Hi Mathieu,
On Fri, Jun 15, 2018 at 01:41:25PM -0400, Mathieu Desnoyers wrote:
> > diff --git a/arch/mips/kernel/entry.S b/arch/mips/kernel/entry.S
> > index 38a302919e6b..d7de8adcfcc8 100644
> > --- a/arch/mips/kernel/entry.S
> > +++ b/arch/mips/kernel/entry.S
> > @@ -79,6 +79,10 @@ FEXPORT(ret_from_fork)
> > jal schedule_tail # a0 = struct task_struct *prev
> >
> > FEXPORT(syscall_exit)
> > +#ifdef CONFIG_DEBUG_RSEQ
> > + move a0, sp
> > + jal rseq_syscall
> > +#endif
> > local_irq_disable # make sure need_resched and
> > # signals dont change between
> > # sampling and return
> > @@ -141,6 +145,10 @@ work_notifysig: # deal with pending signals and
> > j resume_userspace_check
> >
> > FEXPORT(syscall_exit_partial)
> > +#ifdef CONFIG_DEBUG_RSEQ
> > + move a0, sp
> > + jal rseq_syscall
> > +#endif
> > local_irq_disable # make sure need_resched doesn't
> > # change between and return
> > LONG_L a2, TI_FLAGS($28) # current->work
>
> Just to double-check: you did test with CONFIG_DEBUG_RSEQ=y, right ?
Yes, I did. Although I only ran the selftests, which I don't believe
would actually trigger the SIGSEGV condition.
Side-note: maybe it'd be useful to have a test that does intentionally
perform a syscall within a restartable sequence & checks that it
actually receives a SIGSEGV?.
> Are there any live registers that need to be saved before calling
> rseq_syscall ?
No - we just need gp/$28 & sp/$29, and the calling convention means
rseq_syscall() should return with those unmodified. Everything else that
we or userland care about is about to be loaded from the stack anyway.
Thanks,
Paul
