linux-kernel - Re: [PATCH] rust: fix bindgen build error with fstrict-flex-arrays

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Date:   Tue, 15 Aug 2023 14:44:11 +0200
From:   Andrea Righi <andrea.righi@...onical.com>
To:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Benno Lossin <benno.lossin@...ton.me>,
        "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        rust-for-linux@...r.kernel.org, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>
Subject: Re: [PATCH] rust: fix bindgen build error with fstrict-flex-arrays

On Tue, Aug 15, 2023 at 02:06:36PM +0200, Miguel Ojeda wrote:
> On Tue, Aug 15, 2023 at 8:54 AM Andrea Righi <andrea.righi@...onical.com> wrote:
> >
> > Commit df8fc4e934c1 ("kbuild: Enable -fstrict-flex-arrays=3") enabled
> > '-fstrict-flex-arrays=3' globally, but bindgen does not recognized this
> 
> It may be more accurate to say libclang here (bindgen forwards the options).
> 
> Also, df8fc4e934c1 did it so only conditionally (if the C compiler
> supports it). This explains what you are seeing: if I am right, you
> are compiling with a modern enough GCC, which enables the option, but
> with an old enough Clang.

Oh yes, indeed! I'm using clang/libclang-14 with gcc-13, if I switch to
clang-15 everything seems fine, so I can simply move to this version.

> 
> > compiler option, triggering the following build error:
> >
> >  error: unknown argument: '-fstrict-flex-arrays=3', err: true
> 
> This should only be true with libclang < 16, since Clang 16
> implemented the option, right?
> 
> In fact, Clang 15 seems to work too -- it seems the compiler does not
> error if the option is not within [0,3] (unlike GCC).

The combo gcc-13 + libclang-15 seems to work in my case, instead with
libclang-16 I get this:

  BINDGEN rust/bindings/bindings_generated.rs
  thread 'main' panicked at '"ftrace_branch_data_union_(anonymous_at__/_/include/linux/compiler_types_h_146_2)" is not a valid Ident', /build/rust-bindgen-0.56-DgAMvF/rust-bindgen-0.56-0.56.0/debian/vendor/proc-macro2-1.0.24/src/fallback.rs:693:9

Thanks,
-Andrea