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Commit 99e818cc authored by Jiri Olsa's avatar Jiri Olsa Committed by Arnaldo Carvalho de Melo
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perf: Return empty callchain instead of NULL 

It simplifies the code a bit, because we dump the callchain
Link: http://lkml.kernel.org/n/tip-uqp7qd6aif47g39glnbu95yl@git.kernel.org


even if it's empty. With 'empty' callchain we can remove
all the NULL-checking code paths.

Original-patch-from: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarJiri Olsa <jolsa@kernel.org>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/20180107160356.28203-7-jolsa@kernel.org


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 8cf7e0e2

kernel/events/core.c

+12 −18
Original line number Diff line number Diff line
@@ -5815,19 +5815,11 @@ void perf_output_sample(struct perf_output_handle *handle, 
		perf_output_read(handle, event);



	if (sample_type & PERF_SAMPLE_CALLCHAIN) {

		if (data->callchain) {

		int size = 1;



			if (data->callchain)

		size += data->callchain->nr;



		size *= sizeof(u64);



		__output_copy(handle, data->callchain, size);

		} else {

			u64 nr = 0;

			perf_output_put(handle, nr);

		}

	}



	if (sample_type & PERF_SAMPLE_RAW) {
@@ -5980,6 +5972,8 @@ static u64 perf_virt_to_phys(u64 virt) 
	return phys_addr;

}



static struct perf_callchain_entry __empty_callchain = { .nr = 0, };



static struct perf_callchain_entry *

perf_callchain(struct perf_event *event, struct pt_regs *regs)

{
@@ -5988,12 +5982,14 @@ perf_callchain(struct perf_event *event, struct pt_regs *regs) 
	/* Disallow cross-task user callchains. */

	bool crosstask = event->ctx->task && event->ctx->task != current;

	const u32 max_stack = event->attr.sample_max_stack;

	struct perf_callchain_entry *callchain;



	if (!kernel && !user)

		return NULL;

		return &__empty_callchain;



	return get_perf_callchain(regs, 0, kernel, user,

	callchain = get_perf_callchain(regs, 0, kernel, user,

				       max_stack, crosstask, true);

	return callchain ?: &__empty_callchain;

}



void perf_prepare_sample(struct perf_event_header *header,
@@ -6018,8 +6014,6 @@ void perf_prepare_sample(struct perf_event_header *header, 
		int size = 1;



		data->callchain = perf_callchain(event, regs);



		if (data->callchain)

		size += data->callchain->nr;



		header->size += size * sizeof(u64);