Date:   Fri, 10 Feb 2023 10:39:27 -0700
From:   Nathan Chancellor <nathan@kernel.org>
To:     Andrea Righi <andrea.righi@canonical.com>
Cc:     Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        bjorn3_gh@protonmail.com,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, rust-for-linux@vger.kernel.org,
        llvm@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] rust: allow to use INIT_STACK_ALL_ZERO
Message-ID: <Y+aBT8AD9RXde24X@dev-arch.thelio-3990X>
References: <20230210172203.101331-1-andrea.righi@canonical.com>
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On Fri, Feb 10, 2023 at 06:22:03PM +0100, Andrea Righi wrote:
> With CONFIG_INIT_STACK_ALL_ZERO enabled, bindgen is passing
> -ftrivial-auto-var-init=zero to clang, that triggers the following:
> 
>   error: '-ftrivial-auto-var-init=zero' hasn't been enabled; enable it at your own peril for benchmarking purpose only with '-enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang'
> 
> This flag should be dropped in clang-17, but at the moment it seems more
> reasonable to add it to the bindgen CFLAGS to prevent the error above.
> 
> In this way we can enable CONFIG_INIT_STACK_ALL_ZERO with CONFIG_RUST
> without triggering any build error.
> 
> Link: https://reviews.llvm.org/D125142
> Signed-off-by: Andrea Righi <andrea.righi@canonical.com>

If this went via the kbuild tree, would we be able to use
$(CC_AUTO_VAR_INIT_ZERO_ENABLER)?

https://git.kernel.org/masahiroy/linux-kbuild/c/4e3feaad6ff8a7a57e3bf3308a93c93e3a2e17a6

Although, I suppose this could be a problem if the version of clang
being used to build the kernel does not support this flag while the
version of libclang in bindgen requires it?

> ---
>  rust/Makefile | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/rust/Makefile b/rust/Makefile
> index ff70c4c916f8..5e26db07a1dc 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -267,7 +267,8 @@ BINDGEN_TARGET		:= $(BINDGEN_TARGET_$(SRCARCH))
>  # All warnings are inhibited since GCC builds are very experimental,
>  # many GCC warnings are not supported by Clang, they may only appear in
>  # some configurations, with new GCC versions, etc.
> -bindgen_extra_c_flags = -w --target=$(BINDGEN_TARGET)
> +bindgen_extra_c_flags = -w --target=$(BINDGEN_TARGET) \
> +			-enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang
>  
>  bindgen_c_flags = $(filter-out $(bindgen_skip_c_flags), $(c_flags)) \
>  	$(bindgen_extra_c_flags)
> -- 
> 2.37.2
>