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    SubjectRe: [PATCH 02/19] perf: Add ability to attach user level registers dump to sample
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    On Mon, Jun 11, 2012 at 3:19 PM, Jiri Olsa <jolsa@redhat.com> wrote:
    > Introducing sample_regs_user bitmask into perf_event_attr
    > struct to define the user level registers we want to attach
    > to the sample. The dump itself is triggered once the
    > sample_regs_user is not empty.
    >
    > Only user level registers are dump at the moment. Meaning the
    > register values of the user space context as it was before the
    > user entered the kernel for whatever reason (syscall, irq,
    > exception, or a PMI happening in userspace).
    >
    > The layout of the sample_regs_user bitmap is described in
    > asm/perf_regs.h for archs that support register dump.
    >
    > This is going to be useful to bring Dwarf CFI based stack
    > unwinding on top of samples.
    >
    > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
    > Signed-off-by: Jiri Olsa <jolsa@redhat.com>
    > ---
    >  include/linux/perf_event.h |   10 ++++++-
    >  kernel/events/core.c       |   61 ++++++++++++++++++++++++++++++++++++++++++++
    >  2 files changed, 70 insertions(+), 1 deletions(-)
    >
    > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
    > index 1ce887a..d66cbeb 100644
    > --- a/include/linux/perf_event.h
    > +++ b/include/linux/perf_event.h
    > @@ -271,7 +271,13 @@ struct perf_event_attr {
    >                __u64           bp_len;
    >                __u64           config2; /* extension of config1 */
    >        };
    > -       __u64   branch_sample_type; /* enum branch_sample_type */
    > +       __u64   branch_sample_type; /* enum perf_branch_sample_type */
    > +
    > +       /*
    > +        * Defines set of user regs to dump on samples.
    > +        * See asm/perf_regs.h for details.
    > +        */
    > +       __u64   sample_regs_user;
    >  };
    That's not enough. You also need to define PERF_SAMPLE_USER_REGS
    for sample_type. Although the sample_regs_users might look like it's enough
    to capture regs, there is a problem when it comes to parsing the record. You
    need an ordering guarantee that is explicitly spelled out in the API (the header
    file). In your current patch, I have no way of knowing that sample_regs_users
    are saved after BRANCH_STACK (should you have that enabled). Remember
    that you can turn on/off sampled infos at will in sample_type. Yet to find the
    infos when parsing, you need to know the order.

    The enum perf_event_sample_format provides that ordering information. You
    need to add a new type for sampling user regs.

    >
    >  /*
    > @@ -609,6 +615,7 @@ struct perf_guest_info_callbacks {
    >  #include <linux/static_key.h>
    >  #include <linux/atomic.h>
    >  #include <linux/sysfs.h>
    > +#include <linux/perf_regs.h>
    >  #include <asm/local.h>
    >
    >  struct perf_callchain_entry {
    > @@ -1131,6 +1138,7 @@ struct perf_sample_data {
    >        struct perf_callchain_entry     *callchain;
    >        struct perf_raw_record          *raw;
    >        struct perf_branch_stack        *br_stack;
    > +       struct pt_regs                  *regs_user;
    >  };
    >
    >  static inline void perf_sample_data_init(struct perf_sample_data *data,
    > diff --git a/kernel/events/core.c b/kernel/events/core.c
    > index f85c015..e4df59d 100644
    > --- a/kernel/events/core.c
    > +++ b/kernel/events/core.c
    > @@ -3750,6 +3750,33 @@ int perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
    >  }
    >  EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks);
    >
    > +static void
    > +perf_output_sample_regs(struct perf_output_handle *handle,
    > +                       struct pt_regs *regs, u64 mask)
    > +{
    > +       int bit;
    > +
    > +       for_each_set_bit(bit, (const unsigned long *) &mask,
    > +                        sizeof(mask) * BITS_PER_BYTE) {
    > +               u64 val;
    > +
    > +               val = perf_reg_value(regs, bit);
    > +               perf_output_put(handle, val);
    > +       }
    > +}
    > +
    > +static struct pt_regs *perf_sample_regs_user(struct pt_regs *regs)
    > +{
    > +       if (!user_mode(regs)) {
    > +               if (current->mm)
    > +                       regs = task_pt_regs(current);
    > +               else
    > +                       regs = NULL;
    > +       }
    > +
    > +       return regs;
    > +}
    > +
    >  static void __perf_event_header__init_id(struct perf_event_header *header,
    >                                         struct perf_sample_data *data,
    >                                         struct perf_event *event)
    > @@ -4010,6 +4037,23 @@ void perf_output_sample(struct perf_output_handle *handle,
    >                        perf_output_put(handle, nr);
    >                }
    >        }
    > +
    > +       if (event->attr.sample_regs_user) {
    > +               u64 avail = (data->regs_user != NULL);
    > +
    > +               /*
    > +                * If there are no regs to dump, notice it through
    > +                * first u64 being zero.
    > +                */
    > +               perf_output_put(handle, avail);
    > +
    > +               if (avail) {
    > +                       u64 mask = event->attr.sample_regs_user;
    > +                       perf_output_sample_regs(handle,
    > +                                               data->regs_user,
    > +                                               mask);
    > +               }
    > +       }
    >  }
    >
    >  void perf_prepare_sample(struct perf_event_header *header,
    > @@ -4061,6 +4105,19 @@ void perf_prepare_sample(struct perf_event_header *header,
    >                }
    >                header->size += size;
    >        }
    > +
    > +       if (event->attr.sample_regs_user) {
    > +               /* regs dump available bool */
    > +               int size = sizeof(u64);
    > +
    > +               data->regs_user = perf_sample_regs_user(regs);
    > +               if (data->regs_user) {
    > +                       u64 mask = event->attr.sample_regs_user;
    > +                       size += hweight64(mask) * sizeof(u64);
    > +               }
    > +
    > +               header->size += size;
    > +       }
    >  }
    >
    >  static void perf_event_output(struct perf_event *event,
    > @@ -6110,6 +6167,10 @@ static int perf_copy_attr(struct perf_event_attr __user *uattr,
    >                        attr->branch_sample_type = mask;
    >                }
    >        }
    > +
    > +       if (attr->sample_regs_user)
    > +               ret = perf_reg_validate(attr->sample_regs_user);
    > +
    >  out:
    >        return ret;
    >
    > --
    > 1.7.7.6
    >
    --
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