linux-kernel - Re: [PATCH V4 16/17] riscv: compat: Add COMPAT Kbuild skeletal support

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Date:   Tue, 1 Feb 2022 08:44:57 +0100
From:   Christoph Hellwig <hch@....de>
To:     Guo Ren <guoren@...nel.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Arnd Bergmann <arnd@...db.de>,
        Anup Patel <anup@...infault.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        liush <liush@...winnertech.com>, Wei Fu <wefu@...hat.com>,
        Drew Fustini <drew@...gleboard.org>,
        Wang Junqiang <wangjunqiang@...as.ac.cn>,
        Christoph Hellwig <hch@....de>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        linux-csky@...r.kernel.org,
        linux-s390 <linux-s390@...r.kernel.org>,
        sparclinux <sparclinux@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Parisc List <linux-parisc@...r.kernel.org>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH V4 16/17] riscv: compat: Add COMPAT Kbuild skeletal
 support

On Mon, Jan 31, 2022 at 09:50:58PM +0800, Guo Ren wrote:
> On Mon, Jan 31, 2022 at 8:26 PM Christoph Hellwig <hch@...radead.org> wrote:
> >
> > Given that most rv64 implementations can't run in rv32 mode, what is the
> > failure mode if someone tries it with the compat mode enabled?
> A static linked simple hello_world could still run on a non-compat
> support hardware. But most rv32 apps would meet different userspace
> segment faults.
> 
> Current code would let the machine try the rv32 apps without detecting
> whether hw support or not.

Hmm, we probably want some kind of check for not even offer running
rv32 binaries.  I guess trying to write UXL some time during early
boot and catching the resulting exception would be the way to go?

> 
> 
> -- 
> Best Regards
>  Guo Ren
> 
> ML: https://lore.kernel.org/linux-csky/
---end quoted text---