Re: [PATCH 10/15] powerpc/watchpoint: Use loop for thread_struct->ptrace_bps

[Ravi Bangoria]

> > @@ -1628,6 +1628,9 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long usp,
> > ÂÂÂÂÂ void (*f)(void);
> > ÂÂÂÂÂ unsigned long sp = (unsigned long)task_stack_page(p) + THREAD_SIZE;
> > ÂÂÂÂÂ struct thread_info *ti = task_thread_info(p);
> > +#ifdef CONFIG_HAVE_HW_BREAKPOINT
> > +ÂÂÂ int i;
> > +#endif
>
> Could we avoid all those #ifdefs ?
>
> I think if we make p->thread.ptrace_bps[] exist all the time, with a size of 0 when CONFIG_HAVE_HW_BREAKPOINT is not set, then we can drop a lot of #ifdefs.

Hmm.. what you are saying seems possible. But IMO it should be done as
independent series. Will work on it.

> > ÂÂÂÂÂ klp_init_thread_info(p);
> > @@ -1687,7 +1690,8 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long usp,
> > ÂÂÂÂÂ p->thread.ksp_limit = (unsigned long)end_of_stack(p);
> > Â #endif
> > Â #ifdef CONFIG_HAVE_HW_BREAKPOINT
> > -ÂÂÂ p->thread.ptrace_bps[0] = NULL;
> > +ÂÂÂ for (i = 0; i < nr_wp_slots(); i++)
> > +ÂÂÂÂÂÂÂ p->thread.ptrace_bps[i] = NULL;
> > Â #endif
> > ÂÂÂÂÂ p->thread.fp_save_area = NULL;
> > diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
> > index f6d7955fc61e..e2651f86d56f 100644
> > --- a/arch/powerpc/kernel/ptrace.c
> > +++ b/arch/powerpc/kernel/ptrace.c
>
> You'll have to rebase all this on the series https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=161356 which is about to go into powerpc-next

Sure. Thanks for heads up.

> > @@ -2829,6 +2829,19 @@ static int set_dac_range(struct task_struct *child,
> > Â }
> > Â #endif /* CONFIG_PPC_ADV_DEBUG_DAC_RANGE */
> > +#ifdef CONFIG_HAVE_HW_BREAKPOINT
> > +static int empty_ptrace_bp(struct thread_struct *thread)
> > +{
> > +ÂÂÂ int i;
> > +
> > +ÂÂÂ for (i = 0; i < nr_wp_slots(); i++) {
> > +ÂÂÂÂÂÂÂ if (!thread->ptrace_bps[i])
> > +ÂÂÂÂÂÂÂÂÂÂÂ return i;
> > +ÂÂÂ }
> > +ÂÂÂ return -1;
> > +}
> > +#endif
>
> What does this function do exactly ? I seems to do more than what its name suggests.

It finds an empty breakpoint in ptrace_bps[]. But yeah, function name is
misleading. I'll rename it to find_empty_ptrace_bp().

...

> > @@ -2979,10 +2993,10 @@ static long ppc_del_hwdebug(struct task_struct *child, long data)
> > ÂÂÂÂÂÂÂÂÂ return -EINVAL;
> > Â #ifdef CONFIG_HAVE_HW_BREAKPOINT
> > -ÂÂÂ bp = thread->ptrace_bps[0];
> > +ÂÂÂ bp = thread->ptrace_bps[data - 1];
>
> Is data checked somewhere to ensure it is not out of boundaries ? Or are we sure it is always within ?

Yes. it's checked. See patch #9:

  @@ -2955,7 +2975,7 @@ static long ppc_del_hwdebug(struct task_struct *child, long data)
   	}
   	return rc;
   #else
  -	if (data != 1)
  +	if (data < 1 || data > nr_wp_slots())
   		return -EINVAL;
   
   #ifdef CONFIG_HAVE_HW_BREAKPOINT

Thanks,
Ravi