Re: [PATCH 1/2] riscv: fix detection of toolchain Zicbom support

[Nathan Chancellor <nathan@kernel.org>]

On Thu, Oct 13, 2022 at 09:33:29PM +0100, Conor Dooley wrote:
> On Thu, Oct 13, 2022 at 01:22:47PM -0700, Nathan Chancellor wrote:
> > On Thu, Oct 06, 2022 at 06:35:20PM +0100, Conor Dooley wrote:
> > > From: Conor Dooley <conor.dooley@microchip.com>
> > > 
> > > It is not sufficient to check if a toolchain supports a particular
> > > extension without checking if the linker supports that extension too.
> > > For example, Clang 15 supports Zicbom but GNU bintutils 2.35.2 does
> > > not, leading build errors like so:
> > > 
> > > riscv64-linux-gnu-ld: -march=rv64i2p0_m2p0_a2p0_c2p0_zicbom1p0_zihintpause2p0: Invalid or unknown z ISA extension: 'zicbom'
> > > 
> > > Convert CC_HAS_ZICBOM to TOOLCHAIN_HAS_ZICBOM & check if the linker
> > > also supports Zicbom.
> > > 
> > > Reported-by: Kevin Hilman <khilman@baylibre.com>
> > > Link: https://github.com/ClangBuiltLinux/linux/issues/1714
> > > Link: https://storage.kernelci.org/next/master/next-20220920/riscv/defconfig+CONFIG_EFI=n/clang-16/logs/kernel.log
> > > Fixes: 1631ba1259d6 ("riscv: Add support for non-coherent devices using zicbom extension")
> > > Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
> > 
> > The versions look correct to me. I see the LLVM zicbom commit [1] in
> > llvmorg-15.0.0 and I see the binutils zicbom commit [2] in
> > binutils-2_39.
> > 
> > FWIW, if we are adding explicit tool versions to the Kconfig, could you
> > not also drop the cc-option checks? Typically, cc-option is only used
> > when dynamically checking for a feature, in lieu of statically checking
> > a version. No strong opinion though.
> 
> Ehh, the explicit version checks are for linker support, but it could be
> that your linker supports it but other things do not. The compilers
> support can still be checked with cc-option, no?
> 
> This error here happens when the compiler does support it, so the string
> containing zicbom is emitted in the object files. That can't be checked
> dynamically. For the opposite situation, dynamic checking is possible so
> I tried retained them. If it's convention to do one or the other, I can
> easily switch.
> 
> I'm out of my comfort zone when it comes to kbuild plumbing so please,
> please lmk if I'm missing something...

No, you are absolutely correct. That's what I get for reviewing changes
right after being off for a week ;) the cc-option checks should remain
in addition to the new linker checks, so please disregard that feedback
on both changes.

> > 
> > Reviewed-by: Nathan Chancellor <nathan@kernel.org>
> > 
> > [1]: https://github.com/llvm/llvm-project/commit/4f40ca53cefb725aca6564585d0ec4836a79e21a
> > [2]: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=41d6ac5da655a2e78109848f2db47e53552fd61a
> > 
> > > ---
> > >  arch/riscv/Kconfig  | 10 ++++++----
> > >  arch/riscv/Makefile |  3 +--
> > >  2 files changed, 7 insertions(+), 6 deletions(-)
> > > 
> > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > > index d557cc50295d..6da36553158b 100644
> > > --- a/arch/riscv/Kconfig
> > > +++ b/arch/riscv/Kconfig
> > > @@ -401,14 +401,16 @@ config RISCV_ISA_SVPBMT
> > >  
> > >  	   If you don't know what to do here, say Y.
> > >  
> > > -config CC_HAS_ZICBOM
> > > +config TOOLCHAIN_HAS_ZICBOM
> > >  	bool
> > > -	default y if 64BIT && $(cc-option,-mabi=lp64 -march=rv64ima_zicbom)
> > > -	default y if 32BIT && $(cc-option,-mabi=ilp32 -march=rv32ima_zicbom)
> > > +	default y
> > > +	depends on !64BIT || $(cc-option,-mabi=lp64 -march=rv64ima_zicbom)
> > > +	depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zicbom)
> > > +	depends on LLD_VERSION >= 150000 || LD_VERSION >= 23900
> > >  
> > >  config RISCV_ISA_ZICBOM
> > >  	bool "Zicbom extension support for non-coherent DMA operation"
> > > -	depends on CC_HAS_ZICBOM
> > > +	depends on TOOLCHAIN_HAS_ZICBOM
> > >  	depends on !XIP_KERNEL && MMU
> > >  	select RISCV_DMA_NONCOHERENT
> > >  	select RISCV_ALTERNATIVE
> > > diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> > > index 3fa8ef336822..3607d38edb4f 100644
> > > --- a/arch/riscv/Makefile
> > > +++ b/arch/riscv/Makefile
> > > @@ -57,8 +57,7 @@ toolchain-need-zicsr-zifencei := $(call cc-option-yn, -march=$(riscv-march-y)_zi
> > >  riscv-march-$(toolchain-need-zicsr-zifencei) := $(riscv-march-y)_zicsr_zifencei
> > >  
> > >  # Check if the toolchain supports Zicbom extension
> > > -toolchain-supports-zicbom := $(call cc-option-yn, -march=$(riscv-march-y)_zicbom)
> > > -riscv-march-$(toolchain-supports-zicbom) := $(riscv-march-y)_zicbom
> > > +riscv-march-$(CONFIG_TOOLCHAIN_HAS_ZICBOM) := $(riscv-march-y)_zicbom
> > >  
> > >  # Check if the toolchain supports Zihintpause extension
> > >  toolchain-supports-zihintpause := $(call cc-option-yn, -march=$(riscv-march-y)_zihintpause)
> > > -- 
> > > 2.37.3
> > > 
> > >