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SubjectRe: [PATCH v8 2/6] arm64: ptrace: allow tracer to skip a system call
On Thu, Nov 20, 2014 at 05:52:34AM +0000, AKASHI Takahiro wrote:
> On 11/20/2014 02:13 PM, AKASHI Takahiro wrote:
> > On 11/20/2014 04:06 AM, Will Deacon wrote:
> >> Ok, but now userspace sees -ENOSYS for a skipped system call in that case,
> >> whereas it would usually see whatever the trace put in x0, right?
> >
> > Yes.
> > If you don't really like this behavior, how about this patch instead of my [2/6] patch?
> >
> > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> > index 726b910..1ef57d0 100644
> > --- a/arch/arm64/kernel/entry.S
> > +++ b/arch/arm64/kernel/entry.S
> > @@ -668,8 +668,15 @@ ENDPROC(el0_svc)
> > * switches, and waiting for our parent to respond.
> > */
> > __sys_trace:
> > + cmp w8, #-1 // default errno for invalid
>
> I needed to correct the code here:
> w8 should be w26, thinking of compat syscalls.
>
> > + b.ne 1f // system call
> > + mov x0, #-ENOSYS
> > + str x0, [sp, #S_X0]
> > +1:
>
> and this part might better be generalized like the following:
>
> __sys_trace:
> cmp w26, w25 // cannot use x26 and x25 here
> b.hs 1f // scno > sc_nr || scno < 0
> b 2f
> 1:
> mov x0, #-ENOSYS
> str x0, [sp, #S_X0]
> 2:
>
> If you will be comfortable, I will submit a new patch soon.

Yes, please send a new series including this change.

Will


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