Re: [PATCH v2 13/13] RISC-V: add zbb support to string functions

Heiko Stübner
2022-11-30T21:28:41Z

Am Mittwoch, 30. November 2022, 18:14:49 CET schrieb Conor Dooley:
> On Mon, Nov 28, 2022 at 11:26:32AM +0100, Heiko Stuebner wrote:
> > From: Heiko Stuebner <heiko.stuebner@vrull.eu>
> >
> > Add handling for ZBB extension and add support for using it as a
> > variant for optimized string functions.
> >
> > Co-developed-by: Christoph Muellner <christoph.muellner@vrull.eu>
> > Signed-off-by: Christoph Muellner <christoph.muellner@vrull.eu>
> > Signed-off-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
>
> > +config TOOLCHAIN_HAS_ZBB
> > + bool
> > + default y
> > + depends on !64BIT || $(cc-option,-mabi=lp64 -march=rv64ima_zbb)
> > + depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zbb)
> > + depends on LLD_VERSION >= 150000 || LD_VERSION >= 23900
> > +
> > +config RISCV_ISA_ZBB
> > + bool "Zbb extension support for bit manipulation instructions"
> > + depends on TOOLCHAIN_HAS_ZBB
> > + depends on !XIP_KERNEL && MMU
> > + select RISCV_ALTERNATIVE
> > + default y
> > + help
> > + Adds support to dynamically detect the presence of the ZBB
> > + extension (basic bit manipulation) and enable its usage.
> > +
> > + The Zbb extension provides instructions to accelerate a number
> > + of bit-specific operations (count bit population, sign extending,
> > + bitrotation, etc).
> > +
> > + If you don't know what to do here, say Y.
>
> /stuff/linux/arch/riscv/lib/strncmp_zbb.S:23:9: warning: unknown option, expected 'push', 'pop', 'rvc', 'norvc', 'relax' or 'norelax'
> .option arch,+zbb
> ^
> /stuff/linux/arch/riscv/lib/strncmp_zbb.S:56:2: error: instruction requires the following: 'Zbb' (Basic Bit-Manipulation) or 'Zbp' (Permutation 'Zb' Instructions)
> orc.b t3, t0
> ^
> /stuff/linux/arch/riscv/lib/strncmp_zbb.S:67:2: error: instruction requires the following: 'Zbb' (Basic Bit-Manipulation) or 'Zbp' (Permutation 'Zb' Instructions) or 'Zbkb' (Bitmanip instructions for Cryptography)
> rev8 t0, t0
> ^
> /stuff/linux/arch/riscv/lib/strncmp_zbb.S:68:2: error: instruction requires the following: 'Zbb' (Basic Bit-Manipulation) or 'Zbp' (Permutation 'Zb' Instructions) or 'Zbkb' (Bitmanip instructions for Cryptography)
> rev8 t1, t1
> ^
> make[4]: *** [/stuff/linux/scripts/Makefile.build:382: arch/riscv/lib/strncmp_zbb.o] Error 1
>
> So there's something wrong in 13/13 somewhere, but the failure itself is
> a bit odd? At least, at odds with your support stuff here.

Thanks to google I now know that llvm doesn't support the arch
directive yet [0]. The rest is of course just fallout, because of the
not-enabled zbb support.

That review over there also seems to be going slowly, so I guess for
the time being I need way stricter depends, limiting this to binutils.

[0] https://reviews.llvm.org/D123515

> CONFIG_CC_VERSION_TEXT="ClangBuiltLinux clang version 15.0.4 (5c68a1cb123161b54b72ce90e7975d95a8eaf2a4)"
> CONFIG_CC_IS_CLANG=y
> CONFIG_CLANG_VERSION=150004
> CONFIG_AS_IS_LLVM=y
> CONFIG_AS_VERSION=150004
> CONFIG_LD_IS_LLD=y
> CONFIG_LLD_VERSION=150004
>
> Thanks,
> Conor.