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Date: Mon, 7 Sep 2020 23:58:20 +0200
From: Arnd Bergmann <>
Subject: Re: riscv32 v2

On Mon, Sep 7, 2020 at 11:46 PM Rich Felker <> wrote:
> On Mon, Sep 07, 2020 at 11:35:45PM +0200, Arnd Bergmann wrote:
> > On Mon, Sep 7, 2020 at 8:06 PM Rich Felker <> wrote:
> > > On Mon, Sep 07, 2020 at 06:47:00AM -0400, Stefan O'Rear wrote:
> >
> > > > * Copy the IPC_TIME64 bits from arch/arm/bits to trigger the musl code
> > > >   for fixing time64 IPC_STAT results.  I'm not super happy with this,
> > > >   maybe there should be a new mechanism in musl for fixing IPC_STAT for
> > > >   unconditionally-time64 architectures.
> > >
> > > If the riscv32 IPC syscalls don't actually provide in-place time64 but
> > > require translation, I think it's fairly appropriate as-is.
> > >
> > > From the definitions in your patch, it looks like all the time fields
> > > are fixed-word-order (little endian) and possibly not aligned, so it
> > > seems like they can't be used in-place. Is this correct?
> >
> > Yes, rv32 uses the generic system call arguments, which are
> > unfortunately defined this way. In retrospect I wish I had
> > replaced the ipc syscalls with a sane version for time64, but at
> > the time time it seemed as easy way out to use the fields that
> > had been reserved for this purpose despite the broken
> > byte order and alignment.
> Thanks for clarifying. BTW does passing IPC_64 produce an error on
> rv32? If so, this is another advantage of keeping the IPC_TIME64 bit
> -- it would catch programs bypassing libc and making the syscalls
> directly.

Yes, this is now the generic behavior for the split IPC syscalls
(as opposed to sys_ipc on older architectures). The only architectures
that parse the version in the split ipc syscalls are the ones that
already had these and were interpreting IPC_64 before linux-5.1:
alpha, arm32, microblaze, mips-n32, mips-n64, and xtensa.

There are additional architectures that require passing IPC_64
in sys_ipc() but reject it in the split syscalls: m68k, mips-o32,
powerpc, s390, sh, sparc, and x86.


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