Re: [RFC] perf record: missing buildid for callstack modules

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Tue, Jan 12, 2016 at 05:27:19PM +0100, Peter Zijlstra escreveu:
> On Tue, Jan 12, 2016 at 05:10:27PM +0100, Peter Zijlstra wrote:
> > > How will we collect the mtime for the DSOs in PERF_RECORD_MMAP records
> > > if we don't look at those records?

> > Kernel side, the vma has a vm_file member. So

Gotcha, via PERF_RECORD_MMAP3, using something we have (mtime) that
while not good as a content-based cookie (that we don't easily have at
PERF_RECORD_MMAP3 generation time) will allow us to do minimal detection
of mismatched DSOs at analysis time.

> > vma->vm_file->f_inode->i_mtime will get us that for all file based
> > mmap()s.

> > (or maybe ctime, not sure how popular it is these days to switch off
> > mtime accounting).
 
> And this would (obviously) be a good time to see what else we'd like to
> stuff in there.

Perhaps a version number? Else we'll be using those reserved bits again
when we decide to introduce MMAP4 ;-\

But I still think we should have a content-based cookie to be delivered
via that record, so at a minimum leave a cookie there starting with a
size, that, for now, would be zero. If present, that would get into the
current build-id infrastructure existing in the tooling side, something
like:

+	/*
+	 * The MMAP3 records are an augmented version of MMAP2, they add
+	 * mtime and an optional content-based cookie, if available.
+	 *	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;
+	 *	u64				mtime;
+	 *      u32				cookie_len
+	 *	char				cookie[2+];
+	 *	char				filename[];
+	 *	struct sample_id		sample_id;

Then someone (I want to do this, after processing more stuff from a
neverending backlog) should try to experiment with the varios ELF
loaders, etc to, in the process of loading, set that content-based
cookie somehow (ioctl? prctl? whatever).

- Arnaldo

> ---
>  include/uapi/linux/perf_event.h | 26 +++++++++++++++++++++++++-
>  kernel/events/core.c            | 19 +++++++++++++++----
>  2 files changed, 40 insertions(+), 5 deletions(-)
> 
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 1afe9623c1a7..a0f43140a0e2 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -340,7 +340,8 @@ struct perf_event_attr {
>  				comm_exec      :  1, /* flag comm events that are due to an exec */
>  				use_clockid    :  1, /* use @clockid for time fields */
>  				context_switch :  1, /* context switch data */
> -				__reserved_1   : 37;
> +				mmap3          :  1, /* include mmap with mtime */
> +				__reserved_1   : 36;
>  
>  	union {
>  		__u32		wakeup_events;	  /* wakeup every n events */
> @@ -856,6 +857,29 @@ enum perf_event_type {
>  	 */
>  	PERF_RECORD_SWITCH_CPU_WIDE		= 15,
>  
> +	/*
> +	 * The MMAP3 records are an augmented version of MMAP2, they add
> +	 * mtime.
> +	 *
> +	 * 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;
> +	 *	u64				mtime;
> +	 *	char				filename[];
> +	 *	struct sample_id		sample_id;
> +	 * }
> +	 */
> +	PERF_RECORD_MMAP3			= 16,
> +
>  	PERF_RECORD_MAX,			/* non-ABI */
>  };
>  
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index bf8244190d0f..d400da14b923 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -5661,7 +5661,7 @@ perf_event_aux(perf_event_aux_output_cb output, void *data,
>  /*
>   * task tracking -- fork/exit
>   *
> - * enabled by: attr.comm | attr.mmap | attr.mmap2 | attr.mmap_data | attr.task
> + * enabled by: attr.comm | attr.mmap | attr.mmap2 | attr.mmap3 | attr.mmap_data | attr.task
>   */
>  
>  struct perf_task_event {
> @@ -5682,8 +5682,8 @@ struct perf_task_event {
>  static int perf_event_task_match(struct perf_event *event)
>  {
>  	return event->attr.comm  || event->attr.mmap ||
> -	       event->attr.mmap2 || event->attr.mmap_data ||
> -	       event->attr.task;
> +	       event->attr.mmap2 || event->attr.mmap3 ||
> +	       event->attr.mmap_data || event->attr.task;
>  }
>  
>  static void perf_event_task_output(struct perf_event *event,
> @@ -5872,6 +5872,7 @@ struct perf_mmap_event {
>  	u64			ino;
>  	u64			ino_generation;
>  	u32			prot, flags;
> +	u64			mtime;
>  
>  	struct {
>  		struct perf_event_header	header;
> @@ -5892,7 +5893,7 @@ static int perf_event_mmap_match(struct perf_event *event,
>  	int executable = vma->vm_flags & VM_EXEC;
>  
>  	return (!executable && event->attr.mmap_data) ||
> -	       (executable && (event->attr.mmap || event->attr.mmap2));
> +	       (executable && (event->attr.mmap || event->attr.mmap2 || event-attr.mmap3));
>  }
>  
>  static void perf_event_mmap_output(struct perf_event *event,
> @@ -5916,6 +5917,9 @@ static void perf_event_mmap_output(struct perf_event *event,
>  		mmap_event->event_id.header.size += sizeof(mmap_event->prot);
>  		mmap_event->event_id.header.size += sizeof(mmap_event->flags);
>  	}
> +	if (event->attr.mmap3) {
> +		mmap_event->event_id.header.size += sizeof(mmap_event->mtime);
> +	}
>  
>  	perf_event_header__init_id(&mmap_event->event_id.header, &sample, event);
>  	ret = perf_output_begin(&handle, event,
> @@ -5936,6 +5940,9 @@ static void perf_event_mmap_output(struct perf_event *event,
>  		perf_output_put(&handle, mmap_event->prot);
>  		perf_output_put(&handle, mmap_event->flags);
>  	}
> +	if (event->attr.mmap3) {
> +		perf_output_put(&handle, mmap_event->mtime);
> +	}
>  
>  	__output_copy(&handle, mmap_event->file_name,
>  				   mmap_event->file_size);
> @@ -5954,6 +5961,7 @@ static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)
>  	int maj = 0, min = 0;
>  	u64 ino = 0, gen = 0;
>  	u32 prot = 0, flags = 0;
> +	u64 mtime = 0;
>  	unsigned int size;
>  	char tmp[16];
>  	char *buf = NULL;
> @@ -5984,6 +5992,7 @@ static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)
>  		gen = inode->i_generation;
>  		maj = MAJOR(dev);
>  		min = MINOR(dev);
> +		mtime = timespec_to_ns(inode->i_mtime);
>  
>  		if (vma->vm_flags & VM_READ)
>  			prot |= PROT_READ;
> @@ -6054,6 +6063,7 @@ static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)
>  	mmap_event->ino_generation = gen;
>  	mmap_event->prot = prot;
>  	mmap_event->flags = flags;
> +	mmap_event->mtime = mtime;
>  
>  	if (!(vma->vm_flags & VM_EXEC))
>  		mmap_event->event_id.header.misc |= PERF_RECORD_MISC_MMAP_DATA;
> @@ -6096,6 +6106,7 @@ void perf_event_mmap(struct vm_area_struct *vma)
>  		/* .ino_generation (attr_mmap2 only) */
>  		/* .prot (attr_mmap2 only) */
>  		/* .flags (attr_mmap2 only) */
> +		/* .mtime (attr_mmap3 only) */
>  	};
>  
>  	perf_event_mmap_event(&mmap_event);