linux-kernel - Re: Build: arm rustgcc unknown argument '-mno-fdpic'

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Message-ID: <20250407183716.796891-1-ojeda@kernel.org>
Date: Mon,  7 Apr 2025 20:37:16 +0200
From: Miguel Ojeda <ojeda@...nel.org>
To: Christian Schrrefl <chrisi.schrefl@...il.com>
Cc: naresh.kamboju@...aro.org,
	Russell King <rmk+kernel@...linux.org.uk>,
	Rudraksha Gupta <guptarud@...il.com>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Ard Biesheuvel <ardb@...nel.org>,
	anders.roxell@...aro.org,
	arnd@...db.de,
	dan.carpenter@...aro.org,
	laura.nao@...labora.com,
	linux-kernel@...r.kernel.org,
	lkft-triage@...ts.linaro.org,
	regressions@...ts.linux.dev,
	rust-for-linux@...r.kernel.org,
	torvalds@...ux-foundation.org
Subject: Re: Build: arm rustgcc unknown argument '-mno-fdpic'

On Mon, 07 Apr 2025 22:58:02 +0530 Naresh Kamboju <naresh.kamboju@...aro.org> wrote:
>
> Regressions on arm build with config rustgcc-lkftconfig-kselftest on the
> Linux mainline and next failed with CONFIG_RUST=y enabled.

> Bad: next-20250327
> Good: next-20250326

> Unable to generate bindings: clang diagnosed error: error: unknown
> argument: '-mno-fdpic'

I assume this is the arm support, i.e. commit ccb8ce526807 ("ARM: 9441/1:
rust: Enable Rust support for ARMv7").

Clang does not seem to support `-mno-fdpic`, thus you probably need to add it to
`bindgen_skip_c_flags` in `rust/Makefile` so that it gets skipped when the C
compiler is GCC.

If you do so, please double-check if the flag could potentially alter the ABI in
a way that `bindgen` would generate the wrong bindings.

I hope that helps!

Cheers,
Miguel