linux-kernel - Re: [PATCH] rust: allow to use INIT_STACK_ALL

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Message-ID: <Y+a5KQjQopSXwVPJ@righiandr-XPS-13-7390>
Date:   Fri, 10 Feb 2023 22:37:45 +0100
From:   Andrea Righi <andrea.righi@...onical.com>
To:     Nathan Chancellor <nathan@...nel.org>
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>,
        bjorn3_gh@...tonmail.com,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, rust-for-linux@...r.kernel.org,
        llvm@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rust: allow to use INIT_STACK_ALL_ZERO

On Fri, Feb 10, 2023 at 10:39:27AM -0700, Nathan Chancellor wrote:
> 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@...onical.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?

I didn't have much success with CC_AUTO_VAR_INIT_ZERO_ENABLER, but maybe
a better way is to check if the version of libclang used by bindgen is
less than 17, considering that is extra clang option is supposed to be
dropped in clang-17:

https://github.com/llvm/llvm-project/issues/44842

I'll send a v2, unless we find a better way to support this auto var
zero-init feature.

-Andrea