linux-kernel - Re: [PATCH v12 04/17] riscv: Add vector feature to compile

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Date:   Wed, 14 Dec 2022 16:40:52 -0800
From:   Atish Patra <atishp@...shpatra.org>
To:     Chris Stillson <stillson@...osinc.com>
Cc:     Guo Ren <guoren@...ux.alibaba.com>,
        Greentime Hu <greentime.hu@...ive.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Eric Biederman <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Anup Patel <anup@...infault.org>,
        Oleg Nesterov <oleg@...hat.com>, Guo Ren <guoren@...nel.org>,
        Heinrich Schuchardt <heinrich.schuchardt@...onical.com>,
        Arnaud Pouliquen <arnaud.pouliquen@...s.st.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Qinglin Pan <panqinglin2020@...as.ac.cn>,
        Alexandre Ghiti <alexandre.ghiti@...onical.com>,
        Vincent Chen <vincent.chen@...ive.com>,
        Arnd Bergmann <arnd@...db.de>,
        Heiko Stuebner <heiko@...ech.de>,
        Jisheng Zhang <jszhang@...nel.org>,
        Dao Lu <daolu@...osinc.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Sunil V L <sunilvl@...tanamicro.com>,
        Han-Kuan Chen <hankuan.chen@...ive.com>,
        Changbin Du <changbin.du@...el.com>,
        Li Zhengyu <lizhengyu3@...wei.com>,
        Alexander Graf <graf@...zon.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Tsukasa OI <research_trasio@....a4lg.com>,
        Yury Norov <yury.norov@...il.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Myrtle Shah <gatecat@....me>,
        Vitaly Wool <vitaly.wool@...sulko.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Brown <broonie@...nel.org>, Will Deacon <will@...nel.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Huacai Chen <chenhuacai@...nel.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Christian Brauner <brauner@...nel.org>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Colin Cross <ccross@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Barret Rhoden <brho@...gle.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, kvm@...r.kernel.org,
        kvm-riscv@...ts.infradead.org
Subject: Re: [PATCH v12 04/17] riscv: Add vector feature to compile

On Wed, Sep 21, 2022 at 2:47 PM Chris Stillson <stillson@...osinc.com> wrote:
>
> From: Guo Ren <guoren@...ux.alibaba.com>
>
> This patch adds a new config option which could enable assembler's
> vector feature.
>
> Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
> Co-developed-by: Greentime Hu <greentime.hu@...ive.com>
> Signed-off-by: Greentime Hu <greentime.hu@...ive.com>
> ---
>  arch/riscv/Kconfig  | 15 +++++++++++++--
>  arch/riscv/Makefile |  1 +
>  2 files changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index ed66c31e4655..e294d85bfb7d 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -432,7 +432,17 @@ config FPU
>
>           If you don't know what to do here, say Y.
>
> -endmenu # "Platform type"
> +config VECTOR
> +       bool "VECTOR support"
> +       depends on GCC_VERSION >= 120000 || CLANG_VERSION >= 130000
> +       default n
> +       help
> +         Say N here if you want to disable all vector related procedure
> +         in the kernel.
> +
> +         If you don't know what to do here, say Y.
> +
> +endmenu
>
>  menu "Kernel features"
>
> @@ -556,6 +566,7 @@ config CMDLINE_EXTEND
>           cases where the provided arguments are insufficient and
>           you don't want to or cannot modify them.
>
> +
>  config CMDLINE_FORCE
>         bool "Always use the default kernel command string"
>         help
> @@ -648,7 +659,7 @@ config XIP_PHYS_ADDR
>           be linked for and stored to.  This address is dependent on your
>           own flash usage.
>
> -endmenu # "Boot options"
> +endmenu
>
>  config BUILTIN_DTB
>         bool
> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> index 3fa8ef336822..1ec17f3d6d09 100644
> --- a/arch/riscv/Makefile
> +++ b/arch/riscv/Makefile
> @@ -50,6 +50,7 @@ riscv-march-$(CONFIG_ARCH_RV32I)      := rv32ima
>  riscv-march-$(CONFIG_ARCH_RV64I)       := rv64ima
>  riscv-march-$(CONFIG_FPU)              := $(riscv-march-y)fd
>  riscv-march-$(CONFIG_RISCV_ISA_C)      := $(riscv-march-y)c
> +riscv-march-$(CONFIG_VECTOR)           := $(riscv-march-y)v
>
>  # Newer binutils versions default to ISA spec version 20191213 which moves some
>  # instructions from the I extension to the Zicsr and Zifencei extensions.
> --
> 2.25.1
>

Kernel boot hangs if compiled LLVM and vector enabled. Because LLVM
enables auto vectorization by default and it inserts
random vector instructions.

We need to add "-mno-implicit-float" for llvm builds to disable auto
vectorization. Thanks Vineet and Saleem for the hint :).

-- 
Regards,
Atish