Re: [PATCH] riscv: Handle zicsr/zifencei issue between gcc and binutils

[Mingzheng Xing]

On 7/26/23 06:17, Conor Dooley wrote:
> On Tue, Jul 25, 2023 at 07:57:54PM +0100, Conor Dooley wrote:
> > On Tue, Jul 25, 2023 at 10:23:44AM -0700, Nathan Chancellor wrote:
> > > On Wed, Jul 26, 2023 at 01:04:05AM +0800, Mingzheng Xing wrote:
> > > > When compiling the kernel with the toolchain composed of GCC >= 12.1.0 and
> > > > binutils < 2.38, default ISA spec used when building binutils and GCC, the
> > > > following build failure will appear because the
> > > > CONFIG_TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI is not turned on.
> > > > (i.e, gcc-12.1.0 and binutils-2.36, or gcc-12.3.0 and binutils-2.37, use
> > > > default ISA spec.)
> > > >
> > > >    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:79: Error: unrecognized opcode `csrr a5,0xc01'
> > > The gift that keeps on giving :/
> > >
> > > > Binutils has updated the default ISA spec version, and the community has
> > > > responded well to this[1][2][3], but it appears that this is not over yet.
> Also, I just noticed this comment. I disagree with the wording "well",
> and more like "with weeping and gnashing of teeth" ;) This stuff is a
> huge pain in the ass, and mixing toolchains between LLVM & GNU stuff (or
> using an older binutils with a newer GCC) really makes it a lot worse.
At least in the usual way , except in my unusual case...
> Thanks for submitting a fix for this so that Nathan or I didn't have to!
Hopefully this patch will make things better.
> > > > We also need to consider the situation of binutils < 2.38 but
> > > > GCC >= 12.1.0, since the combination between different versions of GCC and
> > > > binutils is not unique, which is to some extent flexible. GCC release
> > > > 12.1.0 updated the default ISA spec version in GCC commit[4].
> > > I suspect this combination is not too common because binutils 2.38 came
> > > out before GCC 12.1.0 but as you note, it is obviously possible. What
> > > toolchain has this combination in the wild, which would be helpful for
> > > documentation purposes?
> > Yeah, that'd be great to know, at least the other niche stuff that we
> > are working around had a clear use-case (testing LLVM in debian containers)
> > whereas there's no clear user for this.
> > That's doubly interesting, as this patch seems to break things for binutils
> > < 2.35, and if we have to make a trade-off between those too, then it'd
> > be good to be able to weigh up the options.
> > Do we perhaps need the misa-spec workaround instead for this case?
> > Haven't tested that though, trying to dig myself out of email backlog.
> I don't think the misa-spec stuff is what we need actually. Instead, the
> workaround/fix that this patch implements just needs to be constrained to
> versions of GAS greater than 2.35.
I'm sorry, I didn't quite understand this, could you provide some more
information, thank you very much!
I'll change the handling in v2. After testing it myself, it seems to 
work fine.

Thanks,
Mingzheng.
> Thanks,
> Conor.
>
> > > > For more information, please refer to:
> > > >
> > > > commit 6df2a016c0c8 ("riscv: fix build with binutils 2.38")
> > > > commit e89c2e815e76 ("riscv: Handle zicsr/zifencei issues between clang and binutils")
> > > >
> > > > [1]:https://groups.google.com/a/groups.riscv.org/g/sw-dev/c/aE1ZeHHCYf4
> > > > [2]:https://lore.kernel.org/all/20230308220842.1231003-1-conor@xxxxxxxxxx
> > > > [3]:https://lore.kernel.org/all/20230223220546.52879-1-conor@xxxxxxxxxx
> > > > [4]:https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=98416dbb0a62579d4a7a4a76bab51b5b52fec2cd
> > btw, please make these regular Link: tags (with a [N] at EOL) and drop
> > the space between them and the sign off. Also, this probably needs to be
> > CC:stable@xxxxxxxxxxxxxxx  too.
> > > > Signed-off-by: Mingzheng Xing<xingmingzheng@xxxxxxxxxxx>
> > > > ---
> > > >   arch/riscv/Kconfig | 6 +++++-
> > > >   1 file changed, 5 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > > > index 4c07b9189c86..b49cea30f6cc 100644
> > > > --- a/arch/riscv/Kconfig
> > > > +++ b/arch/riscv/Kconfig
> > > > @@ -570,11 +570,15 @@ config TOOLCHAIN_HAS_ZIHINTPAUSE
> > > >   config TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI
> > > >   	def_bool y
> > > >   	#https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=aed44286efa8ae8717a77d94b51ac3614e2ca6dc
> > > > -	depends on AS_IS_GNU && AS_VERSION >= 23800
> > > > +	#https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=98416dbb0a62579d4a7a4a76bab51b5b52fec2cd
> > > > +	depends on CC_IS_GCC && GCC_VERSION >= 120100 || \
> > > > +		   AS_IS_GNU && AS_VERSION >= 23800
> > > GCC_VERSION will be 0 for clang, so you don't need the CC_IS_GCC check.
> > > With that change, this should be able to stay on one line:
> > >
> > >      depends on GCC_VERSION >= 120100 || (AS_IS_GNU && AS_VERSION >= 23800)
> > >
> > > >   	help
> > > >   	  Newer binutils versions default to ISA spec version 20191213 which
> > > >   	  moves some instructions from the I extension to the Zicsr and Zifencei
> > > >   	  extensions.
> > > > +	  Similarly, GCC release 12.1.0 has changed the default ISA spec version to
> > > > +	  20191213, so the above situation requires this option to be enabled.
> > > >   
> > > >   config TOOLCHAIN_NEEDS_OLD_ISA_SPEC
> > > >   	def_bool y
> > > > --
> > > > 2.34.1