Re: [PATCH 09/13] Move bp_type_idx to kernel/event/hw_breakpoint.c

Palmer Dabbelt
2015-09-17T03:56:05Z

On Tue, 15 Sep 2015 12:39:10 PDT (-0700), peterz@infradead.org wrote:
> On Tue, Sep 15, 2015 at 11:40:11AM -0700, Palmer Dabbelt wrote:
>> On Tue, 15 Sep 2015 01:06:07 PDT (-0700), peterz@infradead.org wrote:
>> > On Mon, Sep 14, 2015 at 03:50:43PM -0700, Palmer Dabbelt wrote:
>> >> This has a "#ifdef CONFIG_*" that used to be exposed to userspace.
>> >>
>> >> The names in here are so generic that I don't think it's a good idea
>> >> to expose them to userspace (or even the rest of the kernel). Since
>> >> there's only one kernel user, it's been moved to that file.
>> >>
>> >> Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>
>> >> Reviewed-by: Andrew Waterman <waterman@eecs.berkeley.edu>
>> >> Reviewed-by: Albert Ou <aou@eecs.berkeley.edu>
>> >> ---
>> >> include/uapi/linux/hw_breakpoint.h | 10 ----------
>> >> kernel/events/hw_breakpoint.c | 10 ++++++++++
>> >> 2 files changed, 10 insertions(+), 10 deletions(-)
>> >>
>> >> diff --git a/include/uapi/linux/hw_breakpoint.h b/include/uapi/linux/hw_breakpoint.h
>> >> index b04000a2296a..7a6a5a7f9511 100644
>> >> --- a/include/uapi/linux/hw_breakpoint.h
>> >> +++ b/include/uapi/linux/hw_breakpoint.h
>> >> @@ -17,14 +17,4 @@ enum {
>> >> HW_BREAKPOINT_INVALID = HW_BREAKPOINT_RW | HW_BREAKPOINT_X,
>> >> };
>> >>
>> >> -enum bp_type_idx {
>> >> - TYPE_INST = 0,
>> >> -#ifdef CONFIG_HAVE_MIXED_BREAKPOINTS_REGS
>> >> - TYPE_DATA = 0,
>> >> -#else
>> >> - TYPE_DATA = 1,
>> >> -#endif
>> >> - TYPE_MAX
>> >> -};
>> >
>> > This is rather unfortunate; you are correct that the naming is too
>> > generic (and I tend to agree), but I think these values are required by
>> > userspace to fill out:
>> >
>> > perf_event_attr::bp_type
>> >
>> > So removing them will break things.
>> >
>> > Frederic?
>>
>> perf_event_open(2) says
>>
>> bp_type (since Linux 2.6.33)
>> This chooses the breakpoint type. It is one of:
>>
>> HW_BREAKPOINT_EMPTY
>> No breakpoint.
>>
>> HW_BREAKPOINT_R
>> Count when we read the memory location.
>>
>> HW_BREAKPOINT_W
>> Count when we write the memory location.
>>
>> HW_BREAKPOINT_RW
>> Count when we read or write the memory location.
>>
>> HW_BREAKPOINT_X
>> Count when we execute code at the memory location.
>>
>> The values can be combined via a bitwise or, but the combination
>> of HW_BREAKPOINT_R or HW_BREAKPOINT_W with HW_BREAKPOINT_X is
>> not allowed.
>>
>> so I think removing this enum from userspace is OK. Did I miss
>> something?
>
> Nah, could've just been me not being awake. Unless Frederic says
> otherwise I'll chalk it up to not having drank enough morning juice.

Well, I'm going to leave this alone, then -- as Arnd pointed out in a
later email that got mis-threaded, this would be super tricky to fix
if userspace actually relied on it (which is why I was scared I was
wrong).

v4 (which is hopefully the final version of the patch set) will leave
this as it is.