Re: [PATCH 08/18] arm64: convert raw syscall invocation to C
From: Mark Rutland
Date: Tue May 15 2018 - 06:14:05 EST
On Tue, May 15, 2018 at 12:01:58PM +0200, Dominik Brodowski wrote:
> 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 *);
Oh, sure, we do the same on arm64 in this series.
Having a pt_regs wrapper for it (e.g. using SYSCALL_DEFINE0()) would
allow us to avoid that lie (which might be best for CFI stuff), would
allow us to avoid some name mangling on arm64, and would seemingly
confuse people less.