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    SubjectRe: [PATCH 03/24] perf: Add build id data in mmap2 event
    Hi Jiri,

    On Mon, Nov 09, 2020 at 10:53:54PM +0100, Jiri Olsa wrote:
    > Adding support to carry build id data in mmap2 event.
    >
    > The build id data replaces maj/min/ino/ino_generation
    > fields, whichc are also used to identify map's binary,
    > so it's ok to replace them with build id data:
    >
    > union {
    > struct {
    > u32 maj;
    > u32 min;
    > u64 ino;
    > u64 ino_generation;
    > };
    > struct {
    > u8 build_id[20];
    > u8 build_id_size;
    > u8 __reserved_1;
    > u16 __reserved_2;
    > };
    > };
    >
    > Replaced maj/min/ino/ino_generation fields give us size
    > of 24 bytes. We use 20 bytes for build id data, 1 byte
    > for size and rest is unused.
    >
    > There's new misc bit for mmap2 to signal there's build
    > id data in it:
    >
    > #define PERF_RECORD_MISC_BUILD_ID (1 << 14)
    >
    > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
    > ---
    [SNIP]
    > diff --git a/kernel/events/core.c b/kernel/events/core.c
    > index da467e1dd49a..808473b6ce85 100644
    > --- a/kernel/events/core.c
    > +++ b/kernel/events/core.c
    > @@ -51,6 +51,7 @@
    > #include <linux/proc_ns.h>
    > #include <linux/mount.h>
    > #include <linux/min_heap.h>
    > +#include <linux/buildid.h>
    >
    > #include "internal.h"
    >
    > @@ -395,6 +396,7 @@ static atomic_t nr_ksymbol_events __read_mostly;
    > static atomic_t nr_bpf_events __read_mostly;
    > static atomic_t nr_cgroup_events __read_mostly;
    > static atomic_t nr_text_poke_events __read_mostly;
    > +static atomic_t nr_build_id_events __read_mostly;
    >
    > static LIST_HEAD(pmus);
    > static DEFINE_MUTEX(pmus_lock);
    > @@ -4672,6 +4674,8 @@ static void unaccount_event(struct perf_event *event)
    > dec = true;
    > if (event->attr.mmap || event->attr.mmap_data)
    > atomic_dec(&nr_mmap_events);
    > + if (event->attr.build_id)
    > + atomic_dec(&nr_build_id_events);
    > if (event->attr.comm)
    > atomic_dec(&nr_comm_events);
    > if (event->attr.namespaces)
    > @@ -7942,6 +7946,8 @@ struct perf_mmap_event {
    > u64 ino;
    > u64 ino_generation;
    > u32 prot, flags;
    > + u8 build_id[BUILD_ID_SIZE];
    > + u32 build_id_size;
    >
    > struct {
    > struct perf_event_header header;
    > @@ -7997,13 +8003,23 @@ static void perf_event_mmap_output(struct perf_event *event,
    > mmap_event->event_id.pid = perf_event_pid(event, current);
    > mmap_event->event_id.tid = perf_event_tid(event, current);
    >
    > + if (event->attr.mmap2 && event->attr.build_id)
    > + mmap_event->event_id.header.misc |= PERF_RECORD_MISC_BUILD_ID;
    > +
    > perf_output_put(&handle, mmap_event->event_id);
    >
    > if (event->attr.mmap2) {
    > - perf_output_put(&handle, mmap_event->maj);
    > - perf_output_put(&handle, mmap_event->min);
    > - perf_output_put(&handle, mmap_event->ino);
    > - perf_output_put(&handle, mmap_event->ino_generation);
    > + if (event->attr.build_id) {
    > + u8 size[4] = { (u8) mmap_event->build_id_size, 0, 0, 0 };
    > +
    > + __output_copy(&handle, mmap_event->build_id, BUILD_ID_SIZE);
    > + __output_copy(&handle, size, 4);
    > + } else {
    > + perf_output_put(&handle, mmap_event->maj);
    > + perf_output_put(&handle, mmap_event->min);
    > + perf_output_put(&handle, mmap_event->ino);
    > + perf_output_put(&handle, mmap_event->ino_generation);
    > + }
    > perf_output_put(&handle, mmap_event->prot);
    > perf_output_put(&handle, mmap_event->flags);
    > }
    > @@ -8132,6 +8148,11 @@ static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)
    >
    > mmap_event->event_id.header.size = sizeof(mmap_event->event_id) + size;
    >
    > + if (atomic_read(&nr_build_id_events)) {
    > + build_id_parse_size(vma, mmap_event->build_id,
    > + &mmap_event->build_id_size);

    This can fail, right? Then we need to fallback to use dev/ino..

    Thanks,
    Namhyung


    > + }
    > +
    > perf_iterate_sb(perf_event_mmap_output,
    > mmap_event,
    > NULL);
    > @@ -11069,6 +11090,8 @@ 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.build_id)
    > + atomic_inc(&nr_build_id_events);
    > if (event->attr.comm)
    > atomic_inc(&nr_comm_events);
    > if (event->attr.namespaces)
    > --
    > 2.26.2
    >

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