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Thu, 24 Apr 2025 06:39:37 -0700 (PDT) Date: Thu, 24 Apr 2025 09:39:35 -0400 From: Ben Wolsieffer To: Miguel Ojeda Cc: Naresh Kamboju , Miguel Ojeda , Christian Schrrefl , Russell King , Rudraksha Gupta , Alice Ryhl , Ard Biesheuvel , anders.roxell@linaro.org, arnd@arndb.de, dan.carpenter@linaro.org, laura.nao@collabora.com, linux-kernel@vger.kernel.org, lkft-triage@lists.linaro.org, regressions@lists.linux.dev, rust-for-linux@vger.kernel.org, torvalds@linux-foundation.org, Nick Clifton , Richard Earnshaw , Ramana Radhakrishnan Subject: Re: Build: arm rustgcc unknown argument '-mno-fdpic' Message-ID: References: <20250407183716.796891-1-ojeda@kernel.org> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Sat, Apr 19, 2025 at 12:30:01AM +0200, Miguel Ojeda wrote: > Thanks a lot for the details! > > To clarify, this is for GCC kernel builds: skipping the flag is done > for libclang under GCC builds (because `bindgen` always uses libclang, > and `bindgen` is used by Rust to understand C headers). > > So GCC will get the flag for the C side of the kernel builds, but > libclang will not get the flag because Clang doesn't recognize it. > Thus, if Clang vs. GCC differ in how they compute the layout of some > type, then we would have an issue "mixing" them. > > As you can imagine, GCC kernel builds with Rust enabled are a hack due > to that, and it would be ideal to get `bindgen` to somehow be able to > understand C headers as GCC does: > > https://github.com/rust-lang/rust-bindgen/issues/1949 -mno-fdpic disables a GCC feature that we don't want for kernel builds. clang does not support this feature, so it always behaves as though -mno-fdpic is passed. Therefore, it should be fine to mix the two, at least as far as FDPIC is concerned. Ben