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

From: "Heiko Stübner" <heiko@sntech.de>
To: Conor Dooley <conor@kernel.org>
Cc: linux-riscv@lists.infradead.org, palmer@dabbelt.com,
	christoph.muellner@vrull.eu, prabhakar.csengg@gmail.com,
	philipp.tomsich@vrull.eu, ajones@ventanamicro.com,
	emil.renner.berthing@canonical.com
Subject: Re: [PATCH v2 13/13] RISC-V: add zbb support to string functions
Date: Wed, 30 Nov 2022 22:28:19 +0100	[thread overview]
Message-ID: <24615393.6Emhk5qWAg@diego> (raw)
In-Reply-To: <Y4ePiTIwJJfx9qS4@spud>

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.
> 
> 

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