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

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Message-ID: <YgVRu9Z0BDyJdjR5@kroah.com>
Date:   Thu, 10 Feb 2022 18:56:11 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Palmer Dabbelt <palmer@...belt.com>
Cc:     aurelien@...el32.net, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Kito Cheng <kito.cheng@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        aou@...s.berkeley.edu,
        "open list:RISC-V ARCHITECTURE" <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH] riscv: fix build with binutils 2.38

On Thu, Feb 10, 2022 at 09:40:22AM -0800, Palmer Dabbelt wrote:
> On Wed, 26 Jan 2022 09:14:42 PST (-0800), aurelien@...el32.net 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)
> 
> Thanks, this is on fixes.  It's CC stable, but doesn't have a "Fixes" tag --
> I did that on purpose as this isn't really fixing a bug in Linux so I'm not
> sure it's right to point at a particular patch, but I'm not sure how that
> will play with the stable tree.

I will backport it as far back as it easily goes to, and then forget
about it :)

If you have a Fixes: tag, and it doesn't properly backport that far,
then you will get a "FAILED:" email notifying you about it.

hope that helps explain things,

greg k-h