Date:   Fri, 24 Feb 2023 15:27:39 +0000
From:   Conor Dooley <conor.dooley@microchip.com>
To:     Nathan Chancellor <nathan@kernel.org>
CC:     <linux-riscv@lists.infradead.org>, <conor@kernel.org>,
        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>,
        =?iso-8859-1?Q?Bj=F6rn?= Roy Baron <bjorn3_gh@protonmail.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, <rust-for-linux@vger.kernel.org>,
        <linux-doc@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <llvm@lists.linux.dev>
Subject: Re: [RFC RESEND 2/2] RISC-V: enable building the 64-bit kernels with
 rust support
Message-ID: <Y/jXayJucRFxzJGA@wendy>
References: <20230224135044.2882109-1-conor.dooley@microchip.com>
 <20230224135044.2882109-3-conor.dooley@microchip.com>
 <Y/jQSUpXH5XwQTqg@dev-arch.thelio-3990X>
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On Fri, Feb 24, 2023 at 07:57:13AM -0700, Nathan Chancellor wrote:
> Hi Conor,
>=20
> On Fri, Feb 24, 2023 at 01:50:44PM +0000, Conor Dooley wrote:
> > From: Miguel Ojeda <ojeda@kernel.org>
> >=20
> > The rust modules work on 64-bit RISC-V, with no twiddling required.
> > Select HAS_RUST and provide the required flags to kbuild so that the
> > modules can be used.
> > 32-bit is broken in core rust code, so support is limited to 64-bit
> > only: ld.lld: error: undefined symbol: __udivdi3
> >=20
> > Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> > Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
> > ---
> >  Documentation/rust/arch-support.rst | 2 ++
> >  arch/riscv/Kconfig                  | 1 +
> >  arch/riscv/Makefile                 | 3 ++-
> >  3 files changed, 5 insertions(+), 1 deletion(-)
> >=20
> > diff --git a/Documentation/rust/arch-support.rst b/Documentation/rust/a=
rch-support.rst
> > index 6982b63775da..197919158596 100644
> > --- a/Documentation/rust/arch-support.rst
> > +++ b/Documentation/rust/arch-support.rst
> > @@ -15,5 +15,7 @@ support corresponds to ``S`` values in the ``MAINTAIN=
ERS`` file.
> >  =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D  =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D  =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D
> >  Architecture  Level of support  Constraints
> >  =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D  =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D  =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D
> > +``riscv``     Maintained        ``rv64`` only.
> > +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D  =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D  =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D
> >  ``x86``       Maintained        ``x86_64`` only.
> >  =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D  =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D  =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index 81eb031887d2..73174157212d 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -115,6 +115,7 @@ config RISCV
> >  	select HAVE_POSIX_CPU_TIMERS_TASK_WORK
> >  	select HAVE_REGS_AND_STACK_ACCESS_API
> >  	select HAVE_RSEQ
> > +	select HAVE_RUST if 64BIT
>=20
> Just a small drive by comment, you have 'if 64BIT' here...
>=20
> >  	select HAVE_STACKPROTECTOR
> >  	select HAVE_SYSCALL_TRACEPOINTS
> >  	select IRQ_DOMAIN
> > diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> > index 76989561566b..0d6fc4e25221 100644
> > --- a/arch/riscv/Makefile
> > +++ b/arch/riscv/Makefile
> > @@ -29,8 +29,8 @@ ifeq ($(CONFIG_ARCH_RV64I),y)
> > =20
> >  	KBUILD_CFLAGS +=3D -mabi=3Dlp64
> >  	KBUILD_AFLAGS +=3D -mabi=3Dlp64
> > -
> >  	KBUILD_LDFLAGS +=3D -melf64lriscv
> > +	KBUILD_RUSTFLAGS +=3D -Ctarget-cpu=3Dgeneric-rv64
> >  else
> >  	BITS :=3D 32
> >  	UTS_MACHINE :=3D riscv32
> > @@ -38,6 +38,7 @@ else
> >  	KBUILD_CFLAGS +=3D -mabi=3Dilp32
> >  	KBUILD_AFLAGS +=3D -mabi=3Dilp32
> >  	KBUILD_LDFLAGS +=3D -melf32lriscv
> > +	KBUILD_RUSTFLAGS +=3D -Ctarget-cpu=3Dgeneric-rv32
>=20
> but also add KBUILD_RUSTFLAGS for the !64BIT case. Seems like one of
> those can be removed.

Yeah & it's ditto for the rv32 handling in 1/2 as well. Ideally there
wouldn't be implicit 64-bit division and the "if 64BIT" could go
away. I just left things as-lifted, but I'll go drop anything 32-bit
related if this series looses the RFC prefix ;)

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