Re: [PATCH] RISC-V: Fix building rust when using GCC toolchain

From: Gary Guo <gary@garyguo.net>
To: Conor Dooley <conor@kernel.org>
Cc: Jason Montleon <jmontleo@redhat.com>,
	ojeda@kernel.org, alex.gaynor@gmail.com, boqun.feng@gmail.com,
	bjorn3_gh@protonmail.com, benno.lossin@proton.me,
	a.hindborg@kernel.org, aliceryhl@google.com,
	paul.walmsley@sifive.com, palmer@dabbelt.com,
	aou@eecs.berkeley.edu, nathan@kernel.org,
	ndesaulniers@google.com, morbo@google.com,
	justinstitt@google.com, rust-for-linux@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
	llvm@lists.linux.dev, stable@vger.kernel.org
Subject: Re: [PATCH] RISC-V: Fix building rust when using GCC toolchain
Date: Tue, 17 Sep 2024 14:29:50 +0100	[thread overview]
Message-ID: <20240917142950.48d800ac@eugeo> (raw)
In-Reply-To: <334EBB3A-6ABF-4FBF-89D2-DF3A6DCCCEA2@kernel.org>

On Tue, 17 Sep 2024 10:35:12 +0100
Conor Dooley <conor@kernel.org> wrote:

> On 17 September 2024 01:08:48 IST, Jason Montleon <jmontleo@redhat.com> wrote:
> >Clang does not support '-mno-riscv-attribute' resulting in the error
> >error: unknown argument: '-mno-riscv-attribute'  
> 
> This appears to conflict with your subject, which cities gcc, but I suspect that's due to poor wording of the body of the commit message than a mistake in the subject.
> I'd rather disable rust on riscv when building with gcc, I've never been satisfied with the interaction between gcc and rustc's libclang w.r.t. extensions.
> 
> Cheers,
> Conor.

Hi Conor,

What happens is that when building against GCC, Kbuild gathers flag
assuming CC is GCC, but bindgen uses clang instead. In this case, the
CC is GCC and all C code is built by GCC. We have a filtering mechanism
to only give bindgen (libclang) flags that it can understand.

While I do think this is a bit fragile, this is what I think all
distros that enable Rust use. They still prefer to build C code with
GCC. So I hope we can still keep that option around.

Best,
Gary

> 
> >
> >Not setting BINDGEN_TARGET_riscv results in the in the error
> >error: unsupported argument 'medany' to option '-mcmodel=' for target \
> >'unknown'
> >error: unknown target triple 'unknown'
> >
> >Signed-off-by: Jason Montleon <jmontleo@redhat.com>
> >Cc: stable@vger.kernel.org
> >---
> > rust/Makefile | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> >diff --git a/rust/Makefile b/rust/Makefile
> >index f168d2c98a15..73eceaaae61e 100644
> >--- a/rust/Makefile
> >+++ b/rust/Makefile
> >@@ -228,11 +228,12 @@ bindgen_skip_c_flags := -mno-fp-ret-in-387 -mpreferred-stack-boundary=% \
> > 	-fzero-call-used-regs=% -fno-stack-clash-protection \
> > 	-fno-inline-functions-called-once -fsanitize=bounds-strict \
> > 	-fstrict-flex-arrays=% -fmin-function-alignment=% \
> >-	--param=% --param asan-%
> >+	--param=% --param asan-% -mno-riscv-attribute
> > 
> > # Derived from `scripts/Makefile.clang`.
> > BINDGEN_TARGET_x86	:= x86_64-linux-gnu
> > BINDGEN_TARGET_arm64	:= aarch64-linux-gnu
> >+BINDGEN_TARGET_riscv	:= riscv64-linux-gnu
> > BINDGEN_TARGET		:= $(BINDGEN_TARGET_$(SRCARCH))
> > 
> > # All warnings are inhibited since GCC builds are very experimental,
> >
> >base-commit: ad060dbbcfcfcba624ef1a75e1d71365a98b86d8  

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