Re: [PATCH 02/26] perf: Introduce mmap3 version of mmap event

Namhyung Kim
2020-09-14T05:38:47Z

On Mon, Sep 14, 2020 at 6:03 AM Jiri Olsa <jolsa@kernel.org> wrote:
>
> Add new version of mmap event. The MMAP3 record is an
> augmented version of MMAP2, it adds build id value to
> identify the exact binary object behind memory map:
>
> struct {
> struct perf_event_header header;
>
> u32 pid, tid;
> u64 addr;
> u64 len;
> u64 pgoff;
> u32 maj;
> u32 min;
> u64 ino;
> u64 ino_generation;
> u32 prot, flags;
> u32 reserved;
> u8 buildid[20];

Do we need maj, min, ino, ino_generation for mmap3 event?
I think they are to compare binaries, then we can do it with
build-id (and I think it'd be better)..

> char filename[];
> struct sample_id sample_id;
> };
>
> Adding 4 bytes reserved field to align buildid data to 8 bytes,
> so sample_id data is properly aligned.
>
> The mmap3 event is enabled by new mmap3 bit in perf_event_attr
> struct. When set for an event, it enables the build id retrieval
> and will use mmap3 format for the event.
>
> Keeping track of mmap3 events and calling build_id_parse
> in perf_event_mmap_event only if we have any defined.
>
> Having build id attached directly to the mmap event will help
> tool like perf to skip final search through perf data for
> binaries that are needed in the report time. Also it prevents
> possible race when the binary could be removed or replaced
> during profiling.
>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
> include/uapi/linux/perf_event.h | 27 ++++++++++++++++++++++-
> kernel/events/core.c | 38 +++++++++++++++++++++++++++------
> 2 files changed, 57 insertions(+), 8 deletions(-)
>
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 077e7ee69e3d..facfc3c673ed 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -384,7 +384,8 @@ struct perf_event_attr {
> aux_output : 1, /* generate AUX records instead of events */
> cgroup : 1, /* include cgroup events */
> text_poke : 1, /* include text poke events */
> - __reserved_1 : 30;
> + mmap3 : 1, /* include bpf events */

???

> + __reserved_1 : 29;
>
> union {
> __u32 wakeup_events; /* wakeup every n events */
> @@ -1060,6 +1061,30 @@ enum perf_event_type {
> */
> PERF_RECORD_TEXT_POKE = 20,
>
> + /*
> + * The MMAP3 records are an augmented version of MMAP2, they add
> + * build id value to identify the exact binary behind map
> + *
> + * struct {
> + * struct perf_event_header header;
> + *
> + * u32 pid, tid;
> + * u64 addr;
> + * u64 len;
> + * u64 pgoff;
> + * u32 maj;
> + * u32 min;
> + * u64 ino;
> + * u64 ino_generation;
> + * u32 prot, flags;
> + * u32 reserved;
> + * u8 buildid[20];
> + * char filename[];
> + * struct sample_id sample_id;
> + * };
> + */
> + PERF_RECORD_MMAP3 = 21,
> +
> PERF_RECORD_MAX, /* non-ABI */
> };
>
[SNIP]
> @@ -8098,6 +8116,9 @@ static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)
> mmap_event->prot = prot;
> mmap_event->flags = flags;
>
> + if (atomic_read(&nr_mmap3_events))
> + build_id_parse(vma, mmap_event->buildid);

What about if it failed? We should zero out the build-id..

Thanks
Namhyung

> +
> if (!(vma->vm_flags & VM_EXEC))
> mmap_event->event_id.header.misc |= PERF_RECORD_MISC_MMAP_DATA;
>
> @@ -8241,6 +8262,7 @@ void perf_event_mmap(struct vm_area_struct *vma)
> /* .ino_generation (attr_mmap2 only) */
> /* .prot (attr_mmap2 only) */
> /* .flags (attr_mmap2 only) */
> + /* .buildid (attr_mmap3 only) */
> };
>
> perf_addr_filters_adjust(vma);
> @@ -11040,6 +11062,8 @@ static void account_event(struct perf_event *event)
> inc = true;
> if (event->attr.mmap || event->attr.mmap_data)
> atomic_inc(&nr_mmap_events);
> + if (event->attr.mmap3)
> + atomic_inc(&nr_mmap3_events);
> if (event->attr.comm)
> atomic_inc(&nr_comm_events);
> if (event->attr.namespaces)
> --
> 2.26.2
>