[PATCH V4 16/17] riscv: compat: Add COMPAT Kbuild skeletal support

[Arnd Bergmann]

On Tue, Feb 1, 2022 at 10:13 AM Guo Ren <guoren at kernel.org> wrote:
> On Tue, Feb 1, 2022 at 3:45 PM Christoph Hellwig <hch at lst.de> wrote:
> > 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 at infradead.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?
>
> Emm... I think it's unnecessary. Free rv32 app running won't cause
> system problem, just as a wrong elf running. They are U-mode
> privileged.

While it's not a security issue, I think it would be helpful to get a
user-readable error message and a machine-readable /proc/cpuinfo
flag to see if a particular system can run rv32 binaries rather than
relying on SIGILL to kill a process.

        Arnd