linux-kernel - Re: [PATCH] riscv: fix build with binutils 2.38

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Message-ID: <YkXfdyDISV6S6+kY@aurel32.net>
Date:   Thu, 31 Mar 2022 19:05:59 +0200
From:   Aurelien Jarno <aurelien@...el32.net>
To:     Marc Kleine-Budde <mkl@...gutronix.de>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Kito Cheng <kito.cheng@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        "open list:RISC-V ARCHITECTURE" <linux-riscv@...ts.infradead.org>,
        linux-sparse@...r.kernel.org, ukl@...gutronix.de,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>
Subject: Re: [PATCH] riscv: fix build with binutils 2.38

Hi,

On 2022-03-31 12:51, Marc Kleine-Budde wrote:
> Cc += linux-sparse, Uwe, Luc Van Oostenryck
> 
> tl;dr:
> 
> A recent change in the kernel regarding the riscv -march handling breaks
> current sparse.
> 
> On 31.03.2022 12:39:14, Marc Kleine-Budde wrote:
> > On 31.03.2022 12:32:47, Marc Kleine-Budde wrote:
> > > On 26.01.2022 18:14:42, Aurelien Jarno wrote:
> > > > From version 2.38, binutils default to ISA spec version 20191213. This
> > > > means that the csr read/write (csrr*/csrw*) instructions and fence.i
> > > > instruction has separated from the `I` extension, become two standalone
> > > > extensions: Zicsr and Zifencei. As the kernel uses those instruction,
> > > > this causes the following build failure:
> > > > 
> > > >   CC      arch/riscv/kernel/vdso/vgettimeofday.o
> > > >   <<BUILDDIR>>/arch/riscv/include/asm/vdso/gettimeofday.h: Assembler messages:
> > > >   <<BUILDDIR>>/arch/riscv/include/asm/vdso/gettimeofday.h:71: Error: unrecognized opcode `csrr a5,0xc01'
> > > >   <<BUILDDIR>>/arch/riscv/include/asm/vdso/gettimeofday.h:71: Error: unrecognized opcode `csrr a5,0xc01'
> > > >   <<BUILDDIR>>/arch/riscv/include/asm/vdso/gettimeofday.h:71: Error: unrecognized opcode `csrr a5,0xc01'
> > > >   <<BUILDDIR>>/arch/riscv/include/asm/vdso/gettimeofday.h:71: Error: unrecognized opcode `csrr a5,0xc01'
> > > > 
> > > > The fix is to specify those extensions explicitely in -march. However as
> > > > older binutils version do not support this, we first need to detect
> > > > that.
> > > > 
> > > > Cc: stable@...r.kernel.org # 4.15+
> > > > Cc: Kito Cheng <kito.cheng@...il.com>
> > > > Signed-off-by: Aurelien Jarno <aurelien@...el32.net>
> > > > ---
> > > >  arch/riscv/Makefile | 6 ++++++
> > > >  1 file changed, 6 insertions(+)
> > > > 
> > > > diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> > > > index 8a107ed18b0d..7d81102cffd4 100644
> > > > --- a/arch/riscv/Makefile
> > > > +++ b/arch/riscv/Makefile
> > > > @@ -50,6 +50,12 @@ riscv-march-$(CONFIG_ARCH_RV32I)	:= rv32ima
> > > >  riscv-march-$(CONFIG_ARCH_RV64I)	:= rv64ima
> > > >  riscv-march-$(CONFIG_FPU)		:= $(riscv-march-y)fd
> > > >  riscv-march-$(CONFIG_RISCV_ISA_C)	:= $(riscv-march-y)c
> > > > +
> > > > +# Newer binutils versions default to ISA spec version 20191213 which moves some
> > > > +# instructions from the I extension to the Zicsr and Zifencei extensions.
> > > > +toolchain-need-zicsr-zifencei := $(call cc-option-yn, -march=$(riscv-march-y)_zicsr_zifencei)
> > > > +riscv-march-$(toolchain-need-zicsr-zifencei) := $(riscv-march-y)_zicsr_zifencei
> > > > +
> > > >  KBUILD_CFLAGS += -march=$(subst fd,,$(riscv-march-y))
> > > >  KBUILD_AFLAGS += -march=$(riscv-march-y)
> > > 
> > > I'm on current linus/master, this change breaks on current Debian
> > > testing with:
> > > 
> > > | make: Leaving directory 'linux'
> > > |   SYNC    include/config/auto.conf.cmd
> > > |   GEN     Makefile
> > > |   GEN     Makefile
> > > |   CC      scripts/mod/empty.o
> > > |   CHECK   linux/scripts/mod/empty.c
> >       ^^^^^
> > It's actually "sparse" that breaks
> >       
> > > | invalid argument to '-march': '_zicsr_zifencei'
> > 
> > | $ sparse --version
> > | 0.6.4 (Debian: 0.6.4-2)

I confirm the issue. To make things clear, it's not a Makefile issue,
sparse get passed the correct -march=rv64ima_zicsr_zifencei value, and
only display the part it can't parse.

On the medium/long term, sparse should get fixed to support those
extensions. On the short term, we need to find a way to get different
flags for sparse than for as/gcc.

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@...el32.net                 http://www.aurel32.net

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