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

Conor Dooley
2022-11-30T17:15:11Z

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.

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.