linux-kernel - Re: [PATCH] riscv: Set SRCARCH to riscv if ARCH is riscv64 or riscv32

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Date:   Thu, 31 Mar 2022 10:34:42 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Ben Westover <kwestover.kw@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH] riscv: Set SRCARCH to riscv if ARCH is riscv64 or riscv32

On Thu, Mar 31, 2022 at 3:40 AM Ben Westover <kwestover.kw@...il.com> wrote:
>
> Hello Masahiro,
>
> On 3/30/22 11:31 AM, Masahiro Yamada wrote:
> > On Wed, Mar 30, 2022 at 11:34 PM Ben Westover <kwestover.kw@...il.com> wrote:
> >>
> >> When riscv64 or riscv32 are used as the value for ARCH during compilation, like
> >> in tools that get the ARCH value from uname, set SRCARCH to riscv instead of
> >> failing because the riscv64 and riscv32 targets don't exist.
> >
> > Can you refer to the code that really needs this?
> Some software like DKMS compiles out-of-tree modules by running `uname -m`and
> using that for the ARCH value. Without this patch, that compilation fails because
> uname shows either riscv64 or riscv32 while riscv should be used.

It is a bug in DKMS.

The ARCH=* in linux kernel does not necessarily match to 'uname -m'.

For example, we use ARCH=arm64 for arm 64-bit (so called aarch64),
but it does not match "aarch64".

The kernel has freedom to determine the supported string for ARCH=.

DKMS must adjust to the kernel code.

> This code already exists for sparc and parisc, as well as x86 of course.

This is because there is a historical reason.

If you look at the old code  (e.g. 2.6.x,)
arch/i386/ and arch/x86_64 were separate directories.

They were unified into arch/x86/ now, but we still support
ARCH=i386/x86_64.  It helps to choose a different defconfig.
See arch/x86/Makefile.

I do not see such code for riscv, where 32/64-bit is selected
only by Kconfig.

>
> Thanks,
> --
> Ben Westover

-- 
Best Regards
Masahiro Yamada