com> wrote:
> >
> > The C11 _Static_assert() keyword may be used at module scope, and we
> > need to teach genksyms about it to not abort with an error. We currently
> > have a growing number of static_assert() (but also direct usage of
> > _Static_assert()) users at module scope:
> >
> >         git grep -E '^_Static_assert\(|^static_assert\(' | grep -v '^tools' | wc -l
> >         135
> >
> > More recently, when enabling CONFIG_MODVERSIONS with CONFIG_KCSAN, we
> > observe a number of warnings:
> >
> >         WARNING: modpost: EXPORT symbol "<..all kcsan symbols..>" [vmlinux] [...]
> >
> > When running a preprocessed source through 'genksyms -w' a number of
> > syntax errors point at usage of static_assert()s. In the case of
> > kernel/kcsan/encoding.h, new static_assert()s had been introduced which
> > used expressions that appear to cause genksyms to not even be able to
> > recover from the syntax error gracefully (as it appears was the case
> > previously).
> >
> > Therefore, make genksyms ignore all _Static_assert() and the contained
> > expression. With the fix, usage of _Static_assert() no longer cause
> > "syntax error" all over the kernel, and the above modpost warnings for
> > KCSAN are gone, too.
> >
> > Signed-off-by: Marco Elver <elver@google.com>
>
> Ah, genksyms...if only there were a library that we could use to parse
> C code...:P

Hehe -- another usecase for using that library ;-)  If only we could
require LLVM be present even when building the rest of the kernel with
GCC.

I guess this works, for now. Until the next new keyword that is used
at module scope...

> Acked-by: Nick Desaulniers <ndesaulniers@google.com>

Thanks!