Re: [PATCH 08/18] arm64: convert raw syscall invocation to C

From: Dominik Brodowski
Date: Tue May 15 2018 - 06:02:05 EST

On Tue, May 15, 2018 at 09:22:23AM +0100, Mark Rutland wrote:
> On Mon, May 14, 2018 at 10:24:45PM +0200, Dominik Brodowski wrote:
> > On Mon, May 14, 2018 at 12:41:10PM +0100, Mark Rutland wrote:
> > > I agree it would be nicer if it had a wrapper that took a pt_regs, even
> > > if it does nothing with it.
> > >
> > > We can't use SYSCALL_DEFINE0() due to the fault injection muck, we'd
> > > need a ksys_ni_syscall() for our traps.c logic, and adding this
> > > uniformly would involve some arch-specific rework for x86, too, so I
> > > decided it was not worth the effort.
> >
> > Couldn't you just open-code the "return -ENOSYS;" in traps.c?
> I guess so. I was just worried that debug logic might be added to the generic
> ni_syscall() in future, and wanted to avoid potential divergence.
> > Error injection has no reasonable stable ABI/API expectations, so that's not
> > a show-stopper either.
> If people are happy with using SYSCALL_DEFINE0() for ni_syscall, I'm happy to
> do that -- it's just that we'll need a fixup for x86 as that will change the
> symbol name.

For me, it's less about using SYSCALL_DEFINE0() for ni_syscall, but more
about keeping the syscall invokation easy. Therefore, we do pass a pointer
struct pt_regs to sys_ni_syscall() on x86, even though it does not expect

/* this is a lie, but it does not hurt as sys_ni_syscall just returns -EINVAL */
extern asmlinkage long sys_ni_syscall(const struct pt_regs *);