On Mon, May 28, 2018 at 09:31:07PM +1000, Michael Ellerman wrote: > Frederic Weisbecker <[email protected]> writes: > > > On Thu, May 24, 2018 at 12:01:52PM +1000, Michael Ellerman wrote: > >> Frederic Weisbecker <[email protected]> writes: > >> > >> > diff --git a/arch/powerpc/kernel/hw_breakpoint.c > >> > b/arch/powerpc/kernel/hw_breakpoint.c > >> > index 348cac9..fba6527 100644 > >> > --- a/arch/powerpc/kernel/hw_breakpoint.c > >> > +++ b/arch/powerpc/kernel/hw_breakpoint.c > >> > @@ -139,30 +139,31 @@ int arch_bp_generic_fields(int type, int > >> > *gen_bp_type) > >> > /* > >> > * Validate the arch-specific HW Breakpoint register settings > >> > */ > >> > -int arch_validate_hwbkpt_settings(struct perf_event *bp) > >> > +int hw_breakpoint_arch_parse(struct perf_event *bp, > >> > + struct perf_event_attr *attr, > >> > + struct arch_hw_breakpoint *hw) > >> > >> I think the semantics here are that we are reading from bp/attr and > >> writing to hw? > >> > >> If so would some sprinkling of const on the first two parameters help > >> make that clearer? > > > > I seem to remember there was an issue with that due to the various functions > > we call that need to be converted to take const as well. I thought I would > > do it in a seperate series but actually it should be no big deal to do it > > on this one. > > Yeah, that does sometimes snowball out of control. > > > Let me try that and respin. > > Cool. It would be nice to have, but obviously not crucial.
So I managed to constify the perf_event_attr parameter but not the struct perf_event *bp because the task target is fetched from it on is_compat_bp() on ARM64. I could constify it all the way up to test_ti_thread_flag() but the thread info can only be retrieved through a call to task_thread_info() and that's where the qualifier control ends. The const can not be passed there and we can't afford to constify the function either, I fear, as it is used everywhere for any purpose, including thread_info modifications.
